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Comparison of 3T Intracranial Vessel Wall MRI Sequences
Abstract
Background and purpose:
Intracranial vessel wall MR imaging plays an increasing role in diagnosing intracranial vascular diseases. For a complete assessment, pre- and postcontrast sequences are required, and including other sequences, these result in a long scan duration. Ideally, the scan time of the vessel wall sequence should be reduced. The purpose of this study was to evaluate different intracranial vessel wall sequence variants to reduce scan duration, provided an acceptable image quality can be maintained.
Materials and methods:
Starting from the vessel wall sequence that we use clinically (6:42 minutes), 6 scan variants were tested (scan duration ranging between 4:39 and 8:24 minutes), creating various trade-offs among spatial resolution, SNR, and contrast-to-noise ratio. In total, 15 subjects were scanned on a 3T MR imaging scanner: In 5 subjects, all 7 variants were performed precontrast-only, and in 10 other subjects, the fastest variant (4:39 minutes) and our clinically used variant (6:42 minutes) were performed pre- and postcontrast.
Results:
The fastest variant (4:39 minutes) had higher or comparable SNRs/contrast-to-noise ratios of the intracranial vessel walls compared with the reference sequence (6:42 minutes). Qualitative assessment showed that the contrast-to-noise ratio was most suppressed in the fastest variant of 4:39 minutes and the variant of 6:42 minutes pre- and postcontrast. SNRs/contrast-to-noise ratios of the fastest variant were all, except one, higher compared with the variant of 6:42 minutes (P < .008). Furthermore, the fastest variant (4:39 minutes) detected all vessel wall lesions identified on the 6:42-minute variant.
Conclusions:
A 30% faster vessel wall sequence was developed with high SNRs/contrast-to-noise ratios that resulted in good visibility of the intracranial vessel wall.
... The 3D FSE T 1 approach is relatively recent, more complex than 3D FSE T 2 and is less understood. There are many variants [6][7][8], and the best ones apply excessive demands on hardware and software and drain SNR and CNR that can be beneficial to suppress some tissues or not so if the pathologies happen to lose SNR and CNR, meaning suppression of select native tissues without control or knowledge could be problematic [8]. All of these issues are the basis of concern in this commentary against generalization claimed by Zhang et al [1]. ...
... Lindenholz et al [6] have compared 7 variants of 3D FSE VISTA T 1 (Volume Isotropic Turbo Spin Echo Acquisition) from Philips but did not clarify strengths and weaknesses or the mechanistic differences among those. However due to potential misreads, Lindenholz et al [7] also have recommended cautious interpretation of vessel wall imaging and have listed some steps how to do it. ...
... Zhang et al [1] have arbitrarily chosen one of these 4 variants to image diffuse wall thickening pathologies (DWT). Their results seem to have value and they have accidentally benefitted by using a sequence version better than most of the other variants available [6,8]. They achieved reasonable wall resolution in clinically feasible scan times and their dedicated carotid surface RF coil that couple well with neck tissue may be the best choice for now in spite of uneven steady state generation due to non-uniform RF profiles in surface coils at different carotid depths, e.g. ...
This editorial suggests more science and technology need to be invested in "Pseudo-steady state 3D spin echo" sequences, particularly for T1 contrast based applications: currently getting popular for its inherent dark blood capacity in straight, fast flows in large vessels while allowing routine contrast enhancement of plaques and vessel wall inflammations. This MRI/MRA mixed tool at high field high resolution with contrast gives good results (VISTA, CUBE, SPACE) one needs standardization.
... In general, these sequences can take up to 7e10 minutes, although some authors have shown diagnostically acceptable imaging in <5 minutes. 3,5 More recently, whole brain 3D-VWI sequences have been developed, which can image entire brain in about 7 minutes with a resolution of 0.5 mm isotropic. 6 Similarly, some of the recently introduced vendor-specific developments have the potential to shorten the acquisition time further. ...
... Ultimately, a clinical protocol may have a combination of 2D and 3D sequences and isotropic/anisotropic imaging and may be tailored to the specific clinical question. 5,7 For vessel wall assessment, most studies involve at least a T1-weighted (W) pre-and post-contrast sequence. As a general rule, given the variability in various vendor platforms, acceleration techniques, availability of compressed sensing technique on the scanner and a trend towards shorter repetition time (TR)/echo time (TE) (especially for T1W imaging), the optimal parameters vary and are in a continuous state of flux; however, more and more vendors are moving towards providing a baseline VWI technique/ sequence in their sequence database, which can provide a good starting point and can be optimised further, based on the scanner configurations. ...
Vessel wall imaging (VWI) is being increasingly used as a non-invasive diagnostic method to evaluate the intra- and extracranial vascular bed. Whereas conventional vascular imaging primarily assesses the vessel lumen, VWI changes the focus of analysis toward the vessel wall. As the technical challenges of high spatial resolution, signal-to-noise ratio, and contrast-to-noise ratio and long scans times are addressed, interest in the clinical applications of this technique has steadily increased over the years. In this review, the authors will discuss the various applications of VWI as well as principles of interpretation and common imaging findings, focusing on intracranial atherosclerosis, vascular dissection, vasculitides (such as primary angiitis of the central nervous system (PACNS) and neurosarcoidosis), vasculopathies (such as reversible cerebral vasoconstriction syndrome (RCVS), cocaine-induced vasculopathy, moyamoya disease, and radiation-induced arteriopathy), aneurysms, and post-thrombectomy changes. The authors will also discuss the potential pitfalls of VWI and helpful cues to avoid being tricked.
... The technical considerations for VWI vary depending on the magnetic field strength and various hardware configurations. The important considerations to achieve the higher spatial resolution and signal to noise ratio include a 3T or higher magnetic field strength, a 32 or 64-channel head coil over an 8 or 12-channel head coil to increase peripheral resolution, along with combination of a precontrast and postcontrast T1-weighted anisotropic 2D and isotropic 3D sequences based on the specific clinical indication [26,27]. An important consideration in performing VWI, specifically in younger patients, in the evaluation and follow-up of CCV includes repetitive use of gadolinium-based contrast agent [28]. ...
Cerebral vasculitis is increasingly recognized as a common cause of pediatric arterial stroke. It can present with focal neurological deficits, psychiatric manifestations, seizures, and encephalopathy. The etiopathogenesis of childhood cerebral vasculitis (CCV) is multifactorial, making an inclusive classification challenging. In this review, we describe the common and uncommon CCV with a comprehensive discussion of etiopathogenesis, the role of various imaging modalities, and advanced techniques in diagnosing CCV. We also highlight the implications of relevant clinical, laboratory, and genetic findings to reach the final diagnosis. Based on the clinicoradiological findings, a stepwise diagnostic approach is proposed to facilitate CCV diagnosis and rule out potential mimics. Identification of key clinical manifestations, pertinent blood and cerebrospinal fluid results, and evaluation of central nervous system vessels for common and disease-specific findings will be emphasized. We discuss the role of magnetic resonance imaging, MR angiography, and vessel wall imaging as the imaging investigation of choice, and reservation of catheter angiography as a problem-solving tool. We emphasize the utility of brain and leptomeningeal biopsy for diagnosis and exclusion of imitators and masqueraders.
... The CNR between vessel wall and lumen was calculated with the following formula as the normalized difference between the SNR of vessel wall and lumen as in the previous publications 31,33,34 : ...
Purpose
To evaluate MRA and vessel wall imaging (VWI) image quality in the thoracic aorta using a novel method named BRIDGE (bright and dark blood images with multishot gradient‐echo EPI).
Methods
The BRIDGE method consists of 3D multishot gradient‐echo EPI acquisition using pulse gating, navigator gating, and magnetization preparation with a T2‐preparation pulse and a nonselective inversion‐recovery pulse. The BRIDGE and conventional methods (noncontrast MRA based on 3D turbo‐field‐echo [TFE] and VWI based on 3D turbo spin echo with variable refocusing flip angle [VRFA‐TSE]) were performed in 10 healthy volunteers and 10 patients. The SNR, contrast‐to‐noise ratio (CNR), and sharpness in the thoracic aorta were compared for MRA evaluation. The values of SNRlumen, SNRwall, CNRwall−lumen, contrast ratio (CR)lumen−muscle, coefficient of variation, sharpness, lumen area, and wall area in the thoracic aorta were compared for VWI evaluation. Two radiologists independently performed qualitative image‐analysis assessments.
Results
When MRA and VWI were acquired, the acquisition time was 26.6% to 27.8% shorter with BRIDGE than the conventional method. In the MRA evaluation, BRIDGE and TFE methods were comparable. In the VWI evaluation, BRIDGE was superior to the VRFA‐TSE method in blood suppression and evaluation of the ascending aorta. Because the blood signal suppression of BRIDGE is based on the T1 value of blood, the blood signal can be suppressed more uniformly than with the VRFA‐TSE method, regardless of age, blood flow velocity, or vascular anatomy.
Conclusion
The BRIDGE method can provide both MRA, to assess vascular anatomy and luminal changes, and VWI, to assess the vessel wall and detect vulnerable plaques, in a single scan.
... Fifth, only the T1/T2 sequence was selected for the study. The T1-enhanced sequence may provide a more accurate display of the vascular lumen and plaques (36). However, injection of contrast medium is invasive, and there is a risk of gadolinium deposition in the brain (37), and the vast majority of patients were not willing to undergo enhanced MRI scans. ...
Background and Purpose: Ischemic stroke can be caused by atherosclerotic lesions of the middle cerebral artery (MCA). Some studies have described the effects of statin treatment on carotid artery plaques, but little is known about the effects of statin treatment on MCA plaques. The purpose of this study was to validate the efficacy of standard-dose atorvastatin (20 mg/day) in patients with symptomatic MCA atherosclerotic stenosis (SMAS) in northern China.
Materials and Methods: This study is a prospective, single-arm, single-center, 12-month follow-up observational study monitoring imaging, and clinical outcomes of standard-dose atorvastatin treatment among patients with SMAS. The primary outcomes were changes in vessel wall magnetic resonance imaging (VWMRI) and serum lipid profiles before and after (1, 3, 6, and 12 months) statin treatment.
Results: A total of 46 patients were recruited for this study, and 24 patients completed the follow-up. During the follow-up period, serum non-high-density lipoprotein cholesterol concentrations gradually decreased in the patients. Fourteen patients (54.33%) had a reversal of MCA plaques and 10 patients (41.67%) had no significant progression of MCA plaques and remained stable at the follow-up endpoint. At the 12 months follow-up time-point, the treatment did not reverse vascular remodeling or change the shape and distribution of plaques. Altered serum low-density lipoprotein cholesterol (LDL-C) concentrations in patients were strongly associated with plaque reversal.
Conclusion: Vessel wall magnetic resonance imaging could accurately characterize changes in MCA plaques after lipid-lowering therapy. Standard-dose atorvastatin treatment could stabilize and reverse plaques in northern Chinese patients with SMAS.
... Vessel wall imaging has been suggested as a means to monitor disease activity and treatment response in patients with CNS vasculitis [19,20,59,60]. Several case reports and figures in review articles have been published showing decreasing or completely resolving vessel wall contrast enhancement under immunosuppressive therapy [20,21,61,62]. ...
Objective
To approach the clinical value of MRI with vessel wall imaging (VWI) in patients with central nervous system vasculitis (CNSV), we analyzed patterns of VWI findings both at the time of initial presentation and during follow-up.
Methods
Stenoocclusive lesions, vessel-wall contrast enhancement (VW-CE) and diffusion-restricted lesions were analyzed in patients with a diagnosis of CNSV. On available VWI follow-up, progression, regression or stability of VW-CE were evaluated and correlated with the clinical status.
Results
Of the 45 patients included, 28 exhibited stenoses visible on MR angiography (MRA-positive) while 17 had no stenosis (MRA-negative). VW-CE was found in 2/17 MRA-negative and all MRA-positive patients ( p < 0.05). 79.1% (53/67) of stenoses showed VW-CE. VW-CE was concentric in 88.3% and eccentric in 11.7% of cases. Diffusion-restricted lesions were found more frequently in relation to stenoses with VW-CE than without VW-CE ( p < 0.05). 48 VW-CE lesions in 23 patients were followed over a median time of 239.5 days. 13 VW-CE lesions (27.1%) resolved completely, 14 (29.2%) showed partial regression, 17 (35.4%) remained stable and 4 (8.3%) progressed. 22/23 patients received immunosuppressive therapy for the duration of follow-up. Patients with stable or progressive VW-CE were more likely ( p < 0.05) to have a relapse (14/30 cases) than patients with partial or complete regression of VW-CE (5/25 cases).
Conclusion
Concentric VW-CE is a common finding in medium/large-sized vessel CNSV. VW-CE might represent active inflammation in certain situations. However, follow-up VWI findings proved ambiguous as persisting VW-CE despite immunosuppressive therapy and clinical remission was a frequent finding.
... Historically, ICAS has been evaluated by measuring the presence of intracranial stenosis using lumenographic techniques or by detecting vessel wall calcifications that generally reflect a more advanced stage of ICAS (2)(3)(4)(5). Over the last two decades, however, intracranial vessel wall MRI sequences have enabled in vivo visualization of the intracranial vessel wall itself (6)(7)(8). With these dedicated MRI sequences, both subtle (non-stenotic) and more advanced vessel wall pathology of the proximal cerebral large arteries can be assessed. ...
The relevance of intracranial vessel wall lesions detected with MRI is not fully established. In this study (trial identification number: NTR2119; www.trialregister.nl), 7T MRI was used to investigate if a higher vessel wall lesion burden is associated with more cerebral parenchymal changes in patients with ischemic stroke or transient ischemic attack (TIA). MR images of 82 patients were assessed for the number of vessel wall lesions of the large intracranial arteries and for cerebral parenchymal changes, including the presence and number of cortical, small subcortical, and deep gray matter infarcts; lacunes of presumed vascular origin; cortical microinfarcts; and periventricular and deep white matter hyperintensities (WMHs). Regression analyses showed that a higher vessel wall lesion burden was associated with the presence of small subcortical infarcts, lacunes of presumed vascular origin, and deep gray matter infarcts (relative risk 1.18; 95% CI, 1.03–1.35) and presence of moderate-to-severe periventricular WMHs (1.21; 95% CI, 1.03–1.42), which are all manifestations of small vessel disease (SVD). The burden of enhancing vessel wall lesions was associated with the number of cortical microinfarcts only (1.48; 95% CI, 1.04–2.11). These results suggest an interrelationship between large vessel wall lesion burden and cerebral parenchymal manifestations often linked to SVD or, alternatively, that vascular changes occur in both large and small intracranial arteries simultaneously.
Objectives
Central nervous system vasculitis (CNSV) is a rare disease. High-resolution vessel wall imaging (HR-VWI) enables the identification of inflammatory changes within the vessel wall. Few studies have applied HR-VWI to assess CNSV in children. This study delves into the utility of HR-VWI for diagnosing and treating CNSV in children, with the aim of enhancing clinical diagnosis and efficacy evaluation.
Methods
Imaging data were acquired from children who underwent HR-VWI examinations. The study meticulously analysed clinical data and laboratory tests to discern the characteristics and distribution patterns of diverse vasculitis forms.
Results
In children, CNSV mainly involves medium vessels with grade 1 and 2 stenosis (grade 4 stenosis is rare), and the imaging features generally show centripetal and moderate enhancement, suggesting that this feature is specific for the diagnosis of CNSV. High-grade stenosis, concentric enhancement and strong enhancement of the vasculature indicate more severe disease activity. Remarkably, HR-VWI proved to be significantly more sensitive than magnetic resonance angiography in detecting CNSV. Among the 13 cases subjected to imaging review, 8 demonstrated a reduction or resolution of vessel wall inflammation. In contrast, five patients exhibited worsening inflammation in the vessel wall. HR-VWI demonstrated that changes in vessel wall inflammation were closely correlated with changes in brain parenchymal lesions and symptoms.
Conclusion
This study underscores the diagnostic value of HR-VWI in CNSV assessment and treatment monitoring, offering a quantitative evaluation of CNSV in children.
Objectives:
To investigate whether the imaging changes on high-resolution vessel wall imaging (HR-VWI) in patients before and after percutaneous transluminal angioplasty and stenting (PTAS) contribute to predicting the clinical outcome.
Methods:
The study included 24 severe intracranial artery stenosis (SICAS) patients undergoing PTAS with Wingspan Stent between 2018 and 2020 and had a 1-year follow-up. Three HR-VWI sessions (preprocedural, early [within 24 h], and delayed postprocedural [134.7 ± 27.1 days)]) in each subject were performed with 3-Tesla MRI. We evaluated periprocedural HR-VWI changes in patients with and without recurrent cerebral ischemic symptoms (RCIS) within 1-year follow-up.
Results:
On CE-T1WI of the patients without RCIS, a significant decrease in enhanced area was observed on early postprocedural (0.04 ± 0.02 cm2, p = 0.001) and delayed postprocedural (0.04 ± 0.02 cm2; p = 0.001) HR-VWI compared to preprocedural (0.07 ± 0.02 cm2) HR-VWI. Patients with RCIS demonstrated no significant loss of enhanced area on CE-T1WI of early postprocedural HR-VWI (p = 0.180). Significant decreases in calibrated T1 signals were observed in both presence (1.77 ± 0.70 vs. 0.79 ± 0.52; p = 0.018) and absence (1.42 ± 0.62 vs. 0.83 ± 0.40; p = 0.001) of RCIS in early postprocedural HR-VWI.
Conclusion:
The preliminary results showed the presence of reduced contrast enhancement immediately after PTAS may indicate less recurrent stroke events within 1 year. Further studies are necessary to confirm the phenomena in a longer observation period.
Key points:
• Early postprocedural high-resolution vessel imaging (HR-VWI) within 24 h can effectively predict a 1-year outcome following intracranial stenting. • For stenotic lesions after stenting without reduced contrast enhancement on HR-VWI within 24 h may need closer clinical surveillance for potentially higher risk of stroke events within 1 year.
Magnetic resonance (MR) imaging is a crucial tool for evaluation of the skull base, enabling characterization of complex anatomy by utilizing multiple image contrasts. Recent technical MR advances have greatly enhanced radiologists’ capability to diagnose skull base pathology and help direct management. In this paper, we will summarize cutting-edge clinical and emerging research MR techniques for the skull base, including high-resolution, phase-contrast, diffusion, perfusion, vascular, zero echo-time, elastography, spectroscopy, chemical exchange saturation transfer, PET/MR, ultra-high-field, and 3D visualization. For each imaging technique, we provide a high-level summary of underlying technical principles accompanied by relevant literature review and clinical imaging examples.
Purpose of review:
To give an overview regarding the potential usefulness of vessel wall imaging (VWI) in distinguishing various intracranial vascular diseases, their common imaging features, and potential pitfalls.
Recent findings:
VWI provides direct visualization of the vessel wall and allows the discrimination of different diseases such as vasculitis, atherosclerosis, dissection, Moyamoya disease, and reversible cerebral vasoconstriction syndrome. Recent studies showed that concentric and eccentric involvement in the vessel wall, as well as the enhancement pattern were found important for the distinguishing these diseases and evaluating their activity.
Summary:
Most of the imaging techniques currently used are based on luminal imaging. However, these imaging methods are not adequate to distinguish different diseases that can demonstrate similar radiological findings. VWI is being increasingly used as a noninvasive imaging method to offset this limitation.
The purpose of this systematic review is to identify trends and extent of variability in intracranial vessel wall MR imaging (VWI) techniques and protocols. Although variability in selection of protocol design and pulse sequence type is known, data on what and how protocols vary are unknown. Three databases were searched to identify publications using intracranial VWI. Publications were screened by predetermined inclusion/exclusion criteria. Technical development publications were scored for completeness of reporting using a modified Nature Reporting Summary Guideline to assess reproducibility. From 2,431 articles, 122 met the inclusion criteria. Trends over the last 23 years (1995‐2018) show increased use of 3‐Tesla MR (P < .001) and 3D volumetric T1‐weighted acquisitions (P < .001). Most (65%) clinical VWI publications report achieving a noninterpolated in‐plane spatial resolution of ≤.55 mm. In the last decade, an increasing number of technical development (n = 20) and 7 Tesla (n = 12) publications have been published, focused on pulse sequence development, improving cerebrospinal fluid suppression, scan efficiency, and imaging ex vivo specimen for histologic validation. Mean Reporting Summary Score for the technical development publications was high (.87, range: .63‐1.0) indicating strong scientific technical reproducibility. Innovative work continues to emerge to address implementation challenges. Gradual adoption into the research and scientific community was suggested by a shift in the name in the literature from “high‐resolution MR” to “vessel wall imaging,” specifying diagnostic intent. Insight into current practices and identifying the extent of technical variability in the literature will help to direct future clinical and technical efforts to address needs for implementation.
Intracranial vessel wall magnetic resonance (MR) imaging has gained much attention in the past decade and has become part of state-of-the-art MR imaging protocols to assist in diagnosing the cause of ischemic stroke. With intracranial vessel wall imaging, vessel wall characteristics have tentatively been described for atherosclerosis, vasculitis, dissections, Moyamoya disease, and aneurysms. With the increasing demand and subsequently increased use of intracranial vessel wall imaging in clinical practice, radiologists should be aware of the choices in imaging parameters and how they affect image quality, the clinical indications, methods of assessment, and limitations in the interpretation of these images. In this How I do It article, the authors will discuss the technical requirements and considerations for vessel wall image acquisition in general, describe their own vessel wall imaging protocol at 3 T and 7 T, show a step-by-step basic assessment of intracranial vessel wall imaging as performed at their institution-including commonly encountered artifacts and pitfalls-and summarize the commonly reported imaging characteristics of various intracranial vessel wall diseases for direct clinical applicability. Finally, future technical and clinical considerations for full implementation of intracranial vessel wall imaging in clinical practice, including the need for histologic validation and acquisition time reduction, will be discussed.
Background and purpose:
Intracranial vessel wall imaging using MRI has great potential as a clinical method for assessing intracranial atherosclerosis. The purpose of the current study was to compare three 3T MRI vessel wall sequences with different contrast weightings (T1w, PD, T2w) and dedicated sagittal orientation perpendicular to the middle cerebral artery, to the reconstructed sagittal image from a transverse 3D T1w volumetric isotropically reconstructed turbo spin-echo acquisition (VIRTA), and provide a clinical recommendation.
Materials and methods:
The above-mentioned sequences were acquired in 10 consecutive Chinese ischemic stroke or TIA patients (age: 68 years, sex: 4 females) with angiographic-confirmed MCA stenosis at 3T. Institutional review board approval was obtained. Two raters qualitatively scored all images on overall image quality, presence of artifacts, and visibility of plaques. Data were compared using Repeated measures ANOVA and Sidak's adjusted post hoc tests.
Results:
All sequences except the T2w sequence were able to depict the walls of the large vessels of the Circle of Willis (p<0.05). T1w sagittal oblique VIRTA showed significantly more artifacts (p<0.01). Peripherally located plaques were sometimes missed on the sagittal sequences, but could be appreciated on the transverse T1w VIRTA.
Conclusion:
With the 3T multi-sequence vessel wall protocol we were able to assess the intracranial plaque with two different image contrast weightings. The sequence of preference to include in a clinical protocol would be the transverse 3D T1w VIRTA based on absence of artifacts, larger coverage including the whole Circle of Willis, and excellent lesion depiction.
Intracranial vessel wall MR imaging is an adjunct to conventional angiographic imaging with CTA, MRA, or DSA. The technique has multiple potential uses in the context of ischemic stroke and intracranial hemorrhage. There remain gaps in our understanding of intracranial vessel wall MR imaging findings and research is ongoing, but the technique is already used on a clinical basis at many centers. This article, on behalf of the Vessel Wall Imaging Study Group of the American Society of Neuroradiology, provides expert consensus recommendations for current clinical practice.
Objectives:
Several intracranial vessel wall sequences have been described in recent literature, with either 3-T or 7-T magnetic resonance imaging (MRI). In the current study, we compared 3-T and 7-T MRI in visualising both the intracranial arterial vessel wall and vessel wall lesions.
Methods:
Twenty-one elderly asymptomatic volunteers were scanned by 3-T and 7-T MRI with an intracranial vessel wall sequence, both before and after contrast administration. Two raters scored image quality, and presence and characteristics of vessel wall lesions.
Results:
Vessel wall visibility was equal or significantly better at 7 T for the studied arterial segments, even though there were more artefacts hampering assessment. The better visualisation of the vessel wall at 7 T was most prominent in the proximal anterior cerebral circulation and the posterior cerebral artery. In the studied elderly asymptomatic population, 48 vessel-wall lesions were identified at 3 T, of which 7 showed enhancement. At 7 T, 79 lesions were identified, of which 29 showed enhancement. Seventy-one percent of all 3-T lesions and 59 % of all 7-T lesions were also seen at the other field strength.
Conclusions:
Despite the large variability in detected lesions at both field strengths, we believe 7-T MRI has the highest potential to identify the total burden of intracranial vessel wall lesions.
Key points:
• Intracranial vessel wall visibility was equal or significantly better at 7-T MRI • Most vessel wall lesions in the cerebral arteries were found at 7-T MRI • Many intracranial vessel wall lesions showed enhancement after contrast administration • Large variability in detected intracranial vessel wall lesions at both field strengths • Seven-tesla MRI has the highest potential to identify total burden of intracranial atherosclerosis.
Background and purpose:
Intracranial atherosclerosis is a major cause of ischemic stroke worldwide. Intracranial vessel wall imaging is an upcoming field of interest to assess intracranial atherosclerosis. In this study, we investigated total intracranial plaque burden in patients with symptomatic middle cerebral artery stenosis, assessed plaque morphological features, and compared features of symptomatic and asymptomatic lesions using a 3T vessel wall sequence.
Methods:
Nineteen consecutive Chinese patients with ischemic stroke and transient ischemic attack (mean age: 67 years; 7 females) with a middle cerebral artery stenosis were scanned at 3T magnetic resonance imaging; the protocol included a time-of-flight magnetic resonance angiography and the T1-weighted volumetric isotropically reconstructed turbo spin echo acquisition sequence before and after (83%) contrast administration. Chi-square tests were used to assess associations between different plaque features. Statistical significance was set at P<0.05.
Results:
Vessel wall lesions were identified in 18 patients (95%), totaling 57 lesions in 494 segments (12% of segments). Lesions were located primarily in the anterior circulation (82%). Eccentric lesions were associated with a focal thickening pattern and concentric lesions with a diffuse thickening pattern (P<0.001). When differentiating between asymptomatic and symptomatic lesions, an association (P<0.05) was found between eccentricity and asymptomatic lesions, but not for enhancement or a specific thickening pattern. Symptomatic lesions did not have any specific morphological features.
Conclusions:
Our results lead to a 2-fold conclusion: (1) The classification system of both thickening pattern and distribution of the lesion can be simplified by using distribution pattern only and (2) differentiation between symptomatic and asymptomatic atherosclerotic lesions was possible using intracranial vessel wall imaging.
Objectives:
High resolution MRI of the intracranial vessel wall provides important insights in the assessment of intracranial vascular disease. This study aims to refine high resolution 3D MRI techniques for intracranial vessel wall imaging at both 3 and 7 T using customized flip angle train design, and to explore their comparative abilities.
Materials and methods:
11 patients with intracranial artery disease (four atherosclerotic plaques, six aneurysms and one reversible cerebral vasoconstriction syndrome) were imaged at 3 and 7 T with a 3D T 1-weighted fast-spin-echo sequence (SPACE) both pre and post Gd contrast injection. Wall to lumen contrast ratio (CRwall-lumen), contrast enhancement ratio (ER) and the sharpness of the vessel wall were quantified. Two experienced radiologists evaluated the image quality on a 0-5 scale.
Results:
Both 3 and 7 T achieved good image quality with high resolution (nominal 0.5 mm isotropic) and whole brain coverage. The CRwall-lumen and the ER measurements were comparable (p > 0.05). The 7 T images were significantly sharper (sharpness: 2.69 ± 0.50 vs. 1.88 ± 0.53 mm(-1), p < 0.001) with higher image quality (reader 1 score: 3.5 ± 1.1 vs. 2.4 ± 1.1, p = 0.002) compared to 3 T.
Conclusions:
3D T 1-weighted SPACE can be used for intracranial vessel wall evaluation at both 3 and 7 T. 7 T provides significantly better image quality and improves the confidence of diagnosis.
Purpose:
Although three-dimensional (3D) turbo spin echo (TSE) with variable flip angles has proven to be useful for intracranial vessel wall imaging, it is associated with inadequate suppression of cerebrospinal fluid (CSF) signals and limited spatial coverage at 3 Tesla (T). This work aimed to modify the sequence and develop a protocol to achieve whole-brain, CSF-attenuated T1 -weighted vessel wall imaging.
Methods:
Nonselective excitation and a flip-down radiofrequency pulse module were incorporated into a commercial 3D TSE sequence. A protocol based on the sequence was designed to achieve T1 -weighted vessel wall imaging with whole-brain spatial coverage, enhanced CSF-signal suppression, and isotropic 0.5-mm resolution. Human volunteer and pilot patient studies were performed to qualitatively and quantitatively demonstrate the advantages of the sequence.
Results:
Compared with the original sequence, the modified sequence significantly improved the T1 -weighted image contrast score (2.07 ± 0.19 versus 3.00 ± 0.00, P = 0.011), vessel wall-to-CSF contrast ratio (0.14 ± 0.16 versus 0.52 ± 0.30, P = 0.007) and contrast-to-noise ratio (1.69 ± 2.18 versus 4.26 ± 2.30, P = 0.022). Significant improvement in vessel wall outer boundary sharpness was observed in several major arterial segments.
Conclusions:
The new 3D TSE sequence allows for high-quality T1 -weighted intracranial vessel wall imaging at 3 T. It may potentially aid in depicting small arteries and revealing T1 -mediated high-signal wall abnormalities. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
Accurate and timely diagnosis of intracranial vasculopathies is important due to significant risk of morbidity with delayed and/or incorrect diagnosis both from the disease process as well as inappropriate therapies. Conventional vascular imaging techniques for analysis of intracranial vascular disease provide limited information since they only identify changes to the vessel lumen. New advanced MR intracranial vessel wall imaging (IVW) techniques can allow direct characterisation of the vessel wall. These techniques can advance diagnostic accuracy and may potentially improve patient outcomes by better guided treatment decisions in comparison to previously available invasive and non-invasive techniques. While neuroradiological expertise is invaluable in accurate examination interpretation, clinician familiarity with the application and findings of the various vasculopathies on IVW can help guide diagnostic and therapeutic decision-making. This review article provides a brief overview of the technical aspects of IVW and discusses the IVW findings of various intracranial vasculopathies, differentiating characteristics and indications for when this technique can be beneficial in patient management.
Purpose
. Conventional two-dimensional vessel wall imaging has been used to depict the middle cerebral artery (MCA) wall in patients with recent small subcortical infarctions (RSSIs). However, its clinical use has been limited by restricted spatial coverage, low signal-to-noise ratio (SNR), and long scan time. We used a novel three-dimensional high-resolution MR imaging (3D HR-MRI) technique to investigate the presence, locations, and contrast-enhanced patterns of MCA plaques and their relationship with RSSI.
Methods
. Nineteen consecutive patients with RSSI but no luminal stenosis on MR angiography were prospectively enrolled. 3D HR-MRI was performed using a T1w-SPACE sequence at 3.0 T. The presence, locations, and contrast-enhanced patterns of the MCA plaques on the ipsilateral and contralateral sides to the RSSI were analyzed.
Results
. Eighteen patients successfully completed the study. MCA atherosclerotic plaques occurred more frequently on the ipsilateral than the contralateral side to the RSSI (72.2% versus 33.3%,
P
=
0.044
). The occurrence of superiorly located plaques was significantly higher on the ipsilateral than the contralateral side of the MCA (66.7% versus 27.8%;
P
=
0.044
).
Conclusions
. Superiorly located plaques are closely associated with RSSI. 3D high-resolution vessel wall imaging may be a potential tool for etiologic assessment of ischemic stroke.
Vessel wall imaging can depict the morphologies of atherosclerotic plaques, arterial walls, and surrounding structures in the intracranial and cervical carotid arteries beyond the simple luminal changes that can be observed with traditional luminal evaluation. Differentiating vulnerable from stable plaques and characterizing atherosclerotic plaques are vital parts of the early diagnosis, prevention, and treatment of stroke and the neurological adverse effects of atherosclerosis. Various techniques for vessel wall imaging have been developed and introduced to differentiate and analyze atherosclerotic plaques in the cervical carotid artery. High-resolution magnetic resonance imaging (HR-MRI) is the most important and popular vessel wall imaging technique for directly evaluating the vascular wall and intracranial artery disease. Intracranial artery atherosclerosis, dissection, moyamoya disease, vasculitis, and reversible cerebral vasoconstriction syndrome can also be diagnosed and differentiated by using HR-MRI. Here, we review the radiologic features of intracranial artery disease and cervical carotid artery atherosclerosis on HR-MRI and various other vessel wall imaging techniques (e.g., ultrasound, computed tomography, magnetic resonance, and positron emission tomography-computed tomography).
To study the effect of imaging parameters on the contrast of T1 weighted SPACE (Sampling Perfection with Application optimized Contrast using different angle Evolutions, a 3D TSE variant) at 3T for high resolution imaging of intracranial plaques before contrast and with post-gadolinium induced enhancement, and evaluate its relevance to patients with intracranial atherosclerosis.
Optimized parameters giving good T1 contrast between intracranial vessel wall and cerebrospinal fluid (CSF) within a specific scan time and reasonable coverage were found by simulation and validated in a healthy volunteer study. Based on the results, a clinical protocol covering the three major intracranial arteries (middle cerebral arteries, MCA, basilar arteries, BA and petrous internal carotid arteries, ICA) was developed. It was applied in ten patients diagnosed with intracranial arterial lesions. The accuracy of the technique in depicting vessel lumen was assessed by comparison to contrast enhanced MR angiography. The contrast enhancement ratios of the vessel wall/plaque identified were analyzed.
Simulation and volunteer study showed that using T1w-SPACE, good T1 contrast between vessel wall and CSF occurred at TR of around 1000ms using an echo train length of 21 within 10 minutes at an isotropic spatial resolution of 0.5mm. In the 10 patients, 24 plaques were identified in the various segments of the intracranial arterial system of which eight appeared normal on MR angiography. Post contrast enhancement ratio of these plaques varied from 0% up to 156%.
T1w-SPACE provides good T1 contrast between intracranial arterial wall and CSF with high resolution and good coverage within a clinically acceptable scan time. It can depict plaques pre- and post-contrast along the vessels surrounded by CSF in the intracranial arterial system, and would be a useful tool in the clinical assessment of intracranial arterial diseases.
Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
High-resolution MR imaging is an emerging tool for evaluating intracranial artery disease. It has an advantage of defining vessel wall characteristics of intracranial vascular diseases. We investigated high-resolution MR imaging arterial wall characteristics of CNS vasculitis and reversible cerebral vasoconstriction syndrome to determine wall pattern changes during a follow-up period.
We retrospectively reviewed 3T-high-resolution MR imaging vessel wall studies performed on 26 patients with a confirmed diagnosis of CNS vasculitis and reversible cerebral vasoconstriction syndrome during a follow-up period. Vessel wall imaging protocol included black-blood contrast-enhanced T1-weighted sequences with fat suppression and a saturation band, and time-of-flight MRA of the circle of Willis. Vessel wall characteristics including enhancement, wall thickening, and lumen narrowing were collected.
Thirteen patients with CNS vasculitis and 13 patients with reversible cerebral vasoconstriction syndrome were included. In the CNS vasculitis group, 9 patients showed smooth, concentric wall enhancement and thickening; 3 patients had smooth, eccentric wall enhancement and thickening; and 1 patient was without wall enhancement and thickening. Six of 13 patients had follow-up imaging; 4 patients showed stable smooth, concentric enhancement and thickening; and 2 patients had resoluton of initial imaging findings. In the reversible cerebral vasoconstriction syndrome group, 10 patients showed diffuse, uniform wall thickening with negligible-to-mild enhancement. Nine patients had follow-up imaging, with 8 patients showing complete resolution of the initial findings.
Postgadolinium 3T-high-resolution MR imaging appears to be a feasible tool in differentiating vessel wall patterns of CNS vasculitis and reversible cerebral vasoconstriction syndrome changes during a follow-up period.
Atherosclerosis occurs in diverse vascular beds and may result in tissue ischemia. Current understanding of atherosclerotic disease has been advanced by imaging techniques, such as HRMRI studies of the coronary and carotid arteries. In these vessels, atherosclerotic plaque components can be visualized to risk-stratify patients, select treatments, and advance our understanding of atherosclerosis pathophysiology in vivo. These imaging techniques are now being applied to evaluate intracranial arterial disease, both atherosclerotic and nonatherosclerotic. This review highlights the mechanisms by which intracranial atherosclerotic disease (ICAD) causes ischemia, the potential for HRMRI to identify intracranial arterial pathology, the limitations of HRMRI in the intracranial circulation, and future applications of HRMRI for ICAD.
Image quality in MRI depends on several factors (eg, slice thickness, field of view, signal-to-noise ratio, matrix size, and magnetic field strength), but the term HRMRI is not well defined. In this review, the operational definition of HRMRI is limited to magnetic resonance acquisitions using clinically available 1.5 to 3.0 T magnetic field strengths targeted to intracranial arterial pathology that are of sufficient quality to visualize the arterial wall, separate from the lumen, of the proximal circle of Willis vessels. HRMRI can be accomplished at 1.5 T by limiting the field of view to focus on a single vessel or point of interest, but higher field strength at 3.0 T has many advantages over conventional (1.5 T) MRI. Image acquisition is faster1 and there are increased signal-to-noise2 and contrast-to-noise ratios, with better image quality3 for black-blood imaging. The increased signal and contrast that 3 T provides improves the detection of complex atherosclerotic plaque4 and can identify plaque components in larger arteries.5 Two-dimensionally acquired HRMRI is time consuming and must be monitored by a neuroradiologist to ensure adequate sampling of the lesions of interest. HRMRI using 3-dimensional …
Intracranial arterial stenosis (ICAS) in patients with recent ischemic stroke is associated with a high risk of recurrent stroke. More insight into the pathophysiology of ICAS could help identify patients at high risk requiring more aggressive secondary prevention. We evaluated the prevalence, distribution, calcification, and the risk factors predisposing ICAS in a European stroke population.
Consecutive patients with a transient ischemic attack or ischemic stroke (n=786) were evaluated for the presence and distribution of ICAS (≥30% luminal narrowing) by CT angiography. ICAS were categorized as symptomatic or asymptomatic, and the presence of calcification was assessed. The association of traditional cerebrovascular risk factors and the erythrocyte sedimentation rate with ICAS was analyzed.
In 178 of 786 patients (23%), 288 ICAS were observed. Most stenoses (n=194/288; 67%) were located in the posterior circulation arteries. In 59 of 786 patients (8%), ICAS were considered symptomatic. ICAS in the basilar artery and arteries beyond the circle of Willis were mainly noncalcified. In addition to age, gender, and several traditional cerebrovascular risk factors, erythrocyte sedimentation rate was independently associated with the presence of ICAS (OR, 1.20; 95% CI, 1.06-1.36) and with the presence of noncalcified ICAS in particular (OR, 1.20; 95% CI, 1.05-1.37).
ICAS was observed in a noteworthy number of European stroke patients. Particularly, the majority of ICAS was observed in the posterior circulation, possibly conferring worse prognosis. ICAS in distal arteries were mainly noncalcified. Association of noncalcified ICAS and erythrocyte sedimentation rate may indicate a prominent role for inflammatory factors in intracranial atherosclerotic disease.
Intracranial vessel wall magnetic resonance (MR) imaging has gained much attention in the past decade and has become part of state-of-the-art MR imaging protocols to assist in diagnosing the cause of ischemic stroke. With intracranial vessel wall imaging, vessel wall characteristics have tentatively been described for atherosclerosis, vasculitis, dissections, Moyamoya disease, and aneurysms. With the increasing demand and subsequently increased use of intracranial vessel wall imaging in clinical practice, radiologists should be aware of the choices in imaging parameters and how they affect image quality, the clinical indications, methods of assessment, and limitations in the interpretation of these images. In this How I do It article, the authors will discuss the technical requirements and considerations for vessel wall image acquisition in general, describe their own vessel wall imaging protocol at 3 T and 7 T, show a step-by-step basic assessment of intracranial vessel wall imaging as performed at their institution-including commonly encountered artifacts and pitfalls-and summarize the commonly reported imaging characteristics of various intracranial vessel wall diseases for direct clinical applicability. Finally, future technical and clinical considerations for full implementation of intracranial vessel wall imaging in clinical practice, including the need for histologic validation and acquisition time reduction, will be discussed.
Purpose:
To develop and assess a three-dimensional (3D) high resolution black blood MRI (BBMRI) method for evaluation of intracranial vessels with improved cerebrospinal fluid (CSF) suppression.
Materials and methods:
The anti-driven-equilibrium (ADE) pulse was incorporated into a variable flip-angle TSE-based 3D BBMRI to improve CSF suppression. ADE-BBMRI was optimized in 8 participants and compared with BBMRI, with acquired 0.5 mm isotropic resolution and scan time of 5.4 min at 3 Tesla. Contrast-enhanced ADE-BBMRI protocol was implemented in nine patients with intracranial atherosclerosis. Signal and morphological measurements were compared between ADE-BBMRI and BBMRI, as well as pre- and postcontrast ADE-BBMRI. Reliability was assessed by intraclass correlations (ICC).
Results:
ADE-BBMRI effectively suppressed the surrounding CSF signal of intracranial vessels, with a 36-44% reduction compared with BBMRI. ADE-BBMRI also reduced the overall wall signal by 8-8.5%, but provided a significant improvement in wall-to-CSF contrast-to-noise ratio over BBMRI (middle cerebral artery, 5.93 ± 0.59 versus 3.95 ± 1.67, P < 0.01; basilar artery, 3.8 ± 1.76 versus 1.34 ± 0.54, P = 0.01, respectively). No differences were noted in morphological measurements between ADE-BBMRI and BBMRI (lumen area, 6.35 ± 2.87 versus 6.32 ± 2.84 mm(2) ; wall area, 1.28 ± 0.52 versus 1.27 ± 0.53 mm(2) ; mean wall thickness, 0.93 ± 0.30 versus 0.93 ± 0.32 mm; maximum wall thickness, 1.27 ± 0.33 versus 1.28 ± 0.36 mm, all P > 0.05). Contrast enhanced ADE-BBMRI improved the plaque delineation by the increased wall signal, wall-to-CSF and wall-to-blood contrast-to-noise ratio. ICC ranged from 0.54 to 0.95.
Conclusion:
The 3D ADE-BBMRI provides excellent blood and CSF suppression, and accurate measurements of intracranial vessels at 0.5 mm isotropic resolution in 5 min. Its clinical application may provide insight into stroke risk. J. Magn. Reson. Imaging 2016.
Purpose:
To evaluate the feasibility of high-resolution 3D CUBE T1WI for intracranial vessel wall imaging.
Methods:
High-resolution 3D CUBE T1 weighted intracranial vessel wall images (0.4 mm × 0.4 mm × 0.4 mm) of 50 patients were retrospectively evaluated. A 5-point scale (1 poor, 5 excellent) was used to score the imaging quality for displaying the vessel wall of every intracranial artery segments. The inter-observer and intra-observer reproducibility of identifying plaques, intraplaque hemorrhage/luminal thrombosis, and wall enhancement were calculated.
Results:
Totally 893 artery segments were evaluated. 3D CUBE T1WI displayed the arteries wall and lumen clearly, with the highest score (4.920 ± 0.837) for the C6-7 segments and the lowest (3.370 ± 1.107) for the C3 segments of the internal carotid artery (ICA). Both intra-observer and inter-observer reproducibility were high for identification of normal walls (κ=0.928, 95% confidence interval [CI] 0.891-0.954; κ=0.911, CI 0.868-0.940), plaque (κ=0.924, CI 0.884-0.954; κ=0.907, CI 0.866-0.943), luminal thrombosis (κ=1.000, CI 1.000-1.000; κ=1.000, CI 1.000-1.000), and wall enhancement (κ=1.000, CI 1.000-1.000; κ=0.914, CI 0.863-0.961).
Conclusions:
High-resolution 3D CUBE T1WI displayed intracranial wall and lumen clearly, and detected intracranial artery abnormalities with high reproducibility.
Background and purpose:
Preliminary studies suggest that intracranial arteries are capable of accommodating plaque formation by remodeling. We sought to study the ability and extent of intracranial arteries to remodel using 3-dimensional high-resolution black blood magnetic resonance imaging and investigate its relation to ischemic events.
Methods:
Forty-two patients with cerebrovascular ischemic events underwent 3-dimensional time-of-flight magnetic resonance angiography and contrast-enhanced black blood magnetic resonance imaging examinations at 3 T for intracranial atherosclerotic disease. Each plaque was classified by location (eg, posterior versus anterior circulation) and its likelihood to have caused a stroke identified on magnetic resonance imaging (culprit, indeterminate, or nonculprit). Lumen area, outer wall area, and wall area were measured at the lesion and reference sites. Plaque burden was calculated as wall area divided by outer wall area. The arterial remodeling ratio (RR) was calculated as outer wall area at the lesion site divided by outer wall area at the reference site after adjusting for vessel tapering. Arterial remodeling was categorized as positive if RR>1.05, intermediate if 0.95≤RR≤1.05, and negative if RR<0.95.
Results:
One hundred and thirty-seven plaques were identified in 42 patients (37% [50] posterior and 63% [87] anterior). Compared with anterior circulation plaques, posterior circulation plaques had a larger plaque burden (77.7±15.7 versus 69.0±14.0; P=0.008), higher RR (1.14±0.38 versus 0.95±0.32; P=0.002), and more often exhibited positive remodeling (54.0% versus29.9%; P=0.011). Positive remodeling was marginally associated with downstream stroke presence when adjusted for plaque burden (odds ratio 1.34, 95% confidence interval: 0.99-1.81).
Conclusions:
Intracranial arteries remodel in response to plaque formation, and posterior circulation arteries have a greater capacity for positive remodeling and, consequently, may more likely elude angiographic detection. Arterial remodeling may provide insight into stroke risk.
The purpose of this study was to develop a three-dimensional black blood imaging method for simultaneously evaluating the carotid and intracranial arterial vessel walls with high spatial resolution and excellent blood suppression with and without contrast enhancement.
The delay alternating with nutation for tailored excitation (DANTE) preparation module was incorporated into three-dimensional variable flip angle turbo spin echo (SPACE) sequence to improve blood signal suppression. Simulations and phantom studies were performed to quantify image contrast variations induced by DANTE. DANTE-SPACE, SPACE, and two-dimensional turbo spin echo were compared for apparent signal-to-noise ratio, contrast-to-noise ratio, and morphometric measurements in 14 healthy subjects. Preliminary clinical validation was performed in six symptomatic patients.
Apparent residual luminal blood was observed in five (pre-contrast) and nine (post-contrast) subjects with SPACE and only two (post-contrast) subjects with DANTE-SPACE. DANTE-SPACE showed 31% (pre-contrast) and 100% (post-contrast) improvement in wall-to-blood contrast-to-noise ratio over SPACE. Vessel wall area measured from SPACE was significantly larger than that from DANTE-SPACE due to possible residual blood signal contamination. DANTE-SPACE showed the potential to detect vessel wall dissection and identify plaque components in patients.
DANTE-SPACE significantly improved arterial and venous blood suppression compared with SPACE. Simultaneous high-resolution carotid and intracranial vessel wall imaging to potentially identify plaque components was feasible with a scan time under 6 min. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.
© 2015 Wiley Periodicals, Inc.
To develop and evaluate a joint blood and cerebrospinal fluid (CSF) suppression technique for improved intracranial vessel wall MR imaging.
The Delay Alternating with Nutation for Tailored Excitation (DANTE) prepulse was specifically optimized for CSF suppression to improve vessel wall and CSF contrast. It was evaluated on six patients and three healthy volunteers. CSF suppression efficiency, lumen signal to noise ratio, and wall-lumen contrast to noise ratio were compared between images with and without DANTE in major intercranial artery segments. Contrast changes in tissues were also compared with evaluate the technique's compatibility with multicontrast imaging techniques.
The optimized DANTE images significantly improved intracranial vessel wall characterization on all images. Quantitatively, CSF to wall contrast improved by 28% (DANTE-VISTA 1.354 ± 0.216 versus VISTA 1.057 ± 0.13; P < 0.001). DANTE also significantly improved wall-lumen (10.55 ± 3.79 versus 9.34 ± 3.54; P < 0.001) and wall-CSF (4.62 ± 3.19 versus 0.78 ± 2.30; P < 0.001) contrast-to-noise ratios. DANTE prepared images were also found to make only minimal impact on static tissue contrast.
DANTE prepared MR imaging can significantly improve contrast between the vessel wall and cerebral spinal fluid in major intracranial arteries, holding a good potential to be combined with multicontrast protocol for intracranial wall imaging. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.
© 2015 Wiley Periodicals, Inc.
Purpose:
Wall enhancement of saccular cerebral aneurysms has not been researched sufficiently. Our purpose of this study was to investigate the incidence of aneurysmal wall enhancement by the three-dimensional turbo spin-echo sequence with motion-sensitized driven equilibrium (MSDE-3D-TSE) imaging after gadolinium injection.
Methods:
We retrospectively reviewed the pre- and postcontrast MSDE-3D-TSE images of 117 consecutive patients with intracranial aneurysms from September 2011 to July 2013. A total of 61 ruptured and 83 unruptured aneurysms of 61 patients with subarachnoid hemorrhage (SAH) and 56 non-SAH patients were enrolled in this study. We evaluated the wall enhancement of each aneurysm on postcontrast MSDE-3D-TSE images compared with precontrast images. We classified the aneurysmal wall enhancement into three groups as "Strong enhancement," "Faint enhancement," and "No enhancement."
Results:
"Strong/Faint enhancement" of the aneurysm was detected in 73.8/24.6 % of the ruptured aneurysms and 4.8/13.3 % of the unruptured aneurysms. "No enhancement" was found in 1.6 % of the ruptured aneurysms and 81.9 % of the unruptured aneurysms.
Conclusions:
By magnetic resonance vessel wall imaging using the MSDE-3D-TSE sequence, wall enhancement was frequently observed on ruptured aneurysms. Therefore, aneurysmal wall enhancement may be an indicator of the ruptured condition, which is useful information for managing patients with SAH.
Background and purpose:
Arterial wall enhancement on vessel wall MRI was described in intracranial inflammatory arterial disease. We hypothesized that circumferential aneurysmal wall enhancement (CAWE) could be an indirect marker of aneurysmal wall inflammation and, therefore, would be more frequent in unstable (ruptured, symptomatic, or undergoing morphological modification) than in stable (incidental and nonevolving) intracranial aneurysms.
Methods:
We prospectively performed vessel wall MRI in patients with stable or unstable intracranial aneurysms. Two readers independently had to determine whether a CAWE was present.
Results:
We included 87 patients harboring 108 aneurysms. Interreader and intrareader agreement for CAWE was excellent (κ=0.85; 95% confidence interval, 0.75-0.95 and κ=0.90; 95% confidence interval, 0.83-0.98, respectively). A CAWE was significantly more frequently seen in unstable than in stable aneurysms (27/31, 87% versus 22/77, 28.5%, respectively; P<0.0001). Multivariate logistic regression, including CAWE, size, location, multiplicity of aneurysms, and daily aspirin intake, revealed that CAWE was the only independent factor associated with unstable status (odds ratio, 9.20; 95% confidence interval, 2.92-29.0; P=0.0002).
Conclusions:
CAWE was more frequently observed in unstable intracranial aneurysms and may be used as a surrogate of inflammatory activity in the aneurysmal wall.
Intracranial atherosclerosis, one of the leading causes of ischemic stroke, is associated with an increased risk for recurrent stroke and dementia.1,2 Individuals of Asian, Hispanic, and African American ancestry are especially affected. Recent European studies revealed a much higher prevalence of intracranial lesions than commonly presumed, suggesting that intracranial atherosclerotic disease is potentially the most common cause of ischemic stroke worldwide.1,3 Ischemic strokes are clinically categorized into 5 subtypes based on their underlying cause: large-artery atherosclerotic stenosis, small-artery disease (lacunes), cryptogenic, major-risk-source cardiogenic embolism, and unusual (eg, dissections, arteritis). Most nonlacunar ischemic strokes are thought to be thromboembolic, which presumably also accounts for most cryptogenic strokes. Embolic sources include minor-risk or covert cardiac sources, veins via paradoxical embolism, and nonocclusive atherosclerotic plaques in the aortic arch or cervical or cerebral arteries.4 Besides embolic strokes, 2 other mechanisms have been associated with intracranial atherosclerosis-related strokes, namely hypoperfusion through a stenotic artery causing watershed or border-zone stroke and plaque overgrowth of perforator artery ostia, which is associated with penetrating artery disease and lacunar infarcts and has been related to cryptogenic strokes.5–7 Even mild stenosis of intracranial atherosclerotic arteries (<50%) may therefore be clinically relevant, and high-resolution magnetic resonance imaging studies are needed to identify and determine the degree and location of stenosis in this patient group.5,8 The possibly causal role of nonstenotic plaques in ischemic stroke highlights the need for more insight into the mechanisms and occurrence of intracranial atherosclerosis.
In the 1960s and 1970s, large, descriptive autopsy studies were conducted, providing classic morphological features of intracranial arteries. Despite the importance of intracranial atherosclerosis to stroke and dementia, there is a lack of more recent mechanistic studies. Therefore, we intend to draw attention to this neglected research field by …
Objective:
In this retrospective case series study, we used 7.0 tesla MRI to describe patterns of intracranial vessel wall abnormalities in relation to ischemic infarcts in 9 patients with different intracranial vessel wall pathologies.
Methods:
A patient-specific clinical imaging protocol was obtained after regular clinical workup, including a fluid-attenuated inversion recovery and an intracranial vessel wall sequence before and after contrast administration using 7.0 tesla MRI. An attempt was made to describe patterns by grouping the patients by intracranial vessel wall abnormalities (eccentric or concentric; enhancing or nonenhancing), then on the presence of macroinfarcts and cortical microinfarcts (CMIs), and lastly on type of macroinfarct (lacunar, small macroinfarct, or large macroinfarct).
Results:
Intracranial vessel wall abnormalities were identified in all patients, totaling 45 lesions, 12 of which enhanced after contrast administration. CMIs were found in 5 patients. Two patients had eccentric, enhancing wall thickening but differed based on presence or absence of CMIs. Four patients also had eccentric but nonenhancing wall thickening, 2 of whom showed CMIs. The 2 patients lacking CMIs could be subdivided based on the type of macroinfarct. Concentric, enhanced wall thickening was observed in 2 patients with CMIs who differed regarding macroinfarct types. One patient with previous vasculitis showed concentric, nonenhancing wall thickening.
Conclusion:
Our results suggest that the combination of intracranial vessel wall abnormalities and infarct type is related to different stroke etiologies.
To date, the probable cause of ischemic stroke is often inferred from the size and location of the infarct, in combination with an evaluation of the heart and the presence of extracranial arterial occlusion or high-grade stenosis.1 Currently used conventional lumenography-based methods such as digital subtraction angiography, computed tomography angiography, and magnetic resonance (MR) angiography are used to determine the presence of such an acute occlusion or high-grade arterial stenosis. From extracranial studies, it is known that luminal narrowing may be absent in patients with severe atherosclerosis owing to arterial remodeling.2–4 Therefore, these methods do not provide information about the underlying pathological processes, which most often involve the vessel wall.5 Vessel wall changes such as vessel wall thickening, enhancement, or the presence of vulnerable atherosclerotic plaques without luminal stenosis are therefore often missed but might be of importance for a better understanding of ischemic stroke.6 Furthermore, intracranial atherosclerosis is an important cause of ischemic stroke7 and often involves the vessel wall. Patients with intracranial atherosclerosis have high recurrent stroke rates,8 and increasingly more attention is being directed to the assessment of the intracranial vessel wall, necessitating an imaging technique directly assessing the intracranial vessel wall. MR imaging (MRI) seems the most promising technique to reliably image intracranial vessel wall pathologies because of its superior soft tissue contrast. Recent advances in MRI9 have made it possible to obtain information about these abnormalities within the intracranial vessel wall, which provides an imaging tool to investigate the role of intracranial vessel wall abnormalities in the diagnosis of stroke.
In this review, we discuss the current status of intracranial vessel wall MRI and its potential to identify different intracranial vessel wall pathologies. First, we present the state-of-the-art MRI methods to visualize the intracranial vessel wall …
Spin-echo-based acquisitions are the workhorse of clinical MRI because they provide a variety of useful image contrasts and are resistant to image artifacts from radio-frequency or static field inhomogeneity. Three-dimensional (3D) acquisitions provide datasets that can be retrospectively reformatted for viewing in freely selectable orientations, and are thus advantageous for evaluating the complex anatomy associated with many clinical applications of MRI. Historically, however, 3D spin-echo-based acquisitions have not played a significant role in clinical MRI due to unacceptably long acquisition times or image artifacts associated with details of the acquisition method. Recently, optimized forms of 3D fast/turbo spin-echo imaging have become available from several MR-equipment manufacturers (for example, CUBE [GE], SPACE [Siemens], and VISTA [Philips]). Through specific design strategies and optimization, including short non-spatially selective radio-frequency pulses to significantly shorten the echo spacing and variable flip angles for the refocusing radio-frequency pulses to suppress blurring or considerably lengthen the useable duration of the spin-echo train, these techniques permit single-slab 3D imaging of sizeable volumes in clinically acceptable acquisition times. These optimized fast/turbo spin-echo pulse sequences provide a robust and flexible approach for 3D spin-echo-based imaging with a broad range of clinical applications. J. Magn. Reson. Imaging 2014. © 2014 Wiley Periodicals, Inc.
Intracranial atherosclerosis is one of the most common causes of stroke worldwide and is associated with a high risk of recurrent stroke. New therapeutic approaches to treat this high-risk disease include dual antiplatelet treatment, intensive management of risk factors, and endovascular therapy. Early data from randomised trials indicate that aggressive medical therapy is better than stenting for prevention of recurrent stroke in high-risk patients with atherosclerotic stenosis of a major intracranial artery. Nevertheless, there are subgroups of patients who remain at high risk of stroke despite aggressive medical therapy. Further research is needed to identify these high-risk subgroups and to develop more effective treatments. Non-invasive vascular imaging methods that could be used to identify high-risk patients include fractional flow on magnetic resonance angiography (MRA), quantitative MRA, and high-resolution MRI of the atherosclerotic plaque. Alternative therapies to consider for future clinical trials include angioplasty alone, indirect surgical bypass procedures, ischaemic preconditioning, and new anticoagulants (direct thrombin or Xa inhibitors).
Atherosclerotic disease often involves the intracranial arteries including those encased by cranial bones and dura, and those located in the subarachnoid space. Age, hypertension, and diabetes mellitus are independent risk factors for intracranial atherosclerosis. Intracranial atherosclerosis can result in thromboembolism with or without hypoperfusion leading to transient or permanent cerebral ischaemic events. High rates of recurrent ischaemic stroke and other cardiovascular events mandate early diagnosis and treatment. Present treatment is based on a combination of antiplatelet drugs, optimisation of blood pressure and LDL cholesterol values, and intracranial angioplasty or stent placement, or both, in selected patients.
Single subcortical infarction (SSI) may be classified as proximal SSI (pSSI) or distal SSI (dSSI) according to its extension to the middle cerebral artery (MCA). We investigated the differences between pSSI and dSSI in terms of their clinical features, lesion size, and the frequency of MCA plaques detected by high-resolution MRI.
Thirty-nine patients with SSI (20 pSSI and 19 dSSI) were prospectively enrolled who did not show relevant MCA disease on MR angiography. Lesion size, neurological status (initial National Institutes of Health Stroke Scale score and modified Rankin Scale at 3 months), and the presence and location (superior versus inferior) of high-resolution MRI-identified plaques were evaluated.
The frequencies of MCA plaques did not differ between patients with pSSI and those with dSSI (8 [40%] versus 12 [63.2%]; P=0.205); however, superiorly located plaques were significantly more common in patients with pSSI than in those with dSSI (6 [75%] versus 2 [16.7%]; P=0.019). Initial lesion volumes were larger (1.96±1.18 versus 1.11±1.11 mm(3); P=0.025), National Institutes of Health Stroke Scale scores were higher (5 [3-6.75] versus 3 [1-3] points; P=0.017), and microbleeds were fewer (1 [5%] versus 10 [52.6%]; P=0.001) in patients with pSSI than in those with dSSI. Three-month modified Rankin Scale scores were higher in patients with superior plaques than in those with inferior plaques.
Compared with dSSI, pSSI is closely associated with large lesions, severe clinical symptoms, and superiorly located MCA plaques, suggesting that the location, rather than simple presence of plaques, determines the SSI location.
Objectives:
Intracranial vessel wall magnetic resonance imaging (MRI) may improve the diagnosis of vessel wall abnormalities. Current methods are hampered by limited coverage and few contrast weightings. We present a multi-sequence protocol with whole-brain coverage for vessel wall imaging on 7.0-T MRI.
Methods:
A modified magnetisation-preparation inversion recovery turbo-spin-echo (MPIR-TSE) sequence was used to obtain proton density (PD)-, T1-, and T2-weighting with 190-mm whole-brain coverage. Three observers independently scored the visibility of arterial vessel walls in five healthy volunteers, and compared the conspicuity and image contrast of all sequences. Clinical applicability was demonstrated in 17 patients with cerebrovascular disease.
Results:
Conspicuity was good for all acquisitions, with best scores for the original limited-coverage sequence, followed by whole-brain coverage T2-, PD- and T1-weighted sequences, respectively. Mean vessel wall/background MR signal intensity ratios for all whole-brain sequences were similar, with higher scores for the limited-coverage MPIR-TSE sequence. Signal intensity ratios were highest in patients, for the whole-brain T1-weighted sequence.
Conclusions:
The whole-brain multi-sequence vessel wall protocol can assess intracranial arterial vessel walls with full brain coverage, for different image contrast weightings. These sequences could eventually characterise intracranial vessel wall abnormalities similar to current techniques for assessing carotid artery plaques.
Key points:
- Intracranial vessel wall imaging using MRI improves diagnosis of cerebrovascular diseases. - Conventional 7-T MRI sequences cannot image the whole cerebral arterial tree. - New whole-brain 7-T MRI sequences compare favourably with smaller-coverage sequences. - These whole-brain sequences can demonstrate the entire cerebral arterial tree. - These sequences should help in the diagnosis of vessel wall abnormalities.
Intracranial atherosclerosis is worldwide one of the leading causes of stroke. However, surprisingly little is known about its prevalence and risk factors in a community-dwelling population of white descent. In this study, we determined the prevalence and investigated risk factors of intracranial internal carotid artery calcification (ICAC) as a marker of intracranial atherosclerosis.
To quantify the volume of ICAC, 2495 participants (mean age, 69.6 years) from the population-based Rotterdam Study underwent a nonenhanced computed tomography of the intracranial internal carotid arteries. We calculated the prevalence of ICAC. Next, we defined sex-specific quartiles and defined the upper quartile as severe ICAC. Risk factors of ICAC were investigated by linear and logistic multivariate modeling and were stratified by sex.
The overall prevalence of ICAC was 82.2%. The median volume of ICAC was 44 mm3 and was larger in men. Age was independently associated with ICAC in both men and women. In men, excessive alcohol intake and smoking (OR, 1.74 [95% CI, 1.28-2.37] and 1.72 [95% CI, 1.10-2.70]) were strong risk factors of ICAC, whereas diabetes and hypertension were in women (OR, 2.02 [95% CI, 1.29-3.17] and 1.79 [95% CI, 1.20-2.68]). A low high-density-lipoprotein concentration was not associated with ICAC.
ICAC is highly prevalent and occurs in over 80% of older, white persons. Conventional cardiovascular risk factors are associated with ICAC, but risk factor profiles differ between men and women.
Delay alternating with nutation for tailored excitation (DANTE) pulse trains are well appreciated as frequency-selective excitation methods in Fourier transform NMR and for spatial tagging in MRI. In this study, nonselective DANTE pulse trains are used in combination with gradient pulses and short repetition times as motion-sensitive preparation modules. We show that while the longitudinal magnetization of static tissue is mostly preserved, flowing spins are largely (or fully) attenuated as they fail to establish transverse steady state due to a spoiling effect caused by flow along the applied gradient. The attenuation of flowing spins is effectively insensitive to spin velocity (above a low threshold) and can be approximately quantified with a simple T(1) longitudinal magnetization decay model. The relevant analytical equations for moving spins and static spins during DANTE module application are derived for both transient and steady state epochs. The equations are validated by comparing analytical solutions and numerical Bloch equation simulations against experimental observations in phantoms and in vivo. Based on this contrast mechanism, the application of the DANTE preparation to black blood vessel imaging is proposed. A simple demonstration of DANTE black blood imaging modules shows that it provides excellent blood signal suppression and static tissue signal preservation. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
To develop a high isotropic-resolution sequence to evaluate intracranial vessels at 3.0 Tesla (T).
Thirteen healthy volunteers and 4 patients with intracranial stenosis were imaged at 3.0T using 0.5-mm isotropic-resolution three-dimensional (3D) Volumetric ISotropic TSE Acquisition (VISTA; TSE, turbo spin echo), with conventional 2D-TSE for comparison. VISTA was repeated for 6 volunteers and 4 patients at 0.4-mm isotropic-resolution to explore the trade-off between SNR and voxel volume. Wall signal-to-noise-ratio (SNR(wall) ), wall-lumen contrast-to-noise-ratio (CNR(wall-lumen) ), lumen area (LA), wall area (WA), mean wall thickness (MWT), and maximum wall thickness (maxWT) were compared between 3D-VISTA and 2D-TSE sequences, as well as 3D images acquired at both resolutions. Reliability was assessed by intraclass correlations (ICC).
Compared with 2D-TSE measurements, 3D-VISTA provided 58% and 74% improvement in SNR(wall) and CNR(wall-lumen) , respectively. LA, WA, MWT and maxWT from 3D and 2D techniques highly correlated (ICCs of 0.96, 0.95, 0.96, and 0.91, respectively). CNR(wall-lumen) using 0.4-mm resolution VISTA decreased by 27%, compared with 0.5-mm VISTA but with reduced partial-volume-based overestimation of wall thickness. Reliability for 3D measurements was good to excellent.
The 3D-VISTA provides SNR-efficient, highly reliable measurements of intracranial vessels at high isotropic-resolution, enabling broad coverage in a clinically acceptable time.
Recently, the technique of high-resolution magnetic resonance imaging (HR-MRI) has been developed to depict intracranial artery wall. We aimed to compare the vessel wall properties between symptomatic and asymptomatic atherosclerotic middle cerebral arteries (MCA) using HR-MRI.
We studied 26 patients with symptomatic and 35 patients with asymptomatic MCA stenosis. Routine cranial MRI, magnetic resonance angiography and HR-MRI were performed on each patient. The cross-sectional images of MCA wall on HR-MRI were compared between the two groups.
The degree of MCA stenosis was similar between the two groups (67.9% vs 63.9%, P=0.327). On HR-MRI, eccentric plaques were observed in 26 (100%) symptomatic and 28 (80%) asymptomatic stenosis. In the remaining seven (20%) asymptomatic stenosis, only constrictive remodeling (vessel shrinkage) was observed. Compared with the asymptomatic group, symptomatic MCA stenosis had a larger wall area (P<0.001), greater remodeling ratio (P<0.001), higher prevalence of expansive remodeling (outward expansion of the vessel wall) (P=0.003) and lower prevalence of constrictive remodeling (P=0.008).
Different vessel wall properties on HR-MRI were observed between symptomatic and asymptomatic MCA stenosis. Further prospective studies are required to investigate whether HR-MRI is a helpful tool in stratifying stroke risk in patients with MCA atherosclerotic disease.
Medical image registration is an important task in medical image processing. It refers to the process of aligning data sets, possibly from different modalities (e.g., magnetic resonance and computed tomography), different time points (e.g., follow-up scans), and/or different subjects (in case of population studies). A large number of methods for image registration are described in the literature. Unfortunately, there is not one method that works for all applications. We have therefore developed elastix, a publicly available computer program for intensity-based medical image registration. The software consists of a collection of algorithms that are commonly used to solve medical image registration problems. The modular design of elastix allows the user to quickly configure, test, and compare different registration methods for a specific application. The command-line interface enables automated processing of large numbers of data sets, by means of scripting. The usage of elastix for comparing different registration methods is illustrated with three example experiments, in which individual components of the registration method are varied.
Conventional arterial imaging focuses on the vessel lumen but lacks specificity because different pathologies produce similar luminal defects. Wall imaging can characterize extracranial arterial pathology, but imaging intracranial walls has been limited by resolution and signal constraints. Higher-field scanners may improve visualization of these smaller vessels.
Three-tesla contrast-enhanced MRI was used to study the intracranial arteries from a consecutive series of patients at a tertiary stroke center.
Multiplanar T2-weighted fast spin echo and multiplanar T1 fluid-attenuated inversion recovery precontrast and postcontrast images were acquired in 37 patients with focal neurologic deficits. Clinical diagnoses included atherosclerotic disease (13), CNS inflammatory disease (3), dissections (3), aneurysms (3), moyamoya syndrome (2), cavernous angioma (1), extracranial source of stroke (5), and no definitive clinical diagnosis (7). Twelve of 13 with atherosclerotic disease had focal, eccentric vessel wall enhancement, 10 of whom had enhancement only in the vessel supplying the area of ischemic injury. Two of 3 with inflammatory diseases had diffuse, concentric vessel wall enhancement. Three of 3 with dissection showed bright signal on T1, and 2 had irregular wall enhancement with a flap and dual lumen.
Three-tesla contrast-enhanced MRI can be used to study the wall of intracranial blood vessels. T2 and precontrast and postcontrast T1 fluid-attenuated inversion recovery images at 3 tesla may be able to differentiate enhancement patterns of intracranial atherosclerotic plaques (eccentric), inflammation (concentric), and other wall pathologies. Prospective studies are required to determine the sensitivity and specificity of arterial wall imaging for distinguishing the range of pathologic conditions affecting cerebral vasculature.
Black blood MRI is an attractive tool for monitoring normal and pathological wall thickening; however, limited spatial resolutions can conspire with complex vascular geometries to distort the appearance of the wall in ways hitherto unclear. To elucidate this, a thin-walled cylinder model was developed to predict the composite effects of obliqueness, in-plane resolution and voxel anisotropy on the accuracy of MRI-derived wall thickness measurements. These predictions were validated by means of imaging of a thin-walled carotid bifurcation phantom. Typical thick-slice axial acquisitions were found to result in artifactual wall thickening at the carotid bulb, owing to its obliqueness to the nominal imaging plane. Obliqueness was less problematic for near-isotropic resolutions; however, the obligatory reduction of in-plane resolution served to inflate wall thicknesses uniformly by up to 50%. Moreover, the nonlinear relationship between wall thickness and its overestimation served to mask genuine differences in wall thickness, an effect predicted to be worse for thinner coronary artery walls and plaque caps. Therefore, care must be taken when interpreting black blood MRI wall thickness measurements in the presence-or absence-of observed differences within or between individuals.
To overcome the problems associated with gradient-echo (GRE) magnetic resonance (MR) angiography ("bright blood" imaging) and "black blood" imaging with presaturated spin-echo (SE) pulse sequences, the authors devised a new approach for black blood imaging. Their method, selective preinversion fast imaging with steady precession (turboFISP), uses a segmented GRE sequence for fast data acquisition. Nulling of vascular signal results, and stationary tissue appears bright. The method was compared with flow-compensated GRE imaging in a phantom and with GRE imaging and presaturated SE imaging in seven healthy volunteers and nine patients with various cardiac diseases. With phantoms, the selective preinversion turboFISP sequence produced better flow contrast than did GRE sequences. Selective preinversion turboFISP was often superior to SE imaging for depicting vessel lumina, particularly in patients with slowly flowing blood. Arteries appeared dark in selective black blood angiograms, but veins did not. Selective preinversion turboFISP can be used with bright blood GRE imaging to depict vessel lumina, and its capability for image acquisition within a breath hold and with cardiac gating minimizes artifacts from respiration and motion of the vessel wall.
This survey focuses on the fusion of two major lines of recent progress in MRI methodology: parallel imaging with receiver coil arrays and the transition to high and ultra-high field strength for human applications. As discussed in this paper, combining the two developments has vast potential due to multiple specific synergies. First, parallel acquisition and high field are highly complementary in terms of their individual advantages and downsides. As a consequence, the joint approach generally offers enhanced flexibility in the design of scanning strategies. Second, increasing resonance frequency changes the electrodynamics of the MR signal in such a way that parallel imaging becomes more effective in large objects. The underlying conceptual and theoretical considerations are reviewed in detail. In further sections, technical challenges and practical aspects are discussed. The feasibility of parallel MRI at ultra-high field is illustrated by current results of parallel human MRI at 7 T.
The sparsity which is implicit in MR images is exploited to significantly undersample k-space. Some MR images such as angiograms are already sparse in the pixel representation; other, more complicated images have a sparse representation in some transform domain-for example, in terms of spatial finite-differences or their wavelet coefficients. According to the recently developed mathematical theory of compressed-sensing, images with a sparse representation can be recovered from randomly undersampled k-space data, provided an appropriate nonlinear recovery scheme is used. Intuitively, artifacts due to random undersampling add as noise-like interference. In the sparse transform domain the significant coefficients stand out above the interference. A nonlinear thresholding scheme can recover the sparse coefficients, effectively recovering the image itself. In this article, practical incoherent undersampling schemes are developed and analyzed by means of their aliasing interference. Incoherence is introduced by pseudo-random variable-density undersampling of phase-encodes. The reconstruction is performed by minimizing the l(1) norm of a transformed image, subject to data fidelity constraints. Examples demonstrate improved spatial resolution and accelerated acquisition for multislice fast spin-echo brain imaging and 3D contrast enhanced angiography.
Atherosclerotic intracranial arterial stenosis: risk factors, diagnosis, and treatment
- K Ritz
- N P Denswil
- O C Stam
Ritz K, Denswil NP, Stam OC, et al. Cause and mechanisms of intracranial atherosclerosis. Circulation 2014;130:1407-14 CrossRef
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9. Holmstedt CA, Turan TN, Chimowitz MI. Atherosclerotic intracranial arterial stenosis: risk factors, diagnosis, and treatment. Lancet
Neurol 2013;12:1106-14 CrossRef Medline