Optimized Combination of b‑values for IVIM Perfusion Imaging in Acute Ischemic Stroke Patients

Clin Neuroradiol. 2020 Sep;30(3):535-544. doi: 10.1007/s00062-019-00817-w. Epub 2019 Aug 2.

Abstract

Purpose: To determine the optimal combination of low b‑values to generate perfusion information from intravoxel incoherent motion (IVIM) in patients with acute ischemic stroke (AIS) considering the time constraints for these patients.

Methods: A retrospective cohort study of AIS patients with IVIM MRI was performed. A two-step voxel-by-voxel postprocessing was used to derive IVIM perfusion fraction maps with different combinations of b values. Signal values within regions of ischemic core, non-infarcted ischemic hemisphere, and contralateral hemisphere were measured on IVIM (f, D*, fD*, D) parameter maps. Bland-Altman analysis and the Dice similarity coefficient were used to determine quantitative and spatial agreements between the reference standard IVIM (IVIM with 6 b values of 0, 50, 100, 150, 200, 1000 s/mm2) and other combinations of b values. Significance level was set at p < 0.05.

Results: There were 58 patients (36 males, 61.3%; mean age 70.2 ± 13.4 years) included. Considering all IVIM parameters, the combination of b values of 0, 50, 200, 1000 was the most consistent with our reference standard on Bland-Altman analysis. The best voxel-based overlaps of ischemic regions were on IVIM D, while there were good voxel-based overlaps on IVIM f.

Conclusion: The IVIM with these four b values collects diffusion and perfusion information from a single short MRI sequence, which may have important implications for the imaging of AIS patients.

Keywords: Flowing blood volume fraction; MRI; Molecular diffusion coefficient; Multiple b‑values; Pseudodiffusion coefficient.