THE INFLUENCE OF STIMULATED ECHOES ON CONTRAST IN FAST SPIN-ECHO IMAGING

Tissue contrast obtained using fast spin-echo (FSE) and conventional s pin-echo (SE) sequences is not identical and a number of mechanisms ar e thought to contribute to these contrast differences. The effect of s timulated echoes has previously been apparently ruled out as a contrib uting mechanism, Signal-to-noise ratios of single-slice matched FSE an d conventional SE sequences were compared in aqueous solutions of CuSO 4, Cr-2(SO4)(3) and MnSO4 with various T-1 and T-2 values. Enhancement of the FSE signal was observed in short T-2 solutions and the effect was greater in samples where the T-1 to T-2 ratio was high, Reducing t he refocusing pulse flip angle to increase the contribution from stimu lated echoes also resulted in slightly increased enhancement, Experime ntal results were verified by computer simulations, Our results show t hat stimulated echoes do contribute to the contrast differences betwee n FSE acid conventional SE images and may be significant in the imagin g of brain hemorrhage.