Reduced power magnetic resonance spectroscopic imaging of the prostate at 4.0 Tesla

Proton magnetic resonance spectroscopic imaging (MRSI) of the prostate has been described at 1.5 T and 3 T as a means of localizing prostate cancers with high sensitivity and specificity. This technique could be improved by increasing the field strength further; however, it has not been described in detail above 3 T. To address the increase in B1 and SAR at high field strengths, a new protocol is described for reduced power STEAM MRSI of the prostate at 4.0 Tesla, using a pelvic surface coil array for RF transmission and reception, and a solid, reusable endorectal coil for reception only. The optimal STEAM sequence timing parameters for observation of the strongly coupled citrate spin system were determined through simulation to be echo time (TE) = 27 ms and mixing time (TM) = 27 ms, and the results were verified in vitro. Power reduction was achieved by applying the VERSE method to each of the three slice selective pulses in the STEAM sequence, and the B(1)max and SAR were reduced by 43% and 36%, respectively. Finally, in vivo spectroscopic imaging data were acquired from a prostate cancer patient, demonstrating the detection of citrate, choline, and creatine with 0.37 cc nominal resolution in a 10 minute scan.