31P MR Spectroscopic Imaging of the Human Prostate at 7 T: T1 Relaxation Times, Nuclear Overhauser Effect, and Spectral Characterization

PurposeOptimization of phosphorus (P-31) MR spectroscopic imaging (MRSI) of the human prostate at 7 T by the evaluation of T-1 relaxation times and the Nuclear Overhauser Effect (NOE) of phosphorus-containing metabolites. MethodsTwelve patients with prostate cancer and one healthy volunteer were scanned on a 7 T whole-body system using a P-31 endorectal coil combined with an eight-channel H-1 body array coil. T-1 relaxation times were measured using progressive saturation in a two-dimensional localization sequence. P-31 MRSI was performed twice: once without NOE and once with NOE using low-power continuous wave H-1 irradiation to determine NOE enhancements. ResultsT(1) relaxation times of P-31 metabolites in the human prostate at 7 T varied between 3.0 and 8.3 s. Positive but variable NOE enhancements were measured for most metabolites. Remarkably, the P-31 MR spectra showed two peaks in chemical shift range of inorganic phosphate. ConclusionKnowledge of T-1 relaxation times and NOE enhancements enables protocol optimization for P-31 MRSI of the prostate at 7 T. With a strongly reduced P-31 flip angle ( 45 degrees), a P-31 MRSI dataset with optimal signal-to-noise ratio per unit time can be obtained within 15 minutes. The NOE enhancement can improve fitting accuracy, but its variability requires further investigation. Magn Reson Med 73:909-920, 2015. (c) 2014 Wiley Periodicals, Inc.