Improved black-blood imaging using DANTE-SPACE for simultaneous carotid and intracranial vessel wall evaluation

Simulation-based optimization and experimental comparison of intracranial T2-weighted DANTE-SPACE vessel wall imaging at 3T and 7T

PURPOSE

T2-weighted DANTE-SPACE (Delay Alternating with Nutation for Tailored Excitation - Sampling Perfection with Application optimized Contrasts using different flip angle Evolution) sequences facilitate non-invasive intracranial vessel wall imaging at 7T through simultaneous suppression of blood and CSF. However, the achieved vessel wall delineation depends closely on the selected sequence parameters, and little information is available about the performance of the sequence using more widely available 3T MRI. Therefore, in this paper a comprehensive DANTE-SPACE simulation framework is used for the optimization and quantitative comparison of T2-weighted DANTE-SPACE at both 7T and 3T.

METHODS

Simulations are used to propose optimized sequence parameters at both 3T and 7T. At 7T, an additional protocol which uses a parallel transmission (pTx) shim during the DANTE preparation for improved suppression of inflowing blood is also proposed. Data at both field strengths using optimized and literature protocols are acquired and quantitatively compared in six healthy volunteers.

RESULTS

At 7T, more vessel wall signal can be retained while still achieving sufficient CSF suppression by using fewer DANTE pulses than described in previous implementations. The use of a pTx shim during DANTE at 7T provides a modest further improvement to the inner vessel wall delineation. At 3T, aggressive DANTE preparation is required to achieve CSF suppression, resulting in reduced vessel wall signal. As a result, the achievable vessel wall definition at 3T is around half that of 7T.

CONCLUSION

Simulation-based optimization of DANTE parameters facilitates improved T2-weighted DANTE-SPACE contrasts at 7T. The improved vessel definition of T2-weighted DANTE-SPACE at 7T makes DANTE preparation more suitable for T2-weighted VWI at 7T than at 3T.

Direct abdominal vein thrombus imaging (DATI): a contrast-free black-blood MR technique for the diagnosis of abdominal vein thrombosis

OBJECTIVES

To develop and evaluate a direct abdominal vein thrombus imaging (DATI) technique, based on a respiratory navigating SPACE sequence with DANTE black-blood preparation, for diagnosing abdominal vein thrombosis (AVT) without the use of exogenous contrast agents.

METHODS

We prospectively enrolled 10 healthy subjects and 28 suspected AVT patients who underwent DATI scans on 3.0 T MRI. Contrast-enhanced CT venography (CTV) was also conducted on the suspected AVT patients for comparison. All images were analyzed by two blinded radiologists who independently evaluated randomized images and gave image quality and diagnostic confidence scores (1-poor, 4-excellent) for DATI and CTV. The accuracy (ACC), sensitivity (SE), specificity (SP), positive predictive value (PPV), and negative predictive value (NPV) of CTV were calculated using CTV as a standard reference. The diagnostic agreement between DATI and CTV as well as the interobserver agreement were conducted using Cohen κ test.

RESULTS

The patient study demonstrated that DATI can provide adequate thrombus signal intensity and the contrast between the thrombus to dark venous lumen for the diagnosis of AVT. It offers good to excellent image quality (reader1/reader2: 3.50 ± 0.64/3.42 ± 0.63, κ = 0.872) and diagnostic confidence (reader1/reader2: 3.71 ± 0.53/3.78 ± 0.42, κ = 0.804) for the diagnosis of AVT. Taking CTV as a reference, DATI has high accuracy (96.6%), SE (91.5%), SP (98.0%), PPV (92.3%), and NPV (97.8%).

DATA CONCLUSION

DATI can provide good to excellent image quality, effective venous blood signal suppression, and definitive thrombus detection for the diagnosis of AVT without the use of exogenous contrast agents.

Black-Blood Magnetization Prepared 2 Rapid Acquisition Gradient Echoes: A Fast and Three-Dimensional MR Black-Blood T1 Mapping Technique for Quantitative Assessment of Atherosclerosis and Venous Thrombosis

BACKGROUND

Blood flow signals may be a confounder in quantifying T1 values of plaque or thrombus and how to realize black-blood T1 mapping remains a challenge task.

PURPOSE

To develop a fast and three-dimensional black-blood T1 mapping technique for quantitative assessment of atherosclerosis and venous thrombosis.

STUDY TYPE

Sequence development and optimization via phantoms and volunteers as well as pilot prospective.

PHANTOM AND SUBJECTS

Numerical simulations, a standard phantom, 8 healthy volunteers (mean age, 22 ± 1 years; 5 males), and 19 patients (mean age, 57 ± 14 years; 13 males) with atherosclerosis or venous thrombosis.

FIELD STRENGTH/SEQUENCE

3T/inversion recovery spin-echo sequence (IR-SE), magnetization prepared 2 rapid acquisition gradient echoes (MP2RAGE), and black-blood prepared MP2RAGE (BB-MP2RAGE).

ASSESSMENT

The black-blood preparation (i.e., delay alternating with nutation for tailored excitation, DANTE) was incorporated into MP2RAGE for black-blood T1 mapping. The BB-MP2RAGE was optimized numerically based on the Bloch equation, and then the phantom study was performed to verify the accuracy of T1 mapping by BB-MP2RAGE against IR-SE and MP2RAGE. Preliminary clinical validation was prospectively performed to assess the flow suppression effect and its potential application in plaque and thrombosis identification.

STATISTICAL TESTS

Pearson correlation test, Bland-Altman analysis, paired t-test, and intraclass correlation coefficient. A P value <0.05 indicates a statistically significant difference.

RESULTS

Phantom experiments showed comparable accuracy of T1 maps by BB-MP2RAGE with IR-SE and MP2RAGE (all r2 > 0.99); Compared to MP2RAGE, BB-MP2RAGE effectively nulled the blood flow signals, and had a significant improvement in contrast-to-noise ratio between static tissue and blood (250.5 ± 66.6 vs. 91.9 ± 35.9). BB-MP2RAGE can quantify plaque or thrombus T1 relaxation time with blood flow signal suppression.

DATA CONCLUSION

Accurate T1 mapping with sufficient blood flow suppression was achieved by BB-MP2RAGE. BB-MP2RAGE has the potential to quantitatively characterize atherosclerosis and venous thrombosis.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 1.

Efficient and Accurate 3D Thickness Measurement in Vessel Wall Imaging: Overcoming Limitations of 2D Approaches Using the Laplacian Method

The clinical significance of measuring vessel wall thickness is widely acknowledged. Recent advancements have enabled high-resolution 3D scans of arteries and precise segmentation of their lumens and outer walls; however, most existing methods for assessing vessel wall thickness are 2D. Despite being valuable, reproducibility and accuracy of 2D techniques depend on the extracted 2D slices. Additionally, these methods fail to fully account for variations in wall thickness in all dimensions. Furthermore, most existing approaches are difficult to be extended into 3D and their measurements lack spatial localization and are primarily confined to lumen boundaries. We advocate for a shift in perspective towards recognizing vessel wall thickness measurement as inherently a 3D challenge and propose adapting the Laplacian method as an outstanding alternative. The Laplacian method is implemented using convolutions, ensuring its efficient and rapid execution on deep learning platforms. Experiments using digital phantoms and vessel wall imaging data are conducted to showcase the accuracy, reproducibility, and localization capabilities of the proposed approach. The proposed method produce consistent outcomes that remain independent of centerlines and 2D slices. Notably, this approach is applicable in both 2D and 3D scenarios. It allows for voxel-wise quantification of wall thickness, enabling precise identification of wall volumes exhibiting abnormal wall thickness. Our research highlights the urgency of transitioning to 3D methodologies for vessel wall thickness measurement. Such a transition not only acknowledges the intricate spatial variations of vessel walls, but also opens doors to more accurate, localized, and insightful diagnostic insights.

Direct angiographic comparison of different velocity-selective saturation, inversion, and DANTE labeling modules on cerebral arteries

PURPOSE

This study evaluated the velocity-selective (VS) MRA with different VS labeling modules, including double refocused hyperbolic tangent, eight-segment B1-insensitive rotation, delay alternating with nutation for tailored excitation, Fourier transform-based VS saturation, and Fourier transform-based inversion.

METHODS

These five VS labeling modules were evaluated first through Bloch simulations, and then using VSMRA directly on various cerebral arteries of healthy subjects. The relative signal ratios from arterial ROIs and surrounding tissues as well as relative arteria-tissue contrast ratios of different methods were compared.

RESULTS

Double refocused hyperbolic tangent and eight-segment B1-insensitive rotation showed very similar labeling effects. Delay alternating with nutation for tailored excitation yielded high arterial signal but with residual tissue signal due to the spatial banding effect. Fourier transform-based VS saturation with half the time of other techniques serves as an efficient nonsubtractive VSMRA method, but the remaining tissue signal still obscured some small distal arteries that were delineated by other subtraction-based VSMRA, allowing more complete cancelation of static tissue. Fourier transform-based inversion produced the highest arterial signal in VSMRA with minimal tissue background.

CONCLUSION

This is the first study that angiographically compared five different VS labeling modules. Their labeling characteristics on arteries and tissue and implications for VSMRA and VS arterial spin labeling are discussed.

An extended phase graph-based framework for DANTE-SPACE simulations including physiological, temporal, and spatial variations

PURPOSE

The delay alternating with nutation for tailored excitation (DANTE)-sampling perfection with application-optimized contrasts (SPACE) sequence facilitates 3D intracranial vessel wall imaging with simultaneous suppression of blood and CSF. However, the achieved image contrast depends closely on the selected sequence parameters, and the clinical use of the sequence is limited in vivo by observed signal variations in the vessel wall, CSF, and blood. This paper introduces a comprehensive DANTE-SPACE simulation framework, with the aim of providing a better understanding of the underlying contrast mechanisms and facilitating improved parameter selection and contrast optimization.

METHODS

An extended phase graph formalism was developed for efficient spin ensemble simulation of the DANTE-SPACE sequence. Physiological processes such as pulsatile flow velocity variation, varying flow directions, intravoxel velocity variation, diffusion, andB 1 + $$ {\mathrm{B}}_1^{+} $$ effects were included in the framework to represent the mechanisms behind the achieved signal levels accurately.

RESULTS

Intravoxel velocity variation improved temporal stability and robustness against small velocity changes. Time-varying pulsatile velocity variation affected CSF simulations, introducing periods of near-zero velocity and partial rephasing. Inclusion of diffusion effects was found to substantially reduce the CSF signal. Blood flow trajectory variations had minor effects, butB 1 + $$ {\mathrm{B}}_1^{+} $$ differences along the trajectory reduced DANTE efficiency in low-B 1 + $$ {\mathrm{B}}_1^{+} $$ areas. Introducing low-velocity pulsatility of both CSF and vessel wall helped explain the in vivo observed signal heterogeneity in both tissue types.

CONCLUSION

The presented simulation framework facilitates a more comprehensive optimization of DANTE-SPACE sequence parameters. Furthermore, the simulation framework helps to explain observed contrasts in acquired data.

Hybrid dynamic bright and black blood angiography by non-contrast-enhanced vessel selective saturation angiography

The integrity of vessel walls and changes in blood flow are involved in many diseases, and information about these anatomical and physiological conditions is important for a diagnosis. There are several different angiography methods that can be used to generate images for diagnostic purposes, but often using different imaging techniques and MR sequences. The purpose of this study was to develop a method that allows time-resolved, vessel-selective simultaneous bright and black blood imaging by vesselselective blood saturation. Measurements in six volunteers were performed to evaluate the time-resolved bright blood angiography and the significance of the generated black blood contrast. It was shown that this method can be used to generate a black blood contrast with a sufficient signal difference to the surrounding gray matter in addition to the time-resolved and vessel-selective bright blood contrast. Using post-processing methods, whole brain angiograms can be calculated from the acquired data.

Usefulness of Different Imaging Methods in the Diagnosis of Cerebral Vasculopathy

Assessment of cerebral vasculopathies is challenging and requires understanding the utility of different imaging methods. Various techniques are available to image the vessel lumen, each with unique advantages and disadvantages. Bolus-based CT and MR angiography requires careful timing of a contrast bolus to provide optimal luminal enhancement. Non-contrast MRA techniques do not require a contrast agent and can provide images with little venous contamination. Digital subtraction angiography remains the gold standard but is invasive, while VW-MRI provides a non-invasive way of assessing vessel wall pathology. Conventional brain MRI has high sensitivity in the diagnosis of vasculitis but findings are nonspecific.

Visualizing Cerebral Small Vessel Degeneration During Aging and Diseases Using Magnetic Resonance Imaging

Cerebral small vessel disease is a major contributor to brain disorders in older adults. It is associated with a much higher risk of stroke and dementia. Due to a lack of clinical and fluid biomarkers, diagnosing and grading small vessel disease are highly dependent on magnetic resonance imaging. In the past, researchers mostly used brain parenchymal imaging markers to represent small vessel damage, but the relationships between these surrogate markers and small vessel pathologies are complex. Recent progress in high-resolution magnetic resonance imaging methods, including time-of-flight MR angiography, phase-contrast MR angiography, black blood vessel wall imaging, susceptibility-weighted imaging, and contrast-enhanced methods, allow for direct visualization of cerebral small vessel structures. They could be powerful tools for understanding aging-related small vessel degeneration and improving disease diagnosis and treatment. This article will review progress in these imaging techniques and their application in aging and disease studies. Some challenges and future directions are also discussed. EVIDENCE LEVEL: 4. TECHNICAL EFFICACY: 3.

Vessel Wall Imaging of Intracranial Arteries: Fundamentals and Clinical Applications

With the increasing use of 3-tesla MRI scanners and the development of applicable sequences, it has become possible to achieve high-resolution, good contrast imaging, which has enabled the imaging of the walls of small-diameter intracranial arteries. In recent years, the usefulness of vessel wall imaging has been reported for numerous intracranial arterial diseases, such as for the detection of vulnerable plaque in atherosclerosis, diagnosis of cerebral arterial dissection, prediction of the rupture of cerebral aneurysms, and status of moyamoya disease and cerebral vasculitis. In this review, we introduce the histological characteristics of the intracranial artery, discuss intracranial vessel wall imaging methods, and review the findings of vessel wall imaging for various major intracranial arterial diseases.

MR Imaging for Intracranial Vessel Wall Imaging: Pearls and Pitfalls

Conventional vascular imaging methods have primarily focused on evaluating the vascular lumen. However, these techniques are not intended to evaluate vessel wall abnormalities where many cerebrovascular pathologies reside. With increased interest for the visualization and study of the vessel wall, high-resolution vessel wall imaging (VWI) has gained traction.Over the past two decades, there has been a rapid increase in number of VWI publications with improvements in imaging techniques and expansion on clinical applications. With increasing utility and interest in VWI, application of proper protocols and understanding imaging characteristics of vasculopathies are important for the interpreting radiologists to understand.

The Use of Intracranial Vessel Wall Imaging in Clinical Practice

Three-dimensional vessel wall MR imaging has gained popularity in the diagnosis and management of patients with cerebrovascular disease in clinical practice. Vessel wall MR imaging is an imaging technique that delivers a fundamentally different viewpoint by emphasizing on the pathology of the vessel wall as opposed to traditional descriptions that focus on the vessel lumen. It shows a crucial power in detecting vessel wall changes in patients with diseases including, but not limited to, central nervous system vasculitis, moyamoya disease, aneurysms, dissections, and intracranial atherosclerotic disease.

Optimization of workflow for detection of brain metastases at 3T: is a black-blood MTC prepared 3D T1 used alone robust enough to replace the combination of conventional 3D T1 and the black-blood 3D T1 MTC?

PURPOSE

Sampling perfection with application-optimized contrasts by using different flip angle evolutions (SPACE) is a black-blood 3D T1-weighted (T1w) magnetic resonance imaging (MRI) sequence that has shown robust performance for brain metastases detection. However, this could generate false positive results due to suboptimal blood signal suppression. For that reason, SPACE is used in our institution alongside a non-black-blood T1w sequence: volumetric interpolated breath-hold examination (VIBE). Our study aims to (i) evaluate the diagnostic accuracy of SPACE compared to its use in combination with VIBE, (ii) investigate the effect of radiologist's experience in the sequence's performance, and (iii) analyze causes of discordants results.

METHODS

Four hundred seventy-three 3T MRI scans were retrospectively analyzed following a monocentric study design. Two studies were formed: one including SPACE alone and one combining both sequences (SPACE + VIBE, the reference). An experienced neuroradiologist and a radiology trainee independently reviewed the images of each study and reported the number of brain metastases. The sensitivity (Se) and specificity (Sp) of SPACE compared to SPACE + VIBE in metastases detection were reported. Diagnostic accuracy of SPACE compared to SPACE + VIBE was assessed by using McNemar's test. Significance was set at p < 0.05. Cohen's kappa was used for inter-method and inter-observer variability.

RESULTS

No significant difference was found between the two methods, with SPACE having a Se > 93% and a Sp > 87%. No effect of readers' experience was disclosed.

CONCLUSION

Independently of radiologist's experience, SPACE alone is robust enough to replace SPACE + VIBE for brain metastases detection.

Impact on etiology diagnosis by high-resolution vessel wall imaging in young adults with ischemic stroke or transient ischemic attack

PURPOSE

The etiological features of stroke in young adults are different from those in older adults. We aimed to investigate the impact of high-resolution vessel wall imaging (HRVWI) on etiologic diagnosis in young adults with ischemic stroke or transient ischemic attack (TIA).

METHODS

A total of 253 young adults (aged 18-45 years) who consecutively underwent HRVWI for clarifying stroke etiology were retrospectively recruited. Two experienced neurologists classified stroke etiology for each patient using Trial of Org 10,172 in Acute Stroke Treatment categories with and without the inclusion of HRVWI diagnosis. Multivariate logistic regression was performed to determine which etiologic category would be significantly impacted after including HRVWI.

RESULTS

The etiologic classification was altered in 39.1% (99/253) of patients after including HRVWI in the conventional investigations. The proportion of patients classified as having stroke of undetermined etiology (SUE) and the proportion of patients classified as having small-artery occlusion (SAO) both significantly decreased (36.4 to 13.8% and 9.1 to 2.0%), whereas the proportion of patients classified as having large artery atherosclerosis (LAA) significantly increased (28.5 to 58.1%) (all P < 0.001). The inclusion of HRVWI had a significant diagnostic impact on young adults who were primarily classified as SAO (odds ratio [OR] 14.4, 95% confidence interval [CI] [2.9, 71.8], P < 0.001) or SUE (OR 8.3, 95% CI [2.2, 31.5], P < 0.01).

CONCLUSIONS

HRVWI had a substantial impact on etiologic classification in young adults with ischemic stroke or TIA, particularly for those primarily classified as having SAO or SUE. This impact of HRVWI will be beneficial for therapeutic decision-making.

Detecting immunoglobulin G4-related intracranial arteriopathy with magnetic resonance vessel wall imaging: a preliminary experience in two cases

BACKGROUND

Detecting immunoglobulin G4 (IgG4)-related intracranial arteriopathy, a rare neurovascular complication of IgG4-related disease, is challenging. While magnetic resonance (MR) vessel wall imaging (VWI) can visualize various neurovascular pathologies, its application to this arteriopathy has not been reported as of this writing.

CASE PRESENTATION

A 74-year-old male and a 65-year-old female manifested multiple cranial nerve palsy and neck pain, respectively. Both cases exhibited multiorgan masses with markedly elevated serum IgG4 levels and were clinically diagnosed with IgG4-related disease. Three-dimensional T1-weighted black blood VWI with and without contrast agent identified intracranial vascular lesions characterized as nearly-circumferential mural thickening with homogeneous contrast enhancement in the internal carotid and vertebral arteries; some of the lesions had been unrecognized with screening MR angiography due to expansive remodeling. The former patient underwent corticosteroid therapy, and VWI after treatment revealed decreased mural thickening and enhancement.

CONCLUSION

Further studies to elucidate characteristic findings of VWI might contribute to early detection of this treatable pathology.

Improved Blood Suppression of Motion-Sensitized Driven Equilibrium in High-Resolution Whole-Brain Vessel Wall Imaging: Comparison of Contrast-Enhanced 3D T1-Weighted FSE with Motion-Sensitized Driven Equilibrium and Delay Alternating with Nutation for Tailored Excitation

BACKGROUND AND PURPOSE

High-resolution vessel wall MR imaging is prone to slow-flow artifacts, particularly when gadolinium shortens the T1 relaxation time of blood. This study aimed to determine the optimal preparation pulses for contrast-enhanced high-resolution vessel wall MR imaging.

MATERIALS AND METHODS

Fifty patients who underwent both motion-sensitized driven equilibrium and delay alternating with nutation for tailored excitation (DANTE) preparation pulses with contrast-enhanced 3D-T1-FSE were retrospectively included. Qualitative analysis was performed using a 4-grade visual scoring system for black-blood performance in the small-sized intracranial vessels, overall image quality, severity of artifacts, and the degree of blood suppression in all cortical veins as well as transverse sinuses. Quantitative analysis of the M1 segment of the MCA was also performed.

RESULTS

The qualitative analysis revealed that motion-sensitized driven equilibrium demonstrated a significantly higher black-blood score than DANTE in contrast-enhanced 3D-T1-FSE of the A3 segment (3.90 versus 3.58, P < .001); M3 (3.72 versus 3.26, P = .004); P2 to P3 (3.86 versus 3.64, P = .017); the internal cerebral vein (3.72 versus 2.32, P < .001); and overall cortical veins (3.30 versus 2.74, P < .001); and transverse sinuses (2.82 versus 2.38, P < .001). SNR_lumen, contrast-to noise ratio_wall-lumen, and SNR_wall in the M1 vessel were not significantly different between the 2 preparation pulses (all, P > .05).

CONCLUSIONS

Motion-sensitized driven equilibrium demonstrated improved blood suppression on contrast-enhanced 3D-T1-FSE in the small intracranial arteries and veins compared with DANTE. Motion-sensitized driven equilibrium is a useful preparation pulse for high-resolution vessel wall MR imaging to decrease venous contamination and suppress slow-flow artifacts when using contrast enhancement.

Automated morphologic analysis of intracranial and extracranial arteries using convolutional neural networks

OBJECTIVE

To develop an automated method for 3D magnetic resonance (MR) vessel wall image analysis to facilitate morphologic quantification of intra- and extracranial arteries, including vessel centerline tracking, vessel straightening and reformation, vessel wall segmentation based on convoluted neural networks (CNNs), and morphological measurement.

METHODS

MR vessel wall images acquired using DANTE-SPACE sequences and corresponding time-of-flight-MRA images of 67 subjects (including 47 healthy volunteers and 20 patients with atherosclerosis) were included in this study. The centerline of the vessel was firstly extracted from the MRA images and copyed to the 3D MR vessel wall images through the registration relationship between the MRA images and the MR vessel wall images to extract, straighten, and reconstruct interested vessel segments into 2D slices. Then a complete CNN-based Unet-like method was used to automatically segment the vessel wall to obtain quantitative morphological measurements such as maximum wall thicknesses and normalized wall index (NWI).

RESULTS

The proposed automatic segmentation network was trained and validated with 11,735 slices and tested on 2517 slices. The method showed satisfactory agreement with manual segmentation method. The Dice coefficients of intracranial arteries were 0.90 for lumen and 0.78 for vessel wall, while the Dice coefficients of extracranial arteries were 0.90 for lumen and 0.82 for vessel wall. The maximum wall thickness and NWI obtained from the proposed automatic method were slightly larger than those obtained from the manual method for both intra- and extracranial arteries. However, there was no significant difference of the quantitative measurements between the two methods (p > 0.05). In addition, the automatically measured NWI of plaque slice was significantly larger than that of normal slice.

CONCLUSION

We propose an automatic analysis method of MR vessel wall images, which can realize automatic segmentation of intra- and extracranial vessel wall. It is expected to facilitate large-scale arterial vessel wall morphological quantification.

ADVANCES IN KNOWLEDGE

We have proposed an automatic method for analysis of intra- and extracranial MR vessel wall images simultaneously based on CNN, which can facilitate large-scale quantitative analyses of vessel walls.

Vessel wall MR imaging of aortic arch, cervical carotid and intracranial arteries in patients with embolic stroke of undetermined source: A narrative review

Despite advancements in multi-modal imaging techniques, a substantial portion of ischemic stroke patients today remain without a diagnosed etiology after conventional workup. Based on existing diagnostic criteria, these ischemic stroke patients are subcategorized into having cryptogenic stroke (CS) or embolic stroke of undetermined source (ESUS). There is growing evidence that in these patients, non-cardiogenic embolic sources, in particular non-stenosing atherosclerotic plaque, may have significant contributory roles in their ischemic strokes. Recent advancements in vessel wall MRI (VW-MRI) have enabled imaging of vessel walls beyond the degree of luminal stenosis, and allows further characterization of atherosclerotic plaque components. Using this imaging technique, we are able to identify potential imaging biomarkers of vulnerable atherosclerotic plaques such as intraplaque hemorrhage, lipid rich necrotic core, and thin or ruptured fibrous caps. This review focuses on the existing evidence on the advantages of utilizing VW-MRI in ischemic stroke patients to identify culprit plaques in key anatomical areas, namely the cervical carotid arteries, intracranial arteries, and the aortic arch. For each anatomical area, the literature on potential imaging biomarkers of vulnerable plaques on VW-MRI as well as the VW-MRI literature in ESUS and CS patients are reviewed. Future directions on further elucidating ESUS and CS by the use of VW-MRI as well as exciting emerging techniques are reviewed.

Nonlesional Sources of Contrast Enhancement on Postgadolinium "Black-Blood" 3D T1-SPACE Images in Patients with Multiple Sclerosis

BACKGROUND AND PURPOSE

We hypothesized that 3D T1-TSE "black-blood" images may carry an increased risk of contrast-enhancing lesion misdiagnosis in patients with MS because of the misinterpretation of intraparenchymal vein enhancement. Thus, the occurrence of true-positive and false-positive findings was compared between standard MPRAGE and volumetric interpolated brain examination techniques.

MATERIALS AND METHODS

Sampling perfection with application-optimized contrasts by using different flip-angle evolution (SPACE) images obtained from 232 patients with MS, clinically isolated syndrome, or radiologically isolated syndrome were compared with standard MPRAGE and volumetric interpolated brain examination images. The intraparenchymal vein contrast-to-noise ratio was estimated at the level of the thalami. Contrast-enhancing lesions were blindly detected by 2 expert readers and 1 beginner reader. True- and false-positives were determined by senior readers' consensus. True-positive and false-positive frequency differences and patient-level diagnosis probability were tested with the McNemar test and OR. The contrast-to-noise ratio and morphology were compared using the Mann-Whitney U and χ² tests.

RESULTS

The intraparenchymal vein contrast-to-noise ratio was higher in SPACE than in MPRAGE and volumetric interpolated brain examination images (P < .001, both). There were 66 true-positives and 74 false-positives overall. SPACE detected more true-positive and false-positive results (P range < .001-.07) but did not increase the patient's true-positive likelihood (OR = 1 1.29, P = .478-1). However, the false-positive likelihood was increased (OR = 3.03-3.55, P = .008-.027). Venous-origin false-positives (n = 59) with contrast-to-noise ratio and morphology features similar to small-sized (≤14 mm³ P = .544) true-positives occurred more frequently in SPACE images (P < .001).

CONCLUSIONS

Small intraparenchymal veins may confound the diagnosis of enhancing lesions on postgadolinium black-blood SPACE images.

Image-Quality Assessment of 3D Intracranial Vessel Wall MRI Using DANTE or DANTE-CAIPI for Blood Suppression and Imaging Acceleration

BACKGROUND AND PURPOSE

3D intracranial vessel wall MRI techniques are time consuming and prone to artifacts, especially flow artifacts. Our aim was to compare the image quality of accelerated and flow-suppressed 3D intracranial vessel wall MR imaging techniques relative to conventional acquisitions.

MATERIALS AND METHODS

Consecutive patients undergoing MR imaging had conventional postcontrast 3D T1-sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE) and either postcontrast delay alternating with nutation for tailored excitation (DANTE) flow-suppressed or DANTE-controlled aliasing in parallel imaging results in higher acceleration (CAIPI) flow-suppressed and accelerated T1-SPACE sequences performed. The sequences were evaluated using 4- or 5-point Likert scales for overall image quality, SNR, extent/severity of artifacts, motion, blood suppression, sharpness, and lesion assessment. Quantitative assessment of lumen and wall-to-lumen contrast ratios was performed.

RESULTS

Eighty-nine patients were included. T1-DANTE-SPACE had significantly better qualitative ratings relative to T1-SPACE for image quality, SNR, artifact impact, arterial and venous suppression, and lesion assessment (P < .001 for each, respectively), with the exception of motion (P = .16). T1-DANTE-CAIPI-SPACE had significantly better image quality, lesion assessment, arterial and venous blood suppression, less artifact impact, and less motion compared with T1-SPACE (P < .001 for each, respectively). The SNR was higher with T1-SPACE compared with T1-DANTE-CAIPI-SPACE (P < .001). T1-DANTE-CAIPI-SPACE showed significantly worse lumen (P = .005) and wall-to-lumen contrast ratios (P = .001) compared with T1-SPACE, without a significant difference between T1-SPACE and T1-DANTE-SPACE. T1-DANTE-CAIPI-SPACE scan time was 5:11 minutes compared with 8:08 and 8:41 minutes for conventional T1-SPACE and T1-DANTE-SPACE, respectively.

CONCLUSIONS

Accelerated postcontrast T1-DANTE-CAIPI-SPACE had fewer image artifacts, less motion, improved blood suppression, and a shorter scan time, but lower qualitative and quantitative SNR ratings relative to conventional T1-SPACE intracranial vessel wall MR imaging. Postcontrast T1-DANTE-SPACE had superior SNR, blood suppression, higher image quality, and fewer image artifacts, but slightly longer scan times relative to T1-SPACE.

High-resolution MR vessel wall imaging in determining the stroke aetiology and risk stratification in isolated middle cerebral artery disease

PURPOSE

High-resolution MR vessel wall imaging (HRVWI) can characterise vessel wall pathology affecting intracranial circulation and helps in differentiating intracranial vasculopathies. The aim was to differentiate intracranial pathologies involving middle cerebral artery (MCA) in patients with ischemic stroke and characterise the high-risk plaques in intracranial atherosclerotic disease (ICAD) using HRVWI.

METHODS

Patients with ischemic stroke with isolated MCA disease with ≥ 50% luminal narrowing by vascular imaging were enrolled within 2 weeks of onset and underwent high-resolution (3 T) intracranial vessel wall imaging (VWI). The pattern of vessel wall thickening, high signal on T1-weighted images, juxtaluminal hyperintensity, pattern and grade of enhancement were studied. The TOAST classification before and after HRVWI and the correlation of the recurrence of ischemic events at 3 months with imaging characteristics were analysed.

RESULTS

Of the 36 patients, the mean age was 49.53 ± 15.61 years. After luminal imaging, by TOAST classification, 12 of 36 patients had stroke of undetermined aetiology. After vessel wall imaging, lesions in MCA were analysed. Of them, 23 patients had ICAD, 8 had vasculitis, and 2 had partially occlusive thrombus in MCA. The ability of HRVWI to bring a change in diagnosis was significant (p = 0.031). Of the 23 patients with ICAD, 12 patients had recurrent strokes within 3 months. The presence of grade 2 contrast enhancement (p = 0.02) and type 2 wall thickening (p = 0.03) showed a statistically significant association with recurrent ischemic events.

CONCLUSION

High-resolution MRVWI can help in identifying the aetiology of stroke. The HRVWI characteristics in ICAD can help in risk stratification.

Predictive power of high-resolution vessel wall magnetic resonance imaging in ischemic stroke

BACKGROUND AND OBJECTIVE

Intracranial atherosclerotic disease (ICAD) is a key contributor to ischemic stroke and has a high recurrence rate. This study aimed to investigate the function of high-resolution vessel wall MRI (HR-VW-MRI) and evaluate plaque characteristics in patients with ICAD.

METHODS

A consecutive series of patients with ICAD who underwent HR-VW-MRI were enrolled, and imaging measurements were acquired. Baseline clinical characteristics were identified. Telephone follow-up was conducted every three months. The endpoint events were the first onset or recurrence of ischemic stroke and new clinical vascular events. Patients were divided into groups with or without events according to whether the endpoint event occurred.

RESULTS

A total of 70 patients (mean age = 57.6 years old) were enrolled. The median follow-up duration was 182 days. During the follow-up, 10 patients developed ischemic stroke, experienced endpoint events, and were found with 44 plaques in the artery area. A total of 169 plaques were further found in 70 patients. There were significant differences in EI, HST1, surface features, and WA reference between the two groups (P < 0.05). Logistic analysis showed that grade 2 enhancements, stenosis degree ≥ 50%, HST1, and surface features were independent prognostic factors of the onset of stroke, caused by ICAD.

CONCLUSION

This prospective study demonstrates that HR-VW-MRI can identify atherosclerotic plaques in the cerebral artery and high-risk plaques, which may contribute to the prevention of ICAD and guide clinical treatment.

Comparison of contrast-enhanced T1-weighted imaging using DANTE-SPACE, PETRA, and MPRAGE: a clinical evaluation of brain tumors at 3 Tesla

Background

We aimed to compare the performance of three contrast-enhanced T1-weighted three-dimensional (3D) magnetic resonance (MR) sequences to detect brain tumors at 3 Tesla. The three sequences were: (I) delay alternating with nutation for tailored excitation sampling perfection with application-optimized contrasts using different flip angle evolution (DANTE-SPACE), (II) pointwise encoding time reduction with radial acquisition (PETRA), and (III) magnetization-prepared rapid acquisition with gradient echo (MPRAGE).

Methods

This study involved 77 consecutive patients, including 34 patients with known primary brain tumors and 43 patients suspected of intracranial metastases. All patients underwent each of the three sequences with comparable spatial resolution and acquisition time post-injection. Signal-to-noise ratios (SNRs) for gray matter (GM) and white matter (WM), contrast-to-noise ratios (CNRs) for lesion/GM, lesion/WM, and GM/WM were quantitatively compared. Two radiologists determined the total number of enhancing lesions by consensus. Intraclass correlation coefficients (ICCs) between the two radiologists for metastases presence, qualitative ratings for image quality, and acoustic noise level of each sequence were assessed.

Results

Among the three sequences, SNRs and CNRs between lesions and surrounding parenchyma were highest using DANTE-SPACE, but CNR_WM/GM was the lowest with DANTE-SPACE. SNRs for PETRA images were significantly higher than those for MPRAGE (P<0.001). CNRs between lesions and surrounding parenchyma were similar for PETRA and MPRAGE (P>0.05). Significantly more brain metastases were detected with DANTE-SPACE (n=94) compared with MPRAGE (n=71) and PETRA (n=72). The ICCs were 0.964 for MPRAGE, 0.975 for PETRA, and 0.973 for DANTE-SPACE. Qualitative scores for lesion imaging using DANTE-SPACE were significantly higher than those obtained with PETRA and MPRAGE (P=0.002 and P=0.004, respectively). The acoustic noise level for PETRA (64.45 dB) was significantly lower than that for MPRAGE (78.27 dB, P<0.01) and DANTE-SPACE (80.18 dB, P<0.01).

Conclusions

PETRA achieves comparable detection of brain tumors with MPRAGE and is preferred for depicting osseous metastases and meningeal enhancement. DANTE-SPACE with blood vessel suppression showed improved detection of cerebral metastases compared with MPRAGE and PETRA, which could be helpful for the differential diagnosis of tumors.

Symptomatic and Asymptomatic Chronic Carotid Artery Occlusion on High-Resolution MR Vessel Wall Imaging

BACKGROUND AND PURPOSE

Chronic carotid artery occlusion remains a poorly understood risk factor for subsequent stroke, and potential revascularization is dependent on understanding the anatomy and nature of the occlusion. Luminal imaging cannot assess the nature of an occlusion, so the internal structure of the occlusion must be inferred. The present study examines the signal characteristics of symptomatic and asymptomatic carotid occlusion that may point to management differentiation.

MATERIALS AND METHODS

We prospectively recruited patients who were diagnosed with chronic carotid artery occlusion defined as longer than 4 weeks and confirmed by DSA. All patients underwent high-resolution MR vessel wall imaging examinations after enrollment. Baseline characteristics, vessel wall imaging features, and DSA features were collected and evaluated. The vessel wall imaging features included segment involvement, signal intensity, contrast enhancement, and vessel wall thickness. The symptomatic and asymptomatic chronic carotid artery occlusions were compared.

RESULTS

A total of 44 patients with 48 lesions were included in this study from February 2020 to December 2020. Of the 48 lesions, 35 (72.9%) were symptomatic and 13 (27.1%) were asymptomatic. There was no difference in baseline and DSA features. On vessel wall imaging, C1 and C2 were the most commonly involved segments (91.7% and 68.8%, respectively). Compared with symptomatic lesions, asymptomatic lesions were more often isointense (69.2%) in the distal segment (P = .03). Both groups had diffuse wall thickening (80% and 100%).

CONCLUSIONS

Signal characteristics between those with symptomatic and asymptomatic carotid artery occlusions differ in a statistically significant fashion, indicating a different structure of the occlusion.

The Added Value of Vessel Wall MRI in the Detection of Intraluminal Thrombus in Patients Suspected of Craniocervical Artery Dissection

Patients with craniocervical artery dissection (CCAD) have a high short-term risk of ischemic stroke, which is frequently associated with thromboembolism. Previous studies have demonstrated the utility of three-dimensional vessel wall MR imaging (3D-VWMRI) in the diagnosis of dissection. Few have investigated the value of 3D-VWMRI in the detection of intraluminal thrombus. The purpose of the current study was to evaluate the added value of 3D-VWMRI for thrombus identification in patients suspected of CCAD. One hundred and four patients (mean age, 44.2 years ± 13.2) suspected of CCAD and scheduled for digital subtraction angiography (DSA) were prospectively enrolled in the study and underwent VWMRI examination. The diagnostic performance of 3D-VWMRI for CCAD was evaluated using receiver operating characteristic (ROC) analysis with the final diagnosis results as the reference. The presence/absence of intraluminal thrombus on 3D-VWMRI/DSA was independently determined. The sensitivity and specificity of 3D-VWMRI for intraluminal thrombus detection were assessed with DSA serving as the reference. The odds ratio (OR) was used to evaluate the correlation between thrombus presented on 3D-VWMRI/DSA and ischemic stroke. The 3D-VWMRI had high sensitivity (90.0%) and specificity (94.3%) in identifying arteries with CCAD. The area under the ROC curve was 0.96. With DSA as the reference, the sensitivity and accuracy of 3D-VWMRI for the detection of intraluminal thrombus were 97.4% and 79.0%, respectively. An intraluminal thrombus present on 3D-VWMRI was strongly associated with a territorial ischemic stroke (OR: 30.0; 95% confidence interval: 9.1-98.4; P < .001). In conclusion, 3D-VWMRI with a 3.0-T MR system had a high diagnostic performance for CCAD and offered added value for detecting intraluminal thrombus.

Surgical management of anterior clinoidal meningiomas: consensus statement on behalf of the EANS skull base section

BACKGROUND

The optimal management of clinoidal meningiomas (CMs) continues to be debated.

METHODS

We constituted a task force comprising the members of the EANS skull base committee along with international experts to derive recommendations for the management of these tumors. The data from the literature along with contemporary practice patterns were discussed within the task force to generate consensual recommendations.

RESULTS AND CONCLUSION

This article represents the consensus opinion of the task force regarding pre-operative evaluations, patient's counselling, surgical classification, and optimal surgical strategy. Although this analysis yielded only Class B evidence and expert opinions, it should guide practitioners in the management of patients with clinoidal meningiomas and might form the basis for future clinical trials.

Double delay alternating with nutation for tailored excitation facilitates banding-free isotropic high-resolution intracranial vessel wall imaging

The purpose of this study was to evaluate the use of a double delay alternating with nutation for tailored excitation (D-DANTE)-prepared sequence for banding-free isotropic high-resolution intracranial vessel wall imaging (IC-VWI) and to compare its performance with regular DANTE in terms of signal-to-noise ratio (SNR) as well as cerebrospinal fluid (CSF) and blood suppression efficiency. To this end, a D-DANTE-prepared 3D turbo spin echo sequence was implemented by interleaving two separate DANTE pulse trains with different RF phase-cycling schemes, but keeping all other DANTE parameters unchanged, including the total number of pulses and total preparation time. This achieved a reduction of the banding distance compared with regular DANTE enabling banding-free imaging up to higher resolutions. Bloch simulations assuming static vessel wall and flowing CSF spins were performed to compare DANTE and D-DANTE in terms of SNR and vessel wall/CSF contrast. Similar image quality measures were assessed from measurements on 13 healthy middle-aged volunteers. Both simulation and in vivo results showed that D-DANTE had only slightly lower vessel wall/CSF and vessel wall/blood contrast-to-noise ratio values compared with regular DANTE, which originated from a 10%-15% reduction in vessel wall SNR but not from reduced CSF or blood suppression efficiency. As anticipated, IC-VWI acquisitions showed that D-DANTE can successfully remove banding artifacts compared with regular DANTE with equal scan time or DANTE preparation length. Moreover, application was demonstrated in a patient with an intracranial aneurysm, indicating improved robustness to slow flow artifacts compared with clinically available 3D turbo spin echo scans. In conclusion, D-DANTE provides banding artifact-free IC-VWI up to higher isotropic resolutions compared with regular DANTE. This allows for a more flexible choice of DANTE preparation parameters in high-resolution IC-VWI protocols.

Intracranial Atherosclerotic Plaque Characteristics and Burden Associated With Recurrent Acute Stroke: A 3D Quantitative Vessel Wall MRI Study

Background: Intracranial atherosclerotic disease (ICAD) tends to affect multiple arterial segments, and previous studies rarely performed a comprehensive plaque analysis of the entire circle of Willis for the evaluation of recurrent stroke risk. We aimed to investigate the features of circle of Willis ICAD on 3D magnetic resonance vessel wall imaging (MR-VWI) and their relationships with recurrent acute stroke. Methods: Patients with either acute ischemic stroke (within 4 weeks after stroke) or chronic ischemic stroke (after 3 months of stroke) due to intracranial atherosclerotic plaque underwent 3D contrast-enhanced MR-VWI covering major cerebral arteries. Participants were divided into three groups: first-time acute stroke, recurrent acute stroke, and chronic stroke. Culprit plaque (defined as the only lesion or the most stenotic lesion when multiple plaques were present within the same vascular territory of the stroke) and non-culprit plaque characteristics, including total plaque number, plaque thickness, plaque area, plaque burden (calculated as plaque area divided by outer wall area), enhancement ratio (ER), eccentricity, and stenosis, were measured and compared across the three groups. Associations between plaque characteristics and recurrent acute stroke were investigated by multivariate analysis. Results: A total of 176 participants (aged 61 ± 10 years, 109 men) with 702 intracranial plaques were included in this study. There were 80 patients with first-time acute stroke, 42 patients with recurrent acute stroke, and 54 patients with chronic stroke. More intracranial plaques were found per patient in the recurrent acute stroke group than in the first-time acute stroke or chronic stroke group (5.19 ± 1.90 vs. 3.71 ± 1.96 and 3.46 ± 1.33, p < 0.001). Patients in the recurrent acute stroke group had greater culprit plaque burden (p < 0.001) and higher culprit ER (p < 0.001) than the other two groups. After adjustment of clinical demographic factors, in multivariate analysis, coronary artery disease (CAD) (odds ratio, OR = 4.61; p = 0.035), total plaque number (OR = 1.54; p = 0.003), culprit plaque ER (OR = 2.50; p = 0.036), and culprit plaque burden (OR per 10% increment = 2.44; p = 0.010) were all independently associated with recurrent acute stroke compared to the first-time acute stroke. Conclusion: Increased intracranial atherosclerotic plaque number, higher culprit plaque ER, greater culprit plaque burden, and CAD are independently associated with recurrent acute stroke.

Essentials for Interpreting Intracranial Vessel Wall MRI Results: State of the Art

Intracranial vessel wall (VW) MRI has become widely available in clinical practice, providing multiple uses for evaluation of neurovascular diseases. The Vessel Wall Imaging Study Group of the American Society of Neuroradiology has recently reported expert consensus recommendations for the clinical implementation of this technique. However, the complexity of the neurovascular system and caveats to the technique may challenge its application in clinical practice. The purpose of this article is to review concepts essential for accurate interpretation of intracranial VW MRI results. This knowledge is intended to improve diagnostic confidence and performance in the interpretation of VW MRI scans. © RSNA, 2021 Online supplemental material is available for this article.

High-resolution vessel wall magnetic resonance imaging for depicting imaging features of unruptured intracranial vertebrobasilar dissecting aneurysms

Objective

To demonstrate the application value of high-resolution vessel wall magnetic resonance imaging (HR-VW-MRI) for depicting the imaging features of unruptured intracranial vertebrobasilar dissecting aneurysms (VBDAs).

Methods

HR-VW-MRI data of 49 patients with suspected unruptured VBDAs were retrospectively analyzed. The presence of intramural hematomas (IMH), double lumens, intimal flaps, and outer diameter enlargements were recorded. Specificity and sensitivity were calculated for both two-dimensional (2D) and three-dimensional (3D) sequences. Additionally, IMH volumes were measured and posterior inferior cerebellar artery (PICA) involvement was analyzed.

Results

Thirty-five VBDAs were confirmed in 34 patients. The overall sensitivity and specificity were 0.889 (95% confidence interval [CI]: 0.730–0.964) and 0.769 (95% CI: 0.460–0.938) for 2D sequences, and 0.917 (95% CI: 0.764–0.978) and 0.846 (95% CI: 0.537–0.973) for 3D sequences, respectively. Intimal flaps were detected in 57.1%, 87.5%, and 71.4% of all cases on 2D pre-contrast T1-weighted, contrast-enhanced T1-weighted, and 3D T1-weighted black-blood (BB) images, respectively. There was no significant difference in IMH volume between 3D T1-weighted BB and magnetization-prepared rapid gradient-echo sequences. PICA involvement was best visualized using 3D T1 sequences.

Conclusion

3D T1-weighted BB MRI provided good visualization of VBDA features, with large coverage, and was useful for detecting dissection flaps.

Usefulness of 3D High-resolution Vessel Wall MRI in Diffuse Nonaneurysmal SAH Patients

PURPOSE

In 15-20% of patients with nontraumatic diffuse subarachnoid hemorrhage (SAH), the initial conventional angiography does not reveal a causative vascular abnormality, such as intracranial aneurysm. In this study, we evaluated clinical utility of 3D high-resolution vessel wall magnetic resonance imaging (HR-VWI) in patients with diffuse nonaneurysmal SAH.

METHODS

A total of 17 patients with diffuse nonaneurysmal SAH were included in this retrospective study. We characterized demographics and HR-VWI findings and reviewed the clinical management and outcomes.

RESULTS

Of the patients 14 (14/17; 82.4%,) showed abnormal findings on HR-VWI, including 5 with intracranial dissections (29.4%), 3 with blood blister-like aneurysm (17.6%), 1 with ruptured fusiform aneurysm (5.9%), and 5 with focal nodular wall enhancement without unclassified pathology (29.4%). Of these patients were treated with endovascular management. Most patients (16/17) had a favorable modified Rankin scale scores of 0-2 on discharge.

CONCLUSION

The 3D HR-VWI revealed various hidden pathologies, such as intracranial arterial dissection, blood blister-like aneurysm, and fusiform aneurysm in patients with diffuse nonaneurysmal SAH. In addition, 3D HR-VWI had an impact on the management of SAH. The 3D HR-VWI can be a complementary diagnostic method for patients with diffuse nonaneurysmal SAH in a research or clinical setting.

Image Findings of Acute to Subacute Craniocervical Arterial Dissection on Magnetic Resonance Vessel Wall Imaging: A Systematic Review and Proportion Meta-Analysis

Background and Purpose: This systematic review and meta-analysis aimed to evaluate the pooled proportion of image findings of acute to subacute craniocervical arterial dissection (AD) direct signs on magnetic resonance vessel wall imaging (MR-VWI) and to identify factors responsible for the heterogeneity across the included studies.

Methods: A systematic literature search in the Ovid-MEDLINE and EMBASE databases was performed for studies published on the relevant topic before April 14, 2020. Pooled sensitivity and specificity values and their 95% confidence intervals (CIs) were calculated using bivariate random-effects modeling. Meta-regression analyses were also performed to determine factors influencing heterogeneity.

Results: Eleven articles with data for 209 patients with acute to subacute craniocervical AD who underwent MR-VWI were included in this systematic review and meta-analysis. The most common findings on MR-VWI were wall hematoma (84%; 95% CI, 71%−92%), abnormal enhancement (72%; 95% CI, 49%−88%), aneurysmal dilatation (71%, 95% CI, 53%−84%), and intimal flap or double lumen signs (49%; 95% CI, 29%−71%). Among the potential covariates of heterogeneity, the presence of contrast-enhanced T1-weighted imaging (CE-T1WI) within the MR-VWI sequence combination significantly affected the pooled proportion of the intimal flap or double lumen signs.

Conclusion: Wall hematoma and intimal flap or double lumen signs were the most common and least common direct sign image findings, respectively, on MR-VWI in patients with acute to subacute craniocervical AD. Furthermore, the absence of CE-T1WI in MR-VWI protocol was the cause of heterogeneity for the detection of the intimal flap or double lumen signs. This data may help improve MR-VWI interpretation and enhance the understanding of the radiologic diagnosis of craniocervical AD.

Endoscopic Endonasal Surgery of a Large Vidian Nerve Schwannoma With Preparation for Avoiding Major Vascular Injury

Vidian nerve schwannomas are extremely rare, and their surgical management requires an awareness of the surrounding vascular and nervous systems, including the internal carotid artery. Herein, we report a case of a vidian nerve schwannoma that was successfully removed using an endoscopic endonasal approach in a 21-year-old patient who presented with lacrimal hyposecretion. Imaging revealed a large mass extending to the middle cranial fossa posteriorly, to the pterygopalatine fossa laterally, and to the sphenoid sinus medially. The paraclival and petrosal portions of the internal carotid artery were displaced posteriorly. Endoscopic observation of the right nose demonstrated anterior displacement of the inferior portion of the middle turbinate. Based on the above, we suspected a vidian nerve schwannoma, and endoscopic endonasal surgery was performed with particular attention to avoid vascular injuries. An endoscopic transmaxillary approach was used to expose the anterior surface of the tumor. After confirming the pathological diagnosis intraoperatively, intracapsular resection of the tumor was completed using an ultrasonic surgical aspirator with Doppler monitoring of the location of the internal carotid artery. Endoscopic management of the surgical field and preparation to avoid vascular injury are essential for safe and efficient tumor resection.

[Carotid artery wall imaging using 7.0T magnetic resonance imaging with threedimensional DANTE-prepared FLASH in ApoE-/- mice]

OBJECTIVE

To explore the feasibility of three-dimensional (3D) vessel wall imaging of carotid atherosclerotic plaques in ApoE-/- mice using 7.0T magnetic resonance imaging (MRI) with delays alternating with nutations for tailored excitation (DANTE)-prepared fast low-angle shot (DANTE-FLASH) technique.

OBJECTIVE

Numerical simulations were performed for optimizing imaging parameters to maximize the wall-lumen contrast. Six ApoE-/- and three wild-type mice were scanned using a 7.0T MRI scanner with DANTE-FLASH and multi-slice 2D RARE coupled with inflow outflow saturation bands (2D-IOSBRARE). The wall signal-to-noise ratio (SNRwall), lumen SNR (SNRlumen), wall-lumen contrast-to-noise ratio (CNR), lumen area (LA), and wall area (WA) were compared between DANTE- FLASH and 2D-IOSB-RARE sequences. Linear regression analysis was performed to assess the correlation between the MRI measurements and histopathological measurements of LA and WA.

OBJECTIVE

Based on the simulation results, a flip angle of 15° and a train length of 150 were implemented in the live imaging study. Compared with 2D-IOSB-RARE, DANTE-FLASH provided a slightly reduced CNR (P < 0.001) but much improved slice resolution. The LA and WA measurements from the DANTE-FLASH and 2D-IOSB- RARE showed excellent agreement based on ICC analysis (LA: ICC=0.94, P < 0.001; WA: ICC=0.93, P < 0.001) and Bland-Altman plots. Strong correlations were observed between the MRI and histopathological measurements for both LA (P < 0.0001) and WA (P < 0.0001).

OBJECTIVE

As a 3D black-blood MR sequence, DANTE-FLASH provides isotropic high spatial resolution to allow reliable visualization and quantitative evaluation of the arteriosclerotic lesions within the carotid artery of ApoE-/- mice using a 7.0T MRI scanner.

Visualization of lenticulostriate artery by intracranial dark-blood vessel wall imaging and its relationships with lacunar infarction in basal ganglia: a retrospective study

OBJECTIVES

There is close relationship between lenticulostriate arteries (LSAs) and lacunar infarctions (LIs) of the basal ganglia. The study aims to visualize the LSAs using high-resolution vessel wall imaging (VWI) on 3T system and explore the correlation between LSAs and LIs.

METHODS

Fifty-six patients with LIs in basal ganglia, and 44 age-matched control patients were enrolled and analyzed retrospectively. The raw VWI images were reformatted into coronal slices in minimum intensity projection for further observation of LSAs. The risk factors of LIs in basal ganglia were analyzed by univariate and multivariate logistic regression. The correlation and linear regression analysis between the LSAs and LIs, ipsilateral MCA-M1 plaques were investigated.

RESULTS

The total number (p < 0.01) and length (p < 0.01) of LSAs were statistically different between basal ganglias with and without LIs. The total number of LSAs and ipsilateral MCA-M1 plaques were independently related to LIs in basal ganglias. The mean length of LSAs were negatively correlated with number (r = - 0.33, p = 0.002) and volume (r = - 0.37, p = 0.001) of LIs. Age, drinking history, and mean length of LSAs were associated with LI occurrence in basal ganglia, and mean length of LSAs was correlated with larger volume of LIs.

CONCLUSIONS

Number of LSA reduction and ipsilateral MCA-M1 plaques were associated with the presence of LIs in basal ganglias. Age increasing, drinking history, and shorter LSAs were correlated with the increasing of LIs.

KEY POINTS

• Patients with LIs tend to have shorter LSAs. • The characteristics of LSAs and ipsilateral MCA-M1 plaques are associated with LIs in basal ganglias. • Age, drinking history, and mean length of LSAs are correlated with LI features in basal ganglias.

Neural network enhanced 3D turbo spin echo for MR intracranial vessel wall imaging

PURPOSE

To improve the signal-to-noise ratio (SNR) and image sharpness for whole brain isotropic 0.5 mm three-dimensional (3D) T₁ weighted (T₁w) turbo spin echo (TSE) intracranial vessel wall imaging (IVWI) at 3 T.

METHODS

The variable flip angle (VFA) method enables useful optimization across scan efficiency, SNR and relaxation induced point spread function (PSF) for TSE imaging. A convolutional neural network (CNN) was developed to retrospectively enhance the acquired TSE image with PSF blurring. The previously developed VFA method to increase SNR at the expense of blur can be combined with the presented PSF correction to yield long echo train length (ETL) scan while the acquired image remains high SNR and sharp. The overall approach can enable an optimized solution for accelerated whole brain high-resolution 3D T₁w TSE IVWI. Its performance was evaluated on healthy volunteers and patients.

RESULTS

The PSF blurred image acquired by a long ETL scan can be enhanced by CNN to restore similar sharpness as a short ETL scan, which outperforms the traditional linear PSF enhancement approach. For accelerated whole brain IVWI on volunteers, the optimized isotropic 0.5 mm 3D T₁w TSE sequence with CNN based PSF enhancement provides sufficient flow suppression and improved image quality. Preliminary results on patients further demonstrated its improved delineation for intracranial vessel wall and plaque morphology.

CONCLUSION

The CNN enhanced VFA TSE imaging enables an overall image quality improvement for high-resolution 3D T₁w IVWI, and may provide a better tradeoff across scan efficiency, SNR and PSF for 3D TSE acquisitions.

Aneurysm Wall Enhancement in Unruptured Intracranial Aneurysms: A Histopathological Evaluation

Background Unruptured intracerebral aneurysm wall enhancement (AWE) on vessel wall magnetic resonance imaging scans may be a promising predictor for rupture-prone intracerebral aneurysms. However, the pathophysiology of AWE remains unclear. To this end, the association between AWE and histopathological changes was assessed in this study. Methods and Results A total of 35 patients with 41 unruptured intracerebral aneurysms who underwent surgical clipping were prospectively enrolled. A total of 27 aneurysms were available for histological evaluation. The macroscopic and microscopic features of unruptured intracerebral aneurysms with and without enhancement were assessed. The microscopic features studied included inflammatory cell invasion and vasa vasorum, which were assessed using immunohistochemical staining with CD68, CD3, CD20, and myeloperoxidase for the former and CD34 for the latter. A total of 21 (51.2%) aneurysms showed AWE (partial AWE, n=7; circumferential AWE, n=14). Atherosclerotic and translucent aneurysms were identified in 17 and 14 aneurysms, respectively. Aneurysm size, irregularity, and atherosclerotic and translucent aneurysms were associated with AWE on univariate analysis (P<0.05). Multivariate logistic regression analysis showed that atherosclerosis was the only factor significantly and independently associated with AWE (P=0.027). Histological assessment revealed that inflammatory cell infiltration, intraluminal thrombus, and vasa vasorum were significantly associated with AWE (P<0.05). Conclusions Though AWE on vessel wall magnetic resonance imaging scans may be associated with the presence of atherosclerotic lesions in unruptured intracerebral aneurysms, inflammatory cell infiltration within atherosclerosis, intraluminal thrombus, and vasa vasorum may be the main pathological features associated with AWE. However, the underlying pathological mechanism for AWE still needs to be further studied.

Plaque enhancement in multi-cerebrovascular beds associates with acute cerebral infarction

BACKGROUND

It is valuable to explore the relationship between plaque characteristics and stroke by using three-dimensional (3D) magnetic resonance imaging (MRI) of the vessel wall.

PURPOSE

To investigate the association between plaque enhancement score (PES) of co-existing intracranial and extracranial carotid plaques and ischemic stroke using 3D MRI.

MATERIAL AND METHODS

Symptomatic patients were recruited and underwent cerebrovascular 3D MRI of the vessel wall. The number, enhancement degree, and stenosis of plaques in intracranial and extracranial carotid arteries were evaluated. The PES calculated by summing enhancement degree of all detected plaques was compared between patients with and without acute cerebral infarction (ACI) and its association with ACI was determined.

RESULTS

Of 157 recruited patients, 118 (75.2%) had co-existing plaques. Patients with ACI had significantly greater PES of co-existing plaques compared with those without ACI (9, interquartile range [IQR] 5-11 vs. 5, IQR 2-7, P<0.001). The odds ratio for PES of co-existing plaques in discriminating ACI was 1.410 (95% confidence interval [CI] 1.146-1.735, P = 0.001) after adjustment for stenosis, intraplaque hemorrhage, and traditional risk factors. Receiver operating characteristic curve analysis showed that, in discriminating ACI, PES had higher area under the curve (AUC 0.693-0.764) than plaque number (AUC 0.625-0.683) and enhancement degree (AUC 0.570-0.706) alone in any vascular bed. The AUC of PES of co-existing plaques combined with stenosis, NIHSS scores, intraplaque hemorrhage, hyperlipidemia, and blood pressure reached 0.847.

CONCLUSION

Cerebrovascular plaque enhancement score combining plaque number and enhancement degree is independently associated with ACI. The enhancement score of co-existing plaques has higher strength in discriminating ACI compared with plaques in a single vascular bed.

Black-Blood Contrast in Cardiovascular MRI

MRI is a versatile technique that offers many different options for tissue contrast, including suppressing the blood signal, so‐called black‐blood contrast. This contrast mechanism is extremely useful to visualize the vessel wall with high conspicuity or for characterization of tissue adjacent to the blood pool. In this review we cover the physics of black‐blood contrast and different techniques to achieve blood suppression, from methods intrinsic to the imaging readout to magnetization preparation pulses that can be combined with arbitrary readouts, including flow‐dependent and flow‐independent techniques. We emphasize the technical challenges of black‐blood contrast that can depend on flow and motion conditions, additional contrast weighting mechanisms (T₁, T₂, etc.), magnetic properties of the tissue, and spatial coverage. Finally, we describe specific implementations of black‐blood contrast for different vascular beds.

Imaging of intracranial atherosclerotic plaques using 3.0 T and 7.0 T magnetic resonance imaging-current trends and future perspectives

Intracranial atherosclerotic disease (ICAD) is one of the most common causes of ischemic stroke and carries a relatively high risk of stroke recurrence. Advances in high-resolution magnetic resonance imaging (HRMRI) techniques of intracranial arteries now have made it possible to directly visualize atherosclerotic plaque itself, allowing detailed assessments of plaque morphology and components. Currently available intracranial HRMRI could be performed with 2-dimensional (2D) and 3D acquisitions, and multicontrast weightings in clinically reasonable scan times. Until now, HRMRI research of ICAD has focused on the identification of plaque vulnerability, and the relationship between plaque characteristics and ischemic stroke. HRMRI at ultra-high-field strength (7.0 T) holds promise in better visualizing intracranial vessel walls, as well as identifying early lesions and total burden of ICAD. As a result, intracranial HRMRI provides great insights into pathology of intracranial atherosclerotic plaques, stroke mechanisms, and future stroke risk. In this article, we will review the technical implementation, preclinical research, clinical applications, and future directions of HRMRI for the evaluation of ICAD at 3.0 T and 7.0 T.

Wall enhancement on black-blood MRI is independently associated with symptomatic status of unruptured intracranial saccular aneurysm

OBJECTIVE

This study aims to investigate whether aneurysm wall enhancement (AWE) is independently associated with symptomatic status of unruptured intracranial aneurysms (UIAs).

METHODS

One hundred thirty-nine consecutive patients (67 male, mean age 58 ± 11 years) with 79 symptomatic and 87 asymptomatic UIAs were imaged using black-blood MRI pre- and post-gadolinium contrast administration and 3D DSA. Symptoms related to aneurysms were identified including cranial nerve deficits and headache. AWE grade and area were characterized, and aneurysm size was measured on DSA. Multivariate binary logistic regression analysis was used to identify factors associated with symptoms. Further subgroup analysis was performed for aneurysms size < 10 mm.

RESULTS

Symptomatic UIAs had significantly larger aneurysm size (11.2 ± 6.2 mm vs. 6.4 ± 3.3 mm), enhancement grade (1.3 ± 0.6 vs. 0.4 ± 0.6), enhancement area (2.0 ± 0.9 vs. 0.4 ± 0.7), and higher prevalence of thick enhancement (39% vs. 3%) compared with asymptomatic UIAs, all p < 0.001. In multivariate analysis, only AWE area (odds ratio [OR] 6.9, 95% confidence interval [4.0, 11.7]) was independently associated with symptoms. AWE area had an area under curve (AUC) value of 0.888, with 72.2% sensitivity and 92.0% specificity for symptoms, which was superior to aneurysm size (AUC of 0.771, with 75.9% sensitivity and 65.5% specificity). In the subgroup analysis of aneurysms smaller than 10 mm (n = 118), AWE area (OR, 7.0, p < 0.001) remained the only independent risk factor associated with symptoms.

CONCLUSIONS

Larger AWE area is independently associated with symptomatic UIAs, which may provide additional value to guide UIA management and improve patient outcomes.

KEY POINTS

• Symptomatic intracranial aneurysms are larger and more often demonstrate significant wall enhancement than asymptomatic aneurysms. • Larger wall enhancement area is independently associated with symptomatic intracranial aneurysm.

Practical value of three-dimensional high resolution magnetic resonance Vessel Wall imaging in identifying suspicious intracranial vertebrobasilar dissecting aneurysms

Background

Direct evidence of intimal flaps, double lumen and intramural haematomas (IMH) is difficult to detect on conventional angiography in most intracranial vertebrobasilar dissecting aneurysms (VBDAs). Our purpose was to assess the value of three-dimensional high-resolution magnetic resonance vessel wall imaging (3D HRMR VWI) for identifying VBDAs.

Methods

Between August 2013 and January 2016, consecutive patients with suspicious VBDAs were prospectively enrolled to undergo catheter angiography and VWI (pre- and post-contrast). The lesion was diagnosed as definite VBDA when presenting direct signs of dissection; as possible when only presenting indirect signs; and as segmental ectasia when there was local dilation and wall thickness similar to adjacent normal artery’s without mural thrombosis.

Results

Twenty-one patients with 27 lesions suspicious for VBDAs were finally included. Based on findings of VWI and catheter angiography, definite VBDA was diagnosed in 25 and 7 lesions (92.6%, vs 25.9%, p <  0.001), respectively; possible VBDA in 0 and 20 (0 vs 74.1%), respectively; and segmental ectasia in 2 and 0 (7.4% vs 0%), respectively. On VWI and catheter angiography, intimal flap was detected in 21 and 7 lesions (77.8% vs 25.9%, p = 0.001), respectively; double lumen sign in 18 and 7 (66.7% vs 25.9%, p = 0.003), respectively; and IMH sign in 14 and 0 (51.9% vs 0), respectively.

Conclusions

3D HRMR VWI could detect direct dissection signs more frequently than catheter angiography. This may help obtain definite diagnosis of intracranial VBDAs, and allow accurate differentiation between dissecting aneurysm and segmental ectasia as well. Further prospective study with larger sample was required to investigate the superiority of HRMR VWI for definite diagnosis of intracranial VBDAs than catheter angiography.

Assessment of carotid atherosclerotic disease using three-dimensional cardiovascular magnetic resonance vessel wall imaging: comparison with digital subtraction angiography

BACKGROUND

A three-dimensional (3D) cardiovascular magnetic resonance (CMR) vessel wall imaging (VWI) technique based on 3D T1 weighted (T1w) Sampling Perfection with Application-optimized Contrast using different flip angle Evolutions (SPACE) has recently been used as a promising CMR imaging modality for evaluating extra-cranial and intra-cranial vessel walls. However, this technique is yet to be validated against the current diagnostic imaging standard. We therefore aimed to evaluate the diagnostic performance of 3D CMR VWI in characterizing carotid disease using intra-arterial digital subtraction angiography (DSA) as a reference.

METHODS

Consecutive patients with at least unilateral > 50% carotid stenosis on ultrasound were scheduled to undergo interventional therapy were invited to participate. The following metrics were measured using 3D CMR VWI and DSA: lumen diameter of the common carotid artery (CCA) and segments C1-C7, stenosis diameter, reference diameter, lesion length, stenosis degree, and ulceration. We assessed the diagnostic sensitivity, specificity, accuracy, and receiver operating characteristic (ROC) curve of 3D CMR VWI, and used Cohen's kappa, the intraclass correlation coefficient (ICC), and Bland-Altman analyses to assess the diagnostic agreement between 3D CMR VWI and DSA.

RESULTS

The ICC (all ICCs ≥0.96) and Bland-Altman plots indicated excellent inter-reader agreement in all individual morphologic measurements by 3D CMR VWI. Excellent agreement in all individual morphologic measurements were also found between 3D CMR VWI and DSA. In addition, 3D CMR VWI had high sensitivity (98.4, 97.4, 80.0, 100.0%), specificity (100.0, 94.5, 99.1, 98.0%), and Cohen's kappa (0.99, 0.89, 0.84, 0.96) for detecting stenosis > 50%, stenosis > 70%, ulceration, and total occlusion, respectively, using DSA as the standard. The AUC of 3D CMR VWI for predicting stenosis > 50 and > 70% were 0.998 and 0.999, respectively.

CONCLUSIONS

The 3D CMR VWI technique enables accurate diagnosis and luminal feature assessment of carotid artery atherosclerosis, suggesting that this imaging modality may be useful for routine imaging workups and provide comprehensive information for both the vessel wall and lumen.

One-Stop MR Neurovascular Vessel Wall Imaging With a 48-Channel Coil System at 3 T

OBJECTIVE

The purpose of this article was to build a radio frequency (RF) coil system to achieve high vessel wall image quality with coverage extending from the aortic arch to the intracranial vessels.

METHODS

A 48-channel coil system was built and characterized at a 3 tesla (T) Magnetic Resonance Imaging (MRI) scanner (uMR 790, Shanghai United Imaging Healthcare, Shanghai, China). The coil's performance was compared with a commercially available 36-channel coil system. By human studies, signal-to-noise ratio (SNR) units were evaluated and g-factors were calculated in the transverse planes of the brain and neck regions.

RESULTS

The SNR was increased by at least 28% in the brain region and up to fourfold in the neck region. The average g-factor with the acceleration factor, R = 3, was lowered by 21% in the transverse plane of the neck region. Intracranial and carotid arterial wall images with an isotropic spatial resolution of 0.63 mm were acquired within 7.7 minutes and thoracic aorta wall images with an isotropic spatial resolution of 1.1 mm were acquired within 2.7 minutes with the 48-channel coil system. The vessel wall can be more clearly visualized with the 48-channel coil system compared with the 36-channel coil system.

CONCLUSION

A 48-channel coil system was developed and demonstrated superior performance for vessel wall imaging at the intracranial and cervical carotid arteries compared with a commercial 36-channel coil.

SIGNIFICANCE

The 48-channel coil system is potentially useful for clinical diagnostics, especially when attempting to diagnose ischemic stroke.

Cerebral Venous Thrombosis: MR Black-Blood Thrombus Imaging with Enhanced Blood Signal Suppression

BACKGROUND AND PURPOSE

The residual blood flow artifact is a critical confounder for MR black-blood thrombus imaging of cerebral venous sinus thrombosis. This study aimed to conduct a validation of a new MR black-blood thrombus imaging technique with enhanced blood signal suppression.

MATERIALS AND METHODS

Twenty-six participants (13 volunteers and 13 patients) underwent conventional imaging methods followed by 2 randomized black-blood thrombus imaging scans, with a preoptimized delay alternating with nutation for tailored excitation (DANTE) preparation switched on and off, respectively. The signal intensity of residual blood, thrombus, brain parenchyma, normal lumen, and noise on black-blood thrombus images were measured. The thrombus volume, SNR of residual blood, and contrast-to-noise ratio for residual blood versus normal lumen, thrombus versus residual blood, and brain parenchyma versus normal lumen were compared between the 2 black-blood thrombus imaging techniques. Segmental diagnosis of venous sinus thrombosis was evaluated for each black-blood thrombus imaging technique using a combination of conventional imaging techniques as a reference.

RESULTS

In the volunteer group, the SNR of residual blood (11.3 ± 2.9 versus 54.0 ± 23.4, P < .001) and residual blood-to-normal lumen contrast-to-noise ratio (7.5 ± 3.4 versus 49.2 ± 23.3, P < .001) were significantly reduced using the DANTE preparation. In the patient group, the SNR of residual blood (16.4 ± 8.0 versus 75.0 ± 35.1, P = .002) and residual blood-to-normal lumen contrast-to-noise ratio (12.4 ± 7.8 versus 68.8 ± 35.4, P = .002) were also significantly lower on DANTE-prepared black-blood thrombus imaging. The new black-blood thrombus imaging technique provided higher thrombus-to-residual blood contrast-to-noise ratio, significantly lower thrombus volume, and substantially improved diagnostic specificity and agreement with conventional imaging methods.

CONCLUSIONS

DANTE-prepared black-blood thrombus imaging is a reliable MR imaging technique for diagnosing cerebral venous sinus thrombosis.

Association between homocysteine and multivascular atherosclerosis in stroke-related vascular beds determined by three-dimensional magnetic resonance vessel wall imaging

BACKGROUND

Atherosclerosis in stroke-related vascular beds is the major cause of stroke. Studies demonstrated that multivascular atherosclerosis is prevalent in stroke patients and those with multivascular plaques had higher risk of recurrent stroke.

OBJECTIVES

This study investigated the relationship between homocysteine and multivascular atherosclerosis in stroke-related vascular beds using magnetic resonance imaging.

METHODS

Patients with recent ischemic cerebrovascular symptoms were enrolled and underwent three-dimensional magnetic resonance vessel wall imaging for intracranial arteries, extracranial carotid arteries and aortic arch. Traditional risk factors and homocysteine were measured. Presence of multivascular plaques defined as plaques in at least two stroke-related vascular beds on magnetic resonance imaging was determined. The relationship between homocysteine and characteristics of multivascular plaques was determined.

RESULTS

Of 49 enrolled patients (mean age: 56.3 ± 13.8 years; 35 males), 23 had multivascular plaques. Homocysteine (odds ratio, 1.17; 95% confidence interval, 1.02-1.34; p = 0.022) and age (odds ratio, 1.71; 95% confidence interval, 1.22-2.41; p = 0.002) were significantly associated with presence of multivascular plaques. The adjusted associations remained significant (both p < 0.05). In discriminating presence of multivascular plaques, the area-under-the-curve of age, homocysteine and combination of them was 0.79, 0.70 and 0.87 respectively.

CONCLUSIONS

Homocysteine is independently associated with stroke-related multivascular plaques and combination of age and homocysteine has stronger predictive value.