Four in vivo g-ratio-weighted imaging methods: Comparability and repeatability at the group level

Area of Science:

• Neuroimaging
• Biophysics
• Histology

Background:

• In vivo g-ratio-weighted imaging links noninvasive MRI markers to the microscopic g-ratio.
• Optimal combinations of MRI markers for g-ratio imaging remain undetermined.

Purpose of the Study:

• To assess the repeatability and comparability of four g-ratio methods using different MRI markers.
• To evaluate the impact of processing steps like voxel masking and calibration on g-ratio imaging.

Main Methods:

• Scan-rescan experiments were conducted on two groups using four g-ratio methods.
• Methods combined two fiber volume fraction (FVF) markers (TFD, NODDI) and two myelin volume fraction (MVF) markers (MT, MTV).
• The influence of group-level voxel masking and calibration values was analyzed.

Main Results:

• Neurite orientation dispersion and density imaging (NODDI) for FVF showed better repeatability than tract-fiber density (TFD).
• Voxel masking improved both repeatability and comparability.
• The NODDI and MT combination yielded the highest repeatability (90%) and lowest inter-group variability (3.5%).

Conclusions:

• The choice of FVF marker (NODDI preferred) and processing steps significantly affect g-ratio imaging outcomes.
• Calibration procedures are critical and can alter repeatability, comparability, and marker dependencies.
• The NODDI+MT method demonstrates high potential for reliable in vivo g-ratio estimation.