Test-retest repeatability of intravoxel incoherent motion (IVIM) measurements in the cervical cord

This work aimed at assessing the reliability of intravoxel incoherent motion (IVIM) parameters sensitive to perfusion changes in the cervical cord by determining the test-retest variability across subjects and different post-processing fitting algorithms. IVIM test-retest scans were acquired in the cervical cord (C1-C3) of 10 healthy subjects on a 3T MRI scanner, with a 15-minute break in-between. IVIM parameters, including microvascular volume fraction ( F ), pseudo-diffusion coefficient ( D* ), blood flow-related coefficient ( F · D* ), and diffusion coefficient ( D ), were derived using voxel-wise and region of interest (ROI)-wise fits. The reliability of each IVIM parameter was determined with coefficients of variation (CV), intraclass correlation coefficients (ICC), Bland-Altman analysis and linear regression. To assess the effects of the different fitting approaches, a two-way repeated-measures analysis of variance (ANOVA) was conducted on the CVs calculated across fitting algorithms. Mean CVs of IVIM parameters calculated across subjects using the voxel-wise fit was lower in the white matter (WM) and grey matter (GM) (2.6% to 15.6%; 2.2% to 16.4%, respectively) compared with those calculated using the ROI-wise fit approach (WM: 4.5%-32.2%; GM: 3.4%-53.4%). The voxel-wise fit in the WM yielded higher ICC values (good-to-excellent, 0.71 – 0.97) compared to the ROI-wise fit approach (0.49 – 0.90). IVIM parameters, derived using the voxel-wise fitting approach, demonstrated a high reliability in the cervical cord. Robust IVIM metrics, observed across scans and subjects, can facilitate studies targeting perfusion impairment and pave the way to future clinical trials assessing perfusion impairment as a potential quantitative biomarker. ### Competing Interest Statement Simon Levy is an employee of Siemens Healthcare Pty Ltd. The other authors declare no potential conflicts of interest relevant to the manuscript. ### Funding Statement M.S. received funding from the Wings for Life charity (No WFL-CH-19/20), Balgrist Stiftung 2021, International Foundation for Research in Paraplegia (IRP-158), and from Hurka Wilhelm foundation UZH for this project. P.F. is funded by the Eccellenza fellowship/181362 by SNSF. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Ethics Committee of canton Zurich (Kantonale Ethikkommission Zurich, EK-2018-00937) gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Anonymized datasets used and analyzed during the current study are available from the corresponding author on reasonable request.