TE = 32 ms vs TE = 100 ms echo‐time (1)H‐magnetic resonance spectroscopy in prostate cancer: Tumor metabolite depiction and absolute concentrations in tumors and adjacent tissues

PURPOSE: To compare the depiction of metabolite signals in short and long echo time (TE) prostate cancer spectra at 3T, and to quantify their concentrations in tumors of different stage and grade, and tissues adjacent to tumor. MATERIALS AND METHODS: First, single‐voxel magnetic resonance imaging (MRI) spectra were acquired from voxels consisting entirely of tumor, as defined on T (2)‐weighted and diffusion‐weighted (DW)‐MRI and from a biopsy‐positive octant, at TEs of 32 msec and 100 msec in 26 prostate cancer patients. Then, in a separate cohort of 26 patients, single‐voxel TE = 32 msec MR spectroscopy (MRS) was performed over a partial‐tumor region and a matching, contralateral normal‐appearing region, defined similarly. Metabolite depiction was compared between TEs using Cramér‐Rao lower bounds (CRLB), and absolute metabolite concentrations were calculated from TE = 32 msec spectra referenced to unsuppressed water spectra. RESULTS: Citrate and spermine resonances in tumor were better depicted (had significantly lower CRLB) at TE = 32 msec, while the choline resonance was better depicted at TE = 100 msec. Citrate and spermine concentrations were significantly lower in patients of more advanced stage, significantly lower in Gleason grade 3+4 than 3+3 tumors, and significantly lower than expected from the tumor fraction in partial‐tumor voxels (by 14 mM and 4 mM, respectively, P < 0.05). CONCLUSION: Citrate and spermine resonances are better depicted at short TE than long TE in tumors. Reduction in these concentrations is related to increasing tumor stage and grade in vivo, while reductions in the normal‐appearing tissues immediately adjacent to tumor likely reflect tumor field effects. J. Magn. Reson. Imaging 2015;42:1086–1093.