Advanced Metabolic MRI to Refine Targeted Prostate Biopsy

Prostate Imaging and Data Reporting System assessment categories positively correlate with an increased likelihood of detecting clinically significant prostate cancer (csPCa) at targeted biopsy1. A PI-RADS assessment category 3 (intermediate, clinically significant cancer likelihood equivocal) lesion is often not csPCa. Studies evaluating the likelihood of csPCa cancer at targeted biopsy of PI-RADS category 3 lesions have reported variable rates of PCa diagnosis, ranging from 5-30%, with the majority of studies showing a relatively low likelihood of eventual csPCa diagnosis2-4. Management of PI-RADS category 3 lesion is variable, ranging from immediate biopsy to surveillance5,6. Given the disparity in management patterns for PI-RADS category 3 lesions and a small but not insignificant proportion of these lesions harboring csPCa, better classification of category 3 lesion is an unmet need. Previous studies in these patients have shown a correlation of csPCa with older patient age, smaller prostate volumes, higher prostate-specific antigen density (PSAD), and increased clinical stage7-11.

In this study, we will investigate the ability of magnetization transfer (MT) and chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI), without the use of any injected contrast agent, in conjunction with multiparametric magnetic resonance imaging (mpMRI) to aid in the detection of cancer, risk stratification and to decide whether a targeted prostate biopsy is justified. In this study, we propose to use the following ST-MRI techniques:

1. Chemical Exchange Saturation Transfer (CEST) to probe changes in tumour metabolism.
2. Magnetization Transfer (MT) to evaluate tumour environment microstructure.

Up to five healthy volunteers will be recruited for ST-MRI testing and estimation of test/re-test reproducibility. Testing of MR imaging protocols on healthy volunteers (without contrast agent) is required for optimization of sequence parameters including: higher signal intensity, higher contrast between tissue types, decreased scan time, and reduced image artifacts. There will be up to three MRI scans per healthy volunteer. MRI contrast agent will not be injected.

Patient recruitment will be performed at the Odette Cancer Centre. There will be one MRI scan per patient. All patients will undergo ST-MRI scans at Sunnybrook. ST-MRI parameter images including MTR, AREX, and quantitative MT model parameters, in addition to quantitative magnetization relaxation images will be used to identify areas of prostate with altered image contrast. Other quantitative and semiquantitative features will also be evaluated from the images. We hypothesize that ST-MRI will identify cancer suspicious areas that overlap with those identified by mpMRI and potentially additional areas.