Impact of tissue sample preparation methods on myelin-sensitive quantitative MR imaging

Abstract

Purpose: Validation of quantitative MRI (qMRI) parameters with histology is often done with ex vivo fixed tissue samples. Freezing is another common form of tissue preservation, but the effects of freezing and thawing tissue on myelin-sensitive quantitative MRI parameters and their correlation with histology require further analysis. Methods: Myelin water imaging, off-resonance RF saturation magnetization transfer (MT), and selective inversion recovery MT MRI experiments were conducted on 14 fresh, thawed, and fixed sheep brain tissue samples to calculate various surrogate measures of myelin content. These measures were compared with luxol fast blue (LFB) histological stain results. Results: Fresh, thawed, and fixed tissue qMRI values correlated well with LFB. Thawed and fixed tissue exhibited modest increases, between 3% and 32%, for most qMRI parameter values compared to fresh. Histology results showed that thawed samples did not lose tissue integrity from the freezing process. Conclusion: Freezing is a reasonable alternative tissue preservation method to fixation for use in qMRI analysis, but may differentially affect qMRI parameter values in regions with varying myelin content.