Feasibility of Clinical Studies of Chemical Exchange Saturation Transfer at 7T-MRI of Prostate Cancer.

Chemical exchange saturation transfer (CEST) has been explored for differentiation between tumour and benign tissue in prostate cancer (PCa) patients. With ultra-high field strengths such as 7 Tesla (T), the increase of spectral resolution and sensitivity could allow for selective detection of amide proton transfer at 3.5ppm (APT) and a group of compounds that resonate at 2ppm (i.e. (poly)amines and/or creatine). The potential of 7T multipool CEST analysis of the prostate and the detection of PCa was studied in patients with proven localized PCa who were scheduled to undergo robot-assisted radical prostatectomy (RARP). Twelve patients were prospectively included, (mean age 68.0 years, mean serum-PSA 7.8). A total of 24 lesions >2mm were analysed. 7T T2-weighted imaging (T2WI) and 48 spectral points CEST were used. Patients received a 1.5/3T prostate MRI, and galium-68-prostate specific membrane antigen ( 68 Ga-PSMA)-PET/CT to determine location of the single-slice CEST. Based on the histopathological results after RARP, three regions of interest (ROI) were drawn in the T2WI from a known malignant zone and a benign zone in the central zone and peripheral zone. These areas were transposed to the CEST data from which the APT- and 2ppm-CEST were calculated. Statistical significance of the CEST between central zone, peripheral zone and tumour was calculated using a Kruskal-Wallis test. The z-spectra show that APT and even a distinct pool that resonate at 2ppm are detectable. This study showed a difference trend in the APT levels, but no difference in the 2ppm levels when tested between central zone, peripheral zone and tumour (H(2)=4.8, P-value=0.093 and H(2)=0.86, P-value=0.651, respectively). Thus to conclude, we could most likely detect APT and amines and/or creatine levels non-invasively in prostate using CEST effect. On group level, CEST showed a higher level of APT in peripheral zone versus central zone, however no differences of APT and 2ppm levels were observed in tumours.