EMUC 2020: Ultrasound Is Improving: 29 Mhz, mpUS, C-TRUS, Elastography and Microbubble
November 16, 2020 — UroToday.com
At the Fragments of Imaging session at the European Multidisciplinary Congress on Urological Cancers 2020 virtual meeting, Dr. Christophe Mannaerts discussed emerging roles for ultrasound as it relates to prostate cancer detection.
Dr. Mannaerts started by noting that greyscale ultrasound is not a reliable method for detecting prostate cancer, even though some tumors are visible as hypoechoic lesions. However, there are emerging novel ultrasound modalities for prostate cancer detection and localization, including C-Trus, contrast-enhanced ultrasound, shear wave elastography, micro-ultrasound, microbubbles (CEUS with contrast-ultrasound dispersion imaging (CUDI)), etc:
Contrast-ultrasound dispersion imaging focuses on the detection of angiogenetic changes in the microvascular architecture of the prostate with time-intensity curves. Instead of focusing on the qualitative interpretation of contrast-enhanced ultrasound recordings, CUDI provides several parametric maps that can be used for prostate cancer diagnosis. In a recently published study by Dr. Mannaerts’ group, they found that mpMRI- and CUDI-targeted biopsy strategies were inferior to systematic biopsy for GG ≥2 prostate cancer detection and the study was stopped. Systematic biopsy found significantly more GG ≥2 prostate cancer: 39% (56/142), as compared with 29% (41/142) and 28% (40/142) for mpMRI- targeted biopsy and CUDI- targeted biopsy, respectively (p < 0.05).1 However, systematic biopsy found significantly more GG = 1 prostate cancer: 14% (20/142) compared to 1% (two of 142) and 3% (four of 142) with mpMRI- targeted biopsy and CUDI- targeted biopsy, respectively (p < 0.05).
Micro-ultrasound devices operate at 29 MHz compared to 8-12 MHz, which leads to a 300% improved resolution of the microstructures and tissue patterns. In line with the PI-RADS scoring system for mpMRI, the PRI-MUS protocol has been developed for scoring lesions using micro-ultrasound. The scoring system description for PRI-MUS is as follows:
Likert 1 – “Swiss cheese”
Likert 2 – Hyperechoic with ductal patches
Likert 3 – Mild heterogeneity with small bright echos in hyperechoic tissue
Likert 4 – Bright echos
Likert 5 – Irregular shadowing
Recently published multi-center prospective work led by Dr. Laurie Klotz assessed 1,040 men that had a prior mpMRI and underwent ExactVu micro-ultrasound-guided biopsy.2 Overall, 39.5% were positive for clinically significant prostate cancer. Micro-ultrasound and mpMRI sensitivity was 94% vs. 90%, respectively (p=0.03), and NPV was 85% vs. 77%, respectively.
Like mpMRI, multiparametric ultrasound (mpUS) is also being studied, combining grey-scale for hypoechogenicity, CEUS for contrast enhancement, SWE for tissue stiffness, and CUDI for microbubble kinetics. Work from Dr. Mannaerts’ group assessed 48 men that underwent mpUS prior to radical prostatectomy, noting that the region of interest-specific sensitivity of mpUS (Likert 3 or greater) for clinically significant prostate cancer was 74% (95% CI 67-80) compared to 55% (95% CI 47-63), 55% (95% CI 47-63) and 59% (95% CI 51-67) for B-mode, shear wave elastography and contrast-enhanced ultrasound, respectively.
Dr. Mannaerts states that there are reasons we need to investigate ultrasound, considering that there are several concerns with the mpMRI pathway, including (i) costs and accessibility, (ii) inter-reader reproducibility, (iii) inter-operator reproducibility with the necessity of cross-modality registration, and (iv) variability in results from different centers of expertise. The possible benefits of ultrasound include reduced costs, better accessibility, and easier lesion targeting. What is needed according to Dr. Mannaerts is a head-to-head comparison with the mpMRI pathway to establish a role for ultrasound. This will allow a comparison of both pathways for insignificant and clinically significant prostate cancer detection, as well as combining modalities to assess the absolute added value of each pathway (MRI-US pathway).
Dr. Mannaerts concluded with several take-home messages:
Ultrasound imaging for prostate cancer and localization is improving.
Ultrasound can become a more accessible modality for prostate biopsy if we continue working on (i) standardized, validated and reproducible acquisition and reporting for ultrasound, and (ii) high-quality benchmarking with the mpMRI pathway in the same patient group.
Presented by: Christophe K. Mannaerts, Amsterdam University Medical Centers, Nijmegen, The Netherlands; Written by: Zachary Klaassen, MD, MSc – Assistant Professor of Urology, Georgia Cancer Center, Augusta