Gaussian phase distribution approximations for oscillating gradient spin echo diffusion MRI.

Andrada Ianuş, Bernard Siow, Ivana Drobnjak, Hui Zhang, Daniel C Alexander

Center for Medical Image Computing, Department of Computer Science, University College London, UK. a.ianus.11@ucl.ac.uk

Journal of magnetic resonance (San Diego, Calif. : 1997) 2013 Feb

filter terms:

Oscillating gradients provide an optimal probe of small pore sizes in diffusion MRI. While sinusoidal oscillations have been popular for some time, recent work suggests additional benefits of square or trapezoidal oscillating waveforms. This paper presents analytical expressions of the free and restricted diffusion signal for trapezoidal and square oscillating gradient spin echo (OGSE) sequences using the Gaussian phase distribution (GPD) approximation and generalises existing similar expressions for sinusoidal OGSE. Accurate analytical models are necessary for exploitation of these pulse sequences in imaging studies, as they allow model fitting and parameter estimation in reasonable computation times. We evaluate the accuracy of the approximation against synthesised data from the Monte Carlo (MC) diffusion simulator in Camino and Callaghan's matrix method and we show that the accuracy of the approximation is within a few percent of the signal, while providing several orders of magnitude faster computation. Moreover, since the expressions for trapezoidal wave are complex, we test sine and square wave approximations to the trapezoidal OGSE signal. The best approximations depend on the gradient amplitude and the oscillation frequency and are accurate to within a few percent. Finally, we explore broader applications of trapezoidal OGSE, in particular for non-model based applications, such as apparent diffusion coefficient estimation, where only sinusoidal waveforms have been considered previously. We show that with the right apodisation, trapezoidal waves also have benefits by virtue of the higher diffusion weighting they provide compared to sinusoidal gradients. Copyright © 2012 Elsevier Inc. All rights reserved.

Citation

Andrada Ianuş, Bernard Siow, Ivana Drobnjak, Hui Zhang, Daniel C Alexander. Gaussian phase distribution approximations for oscillating gradient spin echo diffusion MRI. Journal of magnetic resonance (San Diego, Calif. : 1997). 2013 Feb;227:25-34