Intracranial Vessel Wall Imaging at 7.0-T MRI

Delayed Enhancement of Intracranial Atherosclerotic Plaque Can Better Differentiate Culprit Lesions: A Multiphase Contrast-Enhanced Vessel Wall MRI Study

BACKGROUND AND PURPOSE

Intracranial plaque enhancement (IPE) identified by contrast-enhanced vessel wall MR imaging (VW-MR imaging) is an emerging marker of plaque instability related to stroke risk, but there was no standardized timing for postcontrast acquisition. We aim to explore the optimal postcontrast timing by using multiphase contrast-enhanced VW-MR imaging and to test its performance in differentiating culprit and nonculprit lesions.

MATERIALS AND METHODS

Patients with acute ischemic stroke due to intracranial plaque were prospectively recruited to undergo VW-MR imaging with 1 precontrast phase and 4 consecutive postcontrast phases (9 minutes and 13 seconds for each phase). The signal intensity (SI) values of the CSF and intracranial plaque were measured on 1 precontrast and 4 postcontrast phases to determine the intracranial plaque enhancement index (PEI). The dynamic changes of the PEI were compared between culprit and nonculprit plaques on the postcontrast acquisitions.

RESULTS

Thirty patients with acute stroke (aged 59 ± 10 years, 18 [60%] men) with 113 intracranial plaques were included. The average PEI of all intracranial plaques significantly increased (up to 14%) over the 4 phases. There was significantly increased PEI over the 4 phases for culprit plaques (an average increase of 23%), but this was not observed for nonculprit plaques. For differentiating culprit and nonculprit plaques, we observed that the performance of IPE in the second postcontrast phase (cutoff = 0.83, AUC = 0.829 [0.746-0.893]) exhibited superior accuracy when compared with PEI in the first postcontrast phase (cutoff = 0.48; AUC = 0.768 [0.680-0.843]) (P = .022).

CONCLUSIONS

A 9-minute delay of postcontrast acquisition can maximize plaque enhancement and better differentiate between culprit and nonculprit plaques. In addition, culprit and nonculprit plaques have different enhancement temporal patterns, which should be evaluated in future studies.

Multimodal Neuroimaging Reveals and Guides Treatment of a Middle Cerebral Artery Web

This case report describes how neuroimaging was used to determine treatment for episodic sudden-onset weakness and numbness in the left limbs.

Co-existing intracranial and extracranial carotid atherosclerosis predicts large-artery atherosclerosis stroke recurrence: a single-center prospective study utilizing combined head-and-neck vessel wall imaging

OBJECTIVES

Intracranial and extracranial plaque features on high-resolution vessel wall imaging (HR-VWI) are associated with large-artery atherosclerosis (LAA) stroke recurrence. However, most studies have focused on a single vascular bed, and the prognostic value of combined intracranial and extracranial plaque features has yet to be studied. This study aimed to investigate the roles of plaque features, plaque number, and co-existing atherosclerosis in predicting stroke recurrence, utilizing combined head-and-neck HR-VWI.

METHODS

From September 2016 to March 2020, participants with acute LAA ischemic strokes were prospectively enrolled and underwent combined head-and-neck HR-VWI. The participants were followed for stroke recurrence for at least 12 months or until a subsequent event occurred. The imaging features at baseline, including conventional and histogram plaque features, plaque number, and co-existing atherosclerosis, were evaluated. Univariable Cox regression analysis and the least absolute shrinkage and selection operator (lasso) method were used for variable screening. Multivariable Cox regression analyses were used to determine the independent risk factors of stroke recurrence.

RESULTS

A total of 97 participants (59 ± 12 years, 63 men) were followed for a median of 30.9 months, and 21 participants experienced recurrent strokes. Multivariable Cox analysis identified co-existing intracranial high signal on T1-weighted fat-suppressed images (HST1) and extracranial carotid atherosclerosis (HR, 6.12; 95% CI, 2.52-14.82; p = 0.001) as an independent imaging predictor of stroke recurrence.

CONCLUSION

Co-existing intracranial HST1 and extracranial carotid atherosclerosis independently predicted LAA stroke recurrence. Combined head-and-neck HR-VWI is a promising technique for atherosclerosis imaging.

CLINICAL RELEVANCE STATEMENT

This prospective study using combined head-and-neck HR-VWI highlighted the necessity of both intracranial culprit plaque evaluation and multi-vascular bed assessment, adding value to the prediction of stroke recurrence.

KEY POINTS

• This study highlighted the necessity of both intracranial culprit plaque evaluation and multi-vascular bed assessment, adding value to the prediction of stroke recurrence. • This prospective study using combined head-and-neck HR-VWI found co-existing intracranial HST1 and extracranial carotid atherosclerosis to be independent predictors of stroke recurrence.

Visualisation of lenticulostriate arteries using contrast-enhanced time-of-flight magnetic resonance angiography at 7 Tesla

7 Tesla-field-strength (7 T) Magnetic Resonance Imaging allows the small perforating arteries in the brain to be visualised, and this modality may allow visualisation of the arterial pathology in cerebral small vessel disease. Most studies have used standard Time-of-Flight (ToF) Magnetic Resonance Angiography (MRA). Whether the use of contrast enhancement improves perforating artery visualisation at 7 T remains unclear. In a prospective study, we compared standard ToF MRA with contrast-enhanced (CE) ToF MRA at 7 T for the visualisation of the lenticulostriate arteries (LSAs). Ten patients with symptomatic lacunar stroke were recruited (mean age, SD, 64 ± 9.9 years). Visualisation was assessed using a visual rating scale administered by two independent expert readers and length of the LSAs visible. Visualisation of the LSAs was improved with CE ToF MRA. The mean Visibility and Sharpness Score was higher for CE ToF MRA over standard ToF MRA (2.55 ± 0.64 vs. 1.75 ± 0.68; P = 0.0008). The mean length of LSA visualised was significantly longer with CE ToF MRA compared to standard ToF MRA (24.4 ± 4.5 vs. 21.9 ± 4.0 mm; P = 0.01). CE ToF MRA offers improved visualisation of the LSAs over standard ToF MRA. The addition of contrast may improve the ability to visualise cerebral small vessel disease arterial pathology.

7T MRI for Intracranial Vessel Wall Lesions and Its Associated Neurological Disorders: A Systematic Review

Intracranial vessel wall lesions are involved in a variety of neurological diseases. The advanced technique 7T MRI provides greater efficacy in the diagnosis of the pathology changes in the vessel wall and helps to identify potential subtle lesions. The purpose of this literature review was to systematically describe and evaluate the existing literature focusing on the use of 7T MRI in the detection and characterization of intracranial vessel wall lesions and their associated neurological disorders, to highlight the current knowledge gaps, and to formulate a framework to guide future applications and investigations. We systematically reviewed the existing articles up to July 2021, seeking the studies that assessed intracranial vessel wall lesions and their associated neurological disorders using 7T MRI. The literature search provided 12 studies that met the inclusion criteria. The most common intracranial vessel wall lesions were changes related to intracranial atherosclerosis (n = 8) and aneurysms (n = 4), such as intracranial atherosclerosis burden and aneurysm wall enhancement. The associated neurological disorders included aneurysms, ischemic stroke or TIA, small vessel disease, cognitive decline, and extracranial atherosclerosis. No paper studied the use of 7T MRI for investigating vessel wall conditions such as moyamoya disease, small vessel disease, or neurological disorders related to central nervous vasculitis. In conclusion, the novel 7T MRI enables the identification of a wider spectrum of subtle changes and associations. Future research on cerebral vascular diseases other than intracranial atherosclerosis and aneurysms may also benefit from 7T MRI.

Disparate trends of atherosclerotic plaque evolution in stroke patients under 18-month follow-up: a 3D whole-brain magnetic resonance vessel wall imaging study

PURPOSE

The trend of atherosclerotic plaque feature evolution is unclear in stroke patients with and without recurrence. We aimed to use three-dimensional whole-brain magnetic resonance vessel wall imaging to quantify the morphological changes of causative lesions during medical therapy in patients with symptomatic intracranial atherosclerotic disease.

METHODS

Patients with acute ischemic stroke attributed to intracranial atherosclerotic disease were retrospectively enrolled if they underwent both baseline and follow-up magnetic resonance vessel wall imaging. The morphological features of the causative plaque, including plaque volume, peak normalized wall index, maximum wall thickness, degree of stenosis, pre-contrast plaque-wall contrast ratio, and post-contrast plaque enhancement ratio, were quantified and compared between the non-recurrent and recurrent groups (defined as the recurrence of a vascular event within 18 months of stroke).

RESULTS

Twenty-nine patients were included in the final analysis. No significant differences were found in plaque features in the baseline scan between the non-recurrent (n = 22) and recurrent groups (n = 7). The changes in maximum wall thickness (-13.32% vs. 8.93%, P = 0.026), plaque-wall contrast ratio (-0.82% vs. 3.42%, P = 0.005) and plaque enhancement ratio (-11.03% vs. 9.75%, P = 0.019) were significantly different between the non-recurrent and recurrent groups. Univariable logistic regression showed that the increase in plaque-wall contrast ratio (odds ratio 3.22, 95% confidence interval 1.55-9.98, P = 0.003) was related to stroke recurrence.

CONCLUSION

Morphological changes of plaque features on magnetic resonance vessel wall imaging demonstrated distinct trends in symptomatic intracranial atherosclerotic disease patients with and without stroke recurrence.

Large Culprit Plaque and More Intracranial Plaques Are Associated with Recurrent Stroke: A Case-Control Study Using Vessel Wall Imaging

BACKGROUND AND PURPOSE

Intracranial atherosclerotic plaque features are potential factors associated with recurrent stroke, but previous studies only focused on a single lesion, and few studies investigated them with perfusion impairment. This study aimed to investigate the association among whole-brain plaque features, perfusion deficit, and stroke recurrence.

MATERIALS AND METHODS

Patients with ischemic stroke due to intracranial atherosclerosis were retrospectively collected and categorized into first-time and recurrent-stroke groups. Patients underwent high-resolution vessel wall imaging and DSC-PWI. Intracranial plaque number, culprit plaque features (such as plaque volume/burden, degree of stenosis, enhancement ratio), and perfusion deficit variables were recorded. Logistic regression analyses were performed to determine the independent factors associated with recurrent stroke.

RESULTS

One hundred seventy-five patients (mean age, 59 [SD, 12] years; 115 men) were included. Compared with the first-time stroke group (n = 100), the recurrent-stroke group (n = 75) had a larger culprit volume (P = .006) and showed more intracranial plaques (P < .001) and more enhanced plaques (P = .003). After we adjusted for other factors, culprit plaque volume (OR, 1.16 per 10-mm³ increase; 95% CI, 1.03-1.30; P = .015) and total plaque number (OR, 1.31; 95% CI, 1.13-1.52; P < .001) were independently associated with recurrent stroke. Combining these factors increased the area under the curve to 0.71.

CONCLUSIONS

Large culprit plaque and more intracranial plaques were independently associated with recurrent stroke. Performing whole-brain vessel wall imaging may help identify patients with a higher risk of recurrent stroke.

Multi-Planar, Multi-Contrast and Multi-Time Point Analysis Tool (MOCHA) for Intracranial Vessel Wall Characterization

BACKGROUND

Three-dimensional (3D) intracranial vessel wall (IVW) magnetic resonance imaging can reliably image intracranial atherosclerotic disease (ICAD). However, an integrated, streamlined, and optimized workflow for IVW analysis to provide qualitative and quantitative measurements is lacking.

PURPOSE

To propose and evaluate an image analysis pipeline (MOCHA) that can register multicontrast and multitime point 3D IVW for multiplanar review and quantitative plaque characterization.

STUDY TYPE

Retrospective.

POPULATION

A total of 11 subjects with ICAD (68 ± 10 years old, 6 males).

FIELD STRENGTH/SEQUENCE

A 3.0 T, 3D time-of-flight gradient echo sequence and T1- and proton density-weighted fast spin echo sequences.

ASSESSMENT

Each participant underwent two IVW sessions within 2 weeks. Scan and rescan IVW images were preprocessed using MOCHA. The presence of atherosclerotic lesions was identified in different intracranial arterial segments by two readers (GC and JS, 12 years of vascular MR imaging experience each) following an established review protocol to reach consensus on each of the reviews. For all locations with identified plaques, plaque length, lumen and vessel wall areas, maximum and mean wall thickness values, normalized wall index and contrast enhancement ratio were measured.

STATISTICAL TESTS

Percent agreement and Cohen's κ were used to test scan-rescan reproducibility of detecting plaques using MOCHA. Intraclass correlation coefficient (ICC) and Bland-Altman analysis were used to evaluate scan-rescan reproducibility for plaque morphologic and enhancement measurements.

RESULTS

In 150 paired intracranial vessel segments, the overall agreement in plaque detection was 92.7% (κ = 0.822). The ICCs (all ICCs > 0.90) and Bland-Altman plots (no bias observed) indicated excellent scan-rescan reproducibility for all morphologic and enhancement measurements.

DATA CONCLUSION

Findings from this study demonstrate that MOCHA provides high scan-rescan reproducibility for identification and quantification of atherosclerosis along multiple intracranial arterial segments and highlight its potential use in characterizing plaque composition and monitoring plaque development.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 2.

Intracranial Atherosclerotic Burden and Cerebral Parenchymal Changes at 7T MRI in Patients With Transient Ischemic Attack or Ischemic Stroke

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.

Optimized Inner-Volume 3D TSE for High-Resolution Vessel Wall Imaging of Intracranial Perforating Arteries at 7T

The impairment of microvessels can lead to neurologic diseases such as stroke and vascular dementia. The imaging of lumen and vessel wall of perforating arteries requires an extremely high resolution due to their small caliber size. Current imaging techniques have the difficulty in observing the wall of perforating arteries. In this study, we developed a 3D inner-volume (IV) TSE (SPACE) sequence with optimized 2D spatially selective excitation (SSE) RF pulses. The optimized SSE RF pulses were designed through a series of optimization including iterative RF pulse design, trajectory optimization, and phase convention of Carr-Purcell-Meiboom-Gill (CPMG) condition to meet the perforating arteries imaging demands. High resolution of isotropic 0.30 mm within 10 min was achieved for the black- blood images of lenticulostriate artery (LSA). The LSA lumen and vessel wall were imaged by the IV-SPACE sequence simultaneously. Images obtained by the optimized RF pulse has fewer aliasing artifacts from outside of ROI than the traditional pulse. The IV-SPACE images showed clearer delineation of vessel wall and lumen of LSA than conventional SPACE images. IV-SPACE might be a promising method for detecting microvasculopathies of cerebral vascular diseases.

A High Resolution MRI Study of the Relationship Between Plaque Enhancement and Perforator Stroke after Stenting for Symptomatic Vertebrobasilar Artery Stenosis

BACKGROUND AND PURPOSE

Perforator stroke is one of the most common complications of vertebrobasilar arterial stenting. We investigated whether perforator stroke after vertebrobasilar arterial stenting is associated with plaque enhancement in patients with severe vertebrobasilar artery stenosis.

METHODS

We studied patients with symptomatic vertebrobasilar arterial stenosis who underwent stenting from January 2017 to July 2020. Patients who underwent high resolution magnetic resonance imaging were recruited among them. Demographic data, risk factors of atherosclerosis, procedure details, and characteristics of imaging were extracted from electronic health records and imaging data. Plaque features were investigated by high resolution magnetic resonance imaging.

RESULTS

136 patients were enrolled in this study, 39 of whom fulfilled the inclusion criteria. 18 patients (46.2%) had obvious plaque enhancement among the 39 patients, and 21 (53.8%) had plaque non-enhancement. 21 patients (53.8%) had diffuse distribution, and 22 patients (56.4%) had irregular plaques surface. Patients were divided into plaque enhanced and plaque non-enhanced groups according to the degree of plaque enhancement. Clinical characteristics and other plaque features were similar between two groups. Procedure-related perforator stroke was identified in 4 patients (10.3%). Patients with plaque enhancement were more likely to have perforator stroke after stenting compared with those with plaque non-enhancement (22.2% versus 0%, P = 0.037).

CONCLUSIONS

Plaque enhancement in high resolution magnetic resonance imaging may be associated with perforator stroke after vertebrobasilar artery stenting.

Subvoxel vessel wall thickness measurements of the intracranial arteries using a convolutional neural network

Vessel wall thickening of the intracranial arteries has been associated with cerebrovascular disease and atherosclerotic plaque development. Visualization of the vessel wall has been enabled by recent advancements in vessel wall MRI. However, quantifying early wall thickening from these MR images is difficult and prone to severe overestimation, because the voxel size of clinically used acquisitions exceeds the wall thickness of the intracranial arteries. In this study, we aimed for accurate and precise subvoxel vessel wall thickness measurements. A convolutional neural network was trained on MR images of 34 ex vivo circle of Willis specimens, acquired with a clinically used protocol (isotropic acquired voxel size: 0.8 mm). Ground truth measurements were performed on images acquired with an ultra-high-resolution protocol (isotropic acquired voxel size: 0.11 mm) and were used for evaluation. Additionally, we determined the robustness of our method by applying Monte Carlo dropout and test time augmentation. Lastly, we applied our method on in vivo images of three intracranial aneurysms to measure their wall thickness. Our method shows resolvability of different vessel wall thicknesses, well below the acquired voxel size. The method described may facilitate quantitative measurements on MRI data for a wider range of clinical applications.

Contrast-Enhanced High-Resolution Intracranial Vessel Wall MRI with Compressed Sensing: Comparison with Conventional T1 Volumetric Isotropic Turbo Spin Echo Acquisition Sequence

OBJECTIVE

Compressed sensing (CS) has gained wide interest since it accelerates MRI acquisition. We aimed to compare the 3D post-contrast T1-weighted volumetric isotropic turbo spin echo acquisition (VISTA) with CS (VISTA-CS) and without CS (VISTA-nonCS) in intracranial vessel wall MRIs (VW-MRI).

MATERIALS AND METHODS

From April 2017 to July 2018, 72 patients who underwent VW-MRI, including both VISTA-CS and VISTA-nonCS, were retrospectively enrolled. Wall and lumen volumes, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured from normal and lesion sites. Two neuroradiologists independently evaluated overall image quality and degree of normal and lesion wall delineation with a four-point scale (scores ≥ 3 defined as acceptable).

RESULTS

Scan coverage was increased in VISTA-CS to cover both anterior and posterior circulations with a slightly shorter scan time compared to VISTA-nonCS (approximately 7 minutes vs. 8 minutes). Wall and lumen volumes were not significantly different with VISTA-CS or VISTA-nonCS (interclass correlation coefficient = 0.964-0.997). SNR was or trended towards significantly higher values in VISTA-CS than in VISTA-nonCS. At normal sites, CNR was not significantly different between two sequences (p = 0.907), whereas VISTA-CS provided lower CNR in lesion sites compared with VISTA-nonCS (p = 0.003). Subjective wall delineation was superior with VISTA-nonCS than with VISTA-CS (p = 0.019), although overall image quality did not differ (p = 0.297). The proportions of images with acceptable quality were not significantly different between VISTA-CS (83.3-97.8%) and VISTA-nonCS (75-100%).

CONCLUSION

CS may be useful for intracranial VW-MRI as it allows for larger scan coverage with slightly shorter scan time without compromising image quality.

Vessel wall MR imaging for the detection of intracranial inflammatory vasculopathies

Intracranial vasculopathies are routinely investigated by lumen-based modalities such as magnetic resonance angiography (MRA), computed tomography angiography (CTA), and digital subtraction angiography (DSA). These techniques are useful to analyze the vessel lumen, allowing to detect vessel stenosis or occlusion. However, the primum movins of the disease, i.e., an abnormal thickening of the vessel wall, remains within the arterial wall. The vasculopathy can moreover be present without always narrowing the lumen or modifying its regularity. Hence, there is a need to detect directly and analyze vessel wall abnormalities. Development of 3D high-resolution black blood sequences for intracranial vessel wall MR imaging (VW-MRI) enabled routine clinical applications not only vasculitis, but also of intracranial atherosclerotic disease (ICAD), intracranial dissections, reversible intracranial dissections, reversible cerebral vasoconstriction syndrome (RCVS), Moyamoya disease, and intracranial aneurysms. This high-resolution intracranial VW- MRI approach is increasingly used on a clinical basis at many centers to solve diagnostic problems, especially in patients with ischemic stroke or intracranial hemorrhage. An expert consensus Guideline from the American Society of Neuroradiology provides recommendations for clinical implementation of intracranial vessel wall MRI. There are several technical aspects needed to be considered when implementing VW-MRI in intracranial vessels, including flow suppression, both in blood and cerebrospinal fluid (CSF), spatial resolution and signal-to-noise ratio (SNR). In this article, we review the technical aspects of VW-MRI, and recommend applications for vascular diseases including non-occlusive intracranial vasculopathies, Moyamoya disease, and identifying culprit plaques. We also give a focus on the utility of VW-MRI for determining stroke etiology in adults and in children and young adults.

MR Intracranial Vessel Wall Imaging: A Systematic Review

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.

MRI Vessel Wall Imaging after Intra-Arterial Treatment for Acute Ischemic Stroke

BACKGROUND AND PURPOSE

Vessel wall imaging is increasingly performed in the diagnostic work-up of patients with ischemic stroke. The aim of this study was to compare vessel wall enhancement after intra-arterial thrombosuction with that in patients not treated with thrombosuction.

MATERIALS AND METHODS

From 2009 to 2017, forty-nine patients with an ischemic stroke underwent 7T MR imaging within 3 months after symptom onset as part of a prospective intracranial vessel wall imaging study. Fourteen of these patients underwent intra-arterial treatment using thrombosuction (intra-arterial treatment group). In the intra-arterial treatment group, vessel walls were evaluated for major vessel wall changes. All patients underwent pre- and postcontrast vessel wall imaging to assess enhancing foci of the vessel wall using coregistered subtraction images. A Wilcoxon signed rank test was performed to test for differences.

RESULTS

In the intra-arterial treatment group, 11 of 14 patients (79%) showed vessel wall enhancement compared with 17 of 35 patients without intra-arterial treatment (49%). In the intra-arterial treatment group, more enhancing foci were detected on the ipsilateral side (n = 18.5) compared with the contralateral side (n = 3, P = .005). Enhancement was more often concentric on the ipsilateral side (n = 8) compared with contralateral side (n = 0, P = .01). No differences were found in the group without intra-arterial treatment between the number and configuration of ipsilateral and contralateral enhancing foci.

CONCLUSIONS

Patients with intra-arterial treatment by means of thrombosuction showed more (concentric) enhancing foci of the vessel wall ipsilateral compared with contralateral to the treated artery than the patients without intra-arterial treatment, suggesting reactive changes of the vessel wall. This finding should be taken into account when assessing vessel wall MR images in patients with stroke.

Focal irregularities in 7-Tesla MRI of unruptured intracranial aneurysms as an indicator for areas of altered blood-flow parameters

OBJECTIVE

In the last several decades, various factors have been studied for a better evaluation of the risk of rupture in incidentally discovered intracranial aneurysms (IAs). With advanced MRI, attempts were made to delineate the wall of IAs to identify weak areas prone to rupture. However, the field strength of the MRI investigations was insufficient for reasonable image resolution in many of these studies. Therefore, the aim of this study was to analyze findings of IAs in ultra-high field MRI at 7 Tesla (7 T).

METHODS

Patients with incidentally found IAs of at least 5 mm in diameter were included in this study and underwent MRI investigations at 7 T. At this field strength a hyperintense intravascular signal can be observed on nonenhanced images with a brighter "rim effect" along the vessel wall. Properties of this rim effect were evaluated and compared with computational fluid dynamics (CFD) analyses.

RESULTS

Overall, 23 aneurysms showed sufficient image quality for further evaluation. In 22 aneurysms focal irregularities were identified within this rim effect. Areas of such irregularities showed significantly higher values in wall shear stress and vorticity compared to areas with a clearly visible rim effect (p = 0.043 in both).

CONCLUSIONS

A hyperintense rim effect along the vessel wall was observed in most cases. Focal irregularities within this rim effect showed higher values of the mean wall shear stress and vorticity when compared by CFD analyses. Therefore, these findings indicate alterations in blood flow in IAs within these areas.

Vessel wall and lumen characteristics with age in healthy participants using 3T intracranial vessel wall magnetic resonance imaging

BACKGROUND

Intracranial vessel wall imaging (VWI) at a clinical field strength of 3T has become more widely available. However, how vessel measurements change with age and sex, over an age range spanning a typical lifespan, are needed.

PURPOSE/HYPOTHESIS

To assess for identifiable changes in arterial wall thickness, outer vessel wall diameter, and lumen diameter with age cross-sectionally in healthy controls without cerebrovascular disease risk factors at the spatial resolution afforded by currently recommended 3T VWI approaches.

STUDY TYPE

Prospective.

POPULATION/SUBJECTS

Healthy subjects (n = 82; age = 8-79 years).

FIELD STRENGTH/SEQUENCE

3T intracranial VWI, angiography, and T1 -weighted anatomical imaging.

ASSESSMENT

Two readers measured lumen and outer wall diameters of the supraclinoid internal carotid artery (ICA) and distal basilar artery. Wall thickness and intraclass correlation coefficients (ICCs) were calculated.

STATISTICAL TESTS

Separate linear regressions were performed to understand the relationship between wall measurements (lumen diameter, outer vessel wall diameter, and wall thickness) and age, gender, side (left or right); significance: two-sided P < 0.05.

RESULTS

Readers showed excellent agreement for lumen and outer wall diameters (ICC 0.83-094). Linear regression of supraclinoid ICA wall measurements showed a statistically significant increase in wall thickness (P = 0.00051) and outer vessel wall diameter (P = 0.030) with age. ICA lumen and outer vessel wall diameters were statistically greater in males vs. females (lumen diameter 3.69 ± 0.41 vs. 3.54 ± 0.35 mm, P = 0.026; outer wall diameter 5.78 ± 0.52 vs. 5.56 ± 0.44 mm, P = 0.0089) with a trend toward increase in wall thickness (1.05 ± 0.12 vs. 1.01 ± 0.10 mm, P = 0.055). No significant difference was found in basilar artery wall thickness (P = 0.45, P = 0.72), lumen diameter (P = 0.15, P = 0.42), or outer vessel wall diameter (P = 0.34, P = 0.41) with age or gender, respectively.

DATA CONCLUSION

Intracranial vessel wall measurements were shown to be consistent between readers. At the available spatial resolution of 3T intracranial VWI sequences, supraclinoid ICA vessel wall thickness and outer vessel wall diameter appear to mildly increase with age. There was no detectable change in basilar artery vessel wall characteristics with age.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;50:1452-1460.

Deep morphology aided diagnosis network for segmentation of carotid artery vessel wall and diagnosis of carotid atherosclerosis on black-blood vessel wall MRI

PURPOSE

Early detection of carotid atherosclerosis on the vessel wall (VW) magnetic resonance imaging (MRI) (VW-MRI) images can prevent the progression of cardiovascular disease. However, the manual inspection process of the VW-MRI images is cumbersome and has low reproducibility. Therefore in this paper, by using the convolutional neural networks (CNNs), we develop a deep morphology aided diagnosis (DeepMAD) network for automated segmentation of the VW of carotid artery and for automated diagnosis of the carotid atherosclerosis with the black-blood (BB) VW-MRI (i.e., the T1-weighted MRI) in a slice-by-slice manner.

METHODS

The proposed DeepMAD network consists of a segmentation subnetwork and a diagnosis subnetwork for performing the segmentation and diagnosis tasks on the BB-VW-MRI images, where the manual labeled lumen area, the manual labeled outer wall area and the manual labeled lesion Types based on the modified American Heart Association (AHA) criteria are used as the ground-truth. Specifically, a deep U-shape CNN with a weighted fusion layer is designed as the segmentation subnetwork, where the lumen area and the outer wall area can be simultaneously segmented under the supervision of the triple Dice loss to provide the vessel wall map as morphological information. Then, the image stream from the BB-VWMRI image and the morphology stream from the obtained vessel wall map are extracted from two deep CNNs and combined to obtain the diagnosis results of atherosclerosis in the diagnosis subnetwork. In addition, the triple input set is formed by three carotid regions of interest (ROIs) from three consecutive slices of the MRI sequence and input to the DeepMAD network, where the first and last slices used as additional adjacent slices to provide 2.5D spatial information along the carotid artery centerline for the intermediate slice, which is the target slice for segmentation and diagnosis in the study.

RESULTS

Compared to other existing methods, the DeepMAD network can achieve promising segmentation performances (0.9594 Dice for the lumen and 0.9657 Dice for the outer wall) and better diagnosis Accuracy of the carotid atherosclerosis (0.9503 AUC and 0.8916 Accuracy) in the test dataset (including invisible subjects) from same source as the training dataset. In addition, the trained DeepMAD model can be successfully transferred to another test dataset for segmentation and diagnosis tasks with remarkable performance (0.9475 Dice for the lumen and 0.9542 Dice for the outer wall, 0. 9227 AUC and 0.8679 Accuracy for diagnosis).

CONCLUSIONS

Even without the intervention of reviewers required for previous works, the proposed DeepMAD network automatically segments the lumen and the outer wall together and diagnoses the carotid atherosclerosis with high performances. The DeepMAD network can be used in clinical trials to help radiologists get rid of tedious reading tasks, such as screening review to separate the normal carotid from the atherosclerotic arteries and outlining the vessel wall contours.

Subacute vessel wall imaging at 7-T MRI in post-thrombectomy stroke patients

PURPOSE

Reports from 3-T vessel wall MRI imaging have shown contrast enhancement following thrombectomy for acute stroke, suggesting potential intimal damage. Comparisons have shown higher SNR and more lesions detected by vessel wall imaging when using 7 T compared with 3 T. The aim of this study was to investigate the vessel walls after stent retriever thrombectomy using high-resolution vessel wall imaging at 7 T.

METHODS

Seven patients with acute stroke caused by occlusion of the distal internal carotid artery (T-occlusion), or proximal medial cerebral artery, and treated by stent retriever thrombectomy with complete recanalization were included and examined by 7-T MRI within 2 days. The MRI protocol included a high-resolution black blood sequence with prospective motion correction (iMOCO), acquired before and after contrast injection. Flow measurements were performed in the treated and untreated M1 segments.

RESULTS

All subjects completed the MRI examination. Image quality was independently rated as excellent by two neuroradiologists for all cases, and the level of motion artifacts did not impair diagnostic quality, despite severe motion in some cases. Contrast enhancement correlated with the deployment location of the stent retrievers. Flow data showed complete restoration of flow after treatment.

CONCLUSION

Vessel wall imaging with prospective motion correction can be performed in patients following thrombectomy with excellent imaging quality at 7 T. We show that vessel wall contrast enhancement is the normal post-operative state and corresponds to the deployment location of the stent retriever.

Characterization of lenticulostriate arteries with high resolution black-blood T1-weighted turbo spin echo with variable flip angles at 3 and 7 Tesla

OBJECTIVES

The lenticulostriate arteries (LSAs) with small diameters of a few hundred microns take origin directly from the high flow middle cerebral artery (MCA), making them especially susceptible to damage (e.g. by hypertension). This study aims to present high resolution (isotropic ∼0.5 mm), black blood MRI for the visualization and characterization of LSAs at both 3 T and 7 T.

MATERIALS AND METHODS

T1-weighted 3D turbo spin-echo with variable flip angles (T1w TSE-VFA) sequences were optimized for the visualization of LSAs by performing extended phase graph (EPG) simulations. Twenty healthy volunteers (15 under 35 years old, 5 over 60 years old) were imaged with the T1w TSE-VFA sequences at both 3 T and 7 T. Contrast-to-noise ratio (CNR) was quantified, and LSAs were manually segmented using ITK-SNAP. Automated Reeb graph shape analysis was performed to extract features including vessel length and tortuosity. All quantitative metrics were compared between the two field strengths and two age groups using ANOVA.

RESULTS

LSAs can be clearly delineated using optimized 3D T1w TSE-VFA at 3 T and 7 T, and a greater number of LSA branches can be detected compared to those by time-of-flight MR angiography (TOF MRA) at 7 T. The CNR of LSAs was comparable between 7 T and 3 T. T1w TSE-VFA showed significantly higher CNR than TOF MRA at the stem portion of the LSAs branching off the medial middle cerebral artery. The mean vessel length and tortuosity were greater on TOF MRA compared to TSE-VFA. The number of detected LSAs by both TSE-VFA and TOF MRA was significantly reduced in aged subjects, while the mean vessel length measured on 7 T TSE-VFA showed significant difference between the two age groups.

CONCLUSION

The high-resolution black-blood 3D T1w TSE-VFA sequence offers a new method for the visualization and quantification of LSAs at both 3 T and 7 T, which may be applied for a number of pathological conditions related to the damage of LSAs.

Intracranial arterial wall imaging: Techniques, clinical applicability, and future perspectives

Purpose

To review the current state of the art and future development of intracranial vessel wall imaging.

Methods

Recent literature review and expert opinion about intracranial arterial wall imaging.

Results

Intracranial large artery diseases represent an important cause of stroke and vascular cognitive impairment worldwide. Our traditional understanding of intracranial large artery diseases is based on the observation of luminal narrowing or occlusion with angiographic or ultrasound techniques. Recently, novel imaging techniques have made the intracranial artery wall accessible for noninvasive visualization. The main advantage of vessel-wall imaging as compared to conventional imaging techniques for visualization of intracranial arteries is the ability to detect vessel wall changes even before they get to cause any significant luminal stenosis. This diagnostic capacity is provoking a revolutionary change in the way we see the intracranial circulation. In this article, we will review the current state of magnetic resonance imaging and computed tomography-based intracranial arterial wall imaging, focusing on technical considerations and their clinical applicability. Moreover, we will provide the readers with our vision on the future development of vessel-wall imaging techniques.

Conclusion

Intracranial arterial wall imaging methods are gaining increasing potential to impact the diagnosis and treatment of patients with cerebrovascular diseases.

Endovascular Therapy for Acute Ischemic Stroke of Intracranial Atherosclerotic Origin-Neuroimaging Perspectives

Large vessel occlusion (LVO) due to intracranial atherosclerosis (ICAS) is a common cause of acute ischemic stroke (AIS) in Asians. Endovascular therapy (EVT) has been established as the mainstay of treatment in patients with AIS and LVO. However, only a few patients of Asian descent with ICAS-related LVO (ICAS-LVO) were included in recent randomized controlled trials of EVT for AIS. Therefore, the findings of these trials cannot be directly applied to Asian patients with ICAS-LVO. In embolic LVO due to thrombus from the heart or a more proximal vessel, rapid, and complete recanalization can be achieved in more than 70-80% of patients, and it is important to exclude patients with large cores. In contrast, patients with ICAS-LVO usually have favorable hemodynamic profiles (good collateral status, small core, and less severe perfusion deficit), but poor response to EVT (more rescue treatments and longer procedure times are required for successful recanalization due to higher rates of reocclusion). Patients with ICAS-LVO may have different anatomic (plaque, angioarchitecture), hemodynamic (collateral status), and pathophysiologic (thrombus composition) features on neuroimaging compared to patients with embolic LVO. In this review, we discuss these neuroimaging features, their clinical implications with respect to determination of EVT responses, and the need for development of specific EVT devices and procedures for patients with ICAS-LVO.

Temporal course and implications of intracranial atherosclerotic plaque enhancement on high-resolution vessel wall MRI

PURPOSE

Little is known about the natural history of intracranial atherosclerotic plaque enhancement and its clinical implications. Our objective was to investigate the value of follow-up high-resolution contrast-enhanced vessel wall MRI (VWMRI) for classifying culprit plaques in patients with intracranial atherosclerotic disease (ICAD).

METHODS

Fourteen patients with symptomatic ICAD (50% females; median age 48 years) underwent serial 3T VWMRI. Fifty-five plaques were identified and graded based on the likelihood of having caused the ischemic event (non-culprit, indeterminate, culprit) and degree of enhancement (0, 1, 2) at baseline and follow-up (median follow-up, 140 days). For accuracy analysis, plaque enhancement at baseline and stable or increasing plaque enhancement at follow-up was tested to identify a culprit plaque, and areas under the receiver operating characteristic curves (AUCs) were compared.

RESULTS

In 37/55 (67.3%) plaques, enhancement grade remained unchanged. Lack of enhancement was only seen in non-culprit plaques at baseline, and none developed enhancement over time. Enhancement never changed more than one grade. Thirty-seven percent (10/27) of non-culprit plaques that enhanced decreased in enhancement grade at follow-up, but no culprit plaques decreased in enhancement. AUC of baseline and follow-up plaque enhancement combined was significantly larger than AUC of baseline plaque enhancement alone to identify culprit plaques (0.733 vs. 0.567, p = 0.0001).

CONCLUSION

Contrast enhancement of ICAD can persist months after the ischemic event. Lack of enhancement at baseline or a decrease in enhancement at follow-up suggests that the plaque is not culprit. Persistent enhancement from baseline to follow-up improves accuracy in identifying culprit plaques.

Whole-brain magnetic resonance imaging of plaque burden and lenticulostriate arteries in patients with different types of stroke

Background

Large-vessel atherosclerotic disease is an important pathogenesis of deep-perforator infarction (DPI). However, altered vessel walls of intracranial large arteries and distribution of small arteries in DPI are unclear because of the limited resolution of current imaging techniques. In this study the intracranial plaque burden and lenticulostriate artery (LSA) distribution in patients with recent DPI and non-DPI using whole-brain vessel-wall imaging (WB-VWI) were investigated.

Methods

A total of 44 patients with recent DPI (23 patients) or non-DPI (21 patients) due to intracranial atherosclerotic disease were prospectively enrolled. WB-VWI was performed in all the patients using a three-dimensional T1-weighted vessel-wall magnetic resonance technique. Hemispheres with DPI and non-DPI were considered as the DPI group and non-DPI group, respectively. Hemispheres without a history of stroke were the control group. The intracranial plaque burden was compared between the DPI and non-DPI groups. The number and length of visualized LSA branches among DPI, non-DPI, and control groups were also evaluated.

Results

A total of 77 hemispheres were analyzed (23 in the DPI group, 21 in the non-DPI group, and 33 in the control group). Plaque burden was lower (p = 0.047) in the DPI group (82.0 ± 45.9 mm³) compared with the non-DPI group (130.9 ± 90.3 mm³). There was a significant reduction (p = 0.002) in length of visualized LSA branches in the DPI group (74.1 ± 21.7 mm) compared with the control group (104.6 ± 33.3 mm).

Conclusions

WB-VWI enables the combination of vessel-wall and LSA imaging in one image setting, which can provide information about plaque burden and LSA distribution.

Intracranial Vessel Wall Segmentation Using Convolutional Neural Networks

OBJECTIVE

To develop an automated vessel wall segmentation method using convolutional neural networks to facilitate the quantification on magnetic resonance (MR) vessel wall images of patients with intracranial atherosclerotic disease (ICAD).

METHODS

Vessel wall images of 56 subjects were acquired with our recently developed whole-brain three-dimensional (3-D) MR vessel wall imaging (VWI) technique. An intracranial vessel analysis (IVA) framework was presented to extract, straighten, and resample the interested vessel segment into 2-D slices. A U-net-like fully convolutional networks (FCN) method was proposed for automated vessel wall segmentation by hierarchical extraction of low- and high-order convolutional features.

RESULTS

The network was trained and validated on 1160 slices and tested on 545 slices. The proposed segmentation method demonstrated satisfactory agreement with manual segmentations with Dice coefficient of 0.89 for the lumen and 0.77 for the vessel wall. The method was further applied to a clinical study of additional 12 symptomatic and 12 asymptomatic patients with >50% ICAD stenosis at the middle cerebral artery (MCA). Normalized wall index at the focal MCA ICAD lesions was found significantly larger in symptomatic patients compared to asymptomatic patients.

CONCLUSION

We have presented an automated vessel wall segmentation method based on FCN as well as the IVA framework for 3-D intracranial MR VWI.

SIGNIFICANCE

This approach would make large-scale quantitative plaque analysis more realistic and promote the adoption of MR VWI in ICAD management.

Assessment of quantitative methods for enhancement measurement on vessel wall magnetic resonance imaging evaluation of intracranial atherosclerosis

PURPOSE

Quantitative measures of vessel wall magnetic resonance imaging (vwMRI) for the evaluation of intracranial atherosclerotic disease (ICAD) offers standardization not available with previously used qualitative approaches that may be difficult to replicate.

METHODS

vwMRI studies performed to evaluate ICAD that had caused a stroke were analyzed. Two blinded reviewers qualitatively rated culprit lesions for the presence of enhancement on T1 delay alternating with nutation for tailored excitation (DANTE) SPACE images. At least 3 months later, quantitative analysis was performed of the same images, comparing lesion enhancement to reference structures. Cohen's kappa and intraclass correlation coefficients were calculated to assess agreement. Ratios of enhancement of lesions to references were compared to qualitative ratings.

RESULTS

Studies from 54 patients met inclusion criteria. A mean of 49 (90.7%) lesions were qualitatively rated as enhancing, with good inter-rater agreement (κ = 0.783). Among reference structure candidates, low infundibulum demonstrated the highest inter-rater agreement on pre- and post-contrast imaging. The ratio of percentage increase in plaque signal following contrast to the same measure in low infundibulum demonstrated the highest agreement with qualitative assessment, with highest agreement seen with a ratio of 0.8 set as a threshold (κ = 0.675).

CONCLUSION

Quantitative metrics can yield objective data to better standardize techniques and acceptance of vwMRI evaluation of ICAD. The low infundibulum had the highest inter-rater agreement on both pre- and post-contrast images and is best suited as a normally enhancing reference structure. Such quantitative techniques should be implemented in future research of vwMRI for the evaluation of ICAD.

Accelerated multi-contrast high isotropic resolution 3D intracranial vessel wall MRI using a tailored k-space undersampling and partially parallel reconstruction strategy

OBJECTIVE

To develop a 3D multi-contrast IVW protocol with 0.5-mm isotropic resolution and a scan time of 5 min per sequence.

MATERIALS AND METHODS

Pre-contrast T1w VISTA, DANTE prepared PDw VISTA, SNAP, and post-contrast T1w VISTA were accelerated using cartesian undersampling with target ordering method (CUSTOM) and self-supporting tailored k-space estimation for parallel imaging reconstruction (STEP). CUSTOM + STEP IVW was compared to full-sample IVW, SENSE-accelerated IVW, and CUSTOM + zero-filled Fourier reconstruction in normal volunteers and subjects with intracranial atherosclerotic disease (ICAD). Image quality, vessel delineation, CSF suppression, and blood suppression were compared.

RESULTS

CUSTOM + STEP vessel wall delineation was comparable to full-sample IVW and better than SENSE IVW for vessel wall delineation on T1w VISTA and luminal contrast on SNAP. Average image quality and wall depiction were significantly improved using STEP reconstruction compared with zero-filled Fourier reconstruction, with no significant difference in CSF or blood suppression.

CONCLUSIONS

CUSTOM + STEP allowed multi-contrast 3D 0.5-mm isotropic IVW within 30 min. Although some quantitative and qualitative scores for CUSTOM - STEP were lower than fully sampled IVW, CUSTOM + STEP provided comparable vessel wall delineation as full-sample IVW and was superior to SENSE. CUSTOM + STEP IVW was well tolerated by patients and showed good delineation of ICAD plaque.

Intracranial artery stenosis magnetic resonance imaging aetiology and progression study: Rationale and design

BACKGROUND

It has been shown that intracranial artery stenosis (ICAS) plays a key role in Chinese ischemic stroke or transient ischemic attack (TIA) patients. Many vascular diseases can lead to ICAS, such as atherosclerosis, dissection, vasculitis, moyamoya disease, and reversible cerebral vasoconstriction syndrome (RCVS). In addition, progression of intracranial atherosclerotic disease (ICAD) will increase the risk of ischemic cerebrovascular events. The ICASMAP study primarily aims to determine the etiology and disease distribution of ICAS using noninvasive magnetic resonance (MR) imaging and evaluate the rate for progression of ICAD in symptomatic population.

METHODS

The ICASMAP study is a prospective, observational, and multicenter study by recruiting 300 subjects (18-80 years old) with recent stroke or TIA (within 2 weeks after onset of symptoms) in China. All the subjects will undergo MR imaging examination including brain and intracranial artery MR imaging at baseline. In addition, the clinical risk factors will be collected and blood biomarkers will be tested. A subgroup of more than 200 subjects who were diagnosed with ICAD according to baseline MR imaging will be followed up for 2 years. During the follow-up study, MR imaging examination will be performed at 12 and 24 months. The primary end point is presence of progression of intracranial artery atherosclerotic plaques.

CONCLUSIONS

The ICASMAP study investigates the etiology of ICAS and progression of ICAD in Chinese stroke patients and may help to improve the precise diagnosis and intervention of ICAS and stroke prevention.

Detecting lenticulostriate artery lesions in patients with acute ischemic stroke using high-resolution MRA at 7 T

BACKGROUND

Recent advances in high-resolution (HR) magnetic resonance angiography (MRA) using ultrahigh-field systems enable direct visualization of the lenticulostriate arteries (LSAs), which had been hardly achieved by conventional MRA. Hence, by using HR-MRA at 7 T, we attempted to assess occlusive changes in the LSAs in patients with LSA territorial infarcts.

METHODS

We prospectively examined 34 consecutive patients with acute ischemic stroke in the LSA territory using a 7 T scanner. We measured the lengths of the relevant LSAs on HR-MRA and the diameters/volume of the infarcts and compared these between the patients with/without occlusive changes in the LSAs.

RESULTS

On HR-MRA, occlusion of the LSAs was observed in 19 (59%) of 32 patients who were eligible for the analyses. The curved/straight lengths of the LSAs in the patients with LSA occlusion (23.1-31.1/17.8-24.3 mm) were significantly shorter than in those without apparent LSA occlusion (25.8-39.5/24.0-30.4 mm) ( P = 0.027/0.003). The anteroposterior/superoinferior diameters of the infarcts were significantly larger in the occluded-LSA group (14.5-21.4/14.9-22.2 mm) than in the intact-LSA group (10.9-16.8/10.8-16.2 mm) ( P = 0.041/0.011). In addition, the curved lengths of the relevant LSAs showed significant correlations with the superoinferior diameters of the infarcts ( r = 0.38, P = 0.034).

CONCLUSION

Occlusive changes in the LSAs were frequently found in patients with acute ischemic stroke within the LSA territory when using HR-MRA at 7 T and were substantially related to superoinferior extension of the infarcts.

Variable impact of CSF flow suppression on quantitative 3.0T intracranial vessel wall measurements

BACKGROUND

Flow suppression techniques have been developed for intracranial (IC) vessel wall imaging (VWI) and optimized using simulations; however, simulation results may not translate in vivo.

PURPOSE

To evaluate experimentally how IC vessel wall and lumen measurements change in identical subjects when evaluated using the most commonly available blood and cerebrospinal fluid (CSF) flow suppression modules and VWI sequences.

STUDY TYPE

Prospective.

POPULATION/SUBJECTS

Healthy adults (n = 13; age = 37 ± 15 years) were enrolled.

FIELD STRENGTH/SEQUENCE

A 3.0T 3D T1 /proton density (PD)-weighted turbo-spin-echo (TSE) acquisition with post-readout anti-driven equilibrium module, with and without Delay-Alternating-with-Nutation-for-Tailored-Excitation (DANTE) was applied. DANTE flip angle (8-12°) and TSE refocusing angle (sweep = 40-120° or 50-120°) were varied.

ASSESSMENT

Basilar artery and internal carotid artery (ICA) wall thicknesses, CSF signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and signal ratio (SR) were assessed. Measurements were made by two readers (radiology resident and board-certified neuroradiologist).

STATISTICAL TESTS

A Wilcoxon signed-rank test was applied with corrected two-sided P < 0.05 required for significance (critical P = 0.008, 0.005, and 0.05 for SNR/CNR, SR, and wall thickness, respectively).

RESULTS

A TSE pulse sweep = 40-120° and sweep = 50-120° provided similar (P = 0.55) CSF suppression. Addition of the DANTE preparation reduced CSF SNR from 17.4 to 6.7, thereby providing significant (P < 0.008) improvement in CSF suppression. The DANTE preparation also resulted in a significant (P < 0.008) reduction in vessel wall SNR, but variable vessel wall to CSF CNR improvement (P = 0.87). There was a trend for a difference in blood SNR with vs. without DANTE (P = 0.05). The outer vessel wall diameter and wall thickness values were lower (P < 0.05) with (basilar artery 4.45 mm, 0.81 mm, respectively) vs. without (basilar artery 4.88 mm, 0.97 mm, respectively) DANTE 8°.

DATA CONCLUSION

IC VWI with TSE sweep = 40-120° and with DANTE flip angle = 8° provides the best CSF suppression and CNR of the approaches evaluated. However, improvements are heterogeneous, likely owing to intersubject vessel pulsatility and CSF flow variations, which can lead to variable flow suppression efficacy in these velocity-dependent modules.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:1120-1128.

Consensus statement on current and emerging methods for the diagnosis and evaluation of cerebrovascular disease

Cerebrovascular disease (CVD) remains a leading cause of death and the leading cause of adult disability in most developed countries. This work summarizes state-of-the-art, and possible future, diagnostic and evaluation approaches in multiple stages of CVD, including (i) visualization of sub-clinical disease processes, (ii) acute stroke theranostics, and (iii) characterization of post-stroke recovery mechanisms. Underlying pathophysiology as it relates to large vessel steno-occlusive disease and the impact of this macrovascular disease on tissue-level viability, hemodynamics (cerebral blood flow, cerebral blood volume, and mean transit time), and metabolism (cerebral metabolic rate of oxygen consumption and pH) are also discussed in the context of emerging neuroimaging protocols with sensitivity to these factors. The overall purpose is to highlight advancements in stroke care and diagnostics and to provide a general overview of emerging research topics that have potential for reducing morbidity in multiple areas of CVD.

Differential Features of Culprit Intracranial Atherosclerotic Lesions: A Whole-Brain Vessel Wall Imaging Study in Patients With Acute Ischemic Stroke

Background

Intracranial atherosclerotic disease tends to affect multiple arterial segments. Using whole‐brain vessel wall imaging, we sought to study the differences in plaque features among various types of plaques in patients with a recent unilateral anterior circulation ischemic stroke.

Methods and Results

Sixty‐one patients with unilateral anterior circulation ischemic stroke were referred to undergo whole‐brain vessel wall imaging (before and after contrast) within 1 month of symptom onset for intracranial atherosclerotic disease evaluations. Each plaque was classified as a culprit, probably culprit, or nonculprit lesion, according to its likelihood of causing the stroke. The associations between plaque features (thickening pattern, plaque‐wall contrast ratio, high signal on T1‐weighted images, plaque contrast enhancement ratio, enhancement grade, and enhancement pattern) and culprit lesions were estimated using mixed multivariable logistic regression after adjustment for maximum wall thickness. In 52 patients without motion corruption in whole‐brain vessel wall imaging, a total of 178 intracranial plaques in the anterior circulation were identified, including 52 culprit lesions (29.2%), 51 probably culprit lesions (28.7%), and 75 nonculprit lesions (42.1%). High signal on T1‐weighted images (adjusted odds ratio, 9.1; 95% confidence interval, 1.9–44.1; P=0.006), grade 2 (enhancement ratio of plaque ≥ enhancement ratio of pituitary) contrast enhancement (adjusted odds ratio, 17.4; 95% confidence interval, 1.8–164.9; P=0.013), and type 2 (≥50% cross‐sectional wall involvement) enhancement pattern (adjusted odds ratio, 10.1; 95% confidence interval, 1.3–82.2; P=0.030) were independently associated with culprit lesions.

Conclusions

High signal on T1‐weighted images, grade 2 contrast enhancement, and type 2 enhancement pattern are associated with cerebrovascular ischemic events, which may provide valuable insights into risk stratification.

3D whole-brain vessel wall cardiovascular magnetic resonance imaging: a study on the reliability in the quantification of intracranial vessel dimensions

BACKGROUND

One of the potentially important applications of three-dimensional (3D) intracranial vessel wall (IVW) cardiovascular magnetic resonance (CMR) is to monitor disease progression and regression via quantitative measurement of IVW morphology during medical management or drug development. However, a prerequisite for this application is to validate that IVW morphologic measurements based on the modality are reliable. In this study we performed comprehensive reliability analysis for the recently proposed whole-brain IVW CMR technique.

METHODS

Thirty-four healthy subjects and 10 patients with known intracranial atherosclerotic disease underwent repeat whole-brain IVW CMR scans. In 19 of the 34 subjects, two-dimensional (2D) turbo spin-echo (TSE) scan was performed to serve as a reference for the assessment of vessel dimensions. Lumen and wall volume, normalized wall index, mean and maximum wall thickness were measured in both 3D and 2D IVW CMR images. Scan-rescan, intra-observer, and inter-observer reproducibility of 3D IVW CMR in the quantification of IVW or plaque dimensions were respectively assessed in volunteers and patients as well as for different healthy subjectsub-groups (i.e. < 50 and ≥ 50 years). The agreement in vessel wall and lumen measurements between the 3D technique and the 2D TSE method was also investigated. In addition, the sample size required for future longitudinal clinical studies was calculated.

RESULTS

The intra-class correlation coefficient (ICC) and Bland-Altman plots indicated excellent reproducibility and inter-method agreement for all morphologic measurements (All ICCs > 0.75). In addition, all ICCs of patients were equal to or higher than that of healthy subjects except maximum wall thickness. In volunteers, all ICCs of the age group of ≥50 years were equal to or higher than that of the age group of < 50 years. Normalized wall index and mean and maximum wall thickness were significantly larger in the age group of ≥50 years. To detect 5% - 20% difference between placebo and treatment groups, normalized wall index requires the smallest sample size while lumen volume requires the highest sample size.

CONCLUSIONS

Whole-brain 3D IVW CMR is a reliable imaging method for the quantification of intracranial vessel dimensions and could potentially be useful for monitoring plaque progression and regression.

Visualization and Classification of Deeply Seated Collateral Networks in Moyamoya Angiopathy with 7T MRI

BACKGROUND AND PURPOSE

Collateral networks in Moyamoya angiopathy have a complex angioarchitecture difficult to comprehend on conventional examinations. This study aimed to evaluate morphologic patterns and the delineation of deeply seated collateral networks using ultra-high-field MRA in comparison with conventional DSA.

MATERIALS AND METHODS

Fifteen white patients with Moyamoya angiopathy were investigated in this prospective trial. Sequences acquired at 7T were TOF-MRA with 0.22 × 0.22 × 0.41 mm³ resolution and MPRAGE with 0.7 × 0.7 × 0.7 mm³ resolution. Four raters evaluated the presence of deeply seated collateral networks and image quality in a consensus reading of DSA, TOF-MRA, and MPRAGE using a 5-point scale in axial source images and maximum intensity projections. Delineation of deeply seated collateral networks by different imaging modalities was compared by means of the McNemar test, whereas image quality was compared using the Wilcoxon signed-rank test.

RESULTS

The relevant deeply seated collateral networks were classified into 2 categories and 6 pathways. A total of 100 collateral networks were detected on DSA; 106, on TOF-MRA; and 73, on MPRAGE. Delineation of deeply seated collateral networks was comparable between TOF-MRA and DSA (P = .25); however, both were better than MPRAGE (P < .001).

CONCLUSIONS

This study demonstrates excellent delineation of 6 distinct deeply seated collateral network pathways in Moyamoya angiopathy in white adults using 7T TOF-MRA, comparable to DSA.

Intracranial Large Artery Disease of Non-Atherosclerotic Origin: Recent Progress and Clinical Implications

Intracranial large artery disease (ILAD) is the major cause of stroke worldwide. With the application of recently introduced diagnostic techniques, the prevalence of non-atherosclerotic ILAD is expected to increase. Herein, we reviewed recent reports and summarized progress in the diagnosis and clinical impact of differentiation between ILAD of atherosclerotic and non-atherosclerotic origin. Our review of the literature suggests that more careful consideration of non-atherosclerotic causes and the application of appropriate diagnostic techniques in patients with ILAD may not only provide better results in the treatment of patients, but it may also lead to more successful clinical trials for the treatment of intracranial atherosclerosis.

Identification of high-risk plaque features in intracranial atherosclerosis: initial experience using a radiomic approach

OBJECTIVES

To evaluate a quantitative radiomic approach based on high-resolution magnetic resonance imaging (HR-MRI) to differentiate acute/sub-acute symptomatic basilar artery plaque from asymptomatic plaque.

METHODS

Ninety-six patients with basilar artery stenosis underwent HR-MRI between January 2014 and December 2016. Patients were scanned with T1- and T2-weighted imaging, as well as T1 imaging following gadolinium-contrast injection (CE-T1). The stenosis value, plaque area/burden, lumen area, minimal luminal area (MLA), intraplaque haemorrhage (IPH), contrast enhancement ratio and 94 quantitative radiomic features were extracted and compared between acute/sub-acute and asymptomatic patients. Multi-variate logistic analysis and a random forest model were used to evaluate the diagnostic performance.

RESULTS

IPH, MLA and enhancement ratio were independently associated with acute/subacute symptoms. Radiomic features in T1 and CE-T1 images were associated with acute/subacute symptoms, but the features from T2 images were not. The combined IPH, MLA and enhancement ratio had an area under the curve (AUC) of 0.833 for identifying acute/sub-acute symptomatic plaques, and the combined T1 and CE-T1 radiomic approach had a significantly higher AUC of 0.936 (p = 0.01). Combining all features achieved an AUC of 0.974 and accuracy of 90.5%.

CONCLUSIONS

Radiomic analysis of plaque texture on HR-MRI accurately distinguished between acutely symptomatic and asymptomatic basilar plaques.

KEY POINTS

• High-resolution magnetic resonance imaging can assess basilar artery atherosclerotic plaque. • Radiomic features in T1 and CE-T1 images are associated with acute symptoms. • Radiomic analysis can accurately distinguish between acute symptomatic and asymptomatic plaque. • The highest accuracy may be achieved by combining radiomic and conventional features.

Clinical vascular imaging in the brain at 7T

Stroke and related cerebrovascular diseases are a major cause of mortality and disability. Even at standard-field-strengths (1.5T), MRI is by far the most sensitive imaging technique to detect acute brain infarctions and to characterize incidental cerebrovascular lesions, such as white matter hyperintensities, lacunes and microbleeds. Arterial time-of-flight (TOF) MR angiography (MRA) can depict luminal narrowing or occlusion of the major brain feeding arteries, and this without the need for contrast administration. Compared to 1.5T MRA, the use of high-field strength (3T) and even more so ultra-high-field strengths (7T), enables the visualization of the lumen of much smaller intracranial vessels, while adding a contrast agent to TOF MRA at 7T may enable the visualization of even more distal arteries in addition to veins and venules. Moreover, with 3T and 7T, the arterial vessel walls beyond the circle of Willis become visible with high-resolution vessel wall imaging. In addition, with 7T MRI, the brain parenchyma can now be visualized on a submillimeter scale. As a result, high-resolution imaging studies of the brain and its blood supply at 7T have generated new concepts of different cerebrovascular diseases. In the current article, we will discuss emerging clinical applications and future directions of vascular imaging in the brain at 7T MRI.

Design of universal parallel-transmit refocusing kT -point pulses and application to 3D T2 -weighted imaging at 7T

PURPOSE

T₂ -weighted sequences are particularly sensitive to the radiofrequency (RF) field inhomogeneity problem at ultra-high-field because of the errors accumulated by the imperfections of the train of refocusing pulses. As parallel transmission (pTx) has proved particularly useful to counteract RF heterogeneities, universal pulses were recently demonstrated to save precious time and computational efforts by skipping B₁ calibration and online RF pulse tailoring. Here, we report a universal RF pulse design for non-selective refocusing pulses to mitigate the RF inhomogeneity problem at 7T in turbo spin-echo sequences with variable flip angles.

METHOD

Average Hamiltonian theory was used to synthetize a single non-selective refocusing pulse with pTx while optimizing its scaling properties in the presence of static field offsets. The design was performed under explicit power and specific absorption rate constraints on a database of 10 subjects using a 8Tx-32Rx commercial coil at 7T. To validate the proposed design, the RF pulses were tested in simulation and applied in vivo on 5 additional test subjects.

RESULTS

The root-mean-square rotation angle error (RA-NRMSE) evaluation and experimental data demonstrated great improvement with the proposed universal pulses (RA-NRMSE ∼8%) compared to the standard circularly polarized mode of excitation (RA-NRMSE ∼26%).

CONCLUSION

This work further completes the spectrum of 3D universal pulses to mitigate RF field inhomogeneity throughout all 3D MRI sequences without any pTx calibration. The approach returns a single pulse that can be scaled to match the desired flip angle train, thereby increasing the modularity of the proposed plug and play approach. Magn Reson Med 80:53-65, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Intracranial Atherosclerosis: From Microscopy to High-Resolution Magnetic Resonance Imaging

Intracranial atherosclerosis is one of the leading causes of ischemic stroke and occurs more commonly in patients of Asian, African or Hispanic origin than in Caucasians. Although the histopathology of intracranial atherosclerotic disease resembles extracranial atherosclerosis, there are some notable differences in the onset and severity of atherosclerosis. Current understanding of intracranial atherosclerotic disease has been advanced by the high-resolution magnetic resonance imaging (HRMRI), a novel emerging imaging technique that can directly visualize the vessel wall pathology. However, the pathological validation of HRMRI signal characteristics remains a key step to depict the plaque components and vulnerability in intracranial atherosclerotic lesions. The purpose of this review is to describe the histological features of intracranial atherosclerosis and to state current evidences regarding the validation of MR vessel wall imaging with histopathology.

Neuroradiologic Characteristics of Primary Angiitis of the Central Nervous System According to the Affected Vessel Size

INTRODUCTION

Magnetic resonance imaging (MRI) has an important impact in diagnosing primary angiitis of the central nervous system (PACNS). However, neuroradiologic findings may vary immensely, making an easy and definite diagnosis challenging.

METHODS

In this retrospective, single center study, we analyzed neuroradiologic findings of patients with PACNS diagnosed at our hospital between 2009 and 2014. Furthermore, we classified patients according to the affected vessel size and compared imaging characteristics between the subgroups.

RESULTS

Thirty-three patients were included (mean age 43 [±15.3] years, 17 females) in this study. Patients with positive angiographic findings were classified as either medium or large vessel PACNS and presented more ischemic lesions (p < 0.001) and vessel wall enhancement (p = 0.017) compared to patients with small vessel PACNS. No significant differences were detected for the distribution of contrast-enhancing lesions (parenchymal or leptomeningeal), hemorrhages, or lesions with mass effect. Twenty-five patients underwent brain biopsy. Patients with medium or large vessel PACNS were less likely to have positive biopsy results.

DISCUSSION

It is essential to differentiate between small and medium/large vessel PACNS since results in MRI, digital subtraction angiography and brain biopsy may differ immensely. Since image quality of MR scanners improves gradually and brain biopsy may often be nonspecific or negative, our results emphasize the importance of MRI/MRA in the diagnosis process of PACNS.

Vessel wall characterization using quantitative MRI: what's in a number?

The past decade has witnessed the rapid development of new MRI technology for vessel wall imaging. Today, with advances in MRI hardware and pulse sequences, quantitative MRI of the vessel wall represents a real alternative to conventional qualitative imaging, which is hindered by significant intra- and inter-observer variability. Quantitative MRI can measure several important morphological and functional characteristics of the vessel wall. This review provides a detailed introduction to novel quantitative MRI methods for measuring vessel wall dimensions, plaque composition and permeability, endothelial shear stress and wall stiffness. Together, these methods show the versatility of non-invasive quantitative MRI for probing vascular disease at several stages. These quantitative MRI biomarkers can play an important role in the context of both treatment response monitoring and risk prediction. Given the rapid developments in scan acceleration techniques and novel image reconstruction, we foresee the possibility of integrating the acquisition of multiple quantitative vessel wall parameters within a single scan session.

Identification and Quantitative Assessment of Different Components of Intracranial Atherosclerotic Plaque by Ex Vivo 3T High-Resolution Multicontrast MRI

BACKGROUND AND PURPOSE

High-resolution 3T MR imaging can visualize intracranial atherosclerotic plaque. However, histologic validation is still lacking. This study aimed to evaluate the ability of 3T MR imaging to identify and quantitatively assess intracranial atherosclerotic plaque components ex vivo with histologic validation.

MATERIALS AND METHODS

Fifty-three intracranial arterial specimens with atherosclerotic plaques from 20 cadavers were imaged by 3T MR imaging with T1, T2, and proton-density-weighted FSE and STIR sequences. The signal characteristics and areas of fibrous cap, lipid core, calcification, fibrous tissue, and healthy vessel wall were recorded on MR images and compared with histology. Fibrous cap thickness and maximum wall thickness were also quantified. The percentage of areas of the main plaque components, the ratio of fibrous cap thickness to maximum wall thickness, and plaque burden were calculated and compared.

RESULTS

The signal intensity of the lipid core was significantly lower than that of the fibrous cap on T2-weighted, proton-density, and STIR sequences (P < .01) and was comparable on T1-weighted sequences (P = 1.00). Optimal contrast between the lipid core and fibrous cap was found on T2-weighted images. Plaque component mean percentages were comparable between MR imaging and histology: fibrous component (81.86% ± 10.59% versus 81.87% ± 11.59%, P = .999), lipid core (19.51% ± 10.76% versus 19.86% ± 11.56%, P = .863), and fibrous cap (31.10% ± 11.28% versus 30.83% ± 8.51%, P = .463). However, MR imaging overestimated mean calcification (9.68% ± 5.21% versus 8.83% ± 5.67%, P = .030) and plaque burden (65.18% ± 9.01% versus 52.71% ± 14.58%, P < .001).

CONCLUSIONS

Ex vivo 3T MR imaging can accurately identify and quantitatively assess intracranial atherosclerotic plaque components, providing a direct reference for in vivo intracranial plaque imaging.