Purpose: Q-space imaging (QSI) is a novel magnetic resonance imaging (MRI) technique that enables assessment of micro-structural changes of white matter. The acquisition time, however, is comparatively long to use for routine clinical assessment. Therefore, the present study investigated the clinically feasible b value combinations to measure the water molecular displacement probability density function (PDF) in healthy subjects.
Methods: The subjects consisted of five healthy volunteers (1 female and 4 male; 40.8 ± 13.2 years). All MRIs were examined at 1.5 T. The QSI was acquired using a single-shot echo-planar imaging and Δ/δ = 142/17 ms. The magnitude of the gradients was incremented in nine steps to reach a maximal b = 10,000 s/mm2. The total acquisition time of this original QSI was 17.4 min. The feasibility of ten alternative b value combinations with the zero-filling or curve fitting technique was assessed. The mean diffusivities (MDs), kurtosis, and zero displacement probability (ZDP) were obtained, and these results were compared in manually segmented regions of interest.
Results: There were alternative b value combinations with a 7.5-min acquisition time and with almost the same PDF.
Conclusion: A few alternative b value combinations with the curve fitting technique were found to be able to shorten the QSI acquisition for its clinical feasibility of MD and ZDP.
Keywords: Mean displacement (MD); Normal brain; Probability density function (PDF); Q-space imaging (QSI); White matter.