Acceleration-selective arterial spin labeling MR angiography for visualization of brain arteriovenous malformations

Diagnostic Performance of TOF, 4D MRA, Arterial Spin-Labeling, and Susceptibility-Weighted Angiography Sequences in the Post-Radiosurgery Monitoring of Brain AVMs

BACKGROUND

Brain AVMs are congenital anomalies of the cerebrovascular system, often discovered incidentally or through symptomatic presentations such as intracranial hemorrhage, seizure, headache, or neurologic deficits. Various treatment modalities exist for AVMs, including radiosurgery, a treatment technique that is noninvasive and efficient. Accurate imaging is crucial for risk assessment, treatment planning, and monitoring of these patients before and after radiosurgery.

PURPOSE

Currently, DSA is the preferred imaging technique. Despite its efficacy, DSA is notably invasive, presenting inherent risks to the patients. This systematic review and meta-analysis aimed to evaluate the efficacy of MRI sequences for monitoring brain AVMs after radiosurgery.

DATA SOURCE

We performed a comprehensive search of PubMed, Scopus, Web of Science, and EMBASE databases and a methodologic quality assessment with the QUADAS-2 checklist diagnostic test accuracy.

STUDY SELECTION

According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, 3,220 abstracts were screened, 98 articles were reviewed in full text, and 14 articles met the inclusion criteria.

DATA ANALYSIS

We used the bivariate random-effects meta-analysis model with STATA/MP 17 software for data analysis.

DATA SYNTHESIS

No publication bias was detected. Fourteen studies were eligible for qualitative and quantitative analysis. MRI offers high sensitivity (85%) and specificity (99%) in detecting residual AVMs. Different MRI sequences, including 3D TOF-MRA, 4D MRA, and arterial spin-labeling (ASL) demonstrated varying diagnostic accuracies with areas under the curve of 0.92, 0.97, and 0.96, respectively. 4D MRA had a sensitivity of 72% and specificity of 99%, ASL showed a sensitivity of 90% and specificity of 92%, while 3D TOF-MRA had 90% sensitivity and 87% specificity.

LIMITATIONS

Meta-regression did not fully explain the sources of heterogeneity. Only 1 study assessed the susceptibility-weighted angiography (SWAN) method, and most studies involved small participant groups with varied MR techniques and sequences. Additionally, the retrospective nature of most studies may introduce bias, warranting cautious interpretation of the results.

CONCLUSIONS

MRI sequences show acceptable diagnostic performance in postradiosurgery monitoring of brain AVMs, with ASL and 4D MRA showing acceptable diagnostic accuracy. Combining different MRI sequences may further enhance diagnostic reliability. However, further investigation is needed to assess whether MRI sequences can serve as a feasible substitute for DSA, considering their risk-benefit profile, with the potential to establish them as the recommended standard.

Reporting of angiographic studies in patients diagnosed with a cerebral arteriovenous malformation: a systematic review

A cerebral arteriovenous malformation (cAVM) is an abnormal tangle of cerebral blood vessels. The consensus document by the Joint Writing Group (JWG) highlighted which cAVM features should be recorded. Subsequent publications have reported cAVM angioarchitecture, but it is unknown if all followed the JWG recommendations. The aim of this systematic review was to describe use of the JWG guidelines. A database search, using the PRISMA checklist, was performed. We describe the proportion of publications that used JWG reporting standards, which standards were used, whether the definitions used differed from the JWG, or if any additional angiographic features were reported. Out of 4306 articles identified, 105 were selected, and a further 114 from other sources. Thirty-three studies (33/219; 15%) specifically referred to using JWG standards. Since the JWG publication, few studies have used their standards to report cAVMs. This implies that the angioarchitecture of cAVMs are not routinely fully described.

Arterial Spin Labeling-Based MR Angiography for Cerebrovascular Diseases: Principles and Clinical Applications

Arterial spin labeling (ASL) is a noninvasive imaging technique that labels the proton spins in arterial blood and uses them as endogenous tracers. Brain perfusion imaging with ASL is becoming increasingly common in clinical practice, and clinical applications of ASL for intracranial magnetic resonance angiography (MRA) have also been demonstrated. Unlike computed tomography (CT) angiography and cerebral angiography, ASL-based MRA does not require contrast agents. ASL-based MRA overcomes most of the disadvantages of time-of-flight (TOF) MRA. Several schemes have been developed for ASL-based MRA; the most common method has been pulsed ASL, but more recently pseudo-continuous ASL, which provides a higher signal-to-noise ratio (SNR), has been used more frequently. New methods that have been developed include direct intracranial labeling methods such as velocity-selective ASL and acceleration-selective ASL. MRA using an extremely short echo time (eg, silent MRA) or ultrashort echo-time (TE) MRA can suppress metal susceptibility artifacts and is ideal for patients with a metallic device implanted in a cerebral vessel. Vessel-selective 4D ASL MRA can provide digital subtraction angiography (DSA)-like images. This review highlights the principles, clinical applications, and characteristics of various ASL-based MRA techniques. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

Diagnostic accuracy of arterial spin labeling MR imaging in detecting cerebral arteriovenous malformations: a systematic review and meta-analysis

Diagnostic accuracy of arteriovenous malformations (AVMs) is imperative for delineating management. The current standard is digital subtraction angiography (DSA). Arterial spin labeling (ASL) is an understudied noninvasive, non-contrast technique that allows angioarchitecture visualization and additionally quantifies cortical and AVM cerebral blood flow and hemodynamics. This meta-analysis aims to compare ASL and DSA imaging in detecting and characterizing cerebral AVMs. EMBASE, Medline, Scopus, and Cochrane databases were queried from inception to July 2022 for reports of AVMs evaluated by DSA and ASL imaging. Fourteen studies with 278 patients evaluated using DSA and ASL imaging prior to intervention were included; pCASL in 11 studies (n = 239, 85.37%) and PASL in three studies (n = 41, 14.64%). The overall AVM detection rate on ASL was 99% (CI 97-100%); subgroup analysis revealed no difference between pCASL vs. PASL (99%; CI 96-100% vs. 100%; CI 95-100% respectively, p = 0.42). The correlation value comparing ASL and DSA nidus size was 0.99. DSA and ASL intermodality agreement Cohen's k factor for Spetzler Martin Grading (SMG) was reported at a median of 0.98 (IQR 0.73-0.1), with a 1.0 agreement on SMG classification. A median of 25 arteries were detected by DSA (IQR 14.5-27), vs. 25 by ASL (IQR 14.5-27.5) at a median 0.92 k factor. ASL provides angioarchitectural visualization noninferior to DSA and additionally quantifies CBF. Our study suggests that ASL should be considered in the detection of AVMs, especially in patients with contrast contraindications or apprehension towards an invasive assessment.

Arterial Spin Labeling for Pediatric Central Nervous System Diseases: Techniques and Clinical Applications

Dynamic susceptibility contrast (DSC) and arterial spin labeling (ASL) are techniques used to evaluate brain perfusion using MRI. DSC requires dynamic image acquisition with a rapid administration of gadolinium-based contrast agent. In contrast, ASL obtains brain perfusion information using magnetically labeled blood water as an endogenous tracer. For the evaluation of brain perfusion in pediatric neurological diseases, ASL has a significant advantage compared to DSC, CT, and single-photon emission CT/positron emission tomography because of the lack of radiation exposure and contrast agent administration. However, in ASL, optimization of several parameters, including the type of labeling, image acquisition, background suppression, and postlabeling delay, is required, because they have a significant effect on the quantification of cerebral blood flow (CBF).In this article, we first review recent technical developments of ASL and age-dependent physiological characteristics in pediatric brain perfusion. We then review the clinical implementation of ASL in pediatric neurological diseases, including vascular diseases, brain tumors, acute encephalopathy with biphasic seizure and late reduced diffusion (AESD), and migraine. In moyamoya disease, ASL can be used for brain perfusion and vessel assessment in pre- and post-treatment. In arteriovenous malformations, ASL is sensitive to detect small degrees of shunt. Furthermore, in vascular diseases, the implementation of ASL-based time-resolved MR angiography is described. In neoplasms, ASL-derived CBF has a high diagnostic accuracy for differentiation between low- and high-grade pediatric brain tumors. In AESD and migraine, ASL may allow for accurate early diagnosis and provide pathophysiological information.

Low-dose contrast-enhanced time-resolved angiography with stochastic trajectories with iterative reconstruction (IT-TWIST-MRA) in brain arteriovenous shunt

OBJECTIVES

To assess the feasibility of low-dose contrast-enhanced four-dimensional (4D) time-resolved angiography with stochastic trajectories (TWIST) with iterative reconstruction (hereafter IT-TWIST-MRA) covering the whole brain and to compare IT-TWIST-MRA and TWIST-MRA with reference to digital subtraction angiography (DSA) in the evaluation of arteriovenous shunts (AVS).

METHODS

Institutional Review Board approval was obtained for this observational study, and the requirement for written informed consent was waived. Twenty-nine patients with known AVS underwent TWIST-MRA on a 3-T MRI scanner, using low-dose injection (0.02 mmol/kg) of gadolinium-based contrast agent (GBCA) with each of Fourier and iterative reconstruction between September 2016 and October 2019. Visual evaluation of image quality was conducted for delineation of (a) the normal cerebral arteries and veins and (b) AVS feeder, shunt, and drainer vessels. Region-of-interest evaluation was conducted to evaluate bolus sharpness and baseline signal fluctuation in the signal intensity of the cerebral vessels. We compared the detection of AVS between TWIST-MRA and IT-TWIST-MRA. The paired-samples Wilcoxon test was used to test the differences between TWIST-MRA and IT-TWIST-MRA.

RESULTS

Visualization scores for normal vasculature and AVS angioarchitecture were significantly better for images produced using IT-TWIST-MRA than those using TWIST-MRA. Peak signal and the enhancement slope of the time-intensity curve were significantly higher for IT-TWIST-MRA than for TWIST-MRA, except for the superior sagittal sinus (SSS). Baseline intensity fluctuation was significantly lower for IT-TWIST-MRA than for TWIST, except for SSS.

CONCLUSIONS

IT-TWIST-MRA yields clinically feasible 4D MR-DSA images and delineates AVS even with low-dose GBCA.

KEY POINTS

• Iterative reconstruction significantly improves the image quality of TWIST-MRA covering the whole brain. • The short temporal footprint and denoising effect of iterative reconstruction enhances the quality of 4D-MRA. • IT-TWIST-MRA yields clinically feasible images of AVS with low-dose GBCA.

Vessel-Selective 4D-MRA Using Superselective Pseudocontinuous Arterial Spin-Labeling with Keyhole and View-Sharing for Visualizing Intracranial Dural AVFs

BACKGROUND AND PURPOSE

An accurate assessment of the hemodynamics of an intracranial dural AVF is necessary for treatment planning. We aimed to investigate the utility of 4D-MRA based on superselective pseudocontinuous arterial spin-labeling with CENTRA-keyhole and view-sharing (4D-S-PACK) for the vessel-selective visualization of intracranial dural AVFs.

MATERIALS AND METHODS

We retrospectively analyzed the images of 21 patients (12 men and 9 women; mean age, 62.2 [SD,19.2] years) with intracranial dural AVFs, each of whom was imaged with DSA, 4D-S-PACK, and nonselective 4D-MRA based on pseudocontinuous arterial spin-labeling combined with CENTRA-keyhole and view-sharing (4D-PACK). The shunt location, venous drainage patterns, feeding artery identification, and Borden classification were evaluated by 2 observers using both MRA methods on separate occasions. Vessel selectivity was evaluated on 4D-S-PACK.

RESULTS

Shunt locations were correctly evaluated in all 21 patients by both observers on both MRA methods. With 4D-S-PACK, observers 1 and 2 detected 76 (80.0%, P < .001) and 73 (76.8%, P < .001) feeding arteries of the 95 feeding arteries identified on DSA but only 39 (41.1%) and 46 (48.4%) feeding arteries with nonselective 4D-PACK, respectively. Both observers correctly identified 10 of the 11 patients with cortical venous reflux confirmed by DSA with both 4D-S-PACK and 4D-PACK (sensitivity = 90.9%, specificity = 90.9% for each method), and they made accurate Borden classifications in 20 of the 21 patients (95.2%) on both MRA methods. Of the 84 vessel territories examined, vessel selectivity was graded 3 or 4 in 73 (91.2%) and 66 (88.0%) territories by observers 1 and 2, respectively.

CONCLUSIONS

4D-S-PACK is useful for the identification of feeding arteries and accurate classifications of intracranial dural AVFs and can be a useful noninvasive clinical tool.

Evaluation of cerebral arteriovenous shunts: a comparison of parallel imaging time-of-flight magnetic resonance angiography (TOF-MRA) and compressed sensing TOF-MRA to digital subtraction angiography

PURPOSE

Time-of-flight (TOF)-MR angiography (MRA) is an important imaging sequence for the surveillance and analysis of cerebral arteriovenous shunt (AVS), including arteriovenous malformation (AVM) and arteriovenous fistula (AVF). However, this technique has the disadvantage of a relatively long scan time. The aim of this study was to compare diagnostic accuracy between compressed sensing (CS)-TOF and conventional parallel imaging (PI)-TOF-MRA for detecting and characterizing AVS.

METHODS

This study was approved by the institutional review board for human studies. Participants comprised 56 patients who underwent both CS-TOF-MRA and PI-TOF-MRA on a 3-T MR unit with or without cerebral AVS between June 2016 and September 2018. Imaging parameters for both sequences were almost identical, except the acceleration factor of 3× for PI-TOF-MRA and 6.5× for CS-TOF-MRA, and the scan time of 5 min 19 s for PI-TOF-MRA and 2 min 26 s for CS-TOF-MRA. Two neuroradiologists assessed the accuracy of AVS detection on each sequence and analyzed AVS angioarchitecture. Concordance between CS-TOF, PI-TOF, and digital subtraction angiography was calculated using unweighted and weighted kappa statistics.

RESULTS

Both CS-TOF-MRA and PI-TOF-MRA yielded excellent sensitivity and specificity for detecting intracranial AVS (reviewer 1, 97.3%, 94.7%; reviewer 2, 100%, 100%, respectively). Interrater agreement on the angioarchitectural features of intracranial AVS on CS-MRA and PI-MRA was moderate to good.

CONCLUSION

The diagnostic performance of CS-TOF-MRA is comparable to that of PI-TOF-MRA in detecting and classifying AVS with a reduced scan time under 2.5 min.

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.

Vessel-selective 4D-MR angiography using super-selective pseudo-continuous arterial spin labeling may be a useful tool for assessing brain AVM hemodynamics

OBJECTIVES

To evaluate the usefulness of 4D-MR angiography based on super-selective pseudo-continuous ASL combined with keyhole and view-sharing (4D-S-PACK) for vessel-selective visualization and to examine the ability of this technique to visualize brain arteriovenous malformations (AVMs).

METHODS

In this retrospective study, 15 patients (ten men and five women, mean age 44.0 ± 16.9 years) with brain AVMs were enrolled. All patients were imaged with 4D-PACK (non-selective), 4D-S-PACK, and digital subtraction angiography (DSA). Observers evaluated vessel selectivity, identification of feeding arteries and venous drainage patterns, visualization scores, and contrast-to-noise ratio (CNR) for each AVM component. Measurements were compared between the MR methods.

RESULTS

Vessel selectivity was graded 4 in 43/45 (95.6%, observer 1) and 42/45 (93.3%, observer 2) territories and graded 3 in two (observer 1) and three (observer 2) territories. The sensitivity and specificity for identification of feeding arteries for both observers was 88.9% and 100% on 4D-PACK, and 100% and 100% on 4D-S-PACK, respectively. For venous drainage, the sensitivity and specificity was 100% on both methods for observer 1. The sensitivity and specificity for observer 2 was 94.4% and 83.3% on 4D-PACK, and 94.4% and 91.7% on 4D-S-PACK, respectively. The CNRs at the timepoint of 1600 ms were slightly lower in 4D-S-PACK than in 4D-PACK for all AVM components (Feeding artery, p = .02; nidus, p = .001; and draining artery, p = .02). The visualization scores for both observers were not significantly different between 4D-PACK and 4D-S-PACK for all components.

CONCLUSIONS

4D-S-PACK could be a useful non-invasive clinical tool for assessing hemodynamics in brain AVMs.

KEY POINTS

• The 4D-MR angiography based on super-selective pseudo-continuous arterial spin labeling combined with CENTRA-keyhole and view-sharing (4D-S-PACK) enabled excellent vessel selectivity. • The 4D-S-PACK enabled the perfect identification of feeding arteries of brain arteriovenous malformation (AVM). • 4D-S-PACK could be a non-invasive clinical tool for assessing hemodynamics in brain AVMs.

A comparison of arterial spin labelling with catheter angiography in evaluating arteriovenous malformations: a systematic review

OBJECTIVES

To compare the performance of arterial spin labelling (ASL) in evaluating arteriovenous malformations (AVMs) against the current gold standard of catheter angiography.

METHODS

We systematically reviewed the published literature using EMBASE and Medline. We included studies that compared ASL to catheter angiography in the assessment of AVMs in three outcome domains: detection, angioarchitectural and haemodynamic features.

RESULTS

From 314 unique citations, 19 studies representing 289 patients with intracranial AVMs met our inclusion criteria. We did not pool data due to marked heterogeneity in study outcome measures. Seven studies showed high diagnostic performance of ASL in identifying arterial feeders, with sensitivity ranging from 84.6 to 100% and specificity ranging from 93.3 to 100%. Six studies showed strong ability in detecting arteriovenous shunting, with sensitivity ranging from 91.7 to 100% and specificity ranging from 90 to 100%. Seven studies demonstrated that ASL could identify nidal location and size as well as catheter angiography, while five studies showed relatively poorer performance in delineating venous drainage. Two studies showed 100% sensitivity of ASL in the identification of residual or obliterated AVMs following stereotactic radiosurgery.

CONCLUSIONS

Despite limitations in the current evidence base and technical challenges, this review suggests that ASL has a promising role in the work-up and post-treatment follow-up of AVMs. Larger scale prospective studies assessing the diagnostic performance of ASL are warranted.

ADVANCES IN KNOWLEDGE

ASL demonstrates overall validity in the evaluation of intracranial AVMs.

Intracranial 3D and 4D MR Angiography Using Arterial Spin Labeling: Technical Considerations

In the 1980’s some of the earliest studies of arterial spin labeling (ASL) MRI have demonstrated its ability to generate MR angiography (MRA) images. Thanks to many technical improvements, ASL has been successfully moving its position from the realm of research into the clinical area, albeit more known as perfusion imaging than as MRA. For MRA imaging, other techniques such as time-of-flight, phase contrast MRA and contrast-enhanced (CE) MRA are more popular choices for clinical applications. In the last decade, however, ASL-MRA has been experiencing a remarkable revival, especially because of its non-invasive nature, i.e. the fact that it does not rely on the use of contrast agent. Very importantly, there are additional benefits of using ASL for MRA. For example, its higher flexibility to achieve both high spatial and temporal resolution than CE dynamic MRA, and the capability of vessel specific visualization, in which the vascular tree arising from a selected artery can be exclusively visualized. In this article, the implementation and recent developments of ASL-based MRA are discussed; not only focusing on the basic sequences based upon pulsed ASL or pseudo-continuous ASL, but also including more recent labeling approaches, such as vessel-selective labeling, velocity-selective ASL, vessel-encoded ASL and time-encoded ASL. Although these ASL techniques have been already utilized in perfusion imaging and their usefulness has been suggested by many studies, some additional considerations should be made when employing them for MRA, since there is something more than the difference of the spatial resolution of the readout sequence. Moreover, extensive discussion is included on what readout sequence to use, especially by highlighting how to achieve high spatial resolution while keeping scan-time reasonable such that the ASL-MRA sequence can easily be included into a clinical examination.