Active Imaging with Dual Spin-Echo Diffusion MRI

Active imaging is a recently developed approach to model-based optimisation of imaging protocols. In the application we discuss here, a diffusion magnetic resonance imaging (dMRI) protocol is optimised for directly measuring aspects of biological tissue microstructure, subject to appropriate scanner hardware and acquisition time constraints. We present the theoretical basis for active imaging with the dual spin-echo (DSE) dMRI pulse sequence, which is more complex than the standard sequence, but widely used due to its robustness to image distortion. The new formulation provides the basis for future active imaging studies using DSE. To demonstrate the approach, we optimise DSE sequences for estimating parameters in a simple model of neural white matter, specifically axon density and diameter. Results show that sensitivity to these important parameters is at least as good as with more traditional pulse sequences that are not robust to image distortion.