Halving imaging time of whole brain diffusion spectrum imaging and diffusion tractography using simultaneous image refocusing in EPI

Purpose: To increase the efficiency of densely encoded diffusion imaging of the brain, such as diffusion spectrum imaging (DSI), we time-multiplex multiple slices within the same readout using simultaneous image refocusing echo-planar imaging (SIR-EPI).

Materials and methods: Inefficiency in total scan time results from the long time of diffusion encoding gradient pulses which must be repeated for each and every image. We present a highly efficient multiplexing method, simultaneous image refocusing (SIR), for reducing the total scan time of diffusion imaging by nearly one-half. SIR DSI is performed in 10 minutes rather than 21 minutes, acceptable for routine clinical application.

Results: Two identical studies were completed, comparing conventional single-slice EPI DSI and SIR-EPI DSI, showing equal signal-to-noise ratio (SNR) and contrast and small differences in registration, likely due to typical subject motion. Comparison of DSI and DTI tractographs showed matching quality and detection of white matter tracts.

Conclusion: The net reduction to nearly half the number of diffusion encoding gradient pulses in SIR-EPI significantly reduces acquisition times of DSI and DTI.