Flow-compensated intravoxel incoherent motion diffusion imaging

PurposeThe pseudo-diffusion coefficient D-* in intravoxel incoherent motion (IVIM) imaging was found difficult to seize. Flow-compensated diffusion gradients were used to test the validity of the commonly assumed biexponential limit and to determine not only D-*, but also characteristic timescale and velocity v of the incoherent motion. Theory and MethodsBipolar and flow-compensated diffusion gradients were inserted into a flow-compensated single-shot EPI sequence. Images were obtained from a pipe-shaped flow phantom and from healthy volunteers. To calculate the IVIM signal outside the biexponential limit, a formalism based on normalized phase distributions was developed. ResultsThe flow-compensated diffusion gradients caused less signal attenuation than the bipolar ones. A signal dependence on the duration of the flow-compensated gradients was found at low b-values in the volunteer datasets. The characteristic IVIM parameters were estimated to be v=4.600.34 mm/s and =144 +/- 10 ms for liver and v=3.91 +/- 0.54 mm/s and =224 +/- 47 ms for pancreas. ConclusionOur results strongly indicate that the biexponential limit does not adequately model the diffusion signal in liver and pancreas. By using both bipolar and flow-compensated diffusion gradients of different duration, the characteristic timescale and velocity of the incoherent motion can be determined. Magn Reson Med 74:410-419, 2015. (c) 2014 Wiley Periodicals, Inc.