Introducing parametric fusion PET/MRI of primary prostate cancer

We assessed the performance of parametric fusion PET/MRI based on (11)C-choline PET/CT and apparent diffusion coefficient (ADC) maps derived from diffusion-weighted MRI for the identification of primary prostate cancer. (11)C-choline PET/CT and MRI were performed in 17 patients with untreated primary prostate cancer, followed by prostatectomy. Registration of in vivo imaging with histology was achieved using a mutual-information objective function and by performing ex vivo MRI of the prostatectomy specimen (obtained at 3 T) and whole-mount sectioning with block-face photography as intermediate steps. Data analysis included volumetrically registered whole-mount histology with Gleason scoring, (11)C-choline, and ADC data (obtained at 1.5 T). Volumes of interest were defined on the basis of histologically proven tumor tissue to calculate tumor-to-benign prostate background ratios (TBRs) for (11)C-choline, ADC, and a derived fusion PET/MRI parameter calculating the quotient of (11)C-choline over ADC (P(CHOL/ADC)). Fifty-one tumor nodules were identified at pathology. The TBRs for (11)C-choline (P < 0.05) and P(CHOL/ADC) (P < 0.005) were significantly higher in prostate cancers with a Gleason score of ≥3 + 4 than with a Gleason score of ≤3 + 3 disease and controls. For Gleason ≥ 3 + 4, the ADC TBRs were significantly lower than controls and Gleason ≤ 3 + 3 disease (P < 0.05). The absolute value of TBRs obtained from Gleason ≥ 3 + 4 cancers increased from ADC to (11)C-choline PET/CT and from (11)C-choline PET/CT to P(CHOL/ADC), with each step being statistically significant. Our data indicate that parametric PET/MRI using P(CHOL/ADC) improves lesion-to-background contrast (TBRs) of Gleason ≥ 3 + 4 disease, compared with (11)C-choline PET/CT or diffusion-weighted MRI, and thus hold promise that parametric imaging performed on hybrid PET/MRI may further improve identification and localization of significant primary prostate cancer.