Improving in vivo MR g-ratio mapping via calibration of linearly transformed MR markers from in situ to ex vivo

In vivo MR g-ratio mapping relies on a calibrated method that relates myelin and axon MR markers to volume fractions. To estimate the calibration parameter, fixed ex vivo tissue measured with MRI and histology is used. The so-determined calibration parameter is then applied in vivo, neglecting the difference in the MR markers due to fixation. Here, we proposed a new calibration method accounting for this difference. The new calibration reduced the variability across MR g-ratios based on different myelin and axon markers, indicating that it can improve the accuracy of MR g-ratios.