Purpose: Diffusion-relaxation correlation spectroscopic imaging (DR-CSI) is a recent microstructure imaging approach that can resolve sub-voxel compartments using a high-dimensional dataset encoded with diffusion and relaxation and spatially-regularized spectrum estimation. This work investigated the feasibility of DR-CSI with an optimized experiment design for in-vivo body imaging.
Methods: DR-CSI datasets were acquired using a diffusion-weighted spin-echo EPI sequence at 3T. For prostate, 31 combinations from 5 b-values (b=0,300,500,1000,1500s/mm^2) and 7 echo times (TE=60,80,105,130,160,300,400ms) were used for contrast encoding as an over-sampled reference. Sixteen combinations were selected using the Cramer-Rao Bound (CRB)-based experiment design to accelerate the scan time. Five healthy volunteers and 2 volunteers with benign prostate hyperplasia (BPH) were scanned. Similarly, for liver, 15 combinations were selected among 25 combinations from 6 b-values (b=0,50,200,500,1000,3000s/mm^2) and 5 echo times (TE=47,60,80,100,120ms). Seven healthy volunteers and one patient with chronic hepatitis B virus infection were scanned.From each dataset, 2D diffusion-T2 correlation spectra were estimated over all voxels. In the spectra, distinct spectral peaks corresponding to different sub-voxel compartments were identified. Spatial maps were generated to indicate the pixel-wise fractions of individual peaks.
Results: In healthy prostates, we consistently observed three sub-voxel compartments that are associated with three well-known prostate microstructure (epithelial, stroma and lumen). However, in the BPH, we observed one additional component. In healthy livers, five sub-voxel compartments were consistently observed. In the hepatitis B liver, while similar five components were observed, their fractions were significantly different from those in healthy livers. Our results suggest that DR-CSI has the potential to detect pathological changes by characterizing the fractional changes of normal components and/or revealing additional components.
Conclusion: DR-CSI is feasible in in-vivo liver and prostate microstructure imaging, demonstrating its abilities to resolve sub-voxel compartments and to detect abnormalities related to pathologies.
Diffusion, Relaxation Times, Tissue Characterization