Enhancing understanding of the PIRADS system to improve its interpretation and communication abilities regarding multiparametric prostate magnetic resonance findings.

This presentation covers normal prostate anatomy, and the use of different sequences in multiparametric magnetic resonance imaging, and ultimately focuses on explaining the various PIRADS categories in a didactic and schematic manner, emphasizing the illustration of possible prostate lesion findings using appropriate technical language.

The assignment of a PI-RADS assessment category for each lesion relies on the evaluation of T2-weighted (T2W), diffusion-weighted imaging/apparent diffusion coefficient (DWI/ADC), and dynamic contrast-enhanced sequences, adhering to zonal anatomy (figure 2). Identifying the zonal location of a lesion is crucial, given that the dominant sequence for PI-RADS assessment differs between the peripheral zone and the transition zone. In the peripheral zone, DWI/ADC serves as the primary determining sequence (dominant technique) for assigning the PI-RADS assessment category. A lesion rated as suspicion category 3 based on ADC/DWI maintains a PI-RADS score of 3 if there is no focal enhancement (negative). However, it is upgraded to a PI-RADS score of 4 if focal enhancement is present (positive). Notable changes in PI-RADS version 2.1 include a more precise description of lesions in the peripheral zone categories 2 and 3.

For the transition zone (figure 3), which surrounds the prostatic urethra and enlarges with age due to benign prostatic hyperplasia, T2W imaging is the primary determining sequence (dominant technique) for assigning the PI-RADS assessment category. A lesion assessed as category 2 based on T2W images retains a PI-RADS score of 2 if the DWI/ADC is ≤ 3. However, it becomes a PI-RADS score of 3 if the DWI is ≥ 4. A lesion categorized as 3 based on T2W images remains a PI-RADS score of 3 if the DWI is ≤ 4. However, it is elevated to a PI-RADS score of 4 if the DWI/ADC is rated 5.

Dynamic contrast-enhanced MRI (DCE MRI) involves rapid T1-weighted gradient echo scans before, during, and after administering a gadolinium-based contrast agent. Prostate cancers typically exhibit early enhancement post-injection, but the kinetics of enhancement vary, with some tumors showing early washout and others retaining contrast for a longer duration. However, early enhancement alone is not conclusive for clinically significant prostate cancer, and the absence of early enhancement does not rule out the possibility. Despite its variability, DCE should be a part of all prostate mpMRI exams to avoid overlooking small yet significant cancers. Focal early enhancement in DCE data should prompt a thorough examination of corresponding T2-weighted and diffusion-weighted images for abnormalities. While the added value of DCE is not firmly established, existing data suggest modest improvement over the combination of T2-weighted and DWI. While Dynamic Contrast-Enhanced (DCE) imaging remains integral to multiparametric magnetic resonance imaging (mpMRI) for the prostate, its role in determining the PI-RAD v2 Assessment Category is subordinate to T2-weighted and DWI sequences. To illustrate, in the peripheral zone, if a lesion receives a suspicion category 3 classification based on DWI/ADC, it maintains a PI-RADS score of 3 when lacking focal enhancement (negative). However, if focal enhancement is observed (positive), it is elevated to a PI-RADS score of 4.