PI-RADS Version 2.1: Key Changes from Version 2
PI-RADS version 2.1 was released in 2019 to address specific limitations in version 2, particularly focusing on reducing inter-reader variability in the transition zone and clarifying ambiguous scoring criteria, though the fundamental framework and overall test performance remain unchanged. 1
Primary Goals of Version 2.1
The update specifically targets improved consistency among radiologists without altering the basic concept of dominant sequences (DWI for peripheral zone, T2-weighted for transition zone). 2 The steering committee acknowledged that while PI-RADS v2 demonstrated clinical utility, moderate interobserver variability persisted, especially for transition zone evaluations. 1
Major Technical Parameter Changes
Mandatory High b-Value DWI
- Ultra-high b-value of at least 1400 s/mm² is now mandatory (previously recommended but not required). 2
- This strengthens the role of diffusion-weighted imaging across all prostate zones. 2
Updated Acquisition Parameters
- Minor but important changes to data acquisition parameters were implemented to improve standardization across centers. 1
- The sector map used for lesion localization was revised. 1
Image Interpretation Clarifications
Transition Zone Scoring
- DWI now plays a stronger, more clearly defined role in transition zone assessment, addressing the previous version's primary source of inter-reader disagreement. 1, 2, 3
- More explicit guidance provided for distinguishing DWI scores of 3 versus 4/5 in the transition zone. 1
- Better criteria for handling nodular benign prostatic hyperplasia that lacks classic encapsulation appearance. 1
Peripheral Zone Refinements
- Clearer distinction between DWI scores of 3 and 4/5 for peripheral zone lesions. 1
- More specific guidance on DCE positivity for nonfocal lesions in the peripheral zone, reducing previous ambiguity. 1
Anatomic Zone Clarifications
- New specific guidance for lesions arising solely from the central zone, which version 2 did not adequately address. 1, 2
- Separate interpretation criteria added for anterior-superior tumors substantially involving the anterior fibromuscular stroma. 1
What Did NOT Change
Core Framework Preserved
- The dominant sequence concept remains: DWI/ADC for peripheral zone, T2-weighted for transition zone. 2, 4
- The 5-point assessment scale (PI-RADS 1-5) is unchanged. 4
- DCE imaging continues to serve an ancillary role, primarily for equivocal peripheral zone lesions (PI-RADS 3). 4
Expected Performance
- Version 2.1 amendments are not expected to change overall test performance (sensitivity/specificity remain similar). 1
- The update aims solely to improve consistency between readers, not to fundamentally alter diagnostic accuracy. 1
Clinical Implementation Considerations
Biparametric MRI
- Version 2.1 does not recommend biparametric MRI (without DCE) for general application, maintaining the multiparametric approach as standard. 2
Quality Control Emphasis
- Greater emphasis placed on PI-RADS compliance and standardized reporting templates. 1
- Recognition that MRI quality varies significantly between centers, affecting diagnostic performance. 5
Common Pitfalls to Avoid
- Do not apply version 2.1 criteria to post-treatment prostates (radiation, hormone therapy, TURP), as PI-RADS was designed specifically for treatment-naïve glands. 5, 6
- Ensure the mandatory high b-value (≥1400 s/mm²) is actually acquired; studies without this cannot be properly scored using version 2.1. 2
- Recognize that version 2.1 does not resolve all interpretation challenges—some areas remain incompletely addressed and await future major revisions. 7
Future Evolution
The PI-RADS steering committee acknowledges this as an incremental update, with the next major revision anticipated to be a multiyear endeavor requiring additional research data on clinical usage and MRI-directed biopsy outcomes. 1 Areas identified for future development include quantitative parameters beyond size, standardized extraprostatic extension assessment, image quality scoring systems, and expansion to active surveillance and recurrence settings. 7