MRI-based virtual pathology of the prostate

Abstract

Prostate cancer poses significant diagnostic challenges, with conventional methods like prostate-specific antigen (PSA) screening and transrectal ultrasound (TRUS)-guided biopsies often leading to overdiagnosis or miss clinically significant cancers. Multiparametric MRI (mpMRI) has emerged as a more reliable tool. However, it is limited by high inter-observer variability and radiologists missing up to 30% of clinically significant cancers. This article summarizes a few of these recent advancements in quantitative MRI techniques that look at the "Virtual Pathology" of the prostate with an aim to enhance prostate cancer detection and characterization. These techniques include T2 relaxation-based techniques such as luminal water imaging, diffusion based such as vascular, extracellular, and restricted diffusion for cytometry in tumors (VERDICT) and restriction spectrum imaging or combined relaxation-diffusion techniques such as hybrid multi-dimensional MRI (HM-MRI), time-dependent diffusion imaging, and diffusion-relaxation correlation spectrum imaging. These methods provide detailed insights into underlying prostate microstructure and tissue composition and have shown improved diagnostic accuracy over conventional MRI. These innovative MRI methods hold potential for augmenting mpMRI, reducing variability in diagnosis, and paving the way for MRI as a 'virtual histology' tool in prostate cancer diagnosis. However, they require further validation in larger multi-center clinical settings and rigorous in-depth radiological-pathology correlation are needed for broader implementation.

Keywords: Prostate cancer; Quantitative MRI; Tissue composition; Virtual pathology.

Fig. 1

Representative example of luminal water imaging (LWI). A patient with a Gleason 4 + 4 cancer in the left peripheral zone, marked by the region of interest (ROI) on the T2-weighted image, is shown. LWI demonstrates a reduced luminal water fraction in the cancer region (left posterior) compared to benign peripheral zone tissue in the surrounding and contralateral side (right) (Courtesy of Dr. Abel Lorente Campos, University of Chicago)

Fig. 2

Representative example of restriction spectrum imaging (RSI). Histology image (with cancer outlined) with corresponding RSI map over higher resolution morphological image is shown. Cancer in the right anterior is characterized by an increased signal from intracellular water, indicating increased cellularity compared to surrounding benign prostatic tissue (Courtesy of Dr. Tyler Siebert, University of California San Diego, and reproduced from Chatterjee et al., reference #14, with permission from Springer Nature)

Fig. 3

Representative example of VERDICT imaging. A 63-year-old patient with a Gleason 3 + 4 lesion in the right posterior peripheral zone is shown. VERDICT maps demonstrate the tumor with increased intracellular volume fraction and cellularity, and reduced extracellular extravascular volume compared to surrounding benign prostatic tissue (Courtesy of Dr. Eleftheria Panagiotaki, University College London, and reproduced from Chatterjee et al., reference #14, with permission from Springer Nature)

Fig. 4

Representative example of hybrid multidimensional MRI (HM-MRI). A 63-year-old patient with a Gleason 4 + 4 lesion in the left posterolateral peripheral zone is shown on whole-mount prostatectomy specimen. On HM-MRI, the cancer exhibits increased epithelium and reduced lumen compared to adjacent benign tissue, accurately predicting it as a clinically significant cancer (Courtesy of Department of Radiology, University of Chicago. Data was part of the study by Chatterjee et al. [51] and used the same criteria for cancer prediction)

Fig. 5

Representative example of time-dependent diffusion MRI. A 68-year-old patient with a Gleason 4 + 5 lesion in the peripheral zone. The cancer region shows increased intracellular fraction (f_in) and higher cellularity (Courtesy of Dr. Yu-Dong Zhang and Dr. Dan Wu, Nanjing Medical University)

Fig. 6

Representative example of MR micro-texture. Prostate spectra from the benign peripheral zone and cancer tissue. The spectra obtained from cancer and benign tissue show significantly different textural feature size (Courtesy of Dr. Timothy James, BioProtonics, Inc.)