Increased diffusion sensitivity with hyperechos.
It is shown that the introduction of a 180 degrees refocusing pulse into a standard diffusion weighted stimulated echo sequence is equivalent to the simplest hyperecho sequence with identical diffusion weighting but equal or greater signal-to-noise (SNR) and thus equal or greater diffusion contrast. For high b-value imaging, the hyperecho sequence thus possesses the high diffusion contrast in the presence of small T(1)/T(2) ratios characteristic of stimulated echo sequences but with less than the 50% loss in SNR that is associated with the stimulated echo. For low b-value imaging, the hyperecho signal converges to that of the standard spin echo. The advantages of the two-pulse diffusion weighted hyperecho sequence are demonstrated theoretically. Experimental results are shown in the application to high angular resolution diffusion encoding (HARD) in normal human brain.
Frank
Lawrence R
LR
UCSD Center for Functional MR1, San Diego, California 92093, USA. lfrank@ucsd.edu
Wong
Eric C
EC
Liu
Thomas T
TT
Buxton
Richard B
RB
D016880:Anisotropy; D001921:Brain / Q000502:physiology*; D038524:Diffusion Magnetic Resonance Imaging; D006801:Humans; D008962:Models, Theoretical