PROJECT SUMMARY The vast majority of men diagnosed with prostate cancer do not die of their disease and can choose to delay or avoid surgical or radiation treatment by undergoing active surveillance. Unfortunately, men on active surveillance remain at risk for progression of prostate cancer and even death from prostate cancer. Therefore, men are carefully followed with transrectal prostate biopsies every 1-2 years. Unlike with tumors in other organs, there is no imaging modality that can be used to accurately detect and monitor prostate tumors. Furthermore, prostate biopsies are painful and associated with a significant risk of sepsis and hospitalization. Therefore, the personal and public health burden of life-long active surveillance is significant. We introduce a novel MRI sequence that improves image quality and resolution. Our preliminary data shows that in men on active surveillance, standard MRI detects only 61% of biopsy-proven prostate tumors. However, our novel HR- MRI detects nearly all (96%) biopsy-proven prostate tumors, which is iimpressive since men on active surveillance tend to have small, low grade tumors. Our HR-MRI used to generate our preliminary data had a 5-fold improvement in resolution; however, the resolution can be improved up to 25-fold at a cost of increased scan time. The first aim will be to further optimize our HR-MRI to improve resolution and image quality while minimizing the scan time. The optimized HR-MRI will be used to detect changes in tumor size or grade in men on active surveillance and consider the possibiity that tumor growth rate or other imaging characteristics predict the risk of disease progression. A more accurate MRI modality for localizing and monitoring prostate tumors will allow men on active surveillance to reduce the number of followup biopsies, identify tumors for biopsies that can be used for molecular characterization, and localize tumors for focal ablative therapies. The HR-MRI can be deployed on existing 1.5T and 3T MRI systems with a simple software installation and does not require new hardware.