Bi-exponential fitting excluding b =0 data improves the scan-rescan stability of liver IVIM parameter measures and particularly so for the perfusion fraction.

Background: A prerequisite to translating intravoxel incoherent motion (IVIM) imaging into meaningful clinical applications is sufficient scan-rescan reproducibility. This study aims to confirm the hypothesis that IVIM data fitting by not using b =0 images will improve the stability of liver IVIM measurement.
Methods: Healthy volunteers' liver IVIM images were prospectively acquired using a 1.5-T magnet or a 3.0 T with 16 b -values. Repeatability study subjects were scanned twice during the same session, resulted in 35 paired scans for 35 subjects (11 men, mean age: 41.82 years, range: 32-60 years; 24 women, mean age: 42.67 years, range: 20-71 years). IVIM analysis was performed with full-fitting and segmented-fitting with a threshold b -value of 60 s/mm ² , and fitting started from b =0 s/mm ² or from b =2 s/mm ² . Reproducibility study subjects were scanned and then rescanned with an interval of 5-18 days, resulted in 20 paired scans for 11 subjects (4 men, mean age: 26.25 years, range: 25-27 years; 7 women, mean age: 25.57 years, range: 24-27 years). IVIM analysis was performed with segmented-fitting with a threshold b -value of 50 s/mm ² , and fitting started from b =0 s/mm ² or from b =3 s/mm ² .
Results: Fitting without b =0 data generally improved the repeatability and reproducibility for both PF and D _slow , and particularly so for PF. For with b =0 data segmented fitting repeatability, PF had within-subject standard deviation of 0.019, bland-Atman 75% agreement limit of -31.52% to 28.35%, and ICC of 0.647, while these values were 0.009, -20.78% to 16.86%, and 0.837 for without b =0 analysis. Though the repeatability and reproducibility for D _fast generally also improved, they remained suboptimal. Measurement stability was better for repeatability than for reproducibility.
Conclusions: Scan-rescan repeatability and reproducibility of liver IVIM parameters can be improved by fitting without b =0 data, which is particularly so for PF.
Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2022-02/coif). Author YXJW serves as the Editor-in-Chief of Quantitative Imaging in Medicine and Surgery. Author YXJW is the founder of Yingran Medicals Co., Ltd., which develops medical image-based diagnostics software. The other authors have no conflicts of interest to declare.
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