Tuned bipolar oscillating gradients for mapping frequency dispersion of diffusion kurtosis in the human brain

Abstract

To introduce frequency tuned bipolar (FTB) gradients as a variation of oscillating gradients to measure frequency dependent differences in kurtosis.Methods: An FTB oscillating gradient waveform is presented that provides encoding of 1.5 net oscillation periods to reduce the echo time of the acquisition. Monte Carlo optimization was performed to determine an optimal protocol based on simulated SNR of kurtosis dispersion maps -defined as the difference in apparent kurtosis between pulsed gradient and oscillating gradient acquisitions. Healthy human subjects were scanned at 7T using traditional pulsed gradient and an optimized 23 Hz FTB oscillating gradient protocol, which featured a b-value of 2500 s/mm 2 . Test and re-test acquisitions were also acquired in each subject to validate optimization results and demonstrate repeatability. Results:The optimized FTB gradient protocol demonstrated consistent reductions in apparent kurtosis values and increased diffusivity in generated dispersion maps from all subjects. Optimization results suggest SNR of kurtosis dispersion maps increases with diffusion weighting which was also apparent in subject data acquired at varied b-value.Conclusions: This work demonstrates the feasibility of generating in vivo kurtosis dispersion maps in humans using oscillating gradients on modern clinical gradient systems.