Perfusion parameter map generation from TOF-MRA in stroke using generative adversarial networks.

PURPOSE: To generate perfusion parameter maps from Time-of-flight magnetic resonance angiography (TOF-MRA) images using artificial intelligence to provide an alternative to traditional perfusion imaging techniques. MATERIALS AND METHODS: This retrospective study included a total of 272 patients with cerebrovascular diseases; 200 with acute stroke (from 2010 to 2018), and 72 with steno-occlusive disease (from 2011 to 2014). For each patient the TOF MRA image and the corresponding Dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) were retrieved from the datasets. The authors propose an adapted generative adversarial network (GAN) architecture, 3D pix2pix GAN, that generates common perfusion maps (CBF, CBV, MTT, TTP, Tmax) from TOF-MRA images. The performance was evaluated by the structural similarity index measure (SSIM). For a subset of 20 patients from the acute stroke dataset, the Dice coefficient was calculated to measure the overlap between the generated and real hypoperfused lesions with a time-to-maximum (Tmax) > 6 s. RESULTS: The GAN model exhibited high visual overlap and performance for all perfusion maps in both datasets: acute stroke (mean SSIM 0.88-0.92, mean PSNR 28.48-30.89, mean MAE 0.02-0.04 and mean NRMSE 0.14-0.37) and steno-occlusive disease patients (mean SSIM 0.83-0.98, mean PSNR 23.62-38.21, mean MAE 0.01-0.05 and mean NRMSE 0.03-0.15). For the overlap analysis for lesions with Tmax>6 s, the median Dice coefficient was 0.49. CONCLUSION: Our AI model can successfully generate perfusion parameter maps from TOF-MRA images, paving the way for a non-invasive alternative for assessing cerebral hemodynamics in cerebrovascular disease patients. This method could impact the stratification of patients with cerebrovascular diseases. Our results warrant more extensive refinement and validation of the method.

A coarse-to-fine cascade deep learning neural network for segmenting cerebral aneurysms in time-of-flight magnetic resonance angiography.

BACKGROUND: Accurate segmentation of unruptured cerebral aneurysms (UCAs) is essential to treatment planning and rupture risk assessment. Currently, three-dimensional time-of-flight magnetic resonance angiography (3D TOF-MRA) has been the most commonly used method for screening aneurysms due to its noninvasiveness. The methods based on deep learning technologies can assist radiologists in achieving accurate and reliable analysis of the size and shape of aneurysms, which may be helpful in rupture risk prediction models. However, the existing methods did not accomplish accurate segmentation of cerebral aneurysms in 3D TOF-MRA. METHODS: This paper proposed a CCDU-Net for segmenting UCAs of 3D TOF-MRA images. The CCDU-Net was a cascade of a convolutional neural network for coarse segmentation and the proposed DU-Net for fine segmentation. Especially, the dual-channel inputs of DU-Net were composed of the vessel image and its contour image which can augment the vascular morphological information. Furthermore, a newly designed weighted loss function was used in the training process of DU-Net to promote the segmentation performance. RESULTS: A total of 270 patients with UCAs were enrolled in this study. The images were divided into the training (N = 174), validation (N = 43), and testing (N = 53) cohorts. The CCDU-Net achieved a dice similarity coefficient (DSC) of 0.616 ± 0.167, Hausdorff distance (HD) of 5.686 ± 7.020 mm, and volumetric similarity (VS) of 0.752 ± 0.226 in the testing cohort. Compared with the existing best method, the DSC and VS increased by 18% and 5%, respectively, while the HD decreased by one-tenth. CONCLUSIONS: We proposed a CCDU-Net for segmenting UCAs in 3D TOF-MRA, and the obtained results show that the proposed method outperformed other existing methods.

Usefulness of Silent Magnetic Resonance Angiography in the Follow-Up of Endovascular-Treated Intracranial Aneurysm: A Prospective Study.

OBJECTIVES: To prospectively evaluate the clinical usefulness of Silent magnetic resonance angiography (Silent MRA) in the follow-up of endovascular-treated intracranial aneurysms by comparing it with time-of-flight magnetic resonance angiography (TOF MRA) and digital subtraction angiography (DSA). METHODS: Patients with endovascular-treated saccular aneurysms and followed with Silent MRA, TOF MRA, and DSA in our center were included. The visualization of the treated sites in the two MRA sequences was assessed using a 5-point scale. The aneurysm occlusion status according to each of the three imaging modalities was assessed using a 3-point scale. RESULTS: Forty-one patients with 46 saccular aneurysms were recruited. The image quality score of Silent MRA was significantly higher than that of TOF MRA (4.32 ± 0.87 vs. 3.08 ± 1.48, P < 0.001). In the aneurysms treated by simple coiling, the maximal aneurysm diameter showed a strong negative correlation with image quality score in TOF MRA (Spearman's r = -0.519, P = 0.033), while it showed no significant correlation in Silent MRA (r = -0.037, P = 0.887). For the aneurysm occlusion status, inter-modality agreement was excellent (κ = 0.845) between DSA and Silent MRA, but poor (κ = 0.185) between DSA and TOF MRA. CONCLUSIONS: Silent MRA was superior to TOF MRA in the follow-up of endovascular-treated intracranial aneurysms and showed excellent consistency with DSA in the evaluation of aneurysm occlusion. Therefore, Silent MRA is useful for the follow-up of endovascular-treated aneurysms.

Circle of Willis variants and their association with outcome in patients with middle cerebral artery-M1-occlusion stroke.

BACKGROUND: An incomplete circle of Willis (CoW) has been associated with a higher risk of stroke and might affect collateral flow in large vessel occlusion (LVO) stroke. We aimed to investigate the distribution of CoW variants in a LVO stroke and transient ischemic attack (TIA) cohort and analyze their impact on 3-month functional outcome. METHODS: CoW anatomy was assessed with time-of-flight magnetic resonance angiography (TOF-MRA) in 193 stroke patients with acute middle cerebral artery (MCA)-M1-occlusion receiving endovascular treatment (EVT) and 73 TIA patients without LVO. The main CoW variants were categorized into four vascular models of presumed collateral flow via the CoW. RESULTS: 82.4% (n = 159) of stroke and 72.6% (n = 53) of TIA patients had an incomplete CoW. Most variants affected the posterior circulation (stroke: 77.2%, n = 149; TIA: 58.9%, n = 43; p = 0.004). Initial stroke severity defined by the National Institutes of Health Stroke Scale (NIHSS) on admission was similar for patients with and without CoW variants. CoW integrity did not differ between groups with favorable (modified Rankin Scale [mRS]): 0-2) and unfavorable (mRS: 3-6) 3-month outcome. However, we found trends towards a higher mortality in patients with any type of CoW variant (p = 0.08) and a higher frequency of incomplete CoW among patients dying within 3 months after stroke onset (p = 0.119). In a logistic regression analysis adjusted for the potential confounders age, sex and atrial fibrillation, neither the vascular models nor anterior or posterior variants were independently associated with outcome. CONCLUSION: Our data provide no evidence for an association of CoW variants with clinical outcome in LVO stroke patients receiving EVT.

Pointwise encoding time reduction with radial acquisition in subtraction-based magnetic resonance angiography to assess saccular unruptured intracranial aneurysms at 3 Tesla.

PURPOSE: To investigate the clinical utility of pointwise encoding time reduction with radial acquisition in subtraction-based magnetic resonance angiography (PETRA-MRA) and time-of-flight magnetic resonance angiography (TOF-MRA) to evaluate saccular unruptured intracranial aneurysms (UIAs). METHODS: A total of 49 patients with 54 TOF-MRA-identified saccular UIAs were enrolled. The morphologic parameters, contrast-to-noise-ratios (CNRs), and sharpness of aneurysms were measured using PETRA-MRA and TOF-MRA. Two radiologists independently evaluated subjective image scores, focusing on aneurysm signal homogeneities and sharpness depictions using a 4-point scale: 4, excellent; 3, good; 2, poor; 1, not assessable. PETRA-MRA and TOF-MRA acoustic noises were measured. RESULTS: All aneurysms were detected with PETRA-MRA. The morphologic parameters of 15 patients evaluated with PETRA-MRA were more closely correlated with those receiving computed tomography angiography over those receiving TOF-MRA. No significant differences between PETRA-MRA and TOF-MRA parameters were seen in the 54 UIAs (p > 0.10), excluding those with inflow angles (p < 0.05). In four patients with inflow angles on PETRA-MRA, the angles were more closely related to those of digital subtraction angiography than those of TOF-MRA. CNRs between TOF-MRA and PETRA-MRA were comparable (p = 0.068), and PETRA-MRA sharpness values and subjective image scores were significantly higher than those of TOF-MRA (p < 0.001). Inter-observer agreements were excellent for both PETRA-MRA and TOF-MRA (intraclass correlation coefficients were 0.90 and 0.97, respectively). The acoustic noise levels of PETRA-MRA were much lower than those of TOF-MRA (59 vs.73 dB, p < 0.01). CONCLUSIONS: PETRA-MRA, with better visualization of aneurysms and lower acoustic noise levels than TOF-MRA, showed a superior diagnostic performance for depicting saccular UIAs.

Automated computer-assisted detection system for cerebral aneurysms in time-of-flight magnetic resonance angiography using fully convolutional network.

BACKGROUND: As the rupture of cerebral aneurysm may lead to fatal results, early detection of unruptured aneurysms may save lives. At present, the contrast-unenhanced time-of-flight magnetic resonance angiography is one of the most commonly used methods for screening aneurysms. The computer-assisted detection system for cerebral aneurysms can help clinicians improve the accuracy of aneurysm diagnosis. As fully convolutional network could classify the image pixel-wise, its three-dimensional implementation is highly suitable for the classification of the vascular structure. However, because the volume of blood vessels in the image is relatively small, 3D convolutional neural network does not work well for blood vessels. RESULTS: The presented study developed a computer-assisted detection system for cerebral aneurysms in the contrast-unenhanced time-of-flight magnetic resonance angiography image. The system first extracts the volume of interest with a fully automatic vessel segmentation algorithm, then uses 3D-UNet-based fully convolutional network to detect the aneurysm areas. A total of 131 magnetic resonance angiography image data are used in this study, among which 76 are training sets, 20 are internal test sets and 35 are external test sets. The presented system obtained 94.4% sensitivity in the fivefold cross-validation of the internal test sets and obtained 82.9% sensitivity with 0.86 false positive/case in the detection of the external test sets. CONCLUSIONS: The proposed computer-assisted detection system can automatically detect the suspected aneurysm areas in contrast-unenhanced time-of-flight magnetic resonance angiography images. It can be used for aneurysm screening in the daily physical examination.

[Visualization of Four Intracranial Stents and In-stent Stenosis with Stenotic Models by 3D-TOF-MRA].

In recent years, various types of stents are deployed for the treatment of intracranial artery stenosis and aneurysms. Digital subtraction angiography has been considered to be the gold standard for the follow-up study. However, magnetic resonance angiography (MRA) is less invasive and the recent advances may contribute to the imaging of patients with intracranial stents. Then, a phantom study was carried out to evaluate the MR lumen visibility with these stents. Four stents [low-profile visualized intraluminal support (LVIS), Neuroform Atlas, Neuroform EZ, and Enterprise 2] were placed into plastic tubes with 3 mm inner diameter, and fixed in a container filled with agar. Time-of-flight MRA (TOF-MRA) was performed for these stents, and the signal intensities inside and outside the stents were measured on ImageJ software. Furthermore, 25%, 50%, and 75% stenosis models were created and passed through these stents to evaluate the diagnostic accuracy of in-stent stenosis. The signal intensity inside the LVIS stent was the highest among the four stents (P<0.001), and no significant difference was found between the signal intensities inside and outside the LVIS stent. The diagnostic accuracy with LVIS was also higher than that of Enterprise 2 (P<0.001). In conclusion, the visibility with LVIS indicates that TOF-MRA could be reliably utilized as a diagnostic tool for the detection of in-stent stenosis.

Improved visualization of superficial temporal artery using segmented time-of-flight MR angiography with venous suppression at 7T.

PURPOSE: To evaluate the quality of time-of-flight MR angiography (TOF-MRA) with venous suppression at 7T on imaging superficial temporal artery (STA). METHODS: A recently developed segmented TOF technique with reduced specific absorption rate (SAR) of venous suppression (VS) module was employed to achieve high-resolution arterial angiography without the contamination of venous signal. Images of segmented TOF with VS at 7T, TOF without VS at 7T, and TOF with VS at 3T were collected on 17 healthy volunteers. The number of STA branches and their local contrast achieved by the three methods were quantified and compared using paired t test. RESULTS: Segmented TOF with VS at 7T successfully suppressed venous signal without reducing the contrast of arterial angiography. The numbers of STA branches in 7T images were significantly higher than that in 3T images (5.79 vs. 4.50, p < 0.001). The contrast of 7T segmented TOF was significantly higher than 3T TOF (7.21 vs. 5.56, p = 0.006). CONCLUSION: Segmented TOF with VS at 7T displayed more branches of STA, while eliminating the signal of superficial temporal vein (STV). The improved visualization of STA will potentially facilitate the pre-operative assessment of STA in STA-MCA bypass surgery.

Diagnostic value of 3D time-of-flight magnetic resonance angiography for detecting intracranial aneurysm: a meta-analysis.

PURPOSE: This meta-analysis is to comprehensively evaluate the diagnostic performance of three-dimensional time-of-flight magnetic resonance angiography (3D-TOF-MRA) for detecting intracranial aneurysm (IA). METHODS: PubMed, Embase, Web of Science, and the Cochrane library were systematically searched for retrieving eligible studies. Study inclusion, data extraction, and risk of bias assessment were performed by two researchers independently. Pooled sensitivity (SEN), specificity (SPE), positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and area under the curve (AUC) were calculated to assess the diagnostic value. In addition, heterogeneity and subgroup analysis were carried out. RESULTS: In total, 18 studies comprising 3463 patients were selected. The results of 3D-TOF-MRA for diagnosing IA were SEN 0.89 (95% CI 0.82-0.94), SPE 0.94 (0.86-0.97), PLR 13.79 (5.92-32.12), NLR 0.11 (0.07-0.19), DOR 121.90 (38.81-382.94), and AUC 0.96 (0.94-0.98), respectively. In the subgroup analysis, studies without subarachnoid hemorrhage (SAH) tend to perform statistical significantly better (P < 0.05) in detecting IAs than studies with SAH 0.99 (0.98-1.00) vs. 0.89 (0.86-0.91). The diagnostic value of studies with a two-image reconstruction method was higher than studies with only one image reconstruction method: 0.99 (0.98-1.00) vs. 0.91 (0.89-0.94) with P < 0.05. The 3D-TOF-MRA had better SEN in aneurysms > 3 mm than the aneurysms ≤ 3 mm in diameter: 0.89 (0.87-0.92) vs. 0.78 (0.71-0.84) with P < 0.05. CONCLUSION: This study demonstrated that 3D-TOF-MRA has an excellent diagnostic performance for the overall assessment of IA and may serve as an alternative for further patient management with IA.

A comparison of basilar artery diameters measured by T2WI and TOF MR angiography.

PURPOSE: The purpose of our study is to compare basilar artery diameters (BAD) measured by T2WI to diameters measured by TOF MR angiography (MRA). By doing this, we hope to understand how compatible these two methodologies are with each other. METHODS: We used data from 100 patients (59 females, 41 males) who underwent a session of both T2W MRI and TOF MRA at the same time (ages between 18 and 83). We measured BAD by both T2WI and TOF MRA in three different levels. We then compared these diameters measured by two different methodologies to each other. RESULTS: In an area between the vertebrobasilar junction and posterior cerebral artery, all data measured by T2WI and TOF MRA in three different levels were analyzed. Average diameters measured by T2WI and TOF MRA turned out to be 79.5% correlated with each other. As a result of our mathematical model that we came up with through regression analysis, we calculated that measurements taken by T2WI on mid-pontine levels could predict TOF MRA measures with 78.3% accuracy. In T2WI and TOF MRA, average diameters measured were 2.982 ± 0.4717 and 3.205 ± 0.4281 mm, respectively. Statistical analyses showed that images measured by T2W series were significantly smaller than those measured by TOF MRA (p < 0.05). CONCLUSION: Our study showed that BAD measured by T2WI were smaller than those measured by TOF MRA. We think that it will be beneficial to refer our results to avoid T2WI and TOF MRA mismatch when evaluating BAD.

[Examination of Lower-extremity MRA Using Single-shot Balanced SSFP with Saturation Recovery].

Currently, non-contrast angiography using the balanced steady-state free precession (b-SSFP) method, which uses a short scan time imaging method, has been reported as an alternative to lower-extremity MRA's conventional method. We investigated a new imaging method using balanced SSFP. This method uses a sequence of spectral attenuated inversion recovery (SPAIR) pulse for fat suppression, selective saturation pre-pulse for imaging range of background signal suppression, and rest slab on the downstream side of the imaging range for vein signal suppression. In the examination, we changed dummy pulse (0, 5, 10), saturation delay time (150 ms, 225 ms, 300 ms), and acquisition time (200 ms, 250 ms, 300 ms). For physical evaluation, we used the ROI method and for visual evaluation, we used the Scheffe's method. CR was the best and the visual evaluation was also good 10 for dummy pulse, a saturation delay time of 150 ms, and an acquisition time of 200 ms. Balanced SSFP with saturation recovery has the potential to shorten scanning times. Balanced SSFP with saturation recovery is useful for lower-extremity MRA.

Multiband multislab 3D time-of-flight magnetic resonance angiography for reduced acquisition time and improved sensitivity.

PURPOSE: To explore the use of multiband (MB) imaging in multislab (MS) 3D time-of-flight-magnetic resonance angiography (TOF-MRA) and to improve acquisition time efficiency (TA), inflow contrast and sensitivity in vessel detection. THEORY AND METHODS: TOF-MRA is commonly used for imaging intracranial vessels. A MB-MS 3D-TOF-MRA sequence was implemented to excite and acquire multiple slabs simultaneously. Controlled aliasing in parallel imaging results in higher acceleration was used in addition to improve the quality of image reconstruction. Compared to a standard protocol which acquired three slabs in total the MB-MS protocol reduced the thickness by 3 while simultaneously acquiring data from 3 slabs. The total TA was also reduced by a factor 3. RESULTS: This technique maintains contrast-to-noise ratio while reducing TA, compared to standard single-band/MOTSA acquisitions, leading to an increase in CNR/TA of 1.65 compared to the standard protocol. Furthermore, the strong inflow contrast and increased magnetization transfer contrast caused by the MB excitation pulses improves the sharpness of the vessel borders which is reflected by a 5% higher full width at half maximum of the vessel size and a 17% higher slope of the vessel borders compared to the standard single-band acquisition. CONCLUSION: MB-MS 3D-TOF-MRA can appreciably accelerate image acquisition and combines the high spatial resolution of 3D imaging with the additional inflow contrast advantage of thinner slab acquisitions without introducing excessive noise arising from the MB reconstruction.

Non-Enhanced MR Imaging of Cerebral Arteriovenous Malformations at 7 Tesla.

OBJECTIVE: To evaluate prospectively 7 Tesla time-of-flight (TOF) magnetic resonance angiography (MRA) and 7 Tesla non-contrast-enhanced magnetization-prepared rapid acquisition gradient-echo (MPRAGE) for delineation of intracerebral arteriovenous malformations (AVMs) in comparison to 1.5 Tesla TOF MRA and digital subtraction angiography (DSA). METHODS: Twenty patients with single or multifocal AVMs were enrolled in this trial. The study protocol comprised 1.5 and 7 Tesla TOF MRA and 7 Tesla non-contrast-enhanced MPRAGE sequences. All patients underwent an additional four-vessel 3D DSA. Image analysis of the following five AVM features was performed individually by two radiologists on a five-point scale: nidus, feeder(s), draining vein(s), relationship to adjacent vessels, and overall image quality and presence of artefacts. RESULTS: A total of 21 intracerebral AVMs were detected. Both sequences at 7 Tesla were rated superior over 1.5 Tesla TOF MRA in the assessment of all considered AVM features. Image quality at 7 Tesla was comparable with DSA considering both sequences. Inter-observer accordance was good to excellent for the majority of ratings. CONCLUSION: This study demonstrates excellent image quality for depiction of intracerebral AVMs using non-contrast-enhanced 7 Tesla MRA, comparable with DSA. Assessment of untreated AVMs is a promising clinical application of ultra-high-field MRA. KEY POINTS: • Non-contrast-enhanced 7 Tesla MRA demonstrates excellent image quality for intracerebral AVM depiction. • Image quality at 7 Tesla was comparable with DSA considering both sequences. • Assessment of intracerebral AVMs is a promising clinical application of ultra-high-field MRA.

Microanatomy of the subcallosal artery: an in-vivo 7 T magnetic resonance angiography study.

OBJECTIVES: To investigate in-vivo microanatomy of the subcallosal artery branching from the anterior communicating artery (ACoA) using time-of-flight (TOF) magnetic resonance angiography (MRA) at 7 Tesla. METHODS: Seventy-five subjects, including 15 healthy volunteers and 60 patients, were included in this prospective study. Three raters characterized branches from ACoA in maximum intensity projections of TOF MRA at 7 Tesla acquired with 0.22 × 0.22 × 0.41 mm(3) resolution. Furthermore, course patterns and anatomical features of the subcallosal artery (maximum diameter, length, and branching angle from ACoA) were measured. RESULTS: Branches from the anterior communicating artery were visualized in 63 of 74 (85.1 %) subjects and were identified as the subcallosal artery (93.7 %) and the accessory anterior cerebral artery (6.3 %). The course of the subcallosal artery was classified into 3 groups; C-shaped (55.9 %), straight (16.9 %), and S-shaped (27.2 %). There was a significant difference between the branching angles of C-shaped and straight (p < 0.0001), between C-shaped and S-shaped (p < 0.0001), as well as between straight and S-shaped (p = 0.0113) course patterns. CONCLUSIONS: High-resolution in-vivo 7 T TOF MRA can delineate the microanatomy of the subcallosal artery. Three main variants of course patterns and branching angles from ACoA could be identified. KEY POINTS: • In-vivo 7 Tesla TOF MRA can delineate the subcallosal artery microanatomy • Three distinct course patterns of the subcallosal artery were identified • Branching angles from ACoA significantly differed between subcallosal artery course patterns.

The applied research of MRI with ASSET-EPI-FLAIR combined with 3D TOF MRA sequences in the assessment of patients with acute cerebral infarction.

Background To extend the time window for thrombolysis, reducing the time for diagnosis and detection of acute cerebral infarction seems to be warranted. Purpose To evaluate the feasibility of implementing an array spatial sensitivity technique (ASSET)-echo-planar imaging (EPI)-fluid attenuated inversion recovery (FLAIR) (AE-FLAIR) sequence into an acute cerebral infarction magnetic resonance (MR) evaluation protocol, and to assess the diagnostic value of AE-FLAIR combined with three-dimensional time-of-flight MR angiography (3D TOF MRA). Material and Methods A total of 100 patients (68 men, 32 women; age range, 44-82 years) with acute cerebral infarction, including 50 consecutive uncooperative and 50 cooperative patients, were evaluated with T1-weighted (T1W) imaging, T2-weighted (T2W) imaging, FLAIR, diffusion-weighted imaging (DWI), 3D TOF, EPI-FLAIR, and AE-FLAIR. Conventional FLAIR, EPI-FLAIR, and AE-FLAIR were assessed by two observers independently for image quality. The optimized group (AE-FLAIR and 3D TOF) and the control group (T1W imaging, T2W imaging, conventional FLAIR, DWI, and 3D TOF) were compared for evaluation time and diagnostic accuracy. Results One hundred and twenty-five lesions were detected and images having adequate diagnostic image quality were in 73% of conventional FLAIR, 62% of EPI-FLAIR, and 89% of AE-FLAIR. The detection time was 12 ± 1 min with 76% accuracy and 4 ± 0.5 min with 100% accuracy in the control and the optimized groups, respectively. Inter-observer agreements of κ = 0.78 and κ = 0.81 were for the optimized group and control group, respectively. Conclusion With reduced acquisition time and better image quality, AE-FLAIR combined with 3D TOF may be used as a rapid diagnosis tool in patients with acute cerebral infarction, especially in uncooperative patients.

Simultaneous imaging of radiation-induced cerebral microbleeds, arteries and veins, using a multiple gradient echo sequence at 7 Tesla.

BACKGROUND: The purpose of this study was to implement and evaluate the utility of a multi-echo sequence at 7 Tesla (T) for simultaneous time-of-flight (TOF) MR-angiography (MRA) and susceptibility-weighted imaging (SWI) of radiation-induced cerebral microbleeds (CMBs), intracranial arteries, and veins. METHODS: A four-echo gradient-echo sequence was implemented on a 7T scanner. The first echo was used to create TOF-MRA images, while the remaining echoes were combined to visualize CMBs and veins on SWI images. The sequence was evaluated on eight brain tumor patients with known radiation-induced CMBs. Single-echo images were also acquired to visually and quantitatively compare the contrast-to-noise ratio (CNR) of small- and intermediate-vessels between acquisitions. The number of CMBs detected with each acquisition was also quantified. Statistical significance was determined using a Wilcoxon signed-rank test. RESULTS: Compared with the single-echo sequences, the CNR of small and intermediate arteries increased 7.6% (P < 0.03) and 9.5% (P = 0.06), respectively, while the CNR of small and intermediate veins were not statistically different between sequences (P = 0.95 and P = 0.46, respectively). However, these differences were not discernible by visual inspection. Also the multi-echo sequence detected 18.3% more CMBs (P < 0.008) due to higher slice resolution. CONCLUSION: The proposed 7T multi-echo sequence depicts arteries, veins, and CMBs on a single image to facilitate quantitative evaluation of radiation-induced vascular injury.

The effectiveness of 3T time-of-flight magnetic resonance angiography for follow-up evaluations after the stent-assisted coil embolization of cerebral aneurysms.

BACKGROUND: Artifacts introduced by stents limit the value of magnetic resonance (MR) imaging as a follow-up modality after the stent-assisted coil embolization of cerebral aneurysms. PURPOSE: To investigate the usefulness of 3 Tesla (3T) time-of-flight (TOF) MR angiography (MRA) for the follow-up evaluation. MATERIAL AND METHODS: Twenty-two aneurysms of 20 patients treated with stent-assisted coil embolization were followed up with 3T TOF MRA and digital subtraction angiography (DSA) with three-dimensional rotational angiography (3DRA). The status of coiled aneurysms was compared with 3T TOF MRA and DSA with 3DRA in terms of complete occlusion, residual neck, and residual aneurysm. TOF MRA at 3T was performed 1 day before DSA with 3DRA, with a mean follow-up period of 20.1 ± 10.8 months. RESULTS: Twenty (90.9%) of 22 cases were concordant between the two modalities. The degree of agreement and correlation between them were high (κ=0.771, P<0.001; r=0.832 and P<0.001). When evaluating the status of residual neck, the sensitivity was 80% (4/5 cases); specificity was not available because there were no cases of complete occlusion. For the status of residual aneurysm, the sensitivity and specificity were 94.1% (16/17 cases) and 100% (all 5 cases), respectively. CONCLUSION: TOF MRA at 3T with source images could be useful as a non-invasive follow-up modality after the stent-assisted coil embolization of cerebral aneurysms. Further study with a larger patient sample is needed to confirm the effectiveness of 3T TOF MRA.

FFCM-MRF: An accurate and generalizable cerebrovascular segmentation pipeline for humans and rhesus monkeys based on TOF-MRA.

PURPOSE: Cerebrovascular segmentation and quantification of vascular morphological features in humans and rhesus monkeys are essential for prevention, diagnosis, and treatment of brain diseases. However, current automated whole-brain vessel segmentation methods are often not generalizable to independent datasets, limiting their usefulness in real-world environments with their heterogeneity in participants, scanners, and species. MATERIALS AND METHODS: In this study, we proposed an automated, accurate and generalizable segmentation method for magnetic resonance angiography images called FFCM-MRF. This method integrated fast fuzzy c-means clustering and Markov random field optimization by vessel shape priors and spatial constraints. We used a total of 123 human and 44 macaque MRA images scanned at 1.5 T, 3 T, and 7 T MRI from 9 datasets to develop and validate the method. RESULTS: FFCM-MRF achieved average Dice similarity coefficients ranging from 69.16 % to 89.63 % across multiple independent datasets, with improvements ranging from 3.24 % to 7.3 % compared to state-of-the-art methods. Quantitative analysis showed that FFCM-MRF can accurately segment major arteries in the Circle of Willis at the base of the brain and small distal pial arteries while effectively reducing noise. Test-retest analysis showed that the model yielded high vascular volume and diameter reliability. CONCLUSIONS: Our results have demonstrated that FFCM-MRF is highly accurate and reliable and largely independent of variations in field strength, scanner platforms, acquisition parameters, and species. The macaque MRA data and user-friendly open-source toolbox are freely available at OpenNeuro and GitHub to facilitate studies of imaging biomarkers for cerebrovascular and neurodegenerative diseases.

High Resolution TOF-MRA Using Compressed Sensing-based Deep Learning Image Reconstruction for the Visualization of Lenticulostriate Arteries: A Preliminary Study.

PURPOSE: To investigate the visibility of the lenticulostriate arteries (LSAs) in time-of-flight (TOF)-MR angiography (MRA) using compressed sensing (CS)-based deep learning (DL) image reconstruction by comparing its image quality with that obtained by the conventional CS algorithm. METHODS: Five healthy volunteers were included. High-resolution TOF-MRA images with the reduction (R)-factor of 1 were acquired as full-sampling data. Images with R-factors of 2, 4, and 6 were then reconstructed using CS-DL and conventional CS (the combination of CS and sensitivity conceding; CS-SENSE) reconstruction, respectively. In the quantitative assessment, the number of visible LSAs (identified by two radiologists), length of each depicted LSA (evaluated by one radiological technologist), and normalized mean squared error (NMSE) value were assessed. In the qualitative assessment, the overall image quality and the visibility of the peripheral LSA were visually evaluated by two radiologists. RESULTS: In the quantitative assessment of the DL-CS images, the number of visible LSAs was significantly higher than those obtained with CS-SENSE in the R-factors of 4 and 6 (Reader 1) and in the R-factor of 6 (Reader 2). The length of the depicted LSAs in the DL-CS images was significantly longer in the R-factor 6 compared to the CS-SENSE result. The NMSE value in CS-DL was significantly lower than in CS-SENSE for R-factors of 4 and 6. In the qualitative assessment of DL-CS images, the overall image quality was significantly higher than that obtained with CS-SENSE in the R-factors 4 and 6 (Reader 1) and in the R-factor 4 (Reader 2). The visibility of the peripheral LSA was significantly higher than that shown by CS-SENSE in all R-factors (Reader 1) and in the R-factors 2 and 4 (Reader 2). CONCLUSION: CS-DL reconstruction demonstrated preserved image quality for the depiction of LSAs compared to the conventional CS-SENSE when the R-factor is elevated.

Spiral time-of-flight magnetic resonance angiography for intracranial vascular imaging: performance compared to conventional Cartesian angiogram.

Background: Computed tomography angiography (CTA) and digital subtraction angiography (DSA) usually raise the risk of potential malignancies with cumulative radiation doses. Current time-of-flight magnetic resonance angiography (TOF-MRA) (dubbed as cTOF), which is based on Cartesian sampling mode, may show limited diagnostic conspicuity at sinuous or branching regions. It is also prone to relatively high false positive diagnoses and undesirable display of distal intracranial vessels. This study aimed to use spiral TOF-MRA (sTOF) as a noninvasive alternative to explore possible improvement, such that the application of magnetic resonance angiography (MRA) can be extended to facilitate clinical examination or cerebrovascular disease diagnosis and follow-up studies. Methods: Initially, 37 patients with symptoms of dizziness or transient ischemic attack were consecutively recruited for suspected intracranial vascular disease examination from Zhongshan Hospital of Xiamen University between July 2020 and April 2021 in this cross-sectional prospective study. After excluding 1 patient with severe scanning artifacts, 1 patient whose scanning scope did not meet the requirement, and 1 patient with confounding tumor lesions, a total of 34 participants were included according to the inclusion and exclusion criteria. Each participant underwent intracranial vascular imaging with both sTOF and cTOF sequences on a 3.0 T MR scanner with a conventional head-neck coil of 16 channels. Contrast CTA or DSA was also performed for 15 patients showing pathology. Qualitative comparisons in terms of image quality and diagnostic efficacy ratings, quantitative comparisons in terms of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), vessel length, and sharpness were evaluated. Pair-wise Wilcoxon test was performed to evaluate the imaging quality derived from cTOF and sTOF acquisitions and weighted Cohen's Kappa was conducted to assess the rating consistency between different physicians. Results: Compared to cTOF, sTOF showed better performance with fewer artifacts. It can effectively alleviate false positives of normal vessels being misdiagnosed as aneurysm or stenosis. Improved conspicuity was observed in cerebral distal regions with more clearly identifiable vasculature at finer scales. Quantitative comparisons in selected regions revealed significant improvement of sTOF in SNR (P<0.01 or P<0.001), CNR (P<0.001), vessel length (P<0.001), and sharpness (P<0.001) as compared to cTOF. Besides, sTOF can depict details of M1 and M2 segments of middle cerebral artery (MCA) at metallic implant region, showing its resistance to magnetic susceptibility. Conclusions: The sTOF shows higher imaging quality and lesion detectability with reduced artifacts and false positives, representing a potentially feasible surrogate in intracranial vascular imaging for future clinic routines.