Does 29Mhz Micro-Ultrasound Provide Uniform Diagnostic Accuracy Within and Beyond the Peripheral Zone?

Background: The PRI-MUSTM (Prostate Risk Identification for Micro-Ultrasound) protocol was developed in 2016 to identify suspicious areas seen by the ExactVu™ micro-ultrasound imaging platform. While a retrospective validation was performed, no prospective validation has been published in the peer-reviewed literature. Further, this protocol was developed for the peripheral zone and it is unclear whether the accuracy to predict clinically significant cancer is uniform throughout the gland.

Methods: 399 prostate biopsies were performed in 372 patients using the ExactVu micro-ultrasound system (Exact Imaging, Markham, Canada) from January 2018 to May 2019 at the Ordensklinikum Linz (Linz, Austria). Subjects had a median PSA of 6.7 (IQR 4.5-11.2) ng/mL and 30% had positive DRE. Suspicious areas were assessed in real-time using PRI-MUS and a TRUS biopsy was performed in the same session under microultrasound guidance. Biopsies were carried out by 5 providers and results from pathology were then compared with the image findings.

Results: Biopsy pathology confirmed a cancer diagnosis in 60% of patients, with 42% of patients harboring Grade Group (GG) > 1 cancer. The PRI-MUS protocol had an area under the receiver-operator characteristic (AUC) of 0.76 for predicting GG>1 cancer in the peripheral zone. This accuracy varied between 0.68-0.83 depending on prostate region, with highest accuracy in the prostate apex and lowest accuracy in the base. Anterior targets were sampled but generally not assigned a PRI-MUS score as the system is currently only validated in the peripheral zone, still, in the 33/737 anterior samples assigned a PRI-MUS score AUC was 0.80.

Conclusion: Micro-ultrasound and the PRI-MUS protocol are useful tools to detect cancer and appear to maintain strong diagnostic value throughout the prostate. This technology holds promise for reducing the high false-negative rate of prostate biopsy, without relying on multimodality, multi-specialty solutions like mpMRI.

Keywords: Exact Imaging; mpMRI; ultrasound; Micro-ultrasound; Biopsy; Prostate cancer

Abbreviations: mpMRI: Multiparametric Magnetic Resonance Imaging; PSA: Prostate Specific antigen; PIRADS v2: Prostate Imaging and Reporting Data System Version 2; TRUS: Trans-Rectal Ultrasound; PRI-MUS: Prostate Risk Identification for Micro-Ultrasound