Double Diffusion Encoding MRI for the Clinic
Microscopic diffusion anisotropy measurements from DDE promise greater specificity to changes in tissue microstructure compared to conventional diffusion tensor imaging, but implementation of DDE sequences on whole-body MRI scanners is challenging due to the limited gradient strengths and lengthy acquisition times. A custom single-refocused DDE sequence was implemented on a 3T whole-body scanner. The DDE gradient orientation scheme and sequence parameters were optimized based on a Gaussian diffusion assumption. Using an optimized five minute DDE acquisition, microscopic fractional anisotropy (mFA) maps were acquired for the first time in multiple sclerosis (MS) patients. Based on simulations and in vivo human measurements, six parallel and six orthogonal diffusion gradient pairs were found to be the minimum number of diffusion gradient pairs necessary to produce a rotationally invariant measurement of mFA. Simulations showed that optimal precision and accuracy of mFA measurements were obtained using b-values between 1500-3000 s/mm2. The mFA maps showed improved delineation of MS lesions compared to conventional FA and distinct contrast from T2-FLAIR and T1-weighted imaging.
Yang G., Tian Q., Leuze C., Wintermark M., McNab J. Double Diffusion Encoding MRI for the Clinic. Magn. Reson. Med., 2017 Nov 17. doi: 10.1002/mrm.27043