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-Kink of Internal carotid artery slmulatlng stenosls at MR anglography. A, Lateral carotid digital subtraction anglogram shows a kink (arrowhead) within proximal Internal carotid artery, near bifurcation. B, On 3D time-of-flight MR angiogram, stenosis (arrowhead)
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Although conventional angiography has traditionally been the preoperative study of choice before carotid endarterectomy, alternative noninvasive methods, particularly MR angiography, are being used increasingly for evaluation of the carotid bifurcation [1, 2]. In this essay, we illustrate the limitations of and artifacts associated with two-dimensi...
Context in source publication
Context 1
... greater, and therefore potentially affect adversely the therapy a patient receives [3]. Similarly, a kink (Fig. 2) or a loop (Fig. 3) within the proximal ICA also can appear as a high-grade stenosis at MR angiography. The signal loss is due to a combination of saturation and dephasing ...
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Aims:
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Citations
... As a result, either the spatial resolution or spatial coverage might be compromised in clinical applications. 7 Recent studies [8][9][10][11] have mainly focused on two types of strategies to shorten the scan time of the intracranial inflow MRA. The first one is to use advanced k-space undersampling and reconstruction methods. ...
Purpose
This work proposes a 2D/3D hybrid inflow MRA technique for fast scanning and high SNR and contrast‐to‐noise (CNR) efficiencies.
Methods
Localized quadratic (LQ) encoding was combined with a sliding‐slice spiral acquisition. Inflow MRAs around the circle of Willis and the carotid bifurcations were collected on four healthy volunteers. Spiral images were deblurred without or with water–fat separation for sliding‐slice LQ (ssLQ) out‐of‐phase (OP) and Dixon inflow MRAs, respectively. Results were compared to multiple overlapping thin slab acquisitions (MOTSA) and 2D OP inflow MRAs. Noise data were also acquired with RF and gradients turned off to compute maps of SNR and SNR efficiency. Quantitative assessment of relative contrast, CNR, and CNR efficiency for flow were performed in regions of interest.
Results
The sliding‐slice spiral technique alone reduces scan time by 10% to 40% compared with a standard spiral acquisition scheme. The proposed spiral ssLQ OP achieves 50% higher scan speed than the spiral MOTSA with comparable SNR and CNR efficiencies, which are ∼100% higher than the Cartesian MOTSA for intracranial inflow MRAs. Spiral ssLQ Dixon inflow MRA provides better visibility for vessels around the fat compared to spiral ssLQ OP inflow MRA, with a trade‐off of scan speed. Spiral ssLQ MRA with thinner slice thickness is two to five times faster than the 2D Cartesian inflow neck MRA around the carotid bifurcations, while also achieving higher SNR efficiency.
Conclusion
The proposed spiral ssLQ is a fast and flexible MRA method with improved SNR and CNR efficiencies over traditional Cartesian inflow MRAs.
... However, TOF-MRA is less sensitive to in-plane flow signals, and its vascular coverage is limited. Moreover, TOF-MRA is also limited by flowrelated dephasing artifacts that could lead to substantial signal losses within vessels in the presence of turbulent or complex blood flow [19]. The signal loss in TOF-MRA images results in heterogeneous signal intensities within intracranial aneurysms, which could cause a failure of aneurysm detection [20] and result in image misinterpretation [7,21,22]. ...
Purpose:
To investigate the clinical utility of pointwise encoding time reduction with radial acquisition in subtraction-based magnetic resonance angiography (PETRA-MRA) and time-of-flight magnetic resonance angiography (TOF-MRA) to evaluate saccular unruptured intracranial aneurysms (UIAs).
Methods:
A total of 49 patients with 54 TOF-MRA-identified saccular UIAs were enrolled. The morphologic parameters, contrast-to-noise-ratios (CNRs), and sharpness of aneurysms were measured using PETRA-MRA and TOF-MRA. Two radiologists independently evaluated subjective image scores, focusing on aneurysm signal homogeneities and sharpness depictions using a 4-point scale: 4, excellent; 3, good; 2, poor; 1, not assessable. PETRA-MRA and TOF-MRA acoustic noises were measured.
Results:
All aneurysms were detected with PETRA-MRA. The morphologic parameters of 15 patients evaluated with PETRA-MRA were more closely correlated with those receiving computed tomography angiography over those receiving TOF-MRA. No significant differences between PETRA-MRA and TOF-MRA parameters were seen in the 54 UIAs (p > 0.10), excluding those with inflow angles (p < 0.05). In four patients with inflow angles on PETRA-MRA, the angles were more closely related to those of digital subtraction angiography than those of TOF-MRA. CNRs between TOF-MRA and PETRA-MRA were comparable (p = 0.068), and PETRA-MRA sharpness values and subjective image scores were significantly higher than those of TOF-MRA (p < 0.001). Inter-observer agreements were excellent for both PETRA-MRA and TOF-MRA (intraclass correlation coefficients were 0.90 and 0.97, respectively). The acoustic noise levels of PETRA-MRA were much lower than those of TOF-MRA (59 vs.73 dB, p < 0.01).
Conclusions:
PETRA-MRA, with better visualization of aneurysms and lower acoustic noise levels than TOF-MRA, showed a superior diagnostic performance for depicting saccular UIAs.
... Conventional 3D-TOF-MRA, which relies on the intrinsic properties of blood flow, allows for high spatial resolution and requires no contrast material [4,5] and without the need for subtraction. However, as a gradient-echo imaging method without refocusing pulse, TOF-MRA produces vascular contrast by flow-related enhancement, the signals would be maximum when the fully relaxed blood perpendicularly flowing into the imaging plane; thus, this method is very sensitive/ susceptible to flow-related dephasing artifacts when there is turbulent or complex flow [6], and the saturation effect may decrease the manifestation of intracranial ICA because the blood flow into the volume is progressively saturated. Flow dephasing artifacts have been problematic for 3D-TOF-MRA because vessels with fast, non-laminar flow or turbulent flow may yield a rapid signal loss, particularly at vessel bifurcations, origins of arteries, and areas with tortuous blood flow [4]. ...
... It can also interfere with normal vasculature depiction [7] and obscure maximum intensity projection (MIP) images [8]. The signal loss may sometimes mimic or even exaggerate vascular diseases, the degree of vessel stenosis may be overestimated because the increased blood flow causes intravoxel dephasing when flowing through the stenotic areas [6,9]. The swirling, fast internal flow in large aneurysms may cancel each other out and this intravoxel dephasing can lead to nonvisualization of giant aneurysms [4]. ...
Objective
Flow dephasing artifacts within intracranial ICA have been problematic for 3D time-of-flight magnetic resonance angiography (3D-TOF-MRA). This study aimed to evaluate pointwise encoding time reduction with radial acquisition subtraction-based MR angiography (PETRA-MRA) for decreasing flow dephasing artifacts compared to 3D-TOF-MRA in intracranial segments of internal carotid artery (ICA) at 3 T.
Methods
Sixty healthy participants and seven patients with intracranial ICA aneurysms were enrolled to undergo 3D-TOF-MRA and PETRA-MRA. Two radiologists each evaluated the image quality of healthy participants using a 4-point scale (1: the best and 4: the worst). Quantitative analysis of the extent of homogeneity in signal intensity within the ICA and intracranial aneurysms was conducted using a parameter d: the higher the d value, the greater the signal homogeneity. Wilcoxon signed rank test, Chi-square test and the weighted kappa (κ) statistic were used for statistical analyses.
Results
The image quality of PETRA-MRA with an overall score of 1.35 ± 0.53 was significantly better than that obtained with 3D-TOF-MRA, with an overall score of 3.50 ± 0.62 (Z = -9.56, p < 0.001). The parameter d of PETRA-MRA was higher than that of 3D-TOF-MRA for both 60 healthy participants (0.97 ± 0.05, 0.87 ± 0.11; z = −13.21, p < 0.001) and 7 patients with intracranial aneurysms (0.81 ± 0.18, 0.74 ± 0.16; z = −2.37, p = 0.018).
Conclusion
Compared with conventional 3D-TOF-MRA, PETRA-MRA remarkably improved the image quality with reduced flow dephasing artifacts in segments of intracranial ICA.
... Time-of-flight MRA (TOF-MRA) is a non-invasive imaging modality that does not require application of intravenous contrast agents or exposure to radiation [9][10][11][12]. However, conventional TOF-MRA can be comparatively slow and achieving high spatial resolution can be challenging [13]. The spatial coverage is frequently compromised in order to attain a below-1-mm resolution and a high signal-to-noise ratio (SNR) while keeping a clinically acceptable scan time [13]. ...
... However, conventional TOF-MRA can be comparatively slow and achieving high spatial resolution can be challenging [13]. The spatial coverage is frequently compromised in order to attain a below-1-mm resolution and a high signal-to-noise ratio (SNR) while keeping a clinically acceptable scan time [13]. Long acquisition times can promote motion artifacts, which impair the detection of vessel pathologies. ...
Objective
To systematically compare time-of-flight magnetic resonance angiography (TOF-MRA) acquired with Compressed SENSE (TOF-CS) to spiral imaging (TOF-Spiral) for imaging of brain-feeding arteries.
Methods
Seventy-one patients (60.2 ± 19.5 years, 43.7% females, 28.2% with pathology) who underwent TOF-MRA after implementation of a new scanner software program enabling spiral imaging were analyzed retrospectively. TOF-CS (standard sequence; duration ~ 4 min) and the new TOF-Spiral (duration ~ 3 min) were acquired. Image evaluation (vessel image quality and detectability, diagnostic confidence (1 (diagnosis very uncertain) to 5 (diagnosis very certain)), quantitative measurement of aneurysm diameter or degree of stenosis according to North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria) was performed by two readers. Quantitative assessments of pathology were compared to computed tomography angiography (CTA) or digital subtraction angiography (DSA).
Results
TOF-CS showed higher image quality for intraosseous and intradural segments of the internal carotid artery while TOF-Spiral better depicted small intracranial vessels like the anterior choroidal artery. All vessel pathologies were correctly identified by both readers for TOF-CS and TOF-Spiral with high confidence (TOF-CS (4.4 ± 0.6 and 4.3 ± 0.8), TOF-Spiral (4.3 ± 0.7 and 4.3 ± 0.8)) and good inter-reader agreement (Cohen’s kappa > 0.8). Quantitative assessments of aneurysm size or stenosis did not significantly differ between TOF-CS or TOF-Spiral and CTA or DSA (p > 0.05).
Conclusions
TOF-Spiral for imaging of brain-feeding arteries enables reductions in scan time without drawbacks in diagnostic confidence. A combination of spiral imaging and CS may help to overcome shortcomings of both sequences alone and could further reduce acquisition times in the future.
Key Points
• TOF-MRA with Compressed SENSE is superior in depicting arteries at the skull base while spiral TOF-MRA is able to better depict small intracranial vessels.
• Both TOF-MRA with Compressed SENSE and TOF-MRA with spiral imaging provide high diagnostic confidence for detection of pathologies of brain-feeding arteries.
• Spiral TOF-MRA is faster (by 25% for the sequence used in this study) than TOF-MRA with Compressed SENSE, thus enabling clear reductions in scan time for the clinical setting.
... 7 MRA has shown promising results but has limitation like overestimation of stenosis, less sensitivity in detection of ulceration, less coverage of anatomic area, flow dependence especially when performed without contrast. 8,9 USCD is safe and easy to perform compared to CTA and widely used to detect carotid artery stenosis and plaque characterization but has less sensitivity and specificity for detection of carotid artery stenosis. Presence of heavy calcification and higher bifurcation of carotid artery may limit its use. ...
... In humans, the MRA image quality of vessels deteriorates at bifurcations and at kinks and loops within vessels owing to turbulent blood flow, which generates intravoxel phase dispersion artifacts. [24][25][26] Those artifacts resemble stenoses because of a decreased or absent intraluminal signal. In dogs, the ICA2 segment spirals, 8,9 and the intraluminal signal may be lost because of artifacts, resulting in a deterioration of image quality for that segment. ...
Objective:
To assess visualization of the intracranial arteries and internal carotid artery (ICA) on 3-D time-of-flight (TOF) magnetic resonance angiography (MRA) images obtained at 1.5 T and to investigate factors that affect the image quality of those arteries in dogs.
Animals:
39 dogs with idiopathic epilepsy.
Procedures:
Each dog underwent 3-D TOF MRA, and 5 pairs of intracranial arteries, the basilar artery, and both ICAs were evaluated. Each artery was assigned an image-quality score on a scale of 0 to 3, where 0 = poor and 3 = excellent. Multivariable regression analysis was used to assess whether age, body weight (BW), serum total cholesterol concentration, intracranial volume (ICV), and mean arterial pressure were significantly associated with the image quality of each vessel.
Results:
In all dogs, the image-quality score was 2 or 3 for the proximal middle cerebral arteries, basilar artery, and caudal aspect of the caudal communicating arteries. In some dogs, the rostral cerebellar arteries, rostral aspect of the caudal communicating arteries, and middle and rostral aspects of the ICA were poorly visualized. For various arteries, image quality was negatively associated with age and positively associated with BW and ICV.
Conclusions and clinical relevance:
Results indicated that 3-D TOF MRA images obtained at 1.5 T did not consistently and clearly delineate the ICA and narrow or peripheral intracranial arteries of dogs; therefore, careful attention is required when such images are assessed. Patient age, BW, and ICV can also affect the image quality of some intracranial arteries on 3-D TOF MRA images. (Am J Vet Res 2019;80:480-489).
... The spatial coverage is often compromised to achieve a half-millimeter resolution and good signalto-noise ratio, while keeping the scan time clinically acceptable. 6 Furthermore, relatively long acquisition times may lead to motion artifacts, which disrupt the detection of vascular lesions. Further limitations of conventional TOF-MRA include a loss of signal intensity related to turbulent and slow flow. ...
Background and purpose:
Time-of-flight MR angiography is the preferred imaging technique to assess intracranial arterial stenosis but is limited by a relatively long acquisition time. Compressed sensing provides an innovative approach in undersampling k-space to minimize the data-acquisition time. We aimed to evaluate the diagnostic accuracy of compressed sensing TOF for detecting intracranial arterial stenosis by comparison with conventional parallel imaging TOF-MRA.
Materials and methods:
Compressed sensing TOF and parallel imaging TOF were performed in 22 patients with intracranial arterial stenosis. The MRA scan times were 2 minutes and 31 seconds and 4 minutes and 48 seconds for compressed sensing TOF and parallel imaging TOF, respectively. The reconstructed resolutions were 0.4 × 0.4 × 0.4 and 0.4 × 0.4 × 0.6 mm3 for compressed sensing TOF and parallel imaging TOF, respectively. The diagnostic quality of the images and visibility of the stenoses were independently ranked by 2 neuroradiologists blinded to the type of method and were compared using the Wilcoxon signed rank test. Concordance was calculated with the Cohen κ. Edge sharpness of the arteries and the luminal stenosis ratio were analyzed and compared using a paired-sample t test.
Results:
The interrater agreement was good to excellent. Compressed sensing TOF resulted in image quality comparable with that of parallel imaging TOF but boosted confidence in diagnosing arterial stenoses (P = .025). The edge sharpness of the intracranial arteries for compressed sensing TOF was significantly higher than that for parallel imaging TOF (P < .001). The luminal stenosis ratio on compressed sensing TOF showed no significant difference compared with that on parallel imaging TOF.
Conclusions:
Compressed sensing TOF both remarkably reduced the scan time and provided adequate image quality for the diagnosis of intracranial arterial stenosis.
... Moving blood produces a much higher signal compared to static tissue with TOF-MRA. This technique, however, is susceptible to image acquisition artifacts [48] and inaccurate imaging results in the presence of complex blood flow [49]. This technique is also susceptible to stenosis size overestimation [50], which motivates the use of flow independent CE-MRA for the diagnosis of atherosclerosis-related diseases. ...
Atherosclerosis is a debilitating condition that increases a patient's risk for intermittent claudication, limb amputation, myocardial infarction, and stroke, thereby causing approximately 50% of deaths in the western world. Current diagnostic imaging techniques, such as ultrasound, digital subtraction angiography, computed tomography angiography, magnetic resonance angiography, and optical imaging remain suboptimal for detecting development of early stage plaques. This is largely due to the lack of compositional information, penetration depth, and/or clinical efficiency of these traditional imaging techniques. Photoacoustic imaging has emerged as a promising modality that could address some of these limitations to improve the diagnosis and characterization of atherosclerosis-related diseases. Photoacoustic imaging uses near-infrared light to induce acoustic waves, which can be used to recreate compositional images of tissue. Recent developments in photoacoustic techniques show its potential in noninvasively characterizing atherosclerotic plaques deeper than traditional optical imaging approaches. In this review, we discuss the significance and development of atherosclerosis, current and novel clinical diagnostic methods, and recent works that highlight the potential of photoacoustic imaging for both experimental and clinical studies of atherosclerosis.
... Die Gefäßrekonstruktion mit der " maximum intensity projection " ist nicht aus jeder beliebigen Richtung möglich, da es zur Überlappung durch die Arteria carotis externa kommt (Elergsma et al 1999). Schwache Flusssignale können von der MIP fälschlicherweise nicht berücksichtigt werden und somit in Höhe der Stenose zu einem artifiziell überschätzen Stenosegrad führen (Anson et al 1993, De Marco et al 1994, Patel et al 1994). Patienten mit orthopädischen und kardialen Implantaten (Klappenersatz) können mittlerweile einer MRT unterzogen werden, da nur in wenigen Fällen mäßiggradige Torsions-und Zugkräfte auftreten. ...
Das Ziel: der Arbeit war die Überprüfung der Aussagekraft der MRA in time-of-flight-technique der Arteria caroits bei 1,0 Tesla im Vergleich zur intaarteriellen DSA und der Wertigkeit in der Einsatzfähigkeit in der klinischen Routine bei der Diagnostik von Carotisstenosen. 101 Patienten wurden zur Abklärung einer Stenose der Arteria carotis vergleichend mittels TOF-MRA und i.a. DSA der Arteriae carotis untersucht. Morphologische Veränderungen wurden für sämliche Gefässe erfasst, wobei die Stenosen der Arteriae carotis entsprechend den NASCET-Kriterien graduiert wurden (geringgrade, mittelgradige,hochgradige Stenose oder Verschluss).Die Ergebnisse wurden mit folgenden drei verschiedenen statistischen Tests ausgewertet: Kappa Test, gewichteter Kappa Test und Intraklassenkorrelationskoeffizient. Von den 84 in die Auswertung eingebezogenen Gefässen wurden 66 Stenosen in der DSA als geringgradig klassifiziert. In dieser Kategorie wurden 60 dieser Stenosen von der MRA korrekt als geringgradig klassifiziert. In der DSA wurden 60 Stenosen der Arteria carotis als mittelgradig klassifiziert. 29 dieser Stenosen wurden von der MRA korrekt als mittelgradig eingeschätzt. 21 Stenosen wurden von der DSA als hochgradig klassifiziert. 20 dieser Stenosen wurden von der MRA korrekt als hochgradige Stenosen eingeschätzt. Die 16 kompletten Gefäsverschlüsse wurden alle von der MRA detektiert. Der Kappa Test ergab eine starke Korrelation der Ergebnisse. Insgesamt zeigte sich eine gute Überstimmung zwischen MRA und DSA. Aber gerade im Bereich der mittelgradigen Stenosen neigte die MRA dazu den Stenosegrad zu überschätzen. Das Ziel der Gefässdiagnostik ist eine präzise und reproduzierbare Bestimmung des Stenosegrades. Die Magnetresonanzangiographie kann als eine akkurate und zuverlässige Methode zur Bestimmung von Carotisstenosen angesehen werden
... MRA and duplex scanning results were concordant for grading severity of ICA disease in 86% of patients, and approached the accuracy range of our earlier experience, 11 despite the compromised duplex scanning in this study. The tendency with MRA of stenosis "overestimation" related to maxi- mum intensity pixel reconstruction techniques, noted by others, 8,14,15 has been explained with better understanding of the hemodynamic causes responsible for MRA signal loss and flow gap formation 16,17 and accurate measurement of maximal stenosis from equivalent rotational projections between MRA and arteriography. 10 Overestimation of lesion severity was not found in our initial MRAangiographic validation experience, 11 and did not occur when results at MRA were compared with those at duplex scanning or arteriography in this study. ...
We prospectively evaluated whether magnetic resonance angiography (MRA) enabled definition of cerebrovascular anatomy after indeterminate or inadequate results at duplex ultrasound scanning to facilitate patient selection for carotid endarterectomy (CEA) and for technical planning.
After implementation of a protocol in October 1998 to minimize use of cerebral arteriography, MRA (arch/cervical two-dimensional and cranial three-dimensional time of flight technique) was performed in 138 consecutive patients with cerebrovascular occlusive disease and inconclusive duplex scans obtained by an ICAVL-approved laboratory. The ability of MRA to define anatomic features unresolved at duplex scanning was compared between categories of duplex scan inadequacies. Operative outcome was compared between patients requiring MRA before CEA (n = 66) and a concurrent cohort undergoing CEA on the basis of duplex scan results only (n = 69).
Incomplete imaging of the carotid bifurcation, because of high bifurcation, long (>3 cm) internal carotid artery (ICA) plaque, or calcific shadows, was the most common reason for inadequate duplex scans (n = 74, 53%), followed by borderline severe ICA disease (23.17%), suspected extracervical disease (supra-aortic trunk, vertebral, or intracranial, 22, 16%), ICA near- occlusion (12.9%), and diffuse recurrent stenosis (7.5%). MRA enabled resolution of duplex scan inadequacies in 95% of patients with disease confined to the carotid bifurcation, and 90% of all patients, but was least accurate for delineation of extracervical lesions (77%) and near-occlusions (75%). In 5 of 8 patients (6%) arteriography was performed to determine operability of ICA near-occlusion or extracervical lesions. Combined stroke and death rates after CEA were not statistically different (P =.3) between patients requiring MRA (3 of 66, 4.6%) and the concurrent group in whom MRA was performed solely on the basis of duplex results (1 of 69, 1.5%). However, intraoperative technical adjustments (anatomy that precluded shunt use, extended endarterectomy length, ICA shortening due to tortuosity) were planned in 71% of patients (12 of 17) with MRA-defined anatomy, but only 36% of patients (4 of 11) with long CEA on the basis of duplex results only (P =.08).
MRA replaces the need for cerebral arteriography in most patients after inadequate carotid duplex scanning. Delineation of cerebrovascular anatomy at MRA assists in determination of CEA candidacy and operative planning.
