Optimal acquisition scheme for flow‐compensated intravoxel incoherent motion diffusion‐weighted imaging in the abdomen: An accurate and precise clinically feasible protocol

Abstract

Purpose: Flow-compensated (FC) diffusion-weighted MRI (DWI) for intravoxel-incoherent motion (IVIM) modeling allows for a more detailed description of tissue microvasculature than conventional IVIM. The long acquisition time of current FC-IVIM protocols, however, has prohibited clinical application. Therefore, we developed an optimized abdominal FC-IVIM acquisition with a clinically feasible scan time. Methods: Precision and accuracy of the FC-IVIM parameters were assessed by fitting the FC-IVIM model to signal decay curves, simulated for different acquisition schemes. Diffusion-weighted acquisitions were added subsequently to the protocol, where we chose the combination of b-value, diffusion time and gradient profile (FC or bipolar) that resulted in the largest improvement to its accuracy and precision. The resulting two optimized FC-IVIM protocols with 25 and 50 acquisitions (FC-IVIM opt25 and FC-IVIM opt50 ), together with a complementary acquisition consisting of 50 diffusion-weighting (FC-IVIM comp ), were acquired in repeated abdominal free-breathing FC-IVIM imaging of seven healthy volunteers. Intersession and intrasession within-subject coefficient of variation of the FC-IVIM parameters were compared for the liver, spleen, and kidneys. Results: Simulations showed that the performance of FC-IVIM improved in tissue with larger perfusion fraction and signal-to-noise ratio. The scan time of the FC-IVIM opt25 and FC-IVIM opt50 protocols were 8 and 16 min. The best in vivo performance was seen in FC-IVIM opt50 . The intersession within-subject coefficients of variation of FC-IVIM opt50 were 11.6%, 16.3%, 65.5%, and 36.0% for FC-IVIM model parameters diffusivity, perfusion fraction, characteristic time and blood flow velocity, respectively. Conclusions: We have optimized the FC-IVIM protocol, allowing for clinically feasible scan times (8-16 min).

Characterisation of microvessel blood velocity and segment length in the brain using multi-diffusion-time diffusion-weighted MRI

“…21 produce estimates of v closer to those expected in brain capillaries when using different assumptions about the phase distribution to Wetscherek. Increased imaging times and sensitivity to eddy currents mean that our proposed method may be more appropriate to clinically implementalthough Gurney-Champion et al 22 do show that a clinically feasible protocol is possible with flowcompensated gradients, but the protocol performs better in highly perfused tissues.…”

Spectral diffusion analysis of kidney intravoxel incoherent motion MRI in healthy volunteers and patients with renal pathologies

“…To further reduce the scan time, an optimal acquisition strategy could be determined using simulations to select the most informative combinations of b values, gradient profiles, diffusion directions, and diffusion times. 57 Second, the NNLS method was able to identify a variable number of decay components without specifying their number beforehand. It has recently been speculated that when fewer components are present within a voxel than assumed in a model, overfitting can affect the parameter estimates.…”

“…First, our IVIM protocol allowed multi‐ b value DWI to be acquired within a clinically feasible time. To further reduce the scan time, an optimal acquisition strategy could be determined using simulations to select the most informative combinations of b values, gradient profiles, diffusion directions, and diffusion times 57 . Second, the NNLS method was able to identify a variable number of decay components without specifying their number beforehand.…”

On the dependence of the cardiac motion artifact on the breathing cycle in liver diffusion-weighted imaging

“…A further promising approach is the use of partially or fully flow-compensated diffusion encodings [ 10 , 17 , 18 ]. Those, however, may suffer from bright blood signal at low b-values [ 17 , 27 , 28 ] and of prolonged echo times because the flow-compensated encoding decreases the b-value efficiency.…”