Usefulness of Silent MR Angiography for Intracranial Aneurysms Treated with a Flow-Diverter Device

Predicting the O'Kelly-Marotta scale score after flow-diverter stent placement using silent MRA

PURPOSE

Flow-diverter (FD) stents were developed to treat aneurysms that are difficult to treat with conventional coiling or surgery. This study aimed to compare usefulness of Silent MRA and TOF (time of flight) -MRA in patients with aneurysms after FD placement.

MATERIALS AND METHODS

We retrospectively collected images from 22 patients with 23 internal carotid artery aneurysms treated with FD. Two radiologists conducted MRA and DSA experiments. In the first reading experiment, the radiologists evaluated the aneurysm filling by employing Silent MRA and TOF-MRA and utilizing the modified O'Kelly-Marotta (OKM) scale, a four-class classification system for aneurysms after FD placement. We then calculated the agreement between the modified OKM scale on MRA and the original OKM scale on DSA. In the second reading experiment, the radiologists rated blood flow within the FD using a five-point scale.

RESULTS

The weighted kappa value of the OKM scale between DSA and TOF-MRA was 0.436 (moderate agreement), and that between DSA and Silent MRA was 0.943 (almost perfect agreement). The accuracies for the four-class classification were 0.435 and 0.870 for TOF-MRA and Silent MRA, respectively. The mean score of blood flow within FD for TOF-MRA was 2.43 ± 0.90 and that for Silent MRA was 3.04 ± 1.02 (P < 0.001).

CONCLUSION

Silent MRA showed a higher degree of agreement than TOF-MRA in aneurysm filling with DSA. In addition, Silent MRA was significantly superior to TOF-MRA in depicting blood flow within the FD. Therefore, Silent MRA is clinically useful for the follow-up of patients after FD placement.

Treatment Outcome of Flow Diverter Device for Medium-Sized Cerebral Aneurysms: A Single-Center Report

Objective

Flow diverters (FDs), first introduced in Japan in 2015, were initially limited to wide-necked large cerebral aneurysms, which pose a high treatment risk. However, based on the results of the PREMIER study, the indications have expanded since 2020, and the number of treatment cases is increasing in Japan. At our hospital, FD placement with adjunctive coil embolization has been actively performed for medium-sized cerebral aneurysms, as indicated in the PREMIER study; herein, we report the outcomes of this treatment.

Methods

Of the 25 patients with 28 aneurysms who underwent FD placement at our institution between April 2022 and June 2023, 15 with 17 wide-necked unruptured cerebral aneurysms with a maximum diameter of <12 mm in the internal carotid artery (ICA) or vertebral artery (VA) were included. Postoperative complications were investigated in each case, and the aneurysm occlusion status was assessed using ultrashort echo time (UTE)-MRA at 3 months postoperatively and angiography at 6 months postoperatively. Fifteen patients who underwent coiling or stent-assisted coiling (SAC) for the same criteria during the same period were compared. Baseline characteristics and treatment results were compared between FD and coiling/SAC cases.

Results

Four males and 11 females with a mean age of 61.7 ± 12.8 years were included, and the median follow-up period was 9 months (6-18 months). There were 14 aneurysms of the ICA and 3 of the VA, and the mean maximum aneurysm diameter was 7.9 ± 1.7 mm. All patients were treated using the Pipeline Flex with Shield Technology (Medtronic, Minneapolis, MN, USA), and 14 aneurysms (82.4%) were treated with adjunctive coil embolization. There were no symptomatic strokes in the perioperative period; only one patient receiving corticosteroid therapy for thyroid eye disease had asymptomatic ICA occlusion at 3 months. Fifteen aneurysms (88.2%) were not visible on UTE-MRA at 3 months postoperatively, and angiography at 6 months showed complete occlusion in 16 (94.1%) aneurysms. The coiling/SAC group had a smaller neck size and higher volume embolization ratio than the FD group; however, complete occlusion was higher in the FD group.

Conclusion

FD placement with adjunctive coil embolization for medium-sized cerebral aneurysms is expected to result in good occlusion rates in the early postoperative period.

Image Follow-Up After Flow Diverter Treatment Using Only Ultra-High Resolution CT Angiography with Model-Based Iterative Reconstruction: A Case Report

Follow-up examinations using magnetic resonance imaging or digital subtraction angiography are mandatory after flow diverter treatment of cerebral aneurysms. However, flow diverter features metal artifacts on magnetic resonance imaging and ischemic complications with digital subtraction angiography. Ultra-high-resolution computed tomography systems have recently become available in clinical practice. The combined use of ultra-high-resolution computed tomography and a reconstruction technique called model-based iterative reconstruction is expected to replace follow-up magnetic resonance imaging and digital subtraction angiography of flow diverter placement. Here, we report a case of ultra-high-resolution computed tomography with model-based iterative reconstruction after flow diverter treatment.

Impact of Various Non-Contrast-Enhanced MRA Techniques on Lumen Visibility in Vascular Flow Models with a Surpass Evolve Flow Diverter

BACKGROUND

Silent MRA has shown promising results in evaluating the stents used for intracranial aneurysm treatment. A deep learning-based denoising and deranging algorithm was recently introduced by GE HealthCare. The purpose of this study was to compare the performance of several MRA techniques regarding lumen visibility in silicone models with flow diverter stents.

METHODS

Two Surpass Evolve stents of different sizes were implanted in two silicone tubes. The tubes were placed in separate boxes in the straight position and in two different curve configurations and connected to a pulsatile pump to construct a flow loop. Using a 3.0T MRI scanner, TOF and silent MRA images were acquired, and deep learning reconstruction was applied to the silent MRA dataset. The intraluminal signal intensity in the stent (SIin-stent), in the tube outside the stent (SIvessel), and of the background (SIbg) were measured for each scan.

RESULTS

The SIin-stent/SIbg and SIin-stent/SIv ratios were higher in the silent scans and DL-based reconstructions than in the TOF images. The stent tips created severe artefacts in the TOF images, which could not be observed in the silent scans.

CONCLUSIONS

Our study demonstrates that the DL reconstruction algorithm improves the quality of the silent MRA technique in evaluating the flow diverter stent patency.

Synthesizing 4D Magnetic Resonance Angiography From 3D Time-of-Flight Using Deep Learning: A Feasibility Study

Objective and background This study aimed to develop a deep convolutional neural network (DCNN) model capable of generating synthetic 4D magnetic resonance angiography (MRA) from 3D time-of-flight (TOF) images, allowing estimation of temporal changes in arterial flow. TOF MRA provides static information about arterial structures through maximum intensity projection (MIP) processing, but it does not capture the dynamic information of contrast agent circulation, which is lost during MIP processing. Considering the principles of TOF, it is hypothesized that dynamic information about arterial blood flow is latent within TOF signals. Although arterial spin labeling (ASL) can extract dynamic arterial information, ASL MRA has drawbacks, such as longer imaging times and lower spatial resolution than TOF MRA. This study's primary aim is to extend the utility of TOF MRA by training a machine-learning model on paired TOF and ASL data to extract latent dynamic information from TOF signals. Methods A DCNN combining a modified U-Net and a long-short-term memory (LSTM) network was trained on a dataset of 13 subjects (11 men and two women, aged 42-77 years) using paired 3D TOF MRA and 4D ASL MRA images. Subjects had no history of cerebral vessel occlusion or significant stenosis. The dataset was acquired using a 3T MRI system with a 32-channel head coil. Preprocessing involved resampling and intensity normalization of TOF and ASL images, followed by data augmentation and arterial mask generation. The model learned to extract flow information from TOF images and generate 8-phase 4D MRA images. The precision of flow estimation was evaluated using the coefficient of determination (R²) and Bland-Altman analysis. A board-certified neuroradiologist validated the quality of the images and the absence of significant stenosis in the major cerebral arteries. Results The generated 4D MRA images closely resembled the ground-truth ASL MRA data, with R² values of 0.92, 0.85, and 0.84 for the internal carotid artery (ICA), proximal middle cerebral artery (MCA), and distal MCA, respectively. Bland-Altman analysis revealed a systematic error of -0.06, with 95% agreement limits ranging from -0.18 to 0.12. Additionally, the model successfully identified flow abnormalities in a subject with left MCA stenosis, displaying a delayed peak and subsequent flattening distal to the stenosis, indicative of reduced blood flow. Visualization of the predicted arterial flow overlaid on the original TOF MRA images highlighted the spatial progression and dynamics of the flow. Conclusions The DCNN model effectively generated synthetic 4D MRA images from TOF images, demonstrating its potential to estimate temporal changes in arterial flow accurately. This non-invasive technique offers a promising alternative to conventional methods for visualizing and evaluating healthy and pathological flow dynamics. It has significant potential to improve the diagnosis and treatment of cerebrovascular diseases by providing detailed temporal flow information without the need for contrast agents or invasive procedures. The practical implementation of this model could enable the extraction of dynamic cerebral blood flow information from routine brain MRI examinations, contributing to the early diagnosis and management of cerebrovascular disorders.

Enhanced vessel wall magnetic resonance imaging in the follow-up of intracranial aneurysms treated with flow diversion

OBJECTIVE

This study aimed to compare the efficacy of enhanced 3D T1-weighted black-blood fast-spin-echo vessel wall magnetic resonance imaging (eVW-MRI) and time-of-flight magnetic resonance angiography (TOF MRA) for follow-up evaluation of aneurysms treated with flow diversion (FD).

METHODS

Our study enrolled 77 patients harboring 84 aneurysms treated with FD. Follow-up was by MRI (eVW-MRI and TOF MRA) and digital subtraction angiography (DSA). Two radiologists, blinded to DSA examination results, independently evaluated the images of aneurysm occlusion and parent artery patency using the Kamran-Byrne Scale. Interobserver diagnostic agreement and intermodality diagnostic agreement were acquired. Pretreatment and follow-up aneurysm wall enhancement (AWE) patterns were collected.

RESULTS

Based on the Kamran-Byrne Scale, the intermodality agreement between eVW-MRI and DSA was better than TOF MRA versus DSA for aneurysm remnant detection (weighted ĸ = 0.891 v. 0.553) and parent artery patency (ĸ = 0.950 v. 0.221). Even with the coil artifact, the consistency of eVW-MRI with DSA for aneurysm remnant detection was better than that of TOF MRA (weighted ĸ = 0.891 v. 0.511). The artifact of adjunctive coils might be more likely to affect the accuracy in evaluating parent artery patency with TOF MRA than with eVW-MRI (ĸ = 0.077 v. 0.788). The follow-up AWE patterns were not significantly associated with pretreatment AWE patterns and aneurysm occlusion.

CONCLUSIONS

The eVW-MRI outperforms TOF MRA as a reliable noninvasive and nonionizing radioactive imaging method for evaluating aneurysm remnants and parent artery patency after FD. The significance of enhancement patterns on eVW-MRI sequences needs more exploration.

CLINICAL RELEVANCE STATEMENT

The application of enhanced vessel wall magnetic resonance imaging has proven to be a promising tool to depict aneurysm remnant and parent artery stenosis in order to tailor the antiplatelet therapy strategy in patients after flow diversion.

KEY POINTS

• Enhanced vessel wall magnetic resonance imaging has an emerging role in depicting aneurysm remnant and parent artery patency after flow diversion. • With or without the artifact from adjunctive coils, enhanced vessel wall magnetic resonance imaging was better than TOF MRA in detecting aneurysm residual and parent artery stenosis by using DSA imaging as the standard. • Enhanced vessel wall magnetic resonance imaging holds potential to be used as an alternative to DSA for routine aneurysm follow-up after flow diversion.

Ultra-short Echo-time MR Angiography Combined with a Modified Signal Targeting Alternating Radio Frequency with Asymmetric Inversion Slabs Technique to Assess Visceral Artery Aneurysm after Coil Embolization

Contrast-enhanced CT and MR angiography are widely used for follow-up of visceral artery aneurysms after coil embolization. However, potential adverse reactions to contrast agents and image deterioration due to susceptibility artifacts from the coils are major drawbacks of these modalities. Herein, we introduced a novel non-contrast-enhanced MR angiography technique using ultra-short TE combined with a modified signal targeting alternating radio frequency with asymmetric inversion slabs, which could provide a serial hemodynamic vascular image with fewer susceptibility artifacts for follow-up after coil embolization.

Utility of follow-up ultra-high-resolution CT angiography with model-based iterative reconstruction after flow diverter treatment for cerebral aneurysms

PURPOSE

Follow-up examinations after flow diverter (FD) treatment for cerebral aneurysms typically involve magnetic resonance imaging (MRI) or digital subtraction angiography (DSA). However, MRI is prone to vascular defects due to metal artifacts from FD, and DSA carries a risk of ischemic complications. In the context of computed tomography angiography (CTA), this study compares the efficacy of ultra-high-resolution CT (UHRCT) and novel reconstruction techniques, such as model-based iterative reconstruction (MBIR), against conventional methods such as filtered back projection (FBP) and hybrid iterative reconstruction (IR), to determine if they are a viable alternative to DSA in clinical settings.

MATERIALS AND METHODS

A phantom study was conducted with the full-width half-maximum considered as the FD thickness. This study compared three reconstruction methods: MBIR, FBP, and hybrid IR. A clinical study was also conducted with 21 patients who underwent follow-up CTA after FD treatment. The FD's visibility was assessed using a 4-point scale in FBP, hybrid IR, and MBIR compared to cone-beam CT (CBCT) with angiographic systems.

RESULTS

In the phantom study, FBP, hybrid IR, and MBIR visualized thinner FD thicknesses and improved detail rendering in that order. MBIR proved to be significantly superior in both the phantom and clinical study.

CONCLUSION

UHRCT with MBIR is highly effective for follow-up evaluations after FD treatment and may become the first-choice modality in the future.

Evaluation of Intra-Aneurysmal Residual Blood Flow with the iMSDE T1-Black Blood Imaging after Flow Diverter Treatment

Objective

We aimed to evaluate the efficacy of the "improved motion-sensitized driven-equilibrium (iMSDE)"-prepared T1-weighted black blood (T1-BB) MRI for monitoring treatment effect with a flow diverter (FD) for cerebral aneurysms.

Methods

Following the exclusion of concomitant coiling and retreatment cases from 60 consecutive cases of cerebral aneurysms treated with FDs at our institution, 32 with imaging data were included in the analysis. Detectability of residual blood flow within the aneurysms was validated as follows: 1) comparison of MRI sequences (iMSDE-prepared T1-BB images, T1-weighted images [ T1WI], and time-of-flight [ TOF]-MRA) in cases of incompletely occluded aneurysms and 2) comparison of angiography and MRI sequences in the same period.

Results

1) The probability of diagnosing intra-aneurysmal blood flow was significantly higher with iMSDE-prepared T1-BB (iMSDE-prepared T1-BB vs. T1WI, p <0.001; iMSDE-prepared T1-BB vs. TOF-MRA, p <0.001). 2) The diagnostic accuracy of residual aneurysmal blood flow was significantly higher with iMSDE-prepared T1-BB than that with T1WI (p = 0.032). Furthermore, in cases of incomplete occlusion, the probability of detecting intra-aneurysmal blood flow was significantly higher with iMSDE-prepared T1-BB (iMSDE-prepared T1-BB vs. T1WI, p <0.001; iMSDE-prepared T1-BB vs. TOF-MRA, p = 0.023).

Conclusion

Our results demonstrated that iMSDE-prepared T1-BB could help distinguish between blood flow and thrombus within the aneurysms after FD treatment, especially in the early stages of FD treatment.

Diagnostic performance of silent magnetic resonance angiography for endovascularly-treated intracranial aneurysm follow-up: a prospective study

BACKGROUND

Multiple studies have reported the clinical usefulness of silent magnetic resonance angiography (MRA) in the follow-up of endovascularly-treated aneurysms. However, most previous studies were retrospective or with small sample sizes. The objective of this study was to prospectively evaluate the diagnostic performance of silent MRA in the follow-up of intracranial aneurysms treated by different interventional approaches.

METHODS

Patients with endovascularly-treated intracranial aneurysms and followed by silent MRA and digital subtraction angiography (DSA) were enrolled. The visualization of treated sites on silent MRA was rated on a 5-point scale. The aneurysm occlusion status was evaluated using the Raymond Scale and a simplified two-grade scale.

RESULTS

A total of 155 patients with 175 treated aneurysms were enrolled. The average score for the visualization of treated sites was 3.92±0.94, and 93.7% (164/175) had a score ≥3. In the subgroup analysis, except for the simple coiling group which had an obviously higher score (4.95±0.21), there was no significant difference among the stent-assisted coiling group (3.51±0.77), flow diversion group (3.74±0.80), and flow diversion with coiling group (3.40±1.17). Regarding aneurysm occlusion status, silent MRA and DSA were discordant for only one aneurysm using the Raymond Scale, and the inter-modality consistency was almost perfect (κ=0.992, 95% CI 0.977 to 1.000).

CONCLUSIONS

Silent MRA showed an excellent diagnostic performance in the follow-up of endovascularly-treated intracranial aneurysms, and may be an ideal option for repeated examinations.

Diagnostic Performance of High-Resolution Vessel Wall MR Imaging Combined with TOF-MRA in the Follow-up of Intracranial Vertebrobasilar Dissecting Aneurysms after Reconstructive Endovascular Treatment

BACKGROUND AND PURPOSE

Few studies have reported the utility of high-resolution vessel wall MR imaging in the follow-up of endovascularly treated vertebrobasilar dissecting aneurysms. This study aimed to evaluate the diagnostic performance of high-resolution vessel wall MR imaging combined with TOF-MRA in the follow-up of intracranial vertebrobasilar dissecting aneurysms after reconstructive endovascular treatment.

MATERIALS AND METHODS

Patients with intracranial vertebrobasilar dissecting aneurysms with reconstructive endovascular treatment and followed up with TOF-MRA, high-resolution vessel wall MR imaging, and DSA were included. With DSA as the criterion standard, the diagnostic performance of TOF-MRA, high-resolution vessel wall MR imaging, and high-resolution vessel wall MR imaging combined with TOF-MRA in the evaluation of aneurysm occlusion status and parent artery patency was assessed. Visualization of the stented artery on TOF-MRA and high-resolution vessel wall MR imaging was rated on a 5-point scale.

RESULTS

Twenty-seven patients with 29 aneurysms were included. The sensitivity, specificity, positive predictive value, and negative predictive value of TOF-MRA, high-resolution vessel wall MR imaging, and high-resolution vessel wall MR imaging combined with TOF-MRA for diagnosing aneurysm remnants were 80.0%, 100.0%, 100.0%, and 82.4%; 53.3%, 100.0%, 100.0%, and 66.7%; and 93.3%, 100.0%, 100.0%, and 93.3%, respectively. For the visualization of the stented artery, the mean score of high-resolution vessel wall MR imaging was significantly higher than that of TOF-MRA (4.88 [SD, 0.32] versus 2.53 [SD, 1.25], P < .001). In the evaluation of parent artery patency (normal or pathologic), whereas TOF-MRA had a sensitivity, specificity, positive predictive value, and negative predictive value of 100.0%, 8.0%, 14.8%, and 100.0%, respectively, high-resolution vessel wall MR imaging was completely consistent with the DSA.

CONCLUSIONS

High-resolution vessel wall MR imaging combined with TOF-MRA at 3T showed good diagnostic performance in the follow-up of intracranial vertebrobasilar dissecting aneurysms after reconstructive endovascular treatment.

Safety and efficacy of pipeline embolization device treatments for intradural internal carotid artery aneurysms in a single center in a Japanese population

Background:

The pipeline embolization device (PED) is the most common flow diverter device in the world. To date, there have been no reports of treatment outcomes specific to intradural internal carotid artery (ICA) aneurysms. The safety and efficacy of the PED treatments for intradural ICA aneurysms are reported.

Methods:

131 patients with 133 aneurysms underwent PED treatments for intradural ICA aneurysms. The mean aneurysm dome size and neck length were 12.7 ± 4.3 mm and 6.1 ± 2.2 mm, respectively. We used adjunctive endosaccular coil embolization for 88 aneurysms (66.2%). A total of 113 aneurysms (85%) were angiographically followed up 6 months following the procedure, and 93 aneurysms (69.9%) were followed up for 1 year.

Results:

The angiographic outcome at 6 months showed that 94 (83.2%) aneurysms had O’Kelly-Marotta (OKM) grade D, 6 (5.3%) had C, 10 (8.8%) had B, and 3 (2.7%) had A. At 1 year, 82 (88.2%) aneurysms had OKM grade D, 6 (6.5%) had C, 3 (3.2%) had B, and 2 (2.2%) had A. Multivariate analysis showed that aneurysm neck size and adjunctive coiling were statistically significant in aneurysm occlusion status. Major morbidity modified Rankin Scale >2 and mortality rates related to procedures were 3.0% and 0%, respectively. Delayed aneurysm ruptures were not observed.

Conclusion:

These results reveal that PED treatment of intradural ICA aneurysms is safe and efficacious. The combined use of adjunctive coil embolization not only prevents delayed aneurysm ruptures but also contributes to an increase in the rate of complete occlusion.

Ultrashort Echo Time Magnetic Resonance Angiography as an Alternative Tool to Digital Subtraction Angiography in the Follow-up of Stent-Assisted Coil Embolization Outcomes

BACKGROUND

Follow-up of aneurysms treated with stent-assisted coil embolization has been performed using digital subtraction angiography (DSA) because in time-of-flight magnetic resonance angiography, metal artifacts from the stent often affect visualization.

OBJECTIVE

To confirm whether ultrashort echo time (TE) MRA may be an alternative for DSA during follow-up.

METHODS

Patients with unruptured aneurysms initially treated with stent-assisted coil embolization between April 2019 and March 2021 were enrolled. After 3 months of treatment, follow-up DSA and ultrashort TE MRA were performed. All images were independently reviewed by neurosurgeons to evaluate in-stent flow and rated from 1 (not visible) to 4 (excellent). Aneurysmal embolization status was assessed as complete obliteration, residual neck, or residual aneurysm. Ultrashort TE MRA findings were classified as evaluative or nonevaluative state based on the presence of metal artifacts. We investigated the types of aneurysms that were evaluative and the agreement between ultrashort TE and DSA.

RESULTS

Overall, 89 aneurysms were examined, of which 74% (n = 66) were classified as evaluative on ultrashort TE. Significant differences were observed in size and stent type. Evaluative cases had an aneurysm size of <7 mm ( P = .0007) and a higher rate of Neuroform Atlas ( P = .0006). The rate of agreement between ultrashort TE with evaluative state and DSA was 95%.

CONCLUSION

Ultrashort TE MRA could evaluate an embolization status treated with stenting, and the findings are in excellent agreement with those of DSA. Aneurysms measuring <7 mm and treated with Neuroform Atlas are evaluative on ultrashort TE, and DSA might not be necessary.

Non-invasive angiographic analysis of dural carotid cavernous fistula using time-of-flight MR angiography and silent MR angiography: a comparative study

BACKGROUND

A non-invasive, reliable imaging modality that characterizes cavernous sinus dural arteriovenous fistula (CSDAVF) is beneficial for diagnosis and to assess resolution on follow-up.

PURPOSE

To assess the utility of 3D time-of-flight (TOF) and silent magnetic resonance angiography (MRA) for evaluation of CSDAVF from an endovascular perspective.

MATERIAL AND METHODS

This prospective study included 37 patients with CSDAVF, who were subjected to digital subtraction angiography (DSA) and 3-T MR imaging with 3D TOF and silent MRA. The main arterial feeders, fistula site, and venous drainage pattern were evaluated, and the results were compared with DSA findings. The diagnostic confidence scores were also recorded using a 4-point Likert scale.

RESULTS

Silent MRA correlated better for shunt site localization and angiographic classification (86% vs. 75% and 83% vs. 75%, respectively) compared to TOF MRA. The proportion of arterial feeders detected was marginally significant for silent MRA over TOF MRA sequences (92.8% vs. 89.5%; P=0.048), though for veins both were comparable. Sensitivity of silent MRA was higher for identification of cortical venous reflux (CVR) (90.9% vs. 81.8%) and deep venous drainage (82.4% vs. 64.7%), while specificity was >90% for both modalities. The overall diagnostic confidence score fared better for silent MRA for venous assessment (P < 0.001) as well as fistula point identification (P < 0.001), while no significant difference was evident with TOF MRA for arterial feeders (P=0.06).

CONCLUSION

Various angiographic components of CSDAVF could be identified and delineated by 3D TOF and silent MRA, though silent MRA was superior for overall diagnostic assessment.

Usefulness of Pointwise Encoding Time Reduction with Radial Acquisition-Magnetic Resonance Angiography after Endovascular Treatment for Intracranial Aneurysms

PURPOSE

Imaging follow-up after endovascular treatment is important; however, time-of-flight magnetic resonance angiography (TOF-MRA) has limitations associated with magnetic susceptibility and radiofrequency shielding caused by the stent and coils. We evaluated the diagnostic performance of pointwise encoding time reduction with radial acquisition (PETRA)-MRA after endovascular treatment for intracranial aneurysms.

MATERIAL AND METHODS

A total of 186 patients with 211 aneurysms who underwent both pointwise encoding time reduction with radial acquisition- and time-of-flight magnetic resonance angiography in the same imaging session for follow-up after endovascular treatment. We subjectively graded the overall image quality, visualization of treated sites, and occlusion status.

RESULTS

Although the overall image quality scores of pointwise encoding time reduction with radial acquisition-magnetic resonance angiography were significantly lower than those of time-of-flight magnetic resonance angiography for both observers (4.04 ± 0.81 vs. 4.85 ± 0.35 [observer 1], 4.60 ± 0.69 vs. 4.94 ± 0.24 [observer 2]) (both P < .001), the visibility of treated sites using pointwise encoding time reduction with radial acquisition-magnetic resonance angiography was significantly better than that of time-of-flight magnetic resonance angiography overall (4.27 ± 0.97 vs. 3.42 ± 1.01; P < .001), in the distal internal carotid artery (4.46 ± 0.79 vs. 3.40 ± 1.00; P < .001), and in the middle cerebral artery (4.19 ± 0.93 vs. 3.08 ± 0.53, P = 0.007). Pointwise encoding time reduction with radial acquisition-magnetic resonance angiography showed a higher area under the curve than time-of-flight magnetic resonance angiography for the evaluation of treated aneurysm occlusion, except for posterior circulation aneurysms.

CONCLUSIONS

Pointwise encoding time reduction with radial acquisition-magnetic resonance angiography showed better visualization of treated sites and better diagnostic performance than time-of-flight magnetic resonance angiography for anterior circulation aneurysms. However, Pointwise encoding time reduction with radial acquisition-magnetic resonance angiography showed limitations in the follow-up evaluation of posterior circulation aneurysms.

Endovascular treatment of challenging aneurysms with FRED Jr flow diverter stents: a single-center experience

PURPOSE

To analyze clinical safety and efficacy of flow re-direction endoluminal device (FRED) Jr flow diverter for treatment of unruptured, ruptured, or recanalyzed aneurysms.

MATERIALS AND METHODS

Between October 2019 and February 2022, 25 patients with 31 aneurysms treated with FRED Jr were included in the study. Clinical and radiological records, procedural details, and follow-up outcomes were retrospectively evaluated. Eighteen (72%) patients were female. Median age was 48.8 (age range 9-85). Mean follow-up was 21 months (6-28 months). Location of the aneurysms were as follows; 13 in middle cerebral artery (MCA), 7 in anterior cerebral artery (ACA), 4 in posterior cerebral artery (PCA), 3 in true posterior communicating artery (PCom), 2 in anterior communicating artery (ACom), 1 in superior cerebellar artery (SCA), 1 in true ophthalmic artery. Five patients (20%) presented with acute subarachnoid hemorrhage (aSAH).

RESULTS

In all procedures, FRED Jr was successfully deployed. Three true Pcom aneurysms and a true ophthalmic aneurysm were treated with FRED Jr. Three patients with two adjacent aneurysms were treated with a single FRED Jr. In two (8%) patients in-stent thrombosis occurred intraoperatively, they were treated with iv tirofiban and thrombectomy without any sequelae. Post-discharge 2 weeks later, intraparenchymal hemorrhage occurred in a patient. He was treated with surgical drainage, the clinical course was modified Rankin score (mRS) 2. Digital subtraction angiography (DSA) was performed on 16 (64%) patients with 21 (67%) aneurysms. Near complete-complete occlusion (O'Kelly-Morata grading scale (OKM C-D) was documented in 15/16 (93.7%) patients, 20/21 (95.2%) aneurysms. In nine (36%) patients, no residual filling was observed in the magnetic resonance angiography (MRA). Good clinical outcome (mRS 0-1) was achieved in 24/25 (96%) of patients.

CONCLUSION

Endovascular treatment of small cerebral aneurysms with FRED Jr is safe and effective even in complex and challenging morphologies allowing high rates of aneurysm occlusion with low periprocedural complications. Our cohort, consisting of a rate 20% acute ruptured aneurysms, is the major additive data to the published literature.

Non-contrast enhanced silent MR angiography to evaluate hemodynamics and morphology of unruptured intracranial aneurysms: a comparative computational fluid dynamics study

BACKGROUND

Silent MR angiography (silent MRA) is a new generation of non-contrast enhanced angiography with outstanding advantages in visualizing cerebrovascular lesions and the follow-up after endovascular treatment for intracranial aneurysms (IAs). This study aims to investigate the reliability of silent MRA-based three-dimensional (3D) geometric description and hemodynamic calculation of IAs.

METHODS

19 patients with 23 unruptured IAs, who underwent both silent MRA and 3D rotational angiography (3DRA), were included in this study. Computational fluid dynamics simulations were performed on all patient-specific 3D reconstruction images to compare the morphology and hemodynamics of the two different imaging models for IAs.

RESULTS

Silent MRA models had smaller maximum and perpendicular height (mm), aneurysmal surface area (mm²), and aneurysmal volume (mm³) than 3DRA (p<0.05); the differences of the above parameters between the two models were 9.0±6.2%, 7.7±7.4%, 15.9±13.0%, and 21.4±17.5%, respectively. However, correlation analysis of morphological parameters in various dimensions and model comparison showed good overall consistency in geometrical characteristics between the two models. Moderate coherence was observed between models in time-averaged wall shear stress of aneurysm and parent vessel (TAWSS, PAWSS), aneurysm velocity (AV), parent vessel velocity, and oscillatory shear index (OSI). However, strong correlations were observed among normalized aneurysm wall shear stress (NWSS), low shear area (LSA), inflow concentration index (ICI), and normalized aneurysm velocity (NAV).

CONCLUSION

Both morphological and hemodynamic assessments of IAs for silent MRA are comparable to 3DRA. Additionally, normalized indicators such as NWSS, LSA, ICI, and NAV were better than TAWSS, AV, and OSI in silent MRA-related hemodynamic evaluation.

Differential Subsampling with Cartesian Ordering-MRA for Classifying Residual Treated Aneurysms

BACKGROUND AND PURPOSE

Differential Subsampling with Cartesian Ordering (DISCO), an ultrafast high-spatial-resolution head MRA, has been introduced. We aimed to determine the diagnostic performance of DISCO-MRA in grading residual aneurysm in comparison with TOF-MRA in patients with treated intracranial aneurysms.

MATERIALS AND METHODS

Patients with endovascular treatment and having undergone DISCO-MRA, TOF-MRA, and DSA were included for review. The voxel size and acquisition time were 0.75 × 0.75 × 1 mm³/6 seconds for DISCO-MRA and 0.6 × 0.6 × 1 mm³/6 minutes for TOF-MRA. Residual aneurysms were determined using the Modified Raymond-Roy Classification on TOF-MRA and DISCO-MRA by 2 neuroradiologists independently and were compared against DSA as the reference standard. Statistical analysis was performed using the κ statistic and the χ² test.

RESULTS

Sixty-eight treated intracranial aneurysms were included. The intermodality agreement was κ = 0.82 (95% CI, 0.67-0.97) between DISCO and DSA and 0.44 (95% CI, 0.28-0.61) between TOF and DSA. Modified Raymond-Roy Classification scores matched DSA scores in 60/68 cases (88%; χ² = 144.4, P < .001 for DISCO and 46/68 cases (68%; χ² = 65.0, P < .001) for TOF. The diagnostic accuracy for the detection of aneurysm remnants was higher for DISCO (0.96; 95% CI, 0.88-0.99) than for TOF (0.79; 95% CI, 0.68-0.88).

CONCLUSIONS

In patients with endovascularly treated intracranial aneurysms, DISCO-MRA provides superior diagnostic performance in comparison with TOF-MRA in delineating residual aneurysms in a fraction of the time.

Long-term outcomes of Y-stent-assisted coil embolization using Low-profile Visualized Intraluminal Support Junior (LVIS Jr) for intracranial bifurcation aneurysms

OBJECTIVE

Y-stent-assisted coil embolization is indicated for the treatment of complex intracranial bifurcation aneurysms. However, the long-term outcomes associated with this technique remain unclear. The purpose of this study was to evaluate the long-term outcomes of Y-stent-assisted coil embolization using the Low-profile Visualized Intraluminal Support Junior (LVIS Jr) device.

METHODS

We retrospectively reviewed our databases to identify patients treated with Y-stent-assisted coiling using LVIS Jr. Digital subtraction angiography, silent magnetic resonance angiography (MRA), and time-of-flight MRA were performed at 1 year after the procedure. Patients also received an annual follow-up using MRA. Aneurysm occlusion status was classified into complete occlusion (CO), neck remnant (NR), and body filling (BF). Clinical outcomes were assessed using the modified Rankin Scale.

RESULTS

Twenty-one patients (22 aneurysms) were included in this study. All procedures were performed successfully. Immediate postprocedural angiograms showed CO in 13 aneurysms (59.1%), NR in two aneurysms (9.1%), and BF in seven aneurysms (31.8%). One-year follow-up angiograms revealed CO in 86.4% of patients. Only one patient had a major recurrence and required retreatment. The mean follow-up duration was 43.5 months. The last angiographic studies demonstrated CO in 18 aneurysms (81.8%), NR in three aneurysms (13.6%), and BF in one aneurysm (4.5%). Periprocedural and delayed complications occurred in two patients and one patient, respectively. There was no permanent morbidity or death. The modified Rankin Scale scores at last clinical follow-up were equal to those before the procedures in all patients.

CONCLUSION

Y-stent-assisted coil embolization using LVIS Jr for intracranial bifurcation aneurysms has favorable long-term angiographic and clinical outcomes.

Non-contrast-enhanced silent magnetic resonance angiography for assessing cerebral aneurysms after PulseRider treatment

Purpose

Conventional time-of-flight (TOF) magnetic resonance angiography (MRA) failed to depict clear visualization of coiled cerebral aneurysms with PulseRider due to metal-induced susceptibility artifacts. Our aim was to overcome the metal artifact using a novel imaging technique of non-contrast-enhanced ultrashort echo-time magnetic resonance angiography (UTE-MRA).

Materials and methods

Five unruptured intracranial aneurysms were treated using PulseRider and the patients underwent silent MRA (UTE-MRA). The images were compared with TOF-MRA and digital subtraction angiography (DSA).

Results

Silent MRA can visualize the residual cavity of the coiled aneurysms, which was not well visualized and rather defective when using TOF-MRA. While a segment of the proximal marker composed of stainless steel was poorly visualized, the other parts of the parent artery and the arteries of bifurcation, including the aneurysmal neck, were clearly visualized, equivalent to that of DSA.

Conclusions

UTE-MRA achieves better visualization of cerebral aneurysms after PulseRider treatment than TOF-MRA.

Magnetic Resonance Angiography after Flow Diversion: The use of complementary MRA techniques to monitor aneurysm occlusion as well as device and arterial branch patency after flow diverter placement

BACKGROUND

Few studies have been performed to evaluate flow diversion with MRA. They have shown better success for MRA to assess the aneurysm response but limited success for the stent patency. Further, the patency of arterial branches on MRA remains to be explored.

METHODS

31 consecutive cases of carotid aneurysms treated with flow diversion were retrospectively evaluated with noncontrast time of flight (TOF), contrast enhanced TOF (CTOF) and cine MRA (TWIST) independently by two investigators for aneurysm occlusion, stent patency and arterial branch patency. DSA served as the gold standard technique.

RESULTS

There were 6 males and 25 females in the age range of years (mean ±SD). Stent patency, aneurysm occlusion and branch patency, mostly revealed substantial to perfect interobserver agreement (k >0.60). The sensitivity, specificity, positive and negative predictive values for the stent patency on source images of TOF were 0.99,0.84, 0.42 and 0.99 and on CTOF were 0.99, 0.89, 0.50 and 0.99 respectively.Sensitivity for the aneurysm response on the three MRAs ranged from 0.88 to 0.93,specificity from 0.64 to 0.75, positive predictive value from 0.69 to 0.79 and negative predictive value from 0.86 to 0.90. Sensitivity for the arterial branch patency among the three MRAs, ranged from 0.55 to 0.93, specificity from 0.61 to 0.68, positive predictive value from 0.79 to 0.93 and negative predictive value from 0.22 to 0.90.

CONCLUSIONS

Aneurysm occlusion, stent patency and arterial branch patency in flow diversion can be successfully evaluated with the combination of three MRA techniques.

Follow-up of Intracranial Aneurysms Treated by Flow Diverters: Evaluation of Parent Artery Patency Using 3D-T1 Gradient Recalled-Echo Imaging with 2-Point Dixon in Combination with 3D-TOF-MRA with Compressed Sensing

BACKGROUND AND PURPOSE

MRA assessment of parent artery patency after flow-diverter placement is complicated by imaging artifacts produced by these devices. The purpose of this study was to assess the accuracy of liver acquisition with volume acceleration-flex technique (LAVA-Flex) MRA in combination with 3D-TOF with HyperSense MRA for the evaluation of parent vessel status after intracranial flow-diverter placement.

MATERIALS AND METHODS

Fifty-six patients treated by flow diversion and followed with both DSA and 3T MRA between November 2020 and August 2021 were included. All patients were evaluated for parent artery patency using the same imaging protocol (DSA, noncontrast MRA including 3D-TOF with HyperSense and LAVA-Flex, and contrast-enhanced MRA, including time-resolved imaging of contrast kinetics MRA and delayed contrast-enhanced MRA).

RESULTS

With DSA as a criterion standard to evaluate the patency of the parent vessel, noncontrast MRA had a good specificity (0.83) and positive predictive value (0.65), better than contrast-enhanced MRA (0.55 and 0.41, respectively). Both had excellent sensitivity and negative predictive value: noncontrast MRA, 0.93 and 0.97, respectively; contrast-enhanced MRA, 0.93 and 0.96, respectively. Specificity and positive predictive value tended to be lower for patients treated with additional devices than for those treated with flow diverters exclusively and for patients treated with a specific type of flow diverter.

CONCLUSIONS

Noncontrast MRA can be used for noninvasive follow-up of intracranial aneurysms treated by flow diverters. The combined use of LAVA-Flex and 3D-TOF with HyperSense sequences allows monitoring the status of the parent artery and aneurysm occlusion.

A comparison between the CS-TOF and the CTA/DSA for WEB device management

PURPOSE

There is no study on the role of three-dimensional compressed sensing time of flight MR angiography (3D-CS-TOF) in the management of the WEB device. We evaluated the efficacy of 3-tesla 3D-CS-TOF for the management and follow-up of the WEB device implantations.

MATERIALS AND METHODS

Seventy-three aneurysms of 69 patients treated with the WEB device were retrospectively examined. Morphological parameters and embolization results of the aneurysms were assessed and compared on 3D-CS-TOF, CTA, and DSA images.

RESULTS

Occluded, neck remnant, and recurrent aneurysms were observed in 61 (83.6%), 7 (9.6%), and 5 (6.8%) aneurysms, respectively. Inter- and intra-reader agreement values related to aneurysm size measurements were perfect. Aneurysms size, age, and proximal vessel tortuosity were negatively correlated with the visibility of the aneurysms and parent vessels on 3D-CS-TOF images (p = 0.043; p = 0.032; p < 0.001, respectively). Subarachnoid hemorrhage and age are associated with 3D-CS-TOF artifacts (p = 0.031; p = 0.005, respectively). 3D-CS-TOF findings are in perfect agreement with DSA or CT angiography (CTA) results (p < 0.001).

CONCLUSION

According to our results, 3D-CS-TOF can be an easy, fast, and reliable alternative for the management or follow-up of WEB assisted embolization.

Usefulness of Silent MRA for Evaluation of Aneurysm after Stent-Assisted Coil Embolization

OBJECTIVE

To determine the usefulness of Silent MR angiography (MRA) for evaluating intracranial aneurysms treated with stent-assisted coil embolization.

MATERIALS AND METHODS

Ninety-nine patients (101 aneurysms) treated with stent-assisted coil embolization (Neuroform atlas, 71 cases; Enterprise, 17; LVIS Jr, 9; and Solitaire AB, 4 cases) underwent time-of-flight (TOF) MRA and Silent MRA in the same session using a 3T MRI system within 24 hours of embolization. Two radiologists independently interpreted both MRA images retrospectively and rated the image quality using a 5-point Likert scale. The image quality and diagnostic accuracy of the two modalities in the detection of aneurysm occlusion were further compared based on the stent design and the site of aneurysm.

RESULTS

The average image quality scores of the Silent MRA and TOF MRA were 4.38 ± 0.83 and 2.78 ± 1.04, respectively (p < 0.001), with an almost perfect interobserver agreement. Silent MRA had a significantly higher image quality score than TOF MRA at the distal internal carotid artery (n = 57, 4.25 ± 0.91 vs. 3.05 ± 1.16, p < 0.001), middle cerebral artery (n = 21, 4.57 ± 0.75 vs. 2.19 ± 0.68, p < 0.001), anterior cerebral artery (n = 13, 4.54 ± 0.66 vs. 2.46 ± 0.66, p < 0.001), and posterior circulation artery (n = 10, 4.50 ± 0.71 vs. 2.90 ± 0.74, p = 0.013). Silent MRA had superior image quality score to TOF MRA in the stented arteries when using Neuroform atlas (4.66 ± 0.53 vs. 3.21 ± 0.84, p < 0.001), Enterprise (3.29 ± 1.59 vs. 1.59 ± 0.51, p = 0.003), LVIS Jr (4.33 ± 1.89 vs. 1.89 ± 0.78, p = 0.033), and Solitaire AB stents (4.00 ± 2.25 vs. 2.25 ± 0.96, p = 0.356). The interpretation of the status of aneurysm occlusion exhibited significantly higher sensitivity with Silent MRA than with TOF MRA when using the Neuroform Atlas stent (96.4% vs. 14.3%, respectively, p < 0.001) and LVIS Jr stent (100% vs. 20%, respectively, p = 0.046).

CONCLUSION

Silent MRA can be useful to evaluate aneurysms treated with stent-assisted coil embolization, regardless of the aneurysm location and type of stent used.

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.

Intensity of arterial structure acquired by Silent MRA estimates cerebral blood flow

BACKGROUND

Cerebral blood flow (CBF) and the morphology of the cerebral arteries are important for characterizing cerebrovascular disease. Silent magnetic resonance angiography (Silent MRA) is a MRA technique focusing on arterial structural delineation. This study was conducted to investigate the correlation between Silent MRA and CBF quantification, which has not yet been reported.

METHODS

Both the Silent MRA and time-of-flight magnetic resonance angiography scans were applied in seventeen healthy participants to acquire the arterial structure and to find arterial intensities. Phase-contrast MRA (PC-MRA) was then used to perform the quantitative CBF measurement of 13 cerebral arteries. Due to different dataset baseline signal level of Silent MRA, the signal intensities of the selected 13 cerebral arteries were normalized to the selected ROIs of bilateral internal carotid arteries. The normalized signal intensities were used to determine the relationship between Silent MRA and CBF.

RESULTS

The image intensity distribution of arterial regions generated by Silent MRA showed similar laminar shape as the phase distribution by PC-MRA (correlation coefficient > 0.62). Moreover, in both the results of individual and group-leveled analysis, the intensity value of arterial regions by Silent MRA showed positively correlation with the CBF by PC-MRA. The coefficient of determination (R²) of individual trends ranged from 0.242 to 0.956, and the R² of group-leveled result was 0.550.

CONCLUSIONS

This study demonstrates that Silent MRA provides valuable CBF information despite arterial structure, rendering it a potential tool for screening for cerebrovascular disease.

Ultra-short Echo-time MR Angiography Combined with a Subtraction Method to Assess Intracranial Aneurysms Treated with a Flow-diverter Device

A flow-diverter (FD) device is a well-established tool for the treatment of unruptured intracranial aneurysms. Time-of-flight (TOF) MR angiography (MRA) is widely used for postoperative assessment after the treatment with FD; however, it cannot fully visualize intra-aneurysmal and intrastent flow signals due to the magnetic susceptibility from the FD. Recently, the utility of MRA with ultra-short TE (UTE) sequence and arterial spin labeling technique in assessing the therapeutic efficacy of intracranial aneurysms treated with metallic devices has been reported, but long image acquisition time is one of the drawbacks of this method. Herein, we introduce a novel UTE MRA using the subtraction method that enables the reduction in susceptibility artifacts with a short image acquisition time.

Long-term Follow-up Results after Flow Diverter Therapy Using the Pipeline Embolization Device for Large or Giant Unruptured Internal Carotid Artery Aneurysms: Single-center Retrospective Analysis in the Japanese Population

Flow diverter (FD) therapy using Pipeline embolization device (PED) has become an important alternative to treat internal carotid artery (ICA) aneurysms. Herein, we report the long-term outcome for 3 years after FD therapy using PED for ICA aneurysms in Japan. The patients who underwent angiographical and/or clinical follow-up for 3 years after the FD therapy using PED of large or giant unruptured ICA aneurysms from December 2012 at our university hospital are the subjects of this study. We retrospectively reviewed the in- and outpatients’ medical charts, and written operative and radiological records. There were 84 patients with 90 aneurysms who could be clinically and/or angiographically followed up for 3 years. Of these, 7 aneurysms were only available for clinical follow-up. Of the remaining 83 aneurysms, 6 aneurysms had vessel occlusion due to stent thrombosis or parent artery occlusion, and 60 of the remaining 77 (77.9%) had complete occlusion. In multivariate analysis, older age (>70 years), wide neck, and non-adjunctive coiling contributed statistically significantly to incomplete occlusion. Of the 84 patients, 2 patients (2.4%) had delayed complications between 6 months and 3 years after the initial FD placement. Three patients (3.6%) had poor outcome due to postoperative major stroke complications, 2 of which were acute complications. The long-term results after FD therapy are good both angiographically and clinically. Endothelialization of the aneurysmal neck and intra-aneurysmal thrombosis contribute to complete occlusion. The primary reason for the somewhat low complete occlusion in Japan may be the patients are generally older.

The implications of magnetic resonance angiography artifacts caused by different types of intracranial flow diverters

BACKGROUND

Serial cerebral angiographic imaging is necessary to ensure cerebral aneurysm occlusion after flow diverter placement. Time-of-flight (TOF)-magnetic resonance angiography (MRA) is used for this purpose due to its lack of radiation, contrast media and complications. The comparative diagnostic yield of TOF-MRA for different flow diverters has not been previously analyzed.

PURPOSE

To evaluate the diagnostic accuracy of TOF-MRA in cerebral aneurysms treated w divertersith different flow diverters.

MATERIALS AND METHODS

Flow-diverted patients whose cerebral follow-up MRA and digital subtraction angiograms (DSA) were obtained within 6 weeks were retrospectively identified. The DSA (as gold standard) and MRA images of these patients were compared by two readers (blinded to both patient data and endovascular procedure data) for residual aneurysms and the status of the parent artery for each type of flow diverter. In a second group of patients, magnetic susceptibility artifacts were manually measured and compared for different FDs.

RESULTS

Seventy-six patients (85 aneurysms) were included in group one, and 86 patients (95 aneurysms) were included in group 2. TOF-MRA and DSA showed almost perfect agreement for residual aneurysms (κ = 0.88, p < 0.001) (positive predictive value (PPV) = 1.00, specificity = 1.00, negative predictive value (NPV) = 0.89, sensitivity = 0.89). Intermodality agreement (κ = 0.97 vs. κ = 0.74, p < 0.005) and sensitivity (0.97 vs. 0.77, NPV: 0.96 vs. 0.77) were highest with nitinol stents. MRA and DSA showed no agreement for occluded or stenotic parent vessels (κ = 0.13, p = 0.015, specificity = 0.44, NPV = 1.00, sensitivity = 1.00). Specificity was lower in chromium-cobalt based FDs than in nitinol devices (specificity = 0.08 vs. 0.60). Chromium-cobalt stents generated the largest artifacts (p < 0.005). The size of the device-related artifact, in millimeters, increased in respective order, for the Silk, Derivo, Pipeline and Surpass devices.

CONCLUSION

Unlike DSA, TOF-MRA is susceptible to dissimilarities between flow diverters. MRA is not well-suited for research studies comparing different flow diverters. Nitinol FDs appear to be advantageous for TOF-MRA follow-up so as not to miss small aneurysm remnants or clinically relevant parent artery stenosis.

The feasibility of non-contrast-enhanced zero echo time magnetic resonance angiography for characterization of intracranial atherosclerotic disease

Background

Accurate and non-invasive assessment of intracranial atherosclerotic disease (ICAD) is important because of its effect on treatment planning. The aim of this study is to investigate if zero echo time (zTE) magnetic resonance angiography (zTE-MRA) is feasible in the characterization of ICAD.

Methods

A total of 175 patients with ICAD were recruited. ZTE-MRA and time-of-flight (TOF)-MRA sequences were conducted for all participants using a 3T clinical MR system. Forty-one patients also underwent digital subtraction angiography (DSA), and were confirmed to have intracranial arterial stenosis (ICAS). Weighted kappa (κ) statistics were used to assess the inter-observer agreement and diagnostic consistency of both zTE- and TOF-MRA, using DSA as a reference. The Wilcoxon signed-rank test was used to evaluate differences in image quality between zTE- and TOF-MRA images. The nonparametric test of multiple paired samples was used to compare the results of vascular stenosis diagnosis between zTE-, TOF-MRA and DSA.

Results

Supported by high inter-observer agreement (weighted κ=0.78), zTE-MRA generated significantly higher scores than TOF-MRA for susceptibility artifact signal (mean: 3.03±0.98 vs. 2.72±1.09; P=0.017) and flow signal in parent artery (mean: 3.63±0.49 vs. 3.07±0.82; P<0.001). Additionally, zTE-MRA showed more robust diagnostic performance than TOF-MRA for patients with ICAD and degree of vascular stenosis (P<0.05), and was highly consistent with reference DSA images (weighted κ=0.80).

Conclusions

ZTE-MRA has potential for use as a routine clinical method for patients with ICAD.

Defective Endothelialization of Pipeline Embolization Device after Flow Diverter Therapy: An Autopsy Case Report

The authors report a rare autopsy case. A 59-year-old woman underwent flow diverter (FD) therapy using a pipeline embolization device (PED) for a large paraclinoid internal carotid artery aneurysm. Follow-up magnetic resonance (MR) examinations were performed 6 months after the treatment. Although the T2-weighted images showed progressive thrombosis of the aneurysm, the silent MR angiography (MRA) clearly showed the residual blood flow within the aneurysm. The patient committed suicide 2 months after the follow-up MR examinations. An autopsy specimen showed a small section of the defective membranes with the PED that matched the entry point of residual blood flow seen clearly in the silent MRA. Macroscopic photograph and hematoxylin and eosin stained sections showed defective endothelialization. In contrast, complete endothelialization was observed in membranes covering the PED. The autopsy findings after FD therapy showed defective endothelialization that perfectly matched and corroborated the silent MRA findings.

Imaging for Treated Aneurysms (Including Clipping, Coiling, Stents, Flow Diverters)

Intracranial aneurysms are common in the adult population and carry a risk of rupture leading to catastrophic subarachnoid hemorrhage. Treatment of aneurysms has evolved significantly, with the introduction of new techniques and devices for minimally invasive and endovascular approaches. Follow-up imaging after aneurysm treatment is standard of care to monitor for recurrence or other complications, and the preferred imaging modality and schedule for follow-up are areas of active research. The modality and follow-up schedule should be tailored to treatment technique, aneurysm characteristics, and patient factors.

Endovascular Treatment for Lateral Wall Paraclinoid Aneurysms and the Influence of Internal Carotid Artery Angle

Lateral wall paraclinoid aneurysms (LPA) are a rare type of aneurysm located on the lesser curve side of the internal carotid artery (ICA) bend, at the level of the anterior clinoid process. The objective of this study was to assess the influence of flexion of the ICA on the morphology of aneurysms and outcome of endovascular treatment. Between 2003 and 2018, we treated 643 cases of unruptured paraclinoid aneurysms with endovascular therapy in our institution. Of those cases, aneurysms projecting laterally on preoperative angiography were defined as LPA. The degree of bending of the ICA (ICA angle) was measured and statistically analyzed in relation to the aneurysm characteristics and the occlusion status after treatment. In all, 43 aneurysms were identified. ICA angle was positively correlated with the maximum dome size of the aneurysm (P <0.01) and the aspect ratio (P <0.01), and negatively correlated with the volume coil embolization ratio (P <0.01). Complete occlusion (CO) was achieved in 23 cases (53.5%) immediately after treatment, and in 35 cases (81.4%) at follow-up. The mean ICA angle in the incomplete occlusion group was significantly larger than in the CO group (P = 0.01). Larger ICA angle resulted in recurrence, whereas smaller ICA angle was more likely to obtain progressive thrombosis (P = 0.02). Endovascular treatment for LPA was safe and effective. The degree of flexion of the ICA may contribute to the level of hemodynamic stress on the aneurysm, its morphology, and the embolization effect.

Noncontrast Magnetic Resonance Angiography in the Era of Nephrogenic Systemic Fibrosis and Gadolinium Deposition

ABSTRACT

Gadolinium-based contrast agents for clinical magnetic resonance imaging are overall safe. However, the discovery of nephrogenic systemic fibrosis in patients with severe renal impairment and gadolinium deposition in patients receiving contrast have generated developments in contrast-free imaging of the vasculature, that is, noncontrast magnetic resonance angiography. This article presents an update on noncontrast magnetic resonance angiography techniques, with comparison to other imaging alternatives. Potential benefits and challenges to implementation, and evidence to date for various clinical applications are discussed.

Usefulness of 3 Tesla Ultrashort Echo Time Magnetic Resonance Angiography (UTE-MRA, SILENT-MRA) for Evaluation of the Mother Vessel after Cerebral Aneurysm Clipping: Case Series of 19 Patients

It is important to assess the cerebral arteries near the clip after cerebral aneurysm clipping. Contrast-enhanced computed tomography angiography has side effects of contrast medium and radiation exposure. Time-of-flight magnetic resonance angiography (TOF-MRA) is a fast and non-invasive method, but clip-induced artifact limits the assessment around the clip. Recently, 3 tesla MRA with ultrashort echo time called SILENT MRA (GE Healthcare Life Sciences, UK) has been reported to have the potential to overcome these disadvantages. We herein present consecutive 19 cerebral aneurysm patients treated by clipping and evaluated using SILENT MRA. The 19 patients (15 women and 4 men) underwent TOF-MRA and SILENT MRA during the same scan session. Two neurosurgeons independently assessed the visibility of the mother vessel at the clipping site in TOF-MRA and SILENT MRA. We also investigated the factors related to visibility in SILENT MRA. All patients’ mother vessels were not described in TOF-MRA, and that of 16 patients (84%) were described in SILENT MRA. Overall agreement was 100% in the two neurosurgeons, and the fixed marginal kappa = 1.00 (95% CI: 0.36–1.00). Univariate analysis revealed that larger aneurysm dome and long clip blade length contributed to the visibility of the mother vessel in SILENT MRA. (p = 0.023, 0.007, each). In conclusion, SILENT MRA can be applied for the assessment of the arteries and aneurysm neck remnants near the clip. Using clips with long blade and ligation with its tip would be related to the visibility of the mother vessels in SILENT MRA.

Usefulness of Noncontrast-Enhanced Silent Magnetic Resonance Angiography (MRA) for Treated Intracranial Aneurysm Follow-up in Comparison with Time-of-Flight MRA

BACKGROUND

Flow visualization in time-of-flight magnetic resonance angiography (TOF MRA) is limited for treated intracranial aneurysms owing to magnetic susceptibility and radiofrequency shielding.

OBJECTIVE

To assess the clinical usefulness of noncontrast-enhanced magnetic resonance angiography (MRA) using a silent scan (silent MRA) as a follow-up imaging modality in patients with treated intracranial aneurysms.

METHODS

A total of 119 patients with 126 treated aneurysms underwent silent MRA and TOF MRA during the same scan session. Two neuroradiologists independently assessed overall image quality and visualization of the treated site using a 5-point Likert scale to compare the 2 image sets. We used receiver operating characteristic (ROC) curve analysis to investigate the diagnostic performance of the 2 MRA methods in evaluating aneurysm occlusion. Interobserver reliability was also assessed using weighted kappa statistics.

RESULTS

The overall image quality scores of silent MRA and TOF MRA were 4.04 ± 0.22 and 4.64 ± 0.48, respectively (P &lt; .001), and interobserver agreement was substantial (P &lt; .001). For the treated site, the score of flow visualization on silent MRA was higher than that on TOF MRA, 3.94 ± 0.94 vs 2.59 ± 1.37 (P &lt; .001), with substantial interobserver agreement (P &lt; .001). ROC curve analysis showed that silent MRA was superior to TOF MRA in diagnostic performance (area under the curve [AUC] = 0.962; 95% CI: 0.931-0.982 vs AUC = 0.843; 95% CI: 0.792-0.886; P &lt; .001).

CONCLUSION

Silent MRA can be useful to evaluate treated intracranial aneurysms during follow-up without radiation exposure and use of contrast material. It is characterized by higher diagnostic performance and superior visualization for the treated site.