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Aortic and mitral regurgitation: Quantification using moving slice velocity mapping
Abstract
Comprehensive assessment of the severity of valvular insufficiency includes quantification of regurgitant volumes. Previous methods lack reliable slice positioning with respect to the valve and are prone to velocity offsets due to through-plane motion of the valvular plane of the heart. Recently, the moving slice velocity mapping technique was proposed. In this study, the technique was applied for quantification of mitral and aortic regurgitation. Time-efficient navigator-based respiratory artifact suppression was achieved by implementing a prospective k-space reordering scheme in conjunction with slice position correction. Twelve patients with aortic insufficiency and three patients with mitral insufficiency were studied. Aortic regurgitant volumes were calculated from diastolic velocities mapped with a moving slice 5 mm distal to the aortic valve annulus. Mitral regurgitant flow was indirectly assessed by measuring mitral inflow at the level of the mitral annulus and net aortic outflow. Regurgitant fractions, derived from velocity data corrected for through-plane motion, were compared to data without correction for through-plane motion. In patients with mild and moderate aortic regurgitation, regurgitant fractions differed by 60% and 15%, on average, when comparing corrected and uncorrected data, respectively. Differences in severe aortic regurgitation were less (7%). Due to the large orifice area of the mitral valve, differences were still substantial in moderate-to-severe mitral regurgitation (19%). The moving slice velocity mapping technique was successfully applied in patients with aortic and mitral regurgitation. The importance of correction for valvular through-plane motion is demonstrated. J. Magn. Reson. Imaging 2001;14:106–112. © 2001 Wiley-Liss, Inc.
... 16 An early approach for valvular MR used prospectively gated slice-following PC with spin labeling to determine valvular motion. 18,19 More recent work has suggested 4D-flow with valve tracking [20][21][22][23][24] and tagging for aortic valve visualization. 25 However, prospectively gated sequences do not capture end diastole, 4D-flow is time-consuming, and tissuetagging methods are challenging to implement robustly. ...
... Slice-following PC also provided physiologically accurate flow wave forms, and the ability to measure mitral regurgitant flow as backward systolic flow. Kozerke et al introduced the slice-following PC concept and studied regurgitation in three mitral valve patients, but did not compare aortic and mitral SV. 18,19 That method used spin labeling to track the slice, which differs from the feature-tracking approach shown here. Westenberg et al showed that slice-following in postprocessing of 4D-flow improved mitral SV compared to static PC. 20 Calculation of aortic SV as net flow over the heartbeat is well established and based on physiology. ...
... 18 Furthermore, the aortic valve closes due to backflow of blood from the ascending aorta towards the valve, justifying the accounting of negative flow in SV quantification. In contrast, the definition of mitral SV is less established and previous slice-following studies used either diastolic inflow 19 or net flow over the heartbeat. 20 The division of systolic and diastolic flow, however, is important when studying mitral flow. ...
Background:
In mitral valve dysfunction, noninvasive measurement of transmitral blood flow is an important clinical examination. Flow imaging of the mitral valve, however, is challenging, since it moves in and out of the image plane during the cardiac cycle.
Purpose:
To more accurately measure mitral flow, a slice-following MRI phase contrast sequence is proposed. This study aimed to implement such a sequence, validate its slice-following functionality in a phantom and healthy subjects, and test its feasibility in patients with mitral valve dysfunction.
Study type:
Prospective.
Phantom and subjects:
The slice-following functionality was validated in a cone-shaped phantom by measuring the depicted slice radius. Sixteen healthy subjects and 10 mitral valve dysfunction patients were enrolled at two sites.
Field strength/sequence:
1.5T and 3T gradient echo cine phase contrast.
Assessment:
A single breath-hold retrospectively gated sequence using offline feature-tracking of the mitral valve was developed. Valve displacements were measured and imported to the scanner, allowing the slice position to change dynamically based on the cardiac phase. Mitral valve imaging was performed with slice-following and static imaging planes. Validation was performed by comparing mitral stroke volume with planimetric and aortic stroke volume.
Statistical tests:
Measurements were compared using linear regression, Pearson's R, parametric paired t-tests, Bland-Altman analysis, and intraclass correlation coefficient (ICC).
Results:
Phantom experiments confirmed accurate slice displacements. Slice-following was feasible in all subjects, yielding physiologically accurate mitral flow patterns. In healthy subjects, mitral and aortic stroke volumes agreed, with ICC = 0.72 and 0.90 for static and slice-following planes; with bias ±1 SDs 23.2 ± 13.2 mls and 8.4 ± 10.8 mls, respectively. Agreement with planimetry was stronger, with ICC = 0.84 and 0.96; bias ±1 SDs 13.7 ± 13.7 mls and -2.0 ± 8.8 mls for static and slice-following planes, respectively.
Data conclusion:
Slice-following outperformed the conventional sequence and improved the accuracy of transmitral flow, which is important for assessment of diastolic function and mitral regurgitation.
Level of evidence:
2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019.
... Kozerke et al. 20,21 first showed that 2D PC of the valves was possible using a dynamic slice with valve-tracking, in which motion is estimated using a slice tagging method. More recently, a semi-automated feature-tracking of the valve plane on long-axis cine images has been developed 22 . ...
... The tricuspid valve has not been studied with prior valvetracking 2D-PC methods. Rotations were not included in a recent valve-tracking study of the mitral valve,23 but appeared to have been incorporated in earlier valve-tracking 20,21 . Rotations are highly challenging to implement but might be needed for the tricuspid valve. ...
Purpose
Tricuspid valve flow velocities are challenging to measure with cardiovascular MR, as the rapidly moving valvular plane prohibits direct flow evaluation, but they are vitally important to diastolic function evaluation. We developed an automated valve‐tracking 2D method for measuring flow through the dynamic tricuspid valve.
Methods
Nine healthy subjects and 2 patients were imaged. The approach uses a previously trained deep learning network, TVnet, to automatically track the tricuspid valve plane from long‐axis cine images. Subsequently, the tracking information is used to acquire 2D phase contrast (PC) with a dynamic (moving) acquisition plane that tracks the valve. Direct diastolic net flows evaluated from the dynamic PC sequence were compared with flows from 2D‐PC scans acquired in a static slice localized at the end‐systolic valve position, and also ventricular stroke volumes (SVs) using both planimetry and 2D PC of the great vessels.
Results
The mean tricuspid valve systolic excursion was 17.8 ± 2.5 mm. The 2D valve‐tracking PC net diastolic flow showed excellent correlation with SV by right‐ventricle planimetry (bias ± 1.96 SD = −0.2 ± 10.4 mL, intraclass correlation coefficient [ICC] = 0.92) and aortic PC (−1.0 ± 13.8 mL, ICC = 0.87). In comparison, static tricuspid valve 2D PC also showed a strong correlation but had greater bias (p = 0.01) versus the right‐ventricle SV (10.6 ± 16.1 mL, ICC = 0.61). In most (8 of 9) healthy subjects, trace regurgitation was measured at begin‐systole. In one patient, valve‐tracking PC displayed a high‐velocity jet (380 cm/s) with maximal velocity agreeing with echocardiography.
Conclusion
Automated valve‐tracking 2D PC is a feasible route toward evaluation of tricuspid regurgitant velocities, potentially solving a major clinical challenge.
... Current guidelines recommend performing CMR for RegF quantification in cases with inconclusive echocardiographic workup, however, there is no consensus on how to define severe AR by CMR [7,8]. Several cut-off values for RegF have been suggested, ranging from 27-33% [9][10][11]. ...
... Consistent with previous literature, we defined severe AR as RegF ≥ 30%. Sensitivity analyses were performed for each published cut-off value, namely a RegF ≥ 27% and ≥33% [9][10][11][12]. Diagnostic performance of published upper limits of normal to define LV dilatation was assessed. ...
Background:
Left ventricular (LV) dilatation is a key compensatory feature in patients with chronic aortic regurgitation (AR). However, sex-differences in LV remodeling and outcomes in chronic AR have been poorly investigated so far.
Methods:
We performed cardiovascular magnetic resonance imaging (CMR) including phase-contrast velocity-encoded imaging for the measurement of regurgitant fraction (RegF) at the sinotubular junction, in consecutive patients with at least mild AR on echocardiography. We assessed LV size (end-diastolic volume indexed to body surface area, LVEDV/BSA) and investigated sex differences between LV remodeling and increasing degrees of AR severity. Cox-regression models were used to test differences in outcomes between men and women using a composite of heart failure hospitalization, unscheduled AR intervention, and cardiovascular death.
Results:
270 consecutive patients (59.6% male, 59.8 ± 20.8 y/o, 59.6% with at least moderate AR on echocardiography) were included. On CMR, mean RegF was 18.1 ± 17.9% and a total of 65 (24.1%) had a RegF ≥ 30%. LVEDV/BSA was markedly closer related with AR severity (RegF) in men compared to women. Each 1-SD increase in LVEDV/BSA (mL/m2) was associated with a 9.7% increase in RegF in men and 5.9% in women, respectively (p-value for sex-interaction < 0.001). Based on previously published reference values, women-in contrast to men-frequently had a normal LV size despite severe AR (e.g., for LVEDV/BSA on CMR: 35.3% versus 8.7%, p < 0.001). In a Cox-regression model adjusted for age, LVEDV/BSA and RegF, women were at significantly higher risk for the composite endpoint when compared to men (adj. HR 1.81 (95%CI 1.09-3.03), p = 0.022).
Conclusion:
In patients with chronic AR, LV remodeling is a hallmark feature in men but not in women. Severity of AR may be underdiagnosed in female patients in the absence of LV dilatation. Future studies need to address the dismal prognosis in female patients with chronic AR.
... Further analyses were performed to define the mechanism leading to inaccuracy of flow measurement in the AAo, because multiple factors may contribute to errors in flow measurement. The most relevant include: (i) complex flow patterns with consequent intravoxel dephasing and underestimation in velocity measurement, 7,13 (ii) longitudinal excursion of the aortic annulus with a consequent systolic change in the aortic luminal volume between the fixed plane of velocity acquisition and the moving plane of the aortic valve annulus, 11,14 and (iii) phase-offset errors. 15 The complexity of flow pattern in the AAo was assessed by quantifying flow eccentricity according to the normalized flow displacement from the vessel centre at peak systole, as previously described. ...
... Considering that the myocardial perfusion is predominantly diastolic, this difference is not explainable with coronary flow that quits the aorta before the imaging plane in the AAo. Multiple mechanisms, including the complexity of the flow pattern with flow turbulence, helical flow, and consequent intravoxel dephasing, 12,13,19 but also the longitudinal excursion of the aortic annulus with consequent systolic change in the aortic luminal volume between the fixed plane of velocity acquisition and the moving plane of the aortic valve annulus, 11,14 and phase-offsets may compromise the accuracy of flow measurement. 15 Phase-offsets are due to concomitant field effects, which are related with the distance to the isocentre, and to eddy current effects, which are independent of off-centre effect. ...
Bicuspid aortic valve (BAV) causes complex flow patterns in the ascending aorta (AAo), which may compromise the accuracy of flow measurement by phase-contrast magnetic resonance (PC-MR). Therefore, we aimed to assess and compare the accuracy of forward flow measurement in the AAo, where complex flow is more dominant in BAV patients, with flow quantification in the left ventricular outflow tract (LVOT) and the aortic valve orifice (AV), where complex flow is less important, in BAV patients and controls.
Flow was measured by PC-MR in 22 BAV patients and 20 controls at the following positions: (i) LVOT, (ii) AV, and (iii) AAo, and compared with the left ventricular stroke volume (LVSV). The correlation between the LVSV and the forward flow in the LVOT, the AV, and the AAo was good in BAV patients (r = 0.97/0.96/0.93; P < 0.01) and controls (r = 0.96/0.93/0.93; P < 0.01). However, in relation with the LVSV, the forward flow in the AAo was mildly underestimated in controls and much more in BAV patients [median (inter-quartile range): 9% (4%/15%) vs. 22% (8%/30%); P < 0.01]. This was not the case in the LVOT and the AV. The severity of flow underestimation in the AAo was associated with flow eccentricity.
Flow measurement in the AAo leads to an underestimation of the forward flow in BAV patients. Measurement in the LVOT or the AV, where complex flow is less prominent, is an alternative means for quantifying the systolic forward flow in BAV patients.
... In normal subjects, there is a slight forward flow during late diastole in flow quantification using CMR, caused by the movement of the pulmonary valve during atrioventricular displacement. 20 Therefore, forward flow as a percentage of the net forward flow during the cardiac cycle ( Figure 1) was calculated in 12 healthy children (15 + 3 years) with normal CMR referred for screening of arrythmogenic right ventricular cardiomyopathy because of a family history of this disease. A threshold of mean + 2 SD of the percentage of forward flow during atrial contraction in healthy subjects was set as normal and values above this as restrictive physiology. ...
... We used 2.5% end-diastolic forward flow as a cut-off for restrictive physiology based on the forward flow seen in healthy children due to longitudinal AV-plane movement during atrial contraction. 20 The association of restrictive physiology and RV fibrosis in our patient population does not necessarily mean that RV fibrosis is the cause of restrictive physiology. However, our findings show that restrictive physiology found at follow-up in patients with large RV volumes and RF is strongly associated with myocardial fibrosis in the RVOT. ...
AimsTo determine whether the restrictive physiology seen in Tetralogy of Fallot (TOF) patients can be explained by fibrosis of the right ventricular (RV) outflow tract. The aetiology for restrictive RV physiology after TOF repair is not known.Methods and resultsTOF patients (n = 31, 13 girls, 10.2 years ± 2.8) were included 9.2 ± 2.9 years after total correction and examined with cardiac magnetic resonance (CMR) and Doppler echocardiography. Cine, flow, and late gadolinium contrast enhanced (LGE) CMR imaging were performed to quantify RV volumes, pulmonary flow and regurgitation (PR), and fibrosis. Healthy children (n = 12) were investigated with CMR of the pulmonary flow. Forward flow during atrial contraction above mean + 2 SD of healthy subjects was set as a marker of restrictive physiology. Four patients were excluded due to suboptimal LGE-CMR. Fisher's exact test was used to determine the association between restrictive physiology and fibrosis. Sixteen patients showed fibrosis in the right ventricular outflow tract (RVOT) on LGE-CMR and 14 of them showed restrictive physiology on CMR. Of the 11 patients without fibrosis in the RVOT, 1 showed restrictive physiology. The odds ratio for RVOT fibrosis in patients with restrictive RV physiology was 70.0 (CI: 5.6-882.7, P < 0.001). The transannular patch repair did not differ between the groups (P = 0.37). The degree of RVOT fibrosis correlated positively with PR (r2 = 0.38, P < 0.001) and RV volumes (r2 = 0.51 for end-diastolic volume and r2 = 0.47 for end-systolic volume, P < 0.001).Conclusion
There is a strong association between the restrictive RV physiology detected on CMR and fibrosis of the RVOT in children after TOF repair. © 2013 Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2013. For permissions please email: [email protected]
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... 4D flow methods have had success in tricuspid regurgitant velocity evaluation, using many minutes of scan time, because retrospective valve tracking can be employed 9,10 . Prospective valve-tracking methods have been employed to acquire 2D phase-contrast (PC) with a dynamic slice plane prescription that changes over the cardiac cycle 11,12 . We recently used this approach, but using modern feature-tracking of the mitral valve 13 to enable rapid and accurate valve-tracking of the simple mitral valve translations 14 . ...
Tricuspid regurgitant velocity is a crucial biomarker in identifying pressure overload in the right heart, associated with diastolic dysfunction and pulmonary hypertension. 2D phase-contrast cannot quantify this flow, and echocardiography is used clinically. We developed a phase-contrast method which utilizes deep-learning algorithms to track the valvular slice in a cardiac phase-dependent manner, which we call 2.5D flow. We studied its performance in nine healthy subjects and patients with tricuspid regurgitation. RV stroke volumes correlated better to forward flow volumes by 2.5D flow vs. static 2D phase-contrast (ICC=0.88 vs. 0.62). 2.5D flow characterized regurgitation in a patient.
... A potential limitation with phrase-contrast imaging of the M inflow relates to through-plane motion of the valve plane, which can cause errors in the measurement of flow. For this reason, there is ongoing work in developing prospective section tracking flow cardiac MRI sequences (25). Future directions include larger prospective studies using four-dimensional flow data to help make various comparisons with a time efficient imaging algorithm. ...
Purpose:
To determine the impact of prolapsed volume on regurgitant volume (RegV), regurgitant fraction (RF), and left ventricular ejection fraction (LVEF) in patients with mitral valve prolapse (MVP) using cardiac MRI.
Materials and methods:
Patients with MVP and mitral regurgitation who underwent cardiac MRI from 2005 to 2020 were identified retrospectively from the electronic record. RegV is the difference between left ventricular stroke volume (LVSV) and aortic flow. Left ventricular end-systolic volume (LVESV) and LVSV were obtained from volumetric cine images, with prolapsed volume inclusion (LVESVp, LVSVp) and exclusion (LVESVa, LVSVa) providing two estimates of RegV (RegVp, RegVa), RF (RFp, RFa), and LVEF (LVEFa, LVEFp). Interobserver agreement for LVESVp was assessed using intraclass correlation coefficient (ICC). RegV was also calculated independently using measurements from mitral inflow and aortic net flow phase-contrast imaging as the reference standard (RegVg).
Results:
The study included 19 patients (mean age, 28 years ± 16 [SD]; 10 male patients). Interobserver agreement for LVESVp was high (ICC, 0.98; 95% CI: 0.96, 0.99). Prolapsed volume inclusion resulted in higher LVESV (LVESVp: 95.4 mL ± 34.7 vs LVESVa: 82.4 mL ± 33.8; P < .001), lower LVSV (LVSVp: 100.5 mL ± 33.8 vs LVSVa: 113.5 mL ± 35.9; P < .001), and lower LVEF (LVEFp: 51.7% ± 5.7 vs LVEFa: 58.6% ± 6.3; P < .001). RegV was larger in magnitude when prolapsed volume was excluded (RegVa: 39.4 mL ± 21.0 vs RegVg: 25.8 mL ± 22.8; P = .02), with no evidence of a difference when including prolapsed volume (RegVp: 26.4 mL ± 16.4 vs RegVg: 25.8 mL ± 22.8; P > .99).
Conclusion:
Measurements that included prolapsed volume most closely reflected mitral regurgitation severity, but inclusion of this volume resulted in a lower LVEF.Keywords: Cardiac, MRI© RSNA, 2023See also commentary by Lee and Markl in this issue.
... In prospective triggering, the R wave from the ECG signal is identified and, after a preset trigger delay and within a specified acquisition window, data are acquired. This triggering freezes the heart motion at a specific phase or over a certain number of phases in the cardiac cycle [33][34][35][36][37][38][39]. However, if the chosen acquisition window is too long or occurs during a transient state, then residual motion blurring will be observed [40]. ...
Cardiovascular magnetic resonance (CMR) features a variety of protocols that are sensitive to respiratory, cardiac, and other types of motion. For some applications, physiological motion corresponds to diagnostic data that can be obtained with dedicated sequences. In many other cases, motion is a major source of image artifacts that must be addressed. As such, considerable research efforts have been made in the field to extract diagnostic motion information and/or correct for motion-induced errors in CMR. This chapter will introduce the general challenges that respiratory and cardiac motion pose to CMR, present general techniques that have been developed to measure and correct for motion, and finally describe application-specific solutions that have been proposed to solve this problem.
... Exacerbated by factors like vigorous longitudinal contraction of the LV (common in severe MR). These limitations may be overcome by the use of prospective slice tracking flow CMR sequences [22], but this involves complex software programming and it is not widely available so far. These concerns have resulted in an interest in the use of 4D flow CMR sequences with retrospective valve tracking. ...
Abstract Background Four-dimensional cardiovascular magnetic resonance (CMR) flow assessment (4D flow) allows to derive volumetric quantitative parameters in mitral regurgitation (MR) using retrospective valve tracking. However, prior studies have been conducted in functional MR or in patients with congenital heart disease, thus, data regarding the usefulness of 4D flow CMR in case of a valve pathology like mitral valve prolapse (MVP) are scarce. This study aimed to evaluate the clinical utility of cine-guided valve segmentation of 4D flow CMR in assessment of MR in MVP when compared to standardized routine CMR and transthoracic echocardiography (TTE). Methods Six healthy subjects and 54 patients (55 ± 16 years; 47 men) with MVP were studied. TTE severity grading used a multiparametric approach resulting in mild/mild-moderate (n = 12), moderate-severe (n = 12), and severe MR (n = 30). Regurgitant volume (RVol) and regurgitant fraction (RF) were also derived using standard volumetric CMR and 4D flow CMR datasets with direct measurement of regurgitant flow (4DFdirect) and indirect calculation using the formula: mitral valve forward flow - left ventricular outflow tract stroke volume (4DFindirect). Results There was moderate to strong correlation between methods (r = 0.59–0.84, p
... The extent to which this motion may or may not affect the PC assessment of BMV function has not yet been established. Motion tracking algorithms have been developed and could be utilized to mitigate these effects if clinically indicated [22,23]. In the clinical environment some patients suffer coincident arrhythmias which can reduce the accuracy of many CMR measures. ...
Background:
A comprehensive non-invasive evaluation of bioprosthetic mitral valve (BMV) function can be challenging. We describe a novel method to assess BMV effective orifice area (EOA) based on phase contrast (PC) cardiovascular magnetic resonance (CMR) data. We compare the performance of this new method to Doppler and in vitro reference standards.
Methods:
Four sizes of normal BMVs (27, 29, 31, 33 mm) and 4 stenotic BMVs (27 mm and 29 mm, with mild or severe leaflet obstruction) were evaluated using a CMR- compatible flow loop. BMVs were evaluated with PC-CMR and Doppler methods under flow conditions of; 70 mL, 90 mL and 110 mL/beat (n = 24). PC-EOA was calculated as PC-CMR flow volume divided by the PC- time velocity integral (TVI).
Results:
PC-CMR measurements of the diastolic peak velocity and TVI correlated strongly with Doppler values (r = 0.99, P < 0.001 and r = 0.99, P < 0.001, respectively). Across all conditions tested, the Doppler and PC-CMR measurement of EOA (1.4 ± 0.5 vs 1.5 ± 0.7 cm2, respectively) correlated highly (r = 0.99, P < 0.001), with a minimum bias of 0.13 cm2, and narrow limits of agreement (- 0.2 to 0.5 cm2).
Conclusion:
We describe a novel method to assess BMV function based on PC measures of transvalvular flow volume and velocity integration. PC-CMR methods can be used to accurately measure EOA for both normal and stenotic BMV's and may provide an important new parameter of BMV function when Doppler methods are unobtainable or unreliable.
... Moreover, blood ejected into the aortic sinuses in systole that has not yet crossed the CMR image slice flows back into the left ventricle and, hence, will not contribute to the AR determination: the smaller RVol and RF, the greater the influence on the diagnostic accuracy. These potential limitations may be overcome by the use of slice tracking flow CMR sequences, which follow the valve and capture this potentially "undetected" regurgitation, with an increase in the RF by 60%, 15%, and 7% in mild, moderate and severe AR, respectively [16]. ...
Transthoracic echocardiography (TTE) and cardiac magnetic resonance (CMR) are current standard for assessing aortic regurgitation (AR). Regurgitant fraction (RF) can also be estimated by Doppler examination of the left subclavian artery (LSA-Doppler). However, a comparison of AR grading scales using these methods and a TTE multiparametric approach as reference is lacking. We evaluated the severity of AR in 73 patients (58 ± 15 years; 57 men), with a wide spectrum of AR of the native valve. Using a recommended TTE multiparametric approach the AR was divided in none/trace (n = 12), mild (n = 23), moderate (n = 12), and severe (n = 26). RF was evaluated by LSA-Doppler (ratio between diastolic and systolic velocity–time integrals) and by CMR phase-contrast imaging (performed in the aorta 1 cm above the aortic valve); the grading scales were then calculated. There were a good correlation between all methods, but mean RF values were greater with TTE compared with LSA-Doppler and CMR (39 ± 16% vs. 35 ± 18% vs. 32 ± 20%, respectively; p < 0.037). Mean differences in RF values between methods were significant in the groups with mild and moderate AR. Grading scales that best defined the TTE derived AR severity using CMR were: mild, < 21%; moderate, 22 to 41%; and severe, > 42%; and using LSA-Doppler: mild, < 29%; moderate, 30 to 44%; and severe, > 45%. RF values for AR grading using TTE, LSA-Doppler and CMR correlate well but differ in groups with mild and moderate AR when using a recognized multiparametric echocardiographic approach. Clinical prospective studies should validate these proposed modality adjusted grading scales.
... However, both sets of guidelines lack specifications on how to exactly quantify and grade AR by CMR (6,7). This may be due to the fact that cutoff values for RegV and RegF, which identify hemodynamically significant AR, are not well established (8)(9)(10). HRF in the descending aorta is accepted as a strong indicator of severe AR (2) and is included in the standard assessment of AR by TTE. ...
Objectives:
This study investigated the diagnostic and prognostic value of cardiac magnetic resonance (CMR) imaging in chronic aortic regurgitation (AR).
Background:
Accurate quantification of AR severity by echocardiography frequently remains difficult. CMR is recommended as the complementary method; however, its accuracy and prognostic utility remain unknown.
Methods:
A total of 232 consecutive patients (34.5% were females 55.5 ± 19.8 years of age) with chronic AR (including 40 with moderate to severe and 44 with severe AR on echocardiography) underwent CMR within 4 weeks of echocardiography. CMR included phase-contrast velocity-encoded imaging for the measurement of regurgitant volume and fraction at the sinotubular junction and assessment of holodiastolic retrograde flow (HRF) in the descending aorta. Significant AR was defined as the presence of HRF on CMR. Patients were followed prospectively, and multivariate Cox regression was applied for outcome analysis using a combination of heart failure, hospitalization, and cardiovascular death as primary endpoint.
Results:
AR severity on the basis of echo was reclassified in a significant number of patients according to CMR: 6.8% with mild AR on echo had HRF on CMR, whereas 34.1% with severe AR on echo did not have HRF on CMR and were reclassified as having nonsignificant AR. In 40 patients with uncertain AR severity (moderate to severe) on echo, 45.0% had HRF on CMR, indicating severe AR. Patients were followed for 35.3 ± 26.6 months. During that period, 63 patients (27.2%) reached the combined endpoint, including 43 (18.5%) with heart failure hospitalizations and 20 (8.6%) with cardiovascular deaths. By multivariate regression analysis, including clinical as well as imaging parameters, only N-terminal pro-B-type natriuretic peptide concentration (hazard ratio: 2.184 [95% confidence interval: 1.468 to 3.248]; p < 0.001) and HRF on CMR (hazard ratio: 2.774 [95% confidence interval: 1.131 to 6.802]; p = 0.026) remained significantly associated with outcome.
Conclusions:
In chronic AR, CMR has the potential to add important diagnostic and prognostic information.
... One challenge in CMR, however, is that the acquisition plane remains fixed during the cardiac cycle and does not move with the cyclical motion of the mitral annulus. Acquisition techniques have been introduced using moving slice velocity mapping [25] and three-dimensional three-directional velocity encoding [26]. These have shown better agreement with echo Doppler when discriminating restrictive filling patterns from other grades of diastolic dysfunction [27]. ...
Purpose of review:
To give an update on the emerging role of cardiac magnetic resonance imaging in the evaluation of patients with heart failure with preserved ejection fraction (HFpEF). This is important as the diagnosis of HFpEF remains challenging and cardiac imaging is pivotal in establishing the function of the heart and whether there is evidence of structural heart disease or diastolic dysfunction. Echocardiography is widely available, although the gold standard in quantifying heart function is cardiac magnetic resonance (CMR) imaging.
Recent findings:
This review includes the recently updated 2016 European Society of Cardiology guidelines on diagnosing HFpEF that define the central role of imaging in identifying patients with HFpEF. Moreover, it includes the pathophysiology in HFpEF, how CMR works, and details current CMR techniques used to assess structural heart disease and diastolic function. Furthermore, it highlights promising research techniques that over the next few years may become more used in identifying these patients. CMR has an emerging role in establishing the diagnosis of HFpEF by measuring the left ventricular ejection fraction (LVEF) and evidence of structural heart disease and diastolic dysfunction.
... With regard to the need to undergo MV surgery, one single recent study proposed a validated cut-off value for Reg Vol and RF with CMR [10], and no general consensus exists regarding the most appropriate CMR quantification technique. Several CMR approaches have been used including the comparison of the LVSV with the RVSV [13], LVSV with the Ao forward by phase-contrast cine imaging [15,17], trans-mitral forward flow with Ao forward [12,23], or by direct measurement of the regurgitant orifice area [24]. However, these methods were not specifically validated for MVP patients and they seem not to Fig. 3 Comparison of LVSV and reference SV in 15 patients with no significant mitral regurgitation. ...
Background
To quantify mitral regurgitation (MR) with CMR, the regurgitant volume can be calculated as the difference between the left ventricular (LV) stroke volume (SV) measured with the Simpson’s method and the reference SV, i.e. the right ventricular SV (RVSV) in patients without tricuspid regurgitation. However, for patients with prominent mitral valve prolapse (MVP), the Simpson’s method may underestimate the LV end-systolic volume (LVESV) as it only considers the volume located between the apex and the mitral annulus, and neglects the ventricular volume that is displaced into the left atrium but contained within the prolapsed mitral leaflets at end systole. This may lead to an underestimation of LVESV, and resulting an over-estimation of LVSV, and an over-estimation of mitral regurgitation. The aim of the present study was to assess the impact of prominent MVP on MR quantification by CMR.
Methods
In patients with MVP (and no more than trace tricuspid regurgitation) MR was quantified by calculating the regurgitant volume as the difference between LVSV and RVSV. LVSVuncorr was calculated conventionally as LV end-diastolic (LVEDV) minus LVESV. A corrected LVESVcorr was calculated as the LVESV plus the prolapsed volume, i.e. the volume between the mitral annulus and the prolapsing mitral leaflets. The 2 methods were compared with respect to the MR grading. MR grades were defined as absent or trace, mild (5–29% regurgitant fraction (RF)), moderate (30–49% RF), or severe (≥50% RF).
Results
In 35 patients (44.0 ± 23.0y, 14 males, 20 patients with MR) the prolapsed volume was 16.5 ± 8.7 ml. The 2 methods were concordant in only 12 (34%) patients, as the uncorrected method indicated a 1-grade higher MR severity in 23 (66%) patients. For the uncorrected/corrected method, the distribution of the MR grades as absent-trace (0 vs 11, respectively), mild (20 vs 18, respectively), moderate (11 vs 5, respectively), and severe (4 vs 1, respectively) was significantly different (p < 0.001). In the subgroup without MR, LVSVcorr was not significantly different from RVSV (difference: 2.5 ± 4.7 ml, p = 0.11 vs 0) while a systematic overestimation was observed with LVSVuncorr (difference: 16.9 ± 9.1 ml, p = 0.0007 vs 0). Also, RVSV was highly correlated with aortic forward flow (n = 24, R² = 0.97, p < 0.001).
Conclusion
For patients with severe bileaflet prolapse, the correction of the LVSV for the prolapse volume is suggested as it modified the assessment of MR severity by one grade in a large portion of patients.
... Early works with Doppler ultrasound also described the velocity profiles at the aortic root to be parabolic and skewed towards the right anterior wall [125], and works with 3D probes also provide the evidence of non-flat profiles [91]. PC-MRI data is currently the best imaging modality to interrogate the blood velocity profiles in vivo, and has also been used to report non-flat profiles at the aortic root [103]. It should be noted that the PSF of an MRI acquisition system causes a spatial averaging of the velocity data is now only needed at two planes of the vascular anatomy, and not in the entire lumen or ventricular blood pool. ...
The presence of obstructions to blood flow in the human cardiovascular system can lead to an inability to efficiently and effectively perfuse downstream tissues and increase the work demand of the heart. In this scenario, the pressure drop through a vascular obstruction is a biomarker adopted in clinical guidelines for the management of several disease conditions, such as aortic coarctation and valvular stenosis. While extensively used clinically, current methods and tools to assess the pressure drop suffer from either the associated risks of invasive catheterization procedures, or potential inaccuracies from non-invasive pressure estimations due to simplified formulations or inter-observer variability.
The primary aim of this thesis is to further develop non-invasive methods to estimate pressure drops, increasing current robustness and accuracy. Using the comprehensive spatio-temporal hemodynamic information provided by Four Dimensional Phase-Contrast Magnetic Resonance Imaging, an existing finite element formulation to compute pressure differences is evaluated, illustrating its sensitivity to data when estimating viscous flows and exploring potential approaches to address this. A novel formulation using the work-energy principle is then introduced and validated on in silico test cases, demonstrating an increased accuracy and robustness to noise and to the image segmentation process. Finally, the proposed method is applied for the assessment of the aortic valve function of a cohort of patients with various degree of stenosis, revealing a fundamental bias in the Bernoulli formulation taken in Doppler-based estimation.
... Slice positioning near mobile cardiac valves especially for regurgitation measurement has to balance multiple inaccuracies including distal Windkessel, coronary flow, proximal valve motion and signal loss [79,80], even if repeatability is precise [81]. Prospective [82] and retrospective [83] valveplane tracking may offer improvements beyond what is currently available on commercial scanners. ...
Cardiovascular magnetic resonance (CMR) phase contrast imaging has undergone a wide range of changes with the development and availability of improved calibration procedures, visualization tools, and analysis methods. This article provides a comprehensive review of the current state-of-the-art in CMR phase contrast imaging methodology, clinical applications including summaries of past clinical performance, and emerging research and clinical applications that utilize today’s latest technology.
Electronic supplementary material
The online version of this article (doi:10.1186/s12968-015-0172-7) contains supplementary material, which is available to authorized users.
... 355 Methods to correct for inaccuracies have been developed but are currently not routinely available. 356,357 Stenosis Bicuspid or fused aortic valves can be identified with accurate positioning of the imaging plane in early systole perpendicular to the doming valve leaflets. Direct planimetry of the orifice area is also feasible. ...
This paper was guest edited by Dr. E. Fleck. Deutsches Herzzentrum Berlin, Germany
Cardiovascular magnetic resonance (CMR) is established in clinical practice for the diagnosis and management of diseases of the cardiovascular system. However, current guidelines for when this technique should be employed in clinical practice have not been revised since a Task Force report of 1998.1 Considerable technical and practice advances have been made in the intervening years and the level of interest from clinicians in this field is at an unprecedented level. Therefore the aim of this report from a Consensus Panel of established experts in the field of CMR is to update these guidelines. As CMR is a multi-disciplinary technique with international interest, the Consensus Panel was composed of European and American cardiologists and radiologists with major input from members with additional established expertise in paediatric cardiology, nuclear cardiology, magnetic resonance physics and spectroscopy, as well as health economics. The Consensus Panel was originated, approved and funded in its activities by the Working Group on CMR of the European Society of Cardiology and the Society for Cardiovascular Magnetic Resonance.
The Consensus Panel recommendations are based on evidence compiled from the literature and expert experience. If there is insufficient evidence in the literature, this is indicated in the report but usually no recommendations are made under these circumstances. The appropriateness of using CMR is described for the frequent disease entities where imaging information may be warranted. The diagnostic use of CMR will be described in the context of other, competing imaging techniques, with particular emphasis on the differential indications with respect to echocardiography.
The usefulness of CMR in specific diseases is summarized by means of the following classification:
... However, some reports have suggested that CT can assess tricuspid regurgitation based on early contrast opacification of the inferior vena cava or hepatic veins. 96,97 Clinical Application: CMR phase-contrast (PC) imaging is widely used for quantification of left-sided valvular regurgitation, [98][99][100] and can be applied to the tricuspid and pulmonic valves. Transpulmonic flow quantification can also measure RV stroke volume independent of cine-CMR volumetric assessment. ...
Right ventricular (RV) structure and function is of substantial importance in a broad variety of clinical conditions. Cardiac magnetic resonance (CMR) and computed tomography (CT) each provide three-dimensional RV imaging, high-resolution evaluation of RV structure/anatomy, and accurate functional assessment without geometric assumptions. This is of particular significance for the RV, where complex geometry compromises reliance on indices derived from two-dimensional (2D) imaging planes. CMR flow-based imaging can be applied to right-sided heart valves, enabling evaluation of hemodynamic and valvular dysfunction that may contribute to or result from RV dysfunction. Tissue characterization imaging by both CMR and CT provides valuable complementary assessment of the RV. Changes in myocardial tissue composition provide a mechanistic substrate for RV dysfunction and cardiac arrhythmias. This review provides an overview of RV imaging by both CMR and CT, with focus on assessment of RV structure/function, flow, and tissue characterization. Emerging evidence and established guidelines are discussed in the context of imaging contributions to diagnosis, prognostic risk stratification and disease management of clinical conditions that impact the right ventricle.
Purpose:
In cardiac MRI, valve motion parameters can be useful for the diagnosis of cardiac dysfunction. In this study, a fully automated AI-based valve tracking system was developed and evaluated on 2- or 4-chamber view cine series on a large cardiac MR dataset. Automatically derived motion parameters include atrioventricular plane displacement (AVPD), velocities (AVPV), mitral or tricuspid annular plane systolic excursion (MAPSE, TAPSE), or longitudinal shortening (LS).
Method:
Two sequential neural networks with an intermediate processing step are applied to localize the target and track the landmarks throughout the cardiac cycle. Initially, a localisation network is used to perform heatmap regression of the target landmarks, such as mitral, tricuspid valve annulus as well as apex points. Then, a registration network is applied to track these landmarks using deformation fields. Based on these outputs, motion parameters were derived.
Results:
The accuracy of the system resulted in deviations of 1.44 ± 1.32 mm, 1.51 ± 1.46 cm/s, 2.21 ± 1.81 mm, 2.40 ± 1.97 mm, 2.50 ± 2.06 mm for AVPD, AVPV, MAPSE, TAPSE and LS, respectively. Application on a large patient database (N = 5289) revealed a mean MAPSE and LS of 9.5 ± 3.0 mm and 15.9 ± 3.9 % on 2-chamber and 4-chamber views, respectively. A mean TAPSE and LS of 13.4 ± 4.7 mm and 21.4 ± 6.9 % was measured.
Conclusion:
The results demonstrate the versatility of the proposed system for automatic extraction of various valve-related motion parameters.
An unmet need in cardiac MRI is evaluation of diastolic dysfunction, which by echo requires measurement of LA volumes, E/e' and tricuspid regurgitant flow velocity. Of these parameters, tricuspid regurgitant flow (indicating right heart pressure) is not yet feasible. 4D flow has been investigated, but scan times are long, and trade-offs are needed. 2D flow cannot map TV regurgitant velocities due to the valvular motion. Recently, we adapted 2D valve-following PC that follows the displacement of the mitral valve throughout the heartbeat, to use modern feature tracking. Here we present a pilot study in tricuspid 2D flow using a valve-following slice, which we call 2.5D flow, due to its partial third dimension. The valve-following is now automated using deep-learning networks for tracking the valves.
Cardiovascular disease (CVD) is the leading single cause of morbidity and mortality, causing over 17. 9 million deaths worldwide per year with associated costs of over $800 billion. Improving prevention, diagnosis, and treatment of CVD is therefore a global priority. Cardiovascular magnetic resonance (CMR) has emerged as a clinically important technique for the assessment of cardiovascular anatomy, function, perfusion, and viability. However, diversity and complexity of imaging, reconstruction and analysis methods pose some limitations to the widespread use of CMR. Especially in view of recent developments in the field of machine learning that provide novel solutions to address existing problems, it is necessary to bridge the gap between the clinical and scientific communities. This review covers five essential aspects of CMR to provide a comprehensive overview ranging from CVDs to CMR pulse sequence design, acquisition protocols, motion handling, image reconstruction and quantitative analysis of the obtained data. (1) The basic MR physics of CMR is introduced. Basic pulse sequence building blocks that are commonly used in CMR imaging are presented. Sequences containing these building blocks are formed for parametric mapping and functional imaging techniques. Commonly perceived artifacts and potential countermeasures are discussed for these methods. (2) CMR methods for identifying CVDs are illustrated. Basic anatomy and functional processes are described to understand the cardiac pathologies and how they can be captured by CMR imaging. (3) The planning and conduct of a complete CMR exam which is targeted for the respective pathology is shown. Building blocks are illustrated to create an efficient and patient-centered workflow. Further strategies to cope with challenging patients are discussed. (4) Imaging acceleration and reconstruction techniques are presented that enable acquisition of spatial, temporal, and parametric dynamics of the cardiac cycle. The handling of respiratory and cardiac motion strategies as well as their integration into the reconstruction processes is showcased. (5) Recent advances on deep learning-based reconstructions for this purpose are summarized. Furthermore, an overview of novel deep learning image segmentation and analysis methods is provided with a focus on automatic, fast and reliable extraction of biomarkers and parameters of clinical relevance.
Purpose:
To elucidate the influence of through-plane heart motion on the assessment of aortic regurgitation (AR) severity using phase contrast magnetic resonance imaging (PC-MRI).
Approach:
A patient cohort with chronic AR (n = 34) was examined with PC-MRI. The regurgitant volume (RVol) and fraction (RFrac) were extracted from the PC-MRI data before and after through-plane heart motion correction and was then used for assessment of AR severity.
Results:
The flow volume errors were strongly correlated to aortic diameter (R = 0.80, p < 0.001) with median (IQR 25%;75%): 16 (14; 17) ml for diameter>40mm, compared with 9 (7; 10) ml for normal aortic size (p < 0.001). RVol and RFrac were underestimated (uncorrected:64 ± 37 ml and 39 ± 17%; corrected:76 ± 37 ml and 44 ± 15%; p < 0.001) and ~ 20% of the patients received lower severity grade without correction.
Conclusion:
Through-plane heart motion introduces relevant flow volume errors, especially in patients with aortic dilatation, that may result in underestimation of the severity grade in patients with chronic AR.
Phase-contrast magnetic resonance imaging (PC-MRI) also known as velocity-encoded cine magnetic resonance imaging (VENC-MRI) is the primary technique for blood flow measurements, qualitative and quantitative information on both flow volume and flow velocity in the great vessels. In this chapter, we discuss the basics of phase-contrast MRI techniques, describe the pitfalls and limitations associated with phase-contrast imaging, provide guidelines for post processing and data analysis, and present specific clinical applications.
The intrinsic motion sensitivity of MRI, which is exploited in phase-contrast (PC) MRI, can be used to measure and quantify in vivo blood flow simultaneously with morphological data within a single examination. In clinical routine, the PC-MRI acquisition is typically synchronized with the cardiac cycle (CINE imaging) and based on methods that resolve two spatial dimensions (2D) in individual slices and encode the component of time-resolved velocity-directed perpendicularly to the 2D plane. This approach allows measurements of volume flow, systolic peak velocity, as well as regurgitant and shunt flows in congenital and acquired heart disease. A number of advanced flow MR imaging techniques that build on the fundamental principles of PC-MRI have recently been introduced, including real-time flow imaging for the evaluation of flow changes on short time scales and 4D flow MRI for the comprehensive analysis of complex time-resolved 3D blood flow characteristics. This chapter reviews the fundamental principles, imaging techniques, and applications of 2D CINE PC-MRI and provides and introduction and discussion of advanced flow MR imaging techniques.
Echocardiography remains the principal investigation for valvular heart disease (VHD). Cardiovascular MR provides accurate and reproducible information about the valves (flow, velocities, pressure gradient, volumes, regurgitant fraction), the left ventricle (volumes, mass, function, ischaemia and fibrosis) and the aorta (root measurements and coarctation). This detailed yet diverse information can be appropriately used in complex VHD/congenital cases to further grade disease severity and risk stratify the patient.
The reasons to perform noninvasive studies in patients with aortic regurgitation is to determien the optimal time point and need for valve replacement.
The assessment of valvular heart disease by cardiac MRI has changed little over the last decade. However, with the increasing use and development of percutaneous valve interventions (transcatheter and minimally-invasive surgery), there is an increasing need to use cardiac MRI to define which patients will benefit from treatment, which patients are suitable for a specific treatment and how patients will respond to their treatments. As cardiac MRI is the best available in-vivo test to define great vessel flow and ventricular volumes, whilst at the same time providing beautiful, high-resolution 3D/4D anatomical images of the heart, it may become the imaging modalities of choice for these assessments. Importantly, as long-term outcome data is acquired, this ability of cardiac MRI to accurately measure physiological parameters will help us define when to treat patients, in particular asymptomatic patients with valvular regurgitation. Finally, the development and increasing use of high spatio-temporal real-time data for acquiring flow and function information will enable MR scans to be performed over a short time period (e.g. 15 mins) comparable to the time it takes to perform a full echocardiogram!
Die Magnetresonanztomographie ermöglicht es, sowohl die Klappenmorphologie als auch die Flussgeschwindigkeit über eine Klappe darzustellen. Mit dieser Technik können der Echokardiographie entsprechende Befunde erhoben werden; die Visualisierung der Klappen selbst gelingt zur Zeit allerdings meist besser mit der Echokardiographie. Die Vorteile der Magnetresonanztomographie liegen in der Quantifizierung von Flussvolumina und der Möglichkeit, Insuffizienzen durch den Vergleich von rechts- und linksventrikulären Schlagvolumina zu quantifizieren. Dies gelingt allerdings nur bei Befall lediglich einer Herzklappe. Der folgende Text bezieht sich weitgehend auf chronische Klappenerkrankungen.
This chapter summarizes the contemporary clinical role of cardiovascular magnetic resonance (CMR) in clinical cardiology. Techniques are described which can be applied widely in the cardiovascular system, and these include assessment of anatomy and function, blood flow, ventricular volumes and mass, myocardial abnormality, and the response to stress....
Cardiovascular magnetic resonance (CMR) is an accurate and complementary method for evaluating ventricular function and volume analysis.
Cardiovascular magnetic resonance can readily assess the morphology of all four cardiac valves and accurately determine the severity of stenosis and regurgitation.
Magnetic resonance imaging is a rapidly developing modality in cardiology. It offers an excellent image definition and a large field of view, allowing a more accurate morphological assessment of cardiac malformations. Due to its unique versatility and its ability to provide myocardial tissue characterization, cardiac magnetic resonance (CMR) is now recognized as a central imaging modality for a wide range of congenital heart diseases, including assessment of post-surgical cardiac anatomy, quantification of valvular disease and detection of myocardial ischemia. CMR provides useful diagnostic information without any radiation exposure, and improves the global management of patients with congenital heart disease.
The present prospective study was designed to evaluate the accuracy of quantitative assessment of mitral regurgitant fraction (MRF) by echocardiography and cardiac magnetic resonance imaging (cMRI) in the modern era using as reference method the blinded multiparametric integrative assessment of mitral regurgitation (MR) severity. 2-Dimensional (2D) and 3-dimensional (3D) MRF by echocardiography (2D echo MRF and 3D echo MRF) were obtained by measuring the difference in left ventricular (LV) total stroke volume (obtained from either 2D or 3D acquisition) and aortic forward stroke volume normalized to LV total stroke volume. MRF was calculated by cMRI using either (1) (LV stroke volume - systolic aortic outflow volume by phase contrast)/LV stroke volume (cMRI MRF [volumetric]) or (2) (mitral inflow volume - systolic aortic outflow volume)/mitral inflow volume (cMRI MRF [phase contrast]). Six patients had 1 + MR, 6 patients had 2 + MR, 12 patients had 3 + MR, and 10 had 4 + MR. A significant correlation was observed between MR grading and 2D echo MRF (r = 0.60, p <0.0001) and 3D echo MRF (r = 0.79, p <0.0001), cMRI MRF (volumetric) (r = 0.87, p <0.0001), and cMRI MRF (phase contrast r = 0.72, p <0.001). The accuracy of MRF for the diagnosis of MR ≥3+ or 4+ was the highest with cMRI MRF (volumetric) (area under the receiver-operating characteristic curve [AUC] = 0.98), followed by 3D echo MRF (AUC = 0.96), 2D echo MRF (AUC = 0.90), and cMRI MRF (phase contrast; AUC = 0.83). In conclusion, MRF by cMRI (volumetric method) and 3D echo MRF had the highest diagnostic value to detect significant MR, whereas the diagnostic value of 2D echo MRF and cMRI MRF (phase contrast) was lower. Hence, the present study suggests that both cMRI (volumetric method) and 3D echo represent best approaches for calculating MRF.
Velocity offset errors may influence flow measurement in phase-contrast cardiovascular magnetic resonance (CMR). By using a stationary gel phantom, offset errors probably may be corrected. We tested its impact on flow measurement and, in particular, on shunt calculation in patients proven not to have any shunt.
Flow measurements were carried out in 24 patients with congenital heart disease. Baseline correction was performed by using a stationary gel phantom.
Significantly more patients without shunts incorrectly showed a calculated shunt after baseline correction.
Baseline correction did not improve flow measurement and was clinically not relevant for routine CMR.
Copyright © 2014 Elsevier Inc. All rights reserved.
Background:
Phase-contrast magnetic resonance (MR) has been widely used for quantification of aortic regurgitation. However there is significant practice variability regarding where and how the blood flow data are acquired.
Objective:
To compare the accuracy of flow quantification of aortic regurgitation at three levels: the ascending aorta at the level of the right pulmonary artery (level 1), the aortic valve hinge points at end-diastole (level 2) and the aortic valve hinge points at end-systole (level 3).
Materials and methods:
We performed cardiovascular MR in 43 children with aortic regurgitation. By using phase-contrast MR, we measured the systolic forward, diastolic retrograde and net forward flow volume indices at three levels. At each level, the following comparisons were made: (1) systolic forward flow volume index (FFVI) versus left ventricular cardiac index (LVCI) measured by cine ventricular volumetry; (2) retrograde flow volume index (RFVI) versus estimated aortic regurgitation volume index (which equals LVCI minus pulmonary blood flow index [QPI]); (3) net forward flow volume index (NFVI) versus pulmonary blood flow index.
Results:
The forward flow volume index, retrograde flow volume index and net forward flow volume index measured at each of the three levels were significantly different except for the retrograde flow volume index measured at levels 1 and 3. There were good correlations between the forward flow volume index and the left ventricular cardiac index at all three levels, with measurement at level 2 showing the best correlation. Compared to the forward flow volume indices, the retrograde flow volume index had a lower correlation with the estimated aortic regurgitation volume indices and had widely dispersed data with larger prediction intervals.
Conclusion:
Large variations in systolic forward, diastolic retrograde and net forward flow volumes were observed at different levels of the aortic valve and ascending aorta. Direct measurement of aortic regurgitation volume and fraction is inaccurate and should be abandoned. Instead, calculation of the aortic regurgitation volume from more reliable data is advised. We recommend subtracting pulmonary blood flow from systolic forward flow measured at the aortic valve hinge points at end-diastole as a more accurate and consistent method for calculating the volume of aortic regurgitation.
Die kardiale Schnittbilddiagnostik mit der Magnetresonanztomographie (MRT) und Computertomographie (CT) hat sich in der letzten Dekade technisch rasant weiterentwickelt. Diese Verbesserungen und die breite Verfügbarkeit moderner CT- und MRT-Systeme haben dazu geführt, dass beide Verfahren regelmäßig in der klinischen Routine eingesetzt werden. Dieses deutsche Konsensuspapier wurde daher gemeinsam von der Deutschen Gesellschaft für Kardiologie – Herz- und Kreislaufforschung (DGK), der Deutschen Röntgengesellschaft (DRG) und der Deutschen Gesellschaft für Pädiatrische Kardiologie (DGPK) erarbeitet und orientiert sich nicht an Modalitäten und Methoden, sondern gliedert sich nach großen Krankheitsgruppen. Behandelt werden die koronare Herzerkrankung, Kardiomyopathien, Herzrhythmusstörungen, Klappenvitien, Perikarderkrankungen, erworbene und strukturellen Veränderungen sowie angeborene Herzfehler. Für unterschiedliche klinische Szenarien werden die beiden Schnittbildmodalitäten CT und MRT vergleichend gegenübergestellt und in einem kurzen Textfeld bewertet.
Magnetic resonance imaging (MRI) and multislice computed tomography are three dimensional, non-invasive imaging modalities providing high resolution cardiac images. MRI provides anatomic and functional assessment of all cardiac structures. The myocardial perfusion imaging and the assessment of the late enhancement of the myocardial contrast are the simplest and fastest methods for the detection of myocardial ischemia and viability. On the other hand, multislice computed tomography has become the gold standard in the non-invasive visualization of coronary arteries.
Magnetic resonance (MR) phase velocity mapping (PVM) is a non-invasive technique that can measure the flow velocity in any spatial direction in an imaging slice. This technique has wide application in the clinical field in quantifying blood flow, as well as in non-biomedical areas. This review describes the value and/or potential of MR PVM as a diagnostic/monitoring technique in heart valve regurgitation and in the total cavo-pulmonary connection. A single slice placed in the aortic root can accurately quantify the aortic regurgitant volume. A multi-slice control volume method has high potential for the quantification of the mitral regurgitant volume. In the total cavo-pulmonary connection, MR PVM with its unique clinical ability to measure all three directions of blood velocity provides the ability to visualize the two- or even three-directional blood flow patterns. It also promises a non-invasive quantification of the mechanical energy losses of blood as it flows through the connection. New rapid acquisition sequences show accuracy in quantifying flow and will greatly contribute to the increase of the number of applications of MR PVM.
Cardiovascular magnetic resonance (CMR) has taken on an increasingly important role in the diagnostic evaluation and pre-procedural planning for patients with congenital heart disease. This article provides guidelines for the performance of CMR in children and adults with congenital heart disease. The first portion addresses preparation for the examination and safety issues, the second describes the primary techniques used in an examination, and the third provides disease-specific protocols. Variations in practice are highlighted and expert consensus recommendations are provided. Indications and appropriate use criteria for CMR examination are not specifically addressed.
Bac kground: Cardiac magnetic resonance imaging (MRI) has been established in clinical practice as a valid imaging modality for the diagnosis of various cardiovascular disorders.
Ob ject ives: To underline the importance of cardiac MRI as an alternative non - invasive imaging method for the diagnosis and follow-up of cardiac patients based on findings from our own recent experience.
Pat ients and Methods: The study included all cardiac patients referred for cardiac MRI over a period of one year. Cardiac MRI studies were performed with the use of a 1.5-Tesla scanner using a body phased-array coil, breath and ECG-triggering. Almost all cardiac sequences were gated to the patient’s cardiac cycle. Cine imaging for the evaluation of cardiac volumes and heart motion was performed using a cine breathhold true short-axis and true four-chamber sequence with whole left ventricular coverage. Black blood imaging for the assessment of morphology was acquired on a true short-axis and true four-chamber view. Depending on the pathology under investigation, special sequences were added to the imaging protocol, such as late-enhancement imaging after gadolinium administration.
Results : The study cohort comprised 114 patients who were referred for cardiac MRI with the following indications and clinical diagnoses: myocarditis (n=29), arrhythmogenic right ventricular cardiomyopathy (ARVC; n=27), valvular heart disease (n=23), history of myocardial infarction (n=13; seeking myocardial viability), hypertrophic (n=12), or dilated (n=2), or tako-tsubo (n=1), or non-compaction (n=2) cardiomyopathy, pericardial effusion (n=2) and various intracardiac masses (n=3). Cardiac MRI confirmed the clinical diagnosis and gave further specific information in 52% of myocarditis cases, in 37% of suspected ARVC cases, in 38% of coronary artery disease patients regarding myocardial viability, while it confirmed all other clinical diagnoses (100% match).
Conclusions: Cardiac MRI represents a clinically useful imaging method for the diagnosis of various cardiac disorders since it has the capability of providing highly accurate and reproducible measurements of cardiac hemodynamics in addition to the detailed demonstration of cardiac anatomical structures.
The measurement of blood flow is important to the understanding and management of cardiovascular disease. The development of new imaging methods has allowed detailed quantification of in vivo blood flow that has traditionally been difficult. Both invasive and noninvasive methods have been used to measure blood flow, and this chapter outlines the main techniques of blood flow measurement for cardiovascular research and practical clinical applications. A brief history and the basic principles of each of the methods are presented along with their relative merits and potential pitfalls. Recent development of noninvasive imaging techniques has allowed detailed depiction and quantification of in vivo flow patterns, the main focus of this chapter is therefore directed towards Doppler ultrasound and cardiovascular magnetic resonance (CMR). The future trend of combining different imaging modalities for investigating the relationships between morphological structure and the hemodynamic properties of flow is also outlined.
Cardiovascular magnetic resonance (CMR) has important contributions to make to the assessment of heart valve disease. These
can be complementary to routine echocardiographic assessment, for example in the quantification of valve regurgitation and
clarification of the nature and level(s) of right or left ventricular outflow tract obstruction. In ischemic mitral regurgitation,
CMR allows the assessment of myocardial scarring and viability as well as the nature of valve dysfunction. CMR provides a
noninvasive alternative to echocardiography in patients with inconsistent findings or limited acoustic access. For studies
of multidirectional flow, CMR can measure all three directional components of velocity in voxels distributed in three dimensions
and through the phases of the cycle. More clinically applicable, however, are volumetric flow measurements, forward or regurgitant,
through planes transecting one or both great arteries. These derived measurements are prone to errors caused by slight background
phase offsets, which may require appropriate correction.
KeywordsValvular heart disease-MRI-Haemodynamics-Stenosis-Regurgitation-Fluid dynamics
Cardiac magnetic resonance imaging (CMR) is one of the newer non-invasive cardiac diagnostic imaging modalities. Recent advances
have enabled CMR to come close to the goal of a complete examination of the cardiovascular system by a single modality. It
can provide relevant information on most aspects of the heart–structure, global and regional ventricular function, valve function,
flow patterns, myocardial perfusion, coronary anatomy, and myocardial viability, all obtained non-invasively in a single study
in 30–60 min.
The aim of this chapter is to describe the physics and practical aspects of CMR and then explore the available pulse sequences,
so that the clinical utility of CMR can be maximized.
Visualization and quantification of the cardiac pump activity by means of imaging techniques has become an essential part in the diagnosis of many cardiac diseases. This pump activity comprises a repetitive filling and emptying phase whereby one phase or both phases may be impaired by the underlying cardiac disease. Among the different available imaging modalities, MRI has become a preferred one to assess cardiac function because of its noninvasiveness, and the accuracy and reproducibility of the measurements. Moreover, cardiac function assessment by MRI is part of a more comprehensive approach including other facets such as myocardial perfusion imaging and tissue characterization. This chapter is written from the point of view of the imager, starting with a description of the mechanisms of cardiac contraction and relaxation, and how these lead to myocardial deformation and ventricular volume changes throughout the cardiac cycle. Next, it is discussed how imaging techniques can be used to assess these processes at different levels, and what major hurdles need to be passed to achieve reliable estimates of cardiac function parameters. Finally, normal reference values obtained by current MRI sequences are provided at the end of the chapter.
Conventional Doppler echocardiographic methods still are limited when being used for evaluation of morphology and function of a regurgitant mitral valve. Methods based on two-dimensional image planes may be insufficient to demonstrate exact spatial localization of pathologic structures due to the need for mental reconstruction of the three-dimensional valve anatomy by the examiner. The determination of severity of mitral regurgitation is based either on the estimation of regurgitation jet size or on geometric assumptions on its shape which often are not correct and reduce the accuracy of the method.
New echocardiographic techniques such as 3-D echocardiography provide a comprehensive visualization and assessment of valvular pathomorphology which especially in complex situations will increase sensitivity and diagnostic accuracy when compared to conventional methods. The combination of 3-D echo with three-dimensional Doppler data will allow an even more reliable and precise determination of lesion severity. Other imaging modalities such as magnetic resonance imaging will be a promising alternative due to their three-dimensional data acquisition and the enormous potential for the measurement of intracardiac flow.
Whenever a linear gradient is activated, concomitant magnetic fields with non-linear spatial dependence result. This is a consequence of Maxwell's equations, i.e., within the imaging volume the magnetic field must have zero divergence, and has negligible curl. The concomitant, or Maxwell field has been described in the MRI literature for over 10 years. In this paper, we theoretically and experimentally show the existence of two additional lowest-order terms in the concomitant field, which we call cross-terms. The concomitant gradient cross-terms only arise when the longitudinal gradient Gz is simultaneously active with a transverse gradient (Gx or Gy). The effect of all of the concomitant gradient terms on phase contrast imaging is examined in detail. Several methods for reducing or eliminating phase errors arising from the concomitant magnetic field are described. The feasibility of a joint pulse sequence-reconstruction method, which requires no increase in minimum TE, is demonstrated. Since the lowest-order terms of the concomitant field are proportional to G2/B0, the importance of concomitant gradient terms is expected to increase given the current interest in systems with stronger gradients and/or weaker main magnetic fields.
Quantifying mitral regurgitation is difficult because of the complexity of the flow, geometry and motion of the mitral valve. In this paper a MRI compatible phantom was built incorporating a left ventricle and mitral valve motion. Valve motion was obtained using a pneumatic piston. The mitral valve was made regurgitant and the regurgitant volume quantified using a modified control volume method. The modification to the method was the addition of mitral motion correction. This was attained by moving the control volume in unison with the mitral valve and by correcting for this motion in the integration of velocity. This correction was found to be simple, in that it represented the volume swept out by the moving control surface. The measured regurgitant volume was compared to a second MR measurement using a single slice technique, made possible by the tubular construction of the phantom's left atrium. Regression analysis between these two methods produced a regression line of y = 0 + 1.02 x; R = 0.97; standard error of the estimate = 3.47 ml. Magn Reson Med 43:726–733, 2000. © 2000 Wiley-Liss, Inc.
Velocity-encoded phase imaging using asynchronous gating requires input of a velocity encoding value to set the velocity sensitivity of the pulse sequence. The raw data interpolation and reconstruction scheme that the pulse sequence uses forces the encoding value to be constant throughout the RR interval. The sequence and the raw data interpolation scheme were modified to allow two velocity encodings during the RR interval. Two-hundred cm/s encoding was used in systole, and 30 cm/s in diastole. Changing the encoding in diastole significantly improved the accuracy and precision of ascending aorta flow measurements.
Although several methods have been used clinically to assess aortic regurgitation (AR), there is no “gold standard” for regurgitant volume measurement. Magnetic resonance phase velocity mapping (PVM) can be used for noninvasive blood flow measurements. To evaluate the accuracy of PVM in quantifying AR with a single imaging slice in the ascending aorta, in vitro experiments were performed by using a compliant aortic model. Attention was focused on determining the slice location that provided the best results. The most accurate measurements were taken between the aortic valve annulus and the coronary ostia where the measured (Y) and actual (X) flow rate had close agreement (Y = 0.954 × + 0.126, r2 = 0.995, standard deviation of error = 0.139 L/min). Beyond the coronary ostia, coronary flow and aortic compliance negatively affected the accuracy of the measurements. In vivo measurements taken on patients with AR showed the same tendency with the in vitro results. In making decisions regarding patient treatment, diagnostic accuracy is very important. The results from this study suggest that higher accuracy is achieved by placing the slice between the aortic valve and the coronary ostia and that this is the region where attention should be focused for further clinical investigation.
The segmentation of images obtained by cine magnetic resonance (MR) phase contrast velocity mapping using manual or semi-automated methods is a time consuming and observer-dependent process that still hampers the use of flow quantification in a clinical setting. A fully automatic segmentation method based on active contour model algorithms for defining vessel boundaries has been developed. For segmentation, the phase image, in addition to the magnitude image, is used to address image distortions frequently seen in the magnitude image of disturbed flow fields. A modified definition for the active contour model is introduced to reduce the influence of missing or spurious edge information of the vessel wall. The method was evaluated on flow phantom data and on in vivo images acquired in the ascending aorta of humans. Phantom experiments resulted in an error of 0.8% in assessing the luminal area of a flow phantom equipped with an artificial heart valve. Blinded evaluation of the volume flow rates from automatic vs. manual segmentation of gradient echo (FFE) phase contrast images obtained in vivo resulted in a mean difference of −0.9 ± 3%. The mean difference from automatic vs. manual segmentation of images acquired with a hybrid phase contrast sequence (TFEPI) within a single breath-hold was −0.9 ± 6%.J. Magn. Reson. Imaging 1999;10:41–51. © 1999 Wiley-Liss, Inc.
Background phase distortion and random noise can adversely affect the quality of magnetic resonance (MR) phase velocity measurements. A semiauto-mated method has been developed that substantially reduces both effects. To remove the background phase distortion, the following steps were taken: The time standard deviations of the phase velocity images over a cardiac cycle were calculated. Static regions were identified as those in which the standard deviation was low. A flat surface representing an approximation to the background distortion was fitted to the static regions and subtracted from the phase velocity images to give corrected phase images. Random noise was removed by setting to zero those regions in which the standard deviation was high. The technique is demonstrated with a sample set of data in which the in-plane velocities have been measured in an imaging section showing the left ventricular outflow tract of a human left ventricle. The results are presented in vector and contour form, superimposed on the conventional MR angiographic images.
Fourteen patients with chronic aortic regurgitation were studied by several two-dimensional and Doppler echocardiographic methods to determine the severity of aortic regurgitation. Semiquantitation of aortic regurgitation was performed by various color-flow imaging measurements, diastolic half-time of the continuous-wave regurgitation jet, and pulsed-wave velocity curve in the descending aorta. These measurements were compared with regurgitant volume and fraction by ultrafast computed tomography. All Doppler methods demonstrated a significant correlation for severity of aortic regurgitation with regurgitant fraction by ultrafast computed tomographic scanning, but scatter was present with each method. The methods with the closest correlation were at the lowest level of obtainable results. In clinical practice, all Doppler methods must be used to determine the severity of aortic regurgitation.
When magnetic resonance phase mapping is used to quantitate valvular blood flow, the presence of higher-order-motion terms may cause a loss of phase information. To overcome this problem, a sequence with reduced encoding for higher-order motion was used, achieved by decreasing the duration of the flow-encoding gradient to 2.2 msec. Tested on a flow phantom simulating a severe valvular stenosis, the sequence was found to be robust for higher-order motion within the clinical velocity range. In eight healthy volunteers, mitral and aortic volume flow rates and peak velocities were quantified by means of phase mapping and compared with results of the indicator-dilution technique and Doppler echocardiography, respectively. Statistically significant correlations were found between phase mapping and the other two techniques. Similar studies in patients with valvular disease indicate that phase mapping is also valid for pathologic conditions. Phase mapping may be used as a noninvasive clinical tool for flow quantification in heart valve disease.
A new, rapid magnetic resonance (MR) imaging method, cine MR imaging, was used to determine the regurgitant fraction (RF) in patients with left-sided regurgitant lesions. Right and left ventricular stroke volumes were determined with cine MR imaging and a modified Simpson formula in ten healthy volunteers and 23 patients known to have either predominant mitral (n = 17) or aortic (n = 6) regurgitation. RFs evaluated at cine MR imaging were compared in healthy persons and patients with mild, moderate, or severe regurgitation demonstrated at angiography (n = 10) and Doppler echocardiography (n = 13). Cine MR imaging depicted regurgitant blood flow in all 29 regurgitant lesions in 23 patients as areas of low signal intensity within the regurgitant chamber. The RF was 4% +/- 7% in healthy subjects and 12% +/- 12% in those with mild, 35% +/- 14% in those with moderate, and 63% +/- 5% in those with severe regurgitation. The RFs determined by two observers were similar.
In the management of patients with valvular heart disease, an understanding of the effects of altered loading conditions on the left ventricle is important in reaching a proper decision concerning the timing of corrective operation. In acquired valvular aortic stenosis, concentric hypertrophy generally maintains left ventricular chamber size and ejection fraction within normal limits, but in late stage disease function can deteriorate as preload reserve is lost and aortic stenosis progresses. In this setting, even when the ejection fraction is markedly reduced (less than 25%), it can improve to normal after aortic valve replacement, suggesting that afterload mismatch rather than irreversibly depressed myocardial contractility was responsible for left ventricular failure. Therefore, patients with severe aortic stenosis and symptoms should not be denied operation because of impaired cardiac function. In chronic severe aortic and mitral regurgitation, operation is generally recommended when symptoms are present, but whether to recommend operation to prevent irreversible myocardial damage in patients with few or no symptoms has remained controversial. In aortic regurgitation, left ventricular function generally improves postoperatively, even if it is moderately impaired preoperatively, indicating correction of afterload mismatch. Most such patients can be carefully followed by echocardiography. However, in some patients, severe left ventricular dysfunction fails to improve postoperatively. Therefore, when echocardiographic studies in the patient with severe aortic regurgitation show an ejection fraction of less than 40% (fractional shortening less than 25%) plus enlarging left ventricular end-diastolic diameter (approaching 38 mm/m2 body surface area) and end-systolic diameter (approaching 50 mm or 26 mm/m2), confirmation of these findings by cardiac catheterization and consideration of operation are advisable even in patients with minimal symptoms. In chronic mitral regurgitation, maintenance of a normal ejection fraction can mask depressed myocardial contractility. Pre- and postoperative studies in such patients have shown a poor clinical result after mitral valve replacement, associated with a sharp decrease in the ejection fraction after operation. This response appears to reflect unmasking of decreased myocardial contractility by mitral valve replacement, with ejection of the total stroke volume into the high impedance of the aorta (afterload mismatch produced by operation).(ABSTRACT TRUNCATED AT 400 WORDS)
We examined the interrelationship of afterload, preload and left ventricular (LV) performance at two levels of systolic loading in 20 patients with chronic aortic regurgitation to determine if the concept of afterload mismatch and preload reserve can be applied to this clinical entity. We identified two groups of patients at different stages in the natural history of volume overload. Patients in group 1 had moderate LV enlargement (LV end-diastolic volume < 150 ml/m2), and patients in group 2 had severe LV enlargement (LV end-diastolic volume > 150 ml/m2). Both groups had sufficient eccentric hypertrophy, measured by LV mass, to keep afterload as measured by mean systolic LV wall stress only slightly above normal; LV mean systolic wall stress was similar in each group. Patients in group 2 had a lower LV ejection fraction and velocity of circumferential fiber shortening than those in group 1 at a similar lower level of afterload. At a similar higher level of afterload, which increased end-diastolic volume from 134 ± 4 to 157 ± 6 ml/m2 in group 1 and from 191 ±9 to 218 ± 13 ml/m2 in group 2 (average increase 18% vs 14%, NS), patients in group 1 maintained their ejection fraction and forward stroke volume and had a significant increase in total LV stroke volume, whereas patients in group 2 had a decrease in ejection fraction and in forward stroke volume and no significant change in LV stroke volume. The velocity of circumferential fiber shortening decreased in both groups in response to increased afterload. These data indicate that patients with moderate LV dilatation due to aortic regurgitation and sufficient hypertrophy to normalize afterload have a preload reserve that permits normal LV performance during a basal state as well as during acute increases in afterload. Patients with severe LV dilatation, however, despite sufficient hypertrophy to normalize afterload, have afterload mismatch due to a depressed inotropic state, and have exhausted preload reserve such that acute increases in afterload worsen the afterload mismatch and cause further deterioration of LV performance. The velocity of circumferential fiber shortening appears to be a less useful indicator of afterload mismatch than other ejection-phase indexes of contractility. Thus, the concept of afterload mismatch and preload reserve describes the natural history of hemodynamic alterations in chronic aortic regurgitation.
Left ventricular systolic function is an important determinant of long-term prognosis in patients with chronic aortic regurgitation. Data from several centers, using invasive and noninvasive assessment of left ventricular function, indicate that long-term postoperative survival is excellent, even in symptomatic patients, if preoperative left ventricular systolic function is normal. The long-term postoperative results are significantly worse in symptomatic patients with preoperative left ventricular systolic dysfunction, many of whom appear to have irreversible left ventricular failure before the onset of symptoms and are at a risk of late postoperative death from congestive heart failure. However, within this high risk subgroup long-term prognosis is excellent for patients, despite left ventricular dysfunction, if preoperative exercise capacity is preserved. In these patients, left ventricular dysfunction is likely to be reversible after operation. Hence, all patients with left ventricular dysfunction at rest should undergo aortic valve replacement, even if severe symptoms and deterioration in exercise tolerance have not developed. Once exercise tolerance becomes limited in such patients, the likelihood of irreversible left ventricular dysfunction is increased, and long-term postoperative survival is threatened.
Respiratory motion is a major limiting factor in improving image resolution and signal-to-noise ratio in MR coronary imaging. In this work the effects of respiration on the cardiac position were studied quantitively by imaging the heart during diastole at various positions of tidal respiration with a breath-hold segmented fast gradient echo technique. It was found that during tidal breathing the movement of the heart due to respiration is dominated by superior-inferior (SI) motion, which is linearly related to the SI motion of the diaphragm. The motion of the heart due to respiration is approximately a global translation. These results provide motivation for employing adaptive motion correction techniques to reduce image blurring in nonbreath-hold coronary MR imaging.
The purpose of the present study was to develop a new method of measuring heart valvular regurgitation based on control volume theory and to verify its accuracy in vitro and in vivo. Current methods of quantifying valvular regurgitation rely too much on assumptions about the flow field and therefore are difficult to apply in vivo. In particular, the proximal isovelocity surface area (PISA) method oversimplifies the proximal velocity field by assuming hemispherical isovelocity contours proximal to the orifice. This severely limits the applicability of the PISA method. Use of the basic control volume theory, however, removes the need to assume the manner in which the proximal flow accelerates toward the regurgitant orifice, the shape and size of the orifice, the shape of the orifice plate, and the non-newtonian behavior of the fluid. Apart from a correction that is necessary if the orifice plate is moving, the control volume method assumes only the incompressibility of the fluid and therefore is a potentially more accurate approach. In addition, the use of magnetic resonance imaging (MRI) precludes the need for an acoustic window.
MRI has been used to measure the three-dimensional velocity field proximal to regurgitant orifices, including single and multiple orifices and a cone-shaped orifice plate. Both steady (0 to 7.5 L/min) and pulsatile (2 and 3 L/min) flows were used. By intergrating this velocity over a control volume surrounding the orifice, we calculated the flow rate through the orifice. As a validation, the cardiac output of a 50-kg pig also was measured and was compared with thermodilution measurements. It was found that MRI could be used to measure the three-dimensional flow proximal to regurgitant orifices. This enabled the calculation of the flow rate through the orifice by integrating the velocity over the surface of a control volume covering the orifice. This flow rate correlated well with the actual rate (0.992; correlation line slope, 1.01). Care had to be taken, however, to exclude from the integration regions of aliased velocity. The cardiac output of the pig measured using MRI was in close agreement with the themodilution measurements.
Our new method of measuring valvular regurgitation has been shown to be very accurate in vitro and in vivo and therefore is a potentially accurate way to quantify valvular regurgitation.
Magnetic resonance phase difference techniques are commonly used to study flow velocities in the human body. Acceleration is often present, either in the form of pulsatile flow, or in the form of convective acceleration. Questions have arisen about the exact time point at which the velocity is encoded, and also about the sensitivity to (convective) acceleration and higher order motion derivatives. It has become common practice to interpret the net phase shifts measured with a phase difference velocity technique as being the velocity at a certain (Taylor) expansion time point, chosen somewhere between the RF excitation and the echo readout. However, phase shifts are developed over the duration of the encoding magnetic field gradient wave form, and should therefore be interpreted as a more or less time-averaged velocity. It will be shown that the phase shift as measured with a phase difference velocity technique represents the velocity at the "gravity" center of the encoding bipolar gradient (difference) function, without acceleration contribution. Any attempt to interpret the measured phase shift in terms of velocity on any other time point than the gradient gravity point will automatically introduce acceleration sensitivity.
Lowering of the echo time (TE) has been proposed as a way to reduce effects of phase dispersion in MR velocity mapping, because a low TE reduces sensitivity to higher-order motion terms while first-order velocity sensitivity is maintained. Methods of lowering TE involves the use of extreme gradient ramp times and gradient strengths as well as reduction of the duration of transmit/receive windows, the latter method causing decrements in image resolution. When reducing higher-order sensitivity, however, it is not the overall TE that is the critical parameter, but rather the time pattern of the gradients used in the experiment. Hence, changes in TE without subsequent variations in gradient pattern would, according to theory, not affect quantitative measurements of complex flow and vice versa. In this study, we experimentally demonstrate this relation and utilize the experience to create a sequence robust towards complex flow without sacrifices in image resolution. Our experimental observations show that variations in TE alone while maintaining the time course of the velocity-encoding gradient does not significantly affect measurements of through-plane average complex flow in the studied velocity range. A parameter that cannot be measured as accurately if TE is increased is the peak flow. A phase mapping sequence with prolonged TE from 3 ms to 5 ms but with short duration of the velocity-encoding (section-selective) gradient and improved in-plane resolution was demonstrated in vivo.
The feasibility of velocity-encoded cine nuclear magnetic resonance (NMR) imaging to measure regurgitant volume and regurgitant fraction in patients with mitral regurgitation was evaluated.
Velocity-encoded cine NMR imaging has been reported to provide accurate measurement of the volume of blood flow in the ascending aorta and through the mitral annulus. Therefore, we hypothesized that the difference between mitral inflow and aortic systolic flow provides the regurgitant volume in the setting of mitral regurgitation.
Using velocity-encoded cine NMR imaging at a magnet field strength of 1.5 T and color Doppler echocardiography, 19 patients with isolated mitral regurgitation and 10 normal subjects were studied. Velocity-encoded cine NMR images were acquired in the short-axis plane of the ascending aorta and from the short-axis plane of the left ventricle at the level of the mitral annulus. Two independent observers measured the ascending aortic flow volume and left ventricular inflow volume to calculate the regurgitant volume as the difference between left ventricular inflow volume and aortic flow volume, and the regurgitant fraction was calculated. Using accepted criteria of color flow Doppler imaging and spectral analysis, the severity of mitral regurgitation was qualitatively graded as mild, moderate or severe and compared with regurgitant volume and regurgitant fraction, as determined by velocity-encoded cine NMR imaging.
In normal subjects the regurgitant volume was -6 +/- 345 ml/min (mean +/- SD). In patients with mild, moderate and severe mitral regurgitation, the regurgitant volume was 156 +/- 203, 1,384 +/- 437 and 4,763 +/- 2,449 ml/min, respectively. In normal subjects the regurgitant fraction was 0.7 +/- 6.1%. In patients with mild, moderate and severe mitral regurgitation, the regurgitant fraction was 3.1 +/- 3.4%, 24.5 +/- 8.9% and 48.6 +/- 7.6%, respectively. The regurgitant fraction correlated well with the echocardiographic severity of mitral regurgitation (r = 0.87). Interobserver reproducibilities for regurgitant volume and regurgitant fraction were excellent (r = 0.99, SEE = 238 ml; r = 0.98, SEE = 4.1%, respectively).
These findings suggest that velocity-encoded NMR imaging can be used to estimate regurgitant volume and regurgitant fraction in patients with mitral regurgitation and can discriminate patients with moderate or severe mitral regurgitation from normal subjects and patients with mild regurgitation. It may be useful for monitoring the effect of therapy intended to reduce the severity of mitral regurgitation.
Aortic regurgitation (AR) in five healthy volunteers and 26 patients (mean age, 60.3 years; range, 25-83 years) was quantitatively measured with magnetic resonance (MR) imaging velocity mapping. Cine transverse images of the ascending aorta (32 phases per cardiac cycle) were acquired by using a gradient-echo sequence with a velocity-encoding bipolar pulse applied in the section-selection direction with a 1.5-T MR imaging unit. The aortic flow was calculated by integrating the product of area and mean velocity of the ascending aorta at each phase over a cardiac cycle. The negative and positive velocity values indicated antegrade and regurgitant flow, respectively, which allowed calculation of forward and regurgitant flow. Inter- and intraobserver variation of regurgitant fraction (RF) measurement was small (r = .956, standard error of the estimate [SEE] = 1.2%, n = 31; and r = .998, SEE = 0.35%, n = 10, respectively). RF determined with MR imaging agreed well with Doppler echocardiographic (n = 26) and aortographic (n = 9) grading of AR. Reproducible, quantitative, and noninvasive measurement of AR is possible with MR velocity mapping.
To identify the predictive factors of left ventricular dysfunction (LVD) after surgery, we performed an uni- and multivariate analysis of the data concerning 286 patients operated for pure aortic regurgitation between 1980 and 1994 and 460 patients operated for pure non-ischemic mitral regurgitation over a period of 24 years. Among the aortic regurgitation patients, 28 developed left ventricular dysfunction not attributable to residual aortic valve dysfunction, another valvular lesion or hypertensive or ischemic heart disease. By univariate analysis identified predictive factors of LVD were duration of symptoms prior to surgery, duration of the history of diastolic murmur, NYHA class, cardiothoracic ratio, LV echographic diameters, fractional shortening of short axis, LV end-systolic volume and LV ejection fraction. Multivariate analysis identified three independent predictors: NYHA functional class, LV end-systolic diameter and LV ejection fraction. Of 428 operative survivors with non-ischemic mitral regurgitation 63 developed severe LVD. Univariate analysis identified functional class III or IV, duration of symptoms prior to surgery, atrial fibrillation, echo LV and LA diameters, angio LV volumes, LV ejection fraction, cardiac index and type of surgery as independent predictors of LVD. Multivariate analysis showed that type of surgery, LV ejection fraction, LV end-diastolic and end-systolic volume and echo LV end-systolic diameter were all independent predictors of LVD.
Although several methods have been used clinically to assess aortic regurgitation (AR), there is no "gold standard" for regurgitant volume measurement. Magnetic resonance phase velocity mapping (PVM) can be used for noninvasive blood flow measurements. To evaluate the accuracy of PVM in quantifying AR with a single imaging slice in the ascending aorta, in vitro experiments were performed by using a compliant aortic model. Attention was focused on determining the slice location that provided the best results. The most accurate measurements were taken between the aortic valve annulus and the coronary ostia where the measured (Y) and actual (X) flow rate had close agreement (Y = 0.954 x + 0.126, r2 = 0.995, standard deviation of error = 0.139 L/min). Beyond the coronary ostia, coronary flow and aortic compliance negatively affected the accuracy of the measurements. In vivo measurements taken on patients with AR showed the same tendency with the in vitro results. In making decisions regarding patient treatment, diagnostic accuracy is very important. The results from this study suggest that higher accuracy is achieved by placing the slice between the aortic valve and the coronary ostia and that this is the region where attention should be focused for further clinical investigation.
A new modified type of gating is presented that shows the ability to reduce the total scan time with almost conserved image quality compared with conventional gating. This new motion-adapted gating approach is based on a k-space-dependent gating threshold function. MR data acquired are only accepted if the motion-induced displacements measured from a reference position are below the chosen gating threshold function. During the MR measurement the scanner analyses respiratory motion decides in real-time which data in k-space could be measured according to the gating threshold function and performs data acquisition. In the present paper the approach will be described and discussed. Simulations based on in vivo data and initial in vivo experiments are presented to compare different variants of the new approach mutually and to the conventional technique. The analysis given is focused on spin warp type sequences, which are the best candidates for this approach.
Whenever a linear gradient is activated, concomitant magnetic fields with non-linear spatial dependence result. This is a consequence of Maxwell's equations, i.e., within the imaging volume the magnetic field must have zero divergence, and has negligible curl. The concomitant, or Maxwell field has been described in the MRI literature for over 10 years. In this paper, we theoretically and experimentally show the existence of two additional lowest-order terms in the concomitant field, which we call cross-terms. The concomitant gradient cross-terms only arise when the longitudinal gradient Gz is simultaneously active with a transverse gradient (Gx or Gy). The effect of all of the concomitant gradient terms on phase contrast imaging is examined in detail. Several methods for reducing or eliminating phase errors arising from the concomitant magnetic field are described. The feasibility of a joint pulse sequence-reconstruction method, which requires no increase in minimum TE, is demonstrated. Since the lowest-order terms of the concomitant field are proportional to G2/B0, the importance of concomitant gradient terms is expected to increase given the current interest in systems with stronger gradients and/or weaker main magnetic fields.
Reliable diagnosis and quantification of mitral regurgitation are important for patient management and for optimizing the time for surgery. Previous methods have often provided suboptimal results. The aim of this in vitro study was to evaluate MR phase-velocity mapping in quantifying the mitral regurgitant volume (MRV) using a control volume (CV) method. A number of contiguous slices were acquired with all three velocity components measured. A CV was then selected, encompassing the regurgitant orifice. Mass conservation dictates that the net inflow into the CV should be equal to the regurgitant flow. Results showed that a CV, the boundary voxels of which excluded the region of flow acceleration and aliasing at the orifice, provided accurate measurements of the regurgitant flow. A smaller CV provided erroneous results because of flow acceleration and velocity aliasing close to the orifice. A large CV generally provided inaccurate results because of reduced velocity sensitivity far from the orifice. Aortic outflow, orifice shape, and valve geometry did not affect the accuracy of the CV measurements. The CV method is a promising approach to the problem of quantification of the MRV.
This executive summary and recommendations appears in the November 3, 1998, issue of Circulation . The guidelines in their entirety, including the ACC/AHA Class I, II, and III recommendations, are published in the November 1, 1998, issue of the Journal of the American College of Cardiology . Reprints of both the full text and the executive summary and recommendations are available from both organizations.
During the past 2 decades, major advances have occurred in diagnostic techniques, the understanding of natural history, and interventional cardiological and surgical procedures for patients with valvular heart disease. The information base from which to make clinical management decisions has greatly expanded in recent years, yet in many situations, management issues remain controversial or uncertain. Unlike many other forms of cardiovascular disease, there is a scarcity of large-scale multicenter trials addressing the diagnosis and treatment of valvular disease from which to derive definitive conclusions, and the literature represents primarily the experiences reported by single institutions in relatively small numbers of patients.
The Committee on Management of Patients With Valvular Disease was given the task of reviewing and compiling this information base and making recommendations for diagnostic testing, treatment, and physical activity. These guidelines follow the format established in previous American College of Cardiology/American Heart Association (ACC/AHA) guidelines for classifying indications for diagnostic and therapeutic procedures:
Class I: Conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective
Class II: Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment
IIa. Weight of evidence/opinion is in favor of usefulness/efficacy
IIb. Usefulness/efficacy is less well established by evidence/opinion.
Class III: Conditions for which there is evidence and/or general agreement that the procedure/treatment is not useful and in some cases …
A method for magnetic resonance cine velocity mapping through heart valves with adaptation of both slice offset and angulation according to the motion of the valvular plane of the heart is presented. By means of a subtractive labeling technique, basal myocardial markers are obtained and automatically extracted for quantification of heart motion at the valvular level. The captured excursion of the basal plane is used to calculate the slice offset and angulation of each required time frame for cine velocity mapping. Through-plane velocity offsets are corrected by subtracting velocities introduced by basal plane motion from the measured velocities. For evaluation of the method, flow measurements downstream from the aortic valve were performed both with and without slice adaptation in 11 healthy volunteers and in four patients with aortic regurgitation. Maximum through-plane motion at the aortic root level as calculated from the labeled markers averaged 8.9 mm in the volunteers and 6.5 mm in the patients. The left coronary root was visible in 2-4 (mean: 2.2) time frames during early diastole when imaging with a spatially fixed slice. Time frames obtained with slice adaptation did not contain the coronary roots. Motion correction increased the apparent regurgitant volume by 5.7 +/- 0.4 ml for patients with clinical aortic regurgitation, for an increase of approximately 50%. The proposed method provides flow measurements with correction for through-plane motion perpendicular to the aortic root between the valvular annulus and the coronary ostia throughout the cardiac cycle. Magn Reson Med 42:970-978, 1999.
Timing of operation for chronic aortic regurgitation
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Bonow RO, Rosing DR, Kent KM, Epstein SE. Timing of operation for chronic aortic regurgitation. Am J Cardiol 1982;50:325–336.
Velocity quantitation in arteries using individualized and automated variable velocity encoding (venc) for each heart phase
- Ringgaards Oyres Flaagoyh Stokholmr Pedersenem