Multiparametric MRI and MR Spectroscopic Imaging of Prostate Lesions with Implementation of PI-RADS and Histopathological Correlation: A Prospective Analysis

Abstract

Introduction Majority of the elderly male population suffers from prostatism due to enlargement of the prostate as a result of what is now regarded as male climacteric. For standardizing multiparametric magnetic resonance imaging (MRI) of the prostate, the European Society of Urogenital Radiology published Prostate Imaging Reporting and Data System (PI-RADS) in 2012. Magnetic resonance spectroscopic imaging (MRSI) uses a strong magnetic field to obtain metabolic information that identifies the relative concentrations of various metabolites in the cell cytoplasm and the extracellular space. Prostate carcinoma is associated with proportionately lower levels of citrate and higher levels of choline and creatine than are seen in benign prostatic hyperplasia (BPH) or in normal prostate. This difference can be detected by MRSI. Aim This study has been undertaken with the objective of finding how reliable MRI is in establishing the diagnosis of lesions of prostate and to correlate the histopathological (HPE) findings of transrectal ultrasound (TRUS)–guided targeted prostate biopsy with the PI-RADS scoring (Version 2) on MRI in patients. Also, the study evaluates the accuracy of MRSI in the detection of prostatic carcinoma in men with elevated prostate-specific antigen (PSA) levels. Materials and Methods A prospective study was undertaken at a tertiary care hospital during a period of 2 years from May 2017 to April 2019 on 50 patients with PSA > 4 ng/dL and with palpable lesion on digital rectal examination. MRI and MRSI were performed with a 1.5-Tesla body MRI system. The pelvic phased-array coil was used for both excitation and signal reception. Imaging was done using standard protocols. Histological material was obtained from prostate chippings from transurethral resection of prostate. Results Fifty patients with elevated PSA levels underwent MRI, MRSI, TRUS-guided biopsy and documented PI-RADS scores. Eight patients had PI-RADS 1 score, 2 patients had PI-RADS 2 score, 8 patients had PI-RADS 3 score, 14 patients had PI-RAD 4 score, and 18 patients had PI-RADS 5 score. Thirty-two patients with PI-RADS 4 and PI-RADS 5 on imaging showed positive for malignancy on HPE, showing significant association on Chi-square test with X2 = 16.412 and p < 0.001 (statistically significant). MRSI detected 36 patients on biopsy proven cases of carcinoma (sensitivity 89.5%, specificity 64%, and accuracy 88%). Conclusion This study showed a very good correlation between positivity of prostate carcinoma on HPE and higher PI-RADS (4 and 5, respectively). PI-RADS overall score had 94% sensitivity compared with components such as diffusion-weighted imaging (DWI, 78%) and T2 hypointensity (72%). MRSI is more sensitive and specific compared with T2-weighted images alone.