The main observation at the basis of our diffusion imaging work can be understood as follow. Diffusion-weighted imaging (DWI) involves acquiring several images of an object while varying the diffusion encoding, both in terms of how strong the encoding is (the strength is called ‘b-value’), and in terms of the direction in 3D that is being encoded (different directions are listed/indexed here using the letter ‘d’). The observation at the basis of our work is that if a Fourier transform is applied along both ‘b’ and ‘d’ directions, the result looks mostly empty:
While there may be a lot of signal concentrated in the central cross-shaped region highlighted with dashed gray lines above, there is not much signal anywhere else. The idea here is to use this available real-estate, i.e., the four mostly-empty quadrants, to encode other information. Doing so, we can multiplex the density of the information and the effectiveness of the data acquisition process:
We have applied this sort of trick to various types of DWI methods and sequences, such as HARDI, and we have applied it to different parts of the body, mostly the brain, optic nerve and the prostate. In all cases, our goal was to speed up the acquisition process so that images could be obtained that were less distorted, with better geometrical fidelity than a regular scan would have yielded. Furthermore, these better images could often be obtained in a fraction of the time a full scan would have required. Here is one particular example, for prostate imaging:
- Aksit Ciris P, Chiou Jr-y, Glazer D, Zhang SH, Chao T-C, Tempany-Afdhal CM, Madore B, Maier SE. Accelerated segmented diffusion-weighted prostate imaging for higher resolution, higher geometric fidelity, and multi-b perfusion quantification. Invest Radiol 2019;54:238-46. PMCID: PMC6402959
- Chao TC, Chiou Jr-y, Maier SE, MadoreB. “Fast diffusion imaging with high angular resolution.” Magn Reson Med 2017; 77:696-706. PMCID: PMC4992669.
- Madore B, Chiou J-Y, Chu R, Chao T-C, Maier SE. Accelerated multi-shot diffusion imaging. Magn Reson Med 2014 Aug;72:324-36. PMCID: PMC3942374
- Johansson J, Lagerstrand K, Svensson PA, Chiou Jr-y, Madore B, Hebelka H, and Maier S. 2022. “Segmented accelerated multi-shot diffusion imaging combined with reverse polarity gradient (RPG) correction.” Proceedings of the International Society of Magnetic Resonance in Medicine. London, UK.