In Vivo 1H MR Spectroscopic Imaging of Aggressive Prostate Cancer: Can We Detect Lactate?

Purpose A semi-LASER sequenc was optimized for in vivo lactate detection in the prostate. MethodsThe ethical committee waived the need for informed consent to measure 17 patients with high grade prostate cancer on a 3T system. A semi-LASER sequence was used with an echo time of 144 ms and optimized interpulse timing for a spectral citrate shape with high signal intensity. An LCModel basis set was developed for fitting choline, creatine, spermine, citrate, and lactate and was used to fit all spectra in tumor-containing voxels. For patients without detectable lactate, the minimal detectable lactate concentration was determined by adding in all spectra of tumor tissue a simulated lactate signal. The amplitude of the simulated lactate signal was iteratively decreased until its fit reached a Cramer Rao lower bound >20%, which was then set as the patient-specific detection limit. ResultsIn none of the patients a convincing lactate signal was found. We estimated that on average the lactate levels in high grade prostate cancer are below 1.5 mM (range 0.9-3.5 mM), Interestingly, in one patient with extensive necrosis in the tumor biopsy samples (Gleason score 5+5), large lipid resonances were observed, which originated from the tumor. ConclusionThe minimal detectable lactate concentration of 1.5 mM in high grade prostate cancer indicates that if lactate is increased it remains at low concentrations. Magn Reson Med 71:26-34, 2014. (c) 2013 Wiley Periodicals, Inc.