Frequency dependent diffusion kurtosis measurement in the human brain with oscillating gradients
Abstract
Oscillating gradient spin-echo (OGSE) is an implementation of diffusion MRI that enables shorter effective diffusion times than the conventional pulse gradient spin-echo (PGSE) by periodically modulating the diffusion gradient. Measurements of the diffusion kurtosis, which reflects the degree of restricted diffusion, have previously been prohibited with OGSE due to technical limitations of clinical gradient systems. This thesis presents a novel oscillating gradient waveform that enables the measurement of kurtosis using OGSE without requiring advanced gradient hardware. Decreases of kurtosis are observed in OGSE acquisitions of healthy human subjects relative to PGSE, demonstrating the dependence of the kurtosis on oscillation frequency. This frequency dependence is exploited to generate novel contrast based on the difference between PGSE and OGSE kurtosis measurements acquired with an optimized protocol. This work demonstrates the first in vivo measurements of kurtosis in the human brain using OGSE without the aid of advanced gradient hardware.