PI-RADS 2.1 - Image Interpretation: The Most Important Updates and Their Clinical Implications

Reduced FOV T2-weighted imaging, 2.5D T2-weighted imaging, and high b-value diffusion-weighted imaging of the prostate at 5 T: a comparative study with 3 T

OBJECTIVES

To evaluate the image quality of prostate T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) at 5 T.

METHODS

In this prospective study, asymptomatic adult male volunteers underwent conventional T2WI and multiple b-value DWI at both 3 T and 5 T, along with 2.5D T2WI at 5 T using the 2.5D imaging method. 2.5D imaging method improved in-plane resolution by reducing slice thickness and increasing the number of signal averaged to maintain the signal-to-noise ratio (SNR). Three scanning protocols were compared: conventional T2WI at 5 T vs. 3 T, 2.5D T2WI at 5 T vs. conventional T2WI at 5 T, and DWI at 5 T vs. 3 T. Quantitative analysis encompassed SNR, contrast-to-noise ratio (CNR), prostate dimensions, prostate volume (PV), edge rise distance of the dorsal prostate capsule, and ADC values in benign lesions. Image quality was qualitatively rated using a five-point Likert scale (1 = non-diagnostic, 5 = excellent). Statistical significance was assessed using paired t-test and Wilcoxon signed-rank test, with a significance threshold of P < 0.05.

RESULTS

Twenty participants were enrolled. Compared to 3 T, 5 T significantly increased SNR and CNR for T2WI (sagittal, coronal, and axial planes) and DWI (b-values of 1000, 1500, 2000 s/mm²) (P < 0.05). Image sharpness and clarity were significantly enhanced for T2WI and DWI at 5 T (P < 0.05). The 2.5D imaging method further improved T2WI resolution, overall image quality, and clarity of the prostate capsule. No significant differences were observed in artifact presence or PV between the T2WI groups (P > 0.05).

CONCLUSION

5 T bi-parametric MRI (bp-MRI) of the prostate demonstrated superior image quality.

Recommendations for the creation of benchmark datasets for reproducible artificial intelligence in radiology

Various healthcare domains have witnessed successful preliminary implementation of artificial intelligence (AI) solutions, including radiology, though limited generalizability hinders their widespread adoption. Currently, most research groups and industry have limited access to the data needed for external validation studies. The creation and accessibility of benchmark datasets to validate such solutions represents a critical step towards generalizability, for which an array of aspects ranging from preprocessing to regulatory issues and biostatistical principles come into play. In this article, the authors provide recommendations for the creation of benchmark datasets in radiology, explain current limitations in this realm, and explore potential new approaches. CLINICAL RELEVANCE STATEMENT: Benchmark datasets, facilitating validation of AI software performance can contribute to the adoption of AI in clinical practice. KEY POINTS: Benchmark datasets are essential for the validation of AI software performance. Factors like image quality and representativeness of cases should be considered. Benchmark datasets can help adoption by increasing the trustworthiness and robustness of AI.

Current Status of Biparametric MRI in Prostate Cancer Diagnosis: Literature Analysis

The role of multiparametric MRI (mpMRI) in the detection of prostate cancer is well-established. Based on the limited role of dynamic contrast enhancement (DCE) in PI-RADS v2.1, the risk of potential side effects, and the increased cost and time, there has been an increase in studies advocating for the omission of DCE from MRI assessments. Per PI-RADS v2.1, DCE is indicated in the assessment of PI-RADS 3 lesions in the peripheral zone, with its most pronounced effect when T2WI and DWI are of insufficient quality. The aim of this study was to evaluate the methodology and reporting in the literature from the past 5 years regarding the use of DCE in prostate MRI, especially with respect to the indications for DCE as stated in PI-RADS v2.1, and to describe the different approaches used across the studies. We searched for studies investigating the use of bpMRI and/or mpMRI in the detection of clinically significant prostate cancer between January 2017 and April 2022 in the PubMed, Web of Science, and Google Scholar databases. Through the search process, a total of 269 studies were gathered and 41 remained after abstract and full-text screening. The following information was extracted from the eligible studies: general clinical and technical characteristics of the studies, the number of PI-RADS 3 lesions, different definitions of clinically significant prostate cancer (csPCa), biopsy thresholds, reference standard methods, and number and experience of readers. Forty-one studies were included in the study. Only 51% (21/41) of studies reported the prevalence of csPCa in their equivocal lesion (PI-RADS category 3 lesions) subgroups. Of the included studies, none (0/41) performed a stratified sub-analysis of the DCE benefit versus MRI quality and 46% (19/41) made explicit statements about removing MRI scans based on a range of factors including motion, noise, and image artifacts. Furthermore, the number of studies investigating the role of DCE using readers with varying experience was relatively low. This review demonstrates that a high proportion of the studies investigating whether bpMRI can replace mpMRI did not transparently report information inherent to their study design concerning the key indications of DCE, such as the number of clinically insignificant/significant PI-RADS 3 lesions, nor did they provide any sub-analyses to test image quality, with some removing bad quality MRI scans altogether, or reader-experience-dependency indications for DCE. For the studies that reported on most of the DCE indications, their conclusions about the utility of DCE were heavily definition-dependent (with varying definitions of csPCa and of the PI-RADS category biopsy significance threshold). Reporting the information inherent to the study design and related to the specific indications for DCE as stated in PI-RADS v2.1 is needed to determine whether DCE is helpful or not. With most of the recent literature being retrospective and not including the data related to DCE indications in particular, the ongoing dispute between bpMRI and mpMRI is likely to linger.

Imaging of Prostate Cancer

BACKGROUND

Prostate cancer is the most common type of solid tumor in men and the second most common cause of cancer-related death in males in Germany. The conventional strategy for its primary detection, i.e., systematic ultrasound-guided prostate biopsy in men who have elevated PSA levels and/or positive findings on digital rectal examination, fails to reveal all cases. The same is true of the use of conventional computed tomography (CT), magnetic resonance imaging (MRI), and skeletal scintigraphy for the early detection of recurrences and distant metastases.

METHODS

This review is based on pertinent publications retrieved by a selective search, including the German clinical practice guideline on prostate cancer and systematic review articles.

RESULTS

Prospective multicenter trials have shown that the detection of clinically significant prostate cancer is markedly improved with multiparametric MRI (mpMRI) and MR/TRUS fusion biopsy (TRUS = transrectal ultrasonography), compared to conventional systematic biopsy. A recent Cochrane review showed that the rate of overdiagnosis of low-risk prostate cancer was reduced with mpMRI and MR/TRUS fusion biopsy compared with conventional systematic biopsy (95/1000 vs. 139/1000), and that clinically significant prostate cancer was more reliably detected (sensitivity 72% vs. 63%), albeit with slightly lower specificity (96% vs. 100%). Prostate-specific membrane antigen (PSMA) hybrid imaging improves the detection of lymphogenic and bony metastases in patients with high-risk prostate cancer. PSMA hybrid imaging is most commonly used to detect biochemical recurrences. A meta-analysis showed that the detection rate depends on the PSA concentration: 74.1% overall, 33.7% with PSA <0.2 ng/mL, and 91.7% with PSA ≥ 2.0 ng/mL.

CONCLUSION

The appropriate use of mpMRI and MR/TRUS fusion biopsy improves the initial detection of prostate cancer as well as the assessment of the prognosis. PSMA hybrid imaging is useful for the staging of high-risk patients and for the detection of recurrences. These methods are now recommended in the German clinical practice guideline on prostate cancer as well as in guidelines from other countries.