Synopsis

Keywords: Stroke, Blood vessels, Iron Deposition

In this study, QSM was used to investigate susceptibility differences among infarct region, non- infarct regions of responsible artery and non-responsible artery in acute ischemic stroke (AIS) patients. The results showed that only susceptibility of the infarct region was significantly higher than that of healthy controls. In AIS patients, the susceptibility of infarct region were significantly higher than those of normal cerebral artery regions and non-infarction regions of responsible artery. These results suggest that abnormal iron deposition exists in the infarct region and may not affect other non-infarct regions.

Introduction

Acute ischemic stroke (AIS), a common type of stroke, is one of the leading causes of death and disability among worldwide¹. Although studies have shown that middle cerebral artery stenosis is accompanied by abnormal iron deposition in gray matter nuclei², there are few studies focus on the iron deposition differences in various cerebral artery regions in AIS patients. In this study, quantitative susceptibility mapping (QSM) was used to investigate the difference of iron deposition between infarct region and normal cerebral artery regions in AIS patients.

Methods

MR imaging: Thirty patients with acute ischemic stroke (20 males and 10 females; age: 46-91 years; mean age: 69.367 years; standard deviation (SD): 10.515) and thirty healthy controls (13 males and 17 females; age: 45-78 years; mean: 60.129, SD: 8.672) in the study. MRI data were acquired using 3T MR scanner (MAGNETOM VIDA, Siemens Healthineers, Erlangen, Germany), with a 64-channel head coil. Quantitative sensitivity mapping were acquired using multi-echo GRE sequence, and the parameters were as following: repetition time (TR) =55.0 ms, echo time (TE) = 6.15 ms, flip angle = 15°, field of view (FOV) = 220 × 220 mm², thickness = 2 mm, number of slices = 72, voxel size = 0.9 × 0.9 × 2 mm³, SMS factor = 3, parallel imaging with acceleration factor = 2 (total PAT = 6) , 8 echoes, total scan time is 8min 7sec. High-resolution T1-weighted anatomical 3D scans using MPRAGE sequence with the following parameters: TR = 2300 ms, TE = 2.45 ms, flip angle =9°, FOV =256 × 256 mm², thickness = 0.9 mm, number of slices = 176, voxel size = 1 × 1 × 1 mm³, total scan time is 4min 8sec.

Image Processing: The QSM data were post-processed using MEDI toolbox (Morphology Enabled Dipole Inversion) based on Matlab 2018a software platform (Mathworks, Natick, MA, USA). The QSM images were registered to the 3D T1-weighted imaging using 3D Slicer software. The infarct region of responsible artery (R1), the non-infarct region of responsible artery (R2), the contralateral symmetrical site of the lesion (R3), and the non-responsible cerebral arteries regions (R4, R5, R6, R7) of the AIS patients were selected as the regions of interest (ROI). For the healthy control group, the cerebral arteries region corresponding to the patient was selected as the ROI. ITK-SNAP was used to identify and delineate ROIs in the 3D T1 image, and then copied to the QSM image. The process is shown schematically in Figure 1.

Statistical Analysis: Two-sample T-test was used to compare the differences in corresponding ROI susceptibility between AIS patients and healthy controls, and paired T-test was used to compare the differences in susceptibility between infarct region and non-infarct regions in AIS patients.

Result

Using Two-sample T-test, the results showed that the susceptibility of infarct region in AIS patients was significantly higher than that in healthy controls (p = 0.002). There was no significant difference in non-infarct regions between AIS patients and healthy controls, although the mean susceptibility of R3, R5, R6, and R7 was higher in healthy controls than in AIS patients (all p > 0.05) (Table 1, Figure 2). Using paired T-test, the result showed that the susceptibility of R1 in AIS patients was significantly higher than that of R2 and R3 (p < 0.05). Compared with the non-responsible cerebral artery regions, the susceptibility of the infarct region was significantly increased (p < 0.05) (Figure 3).

Discussion

This study found that the brain iron deposition in the infarct region was significantly higher than that in the healthy control group, which may due to the release of iron ions from the cells in a potentially toxic form in the ischemic and anoxic environment, leading to abnormal iron deposition in the infarction region^{3, 4}. The susceptibility of AIS patients in infarct region is significantly higher than that in non-infarct regions of responsible artery, which may be related to the opening of collateral circulation of cerebral vessels⁵. In AIS patients, the susceptibility of the infarct region was significantly higher than that of the contralateral symmetrical site of the lesion and the non-responsible cerebral arteries region, which indicates that the local infarct region of the AIS responsible vessel does not affect the iron level in the contralateral region and other normal cerebral arteries region. Therefore, QSM may be a useful and promising tool to assess changes in brain iron level after ischemic stroke.

Conclusion

Abnormal iron deposition detected by QSM in the infarct region of AIS patients may not affect the iron level in the non-infarct region of responsible artery and normal cerebral arteries, which may provide imaging reference for clinical diagnosis.

Acknowledgements

We are particularly grateful to all those who helped us with the article.