mpMRI has a magnet strength of either 1.5 Tesla or 3 Tesla. The coil used for the imaging can be endorectal, or body surface or both. The parameters assessed in the mpMRI are the T2W, DWI, and DCE. In tri-planar T2 weighted MRI, we obtain axial, sagittal and coronal images. In T2, tumors can be seen in signal drop. In diffusion-weighted (DWI-ADC map) we evaluate the Brownian motion of the free water within tissue. Tissue diffusion is restricted with increased cellularity and is an indication of prostate cancer. It can also correlate with Gleason score.
Dynamic contrast-enhanced (DCE) evaluates the vascularity of tumors. It incorporates fast MR scanning sequences combined with the rapid administration of low molecular weight Gadolinium. Prostate cancer shows early and rapid enhancement and early washout.
PIRADS version 2 assessment is the standardized reporting system using a 5-point scale based on the likelihood that a combination of mpMRI findings on T2w, DWI, and DCE correlates with the presence of clinically significant cancer for each lesion in the prostate gland.
mpMRI for screening prostate cancer is at this point purely investigational with no evidence to support it in clinical practice. Despite the interest by patients and urologists, there is insufficient data to recommend routine MRI in every biopsy naïve man being considered for a prostate biopsy. However, for a man with a previous negative TRUS biopsy, both the AUA and Society of abdominal radiology (SAR) wrote a consensus statement regarding the usage of mpMRI in this setting. According to these statements, when high quality prostate mpMRI is available, it should be strongly considered in any patient with a prior negative TRUS biopsy who has persistent clinical suspicion for prostate cancer, and who is undergoing a repeat biopsy.
Regarding the issue of whether to perform only a targeted biopsy after a lesion has been identified in the mpMRI or also perform a 12-core systematic biopsy, according to the AUA statement, this is a case specific decision.
When assessing the role of mpMRI for management, it may be useful in the setting of biochemical failure after surgery or radiation when recurrence is suspected. The role of mpMRI in focal therapy is not yet established. In active surveillance (AS), it may be beneficial for identifying AS candidates, but data is insufficient to support its use for monitoring men on AS. When used in the setting of staging before treatment, it may add critical data that can drastically change the planned treatment strategy, but more data is needed in this specific setting to understand the role of mpMRI.
Pinto summarized his talk stating that mpMRI represents a significant medical advance over traditional prostate imaging. MpMRI and targeted prostate biopsy has increased the detection of clinically significant prostate cancer, and has a role after a negative TRUS biopsy with continued suspicion for missed cancer. Additional indications are rapidly evolving but need further mature data.
1. Hashim U Ahmed, et al. Diagnostic accuracy of multi-parametric MRI and TRUS biopsy in prostate cancer (PROMIS): a paired validating confirmatory study. The Lancet, Volume 389, No. 10071, p815–822, 25 February 2017
Presented by: Peter Pinto, MD, NIH, Bethseda, Maryland
Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre @GoldbergHanan at the 2018 AUA Annual Meeting - May 18 - 21, 2018 – San Francisco, CA USA