Synopsis

Keywords: Stroke, Perfusion

We compared the performance of pseudo-continuous arterial spin labeling (ASL) between ultrahigh field 7T MRI and 3T MRI in evaluating collateral circulation based on arterial transit artifact (ATA) in Moyamoya disease (MMD). 7T ASL shows more subtle hypoperfusion and more prominent ATA as compared with 3T ASL. The performance of collateral circulation assessment is more favorable by 7T ASL. These findings render 7T ASL a competing none-invasive approach in the management of MMD.

INTRODUCTION

Collateral circulation assessment is pivotal for patients’ management in patients with Moyamoya disease (MMD). Arterial transit artifact (ATA) is an established none-invasive imaging marker derived from arterial spin labeling (ASL) to depict leptomeningeal collaterals in cerebrovascular occlusive disease¹. We aimed to compare the performance of ASL between ultrahigh field 7T MRI and 3T MRI in evaluating collateral circulation based on ATA.

METHODS

Patients suspected MMD were prospectively recruited in the study from August 2022 to October 2022 in a hospital center. Participants were analyzed in this study if they had performed both 3T (GE Discovery MR 750, GE Healthcare, Milwaukee, WI), and 7T ASL (MAGNETOM Terra, Siemens Healthcare, Erlangen, Germany) and conventional angiography within 1 month. Whole brain ASLs acquired from 3T and 7T scanners were both with pseudo-continuous labeling scheme and with a post-labeling delay (PLD) of 2000 ms. The voxel size of 7T ASL was 2.2 x 2.2 x 4.0 mm³ or 2.2 x 2.2 x 5.0 mm³. A modified Alberta Stroke Program Early Computed Tomography Score (ASPECTS) system, which assessed the global changes of both hemispheres from 0 to 22, is applied for the evaluation of hypoperfusion and ATA in accordance with insular, M1–M6, A1-A2 and P1-P2 regions in the original ASPECTS (Figure 1A). A larger hypoperfusion-ASPECTS or ATA-ASPECTS indicated more prominent hypoperfusion or ATA. In the collateral circulation evaluation, an established scoring system 0-3 was employed which based on the identification of the hypoperfusion region and ATA on ASL². The hypoperfusion was used to determine the ischemic region, and ATA was used to depict the presence and robustness of the collaterals. A larger collateral grade on ASL indicated better collaterals. The gold standard of collateral evaluation was American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR) scale assessed by conventional angiography. Imaging reading was performed by two experienced neuroradiologists (with 6 and 12 years of experience). The differences in opinions between them were resolved by consensus reading. Collateral grades, ATA-ASPECTS and hypoerfusion-ASPECTS from different modalities were statistically compared.

RESULTS

Nine patients were recruited in the final analysis. There were 4 men and 5 females. The mean age was 41.44±11.50 years. Global ATA-ASPECTS on 7T ASL was significantly higher compared with Global ATA-ASPECTS on 3T ASL (median 7 [Interquartile range 2.75-7.25] versus median 3 [Interquartile range 1.75-4], P=0.016, Wilcoxon test). Global Hypoperfusion-ASPECTS on 7T ASL was significantly higher compared with Global ATA-ASPECTS on 3T ASL (median 5 [Interquartile range 2.75-7] versus median 3 [Interquartile range 1.75-4.75], P=0.031, Wilcoxon test) (Figure 1B). In collateral assessment, eleven hemispheres were analyzed since 2 patients were bilateral lesions. Collateral grades on 7T ASL were higher but not significantly compared with collateral grades on 3T ASL (median 2 [interquartile range 2-2] versus median 2 [interquartile range 1-2], P=0.156, Wilcoxon test). Collateral grades on 7T ASL were not significantly correlated with Collateral grades on 3T ASL (rho=0.578, p=0.063, Spearman correlation). Collateral grades on 3T ASL were not significantly correlated with ASITN/SIR grades (rho=0.512, p=0.107, Spearman correlation). Collateral grades on 7T ASL were significantly correlated with ASITN/SIR grades (rho=0.831, p=0.002, Spearman correlation). Representative case was shown in Figure 2.

CONCLUSION

As compared with 3T ASL, 7T ASL shows more subtle hypoperfusion and more prominent ATA. The accuracy of collateral circulation assessment is more favorable by 7T ASL. These findings render 7T ASL a competing none-invasive approach in the management of MMD.

Acknowledgements

This work was supported by The National Natural Science Foundation of China (Contract grant number: 81901708 to J.H.L. and Contract grant number: 81825012, 81730048 and 82151309 to X.L.).