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Investigation of collateral circulation compensatory capacity of Willis ring using vessel selective arterial spin labeling1radiology, The first hospital of Jilin University, Changchun, China, 2The third people's hospital of Datong, Datong, China, 3GE Healthcare, MR Research China,Beijing, Beijing, China
Synopsis
The Willis ring plays an important role in the collateral circulation especially in patients with internal carotid artery (ICA) stenosis. However conventional time of flight (TOF) MR angiography may only offer limited knowledge of the compensatory blood flow attributed to collateral circulation for patients with stenosis. Vessel selective arterial spin labeling allows the assessment of blood flow of a specific vessel. The purpose of this study was to quantify the influence of various anatomical types on the compensatory capacity of the Willis ring for patients with severe stenosis or occlusion using combined TOF MRA and vessel selective ASL method.
Introduction
The Willis ring plays an important role in the collateral circulation especially in patients with internal carotid artery (ICA) stenosis. However conventional time of flight (TOF) MR angiography may only offer limited knowledge of the compensatory blood flow attributed to collateral circulation for patients with stenosis. Vessel selective arterial spin labeling allows the assessment of blood flow of a specific vessel. The purpose of this study was to quantify the influence of various anatomical types on the compensatory capacity of the Willis ring for patients with severe stenosis or occlusion using combined TOF MRA and vessel selective ASL method.METHODS
40 patients with severe stenosis or occlusion of the unilateral ICA confirmed by TOF-MRA, CTA, and TCD and 30 normal volunteers were prospectively collected from 2018-01 to 2019-01 in the Department of Neurosurgery, First Hospital of Jilin University. All participants were scanned with the TOF-MRA and vessel selective arterial spin labeling using the GE Discovery750 3.0T MRI scanner. The results were separately evaluated by two imaging physicians. All image data were processed as follows: (1) Estimate the circle condition of anterior communicating artery (AcoA) and posteior communicating artery (PcoA) through TOF-MRA and measure the diameter of P1 segment on A1 segment, PcoP and posterior cerebral artery（PCA）of bilateral anterior cerebral artery （ACA）by RadiAnt DICOM Viewer software; (2) With MATLAB (Mathworks, Natick, Mass), the affected-side ICA and vertebral-basilar artery (VBA) were semi-automatically segmented and defined as the cerebral hemisphere compensation range of the affected side, and the compensatory volume ratios of the unaffected-side ICA and VBA were calculated, as illustrated by a case in Figure 1. In this study, patients were divided into the transient ischemic attack (TIA) group and the cerebral infarction (CI) group according to clinical manifestations. The diameters of Willis ring between the affected and unaffected side in the patient group as well as between the patient group and the normal volunteers were compared. The differences in diameter of each component of the ring, the effects of AcoA and PcoP with or without opening branches and of the diameters of the Willis ring on the compensatory capacity in the healthy ICA and VBA.RESULTS
31 males (77.5%) with an average of 61.28 ± 8.735 years in the TIA group and 14 patients (46.7%) with an average age of 54.18±13.17 in 30 healthy controls were enrolled in this study. 23 patients (57.5%) in the TIA group and 17 patients (42.5%) in the cerebral infarction group were discovered. The diameters of the blood vessels in A1 segment and PcoP were statistically different between the affected and unaffected side of the Willis ring in the TIA (P<0.05), and the diameter of the unaffected-side A1 segment (2.12±0.682) was larger than the affected-side one (P<0.05) while PcoP diameter in the affected side (1.27 ± 0.652) was greater than the healthy side. Only the diameter of the A1 segment (2.06±0.725) was larger than the healthy side (1.36±0.615) in the cerebral infarction group (P<0.05). Compared to the normal control group, significant larger A1 segment, bilateral PcoP and bilateral P1 segments in both the TIA and CI group were found (P<0.05). The unaffected-side A1 segment and PcoP as well as the bilateral P1 segments in the cerebral infarction group were significantly larger than in the normal group (P<0.05) (Table 1, Table 2 and Figure2). The compensation range of ICA was significantly larger in the CI group when the AcoA with the opening branch (0.294±0.144) than without the opening branch (0.177±0.189). The compensation volume of unaffected-side ICA was significantly smaller when the PcoP with the opening branch (0.208±0.171) than without the opening branch (0.338±0.130) (P<0.05) (Table3 and Figure 3). The compensation range of unaffected-side VBA was significantly larger when the PcoP with the opening branch (0.223) than without the opening branch (0.056 ± 0.042) (P<0.05) (Table 4 and Figure 4). The linear correlation coefficient between the diameters of unaffected-side A1 segment and the corresponding compensatory ability in the ICA group and between the diameters of unaffected-side PcoP and corresponding compensatory ability in the VBA group was 0.581 and 0.727, respectively.Discussion and CONCLUSIONS
Severe stenosis or occlusion of ICA might change the arterial diameter of the Willis ring, and the opening conditions and anatomical structure of the Willis circle has different effects on the post-circulation compensation capability of healthy-side ICA. Previously, the assessment of collateral circulation is either based on MRA or perfusion, however neither method alone may offer complete picture of the compensatory blood flow. This preliminary study show the compensatory blood flow attributed by collateral circulation may be quantitatively assessed by the simultaneous use of TOF-MRA and vessel selective ASL. Further study with a larger patient cohort and other clinical complications would be needed for the clinical application of this method.Acknowledgements
References
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Figures
A-I: A patient with opening ACoA, but without PcoP(as indicated by a red arrow). B-E represent the compensation range of the unaffected-side ICA. F-I represent the compensation range of the VBA, and no obvious VBA compensation was seen in this patient. J-R : A patient without opening ACoA ,but with PcoP(as indicated by a red arrow).K-N represent the compensation range of the unaffected-side ICA, and no obvious compensation.O-R represent the compensation range of the VBA.
