PI-RADS v2.1 is a standardized MRI scoring system for prostate cancer risk. This interactive tool calculates PI-RADS scores for Peripheral Zone or Transition Zone lesions based on ACR/ESUR guidelines.
What is PI-RADS 2.1?
PI-RADS (Prostate Imaging Reporting and Data System) version 2.1 is an internationally recognized standardized reporting system developed jointly by the American College of Radiology (ACR) and European Society of Urogenital Radiology (ESUR). It provides a structured framework for radiologists to interpret prostate multiparametric MRI (mpMRI) and assess the likelihood of clinically significant prostate cancer.
This calculator helps healthcare professionals systematically evaluate prostate lesions using diffusion-weighted imaging (DWI), T2-weighted imaging (T2W), and dynamic contrast-enhanced (DCE) sequences to generate a PI-RADS score that predicts cancer risk.
Disclaimer: The author makes no claims of the accuracy of the information contained herein; this information is for educational purposes only and is not a substitute for clinical judgment. This calculator is based upon the American College of Radiology (ACR) PI-RADS 2.1 classification but is not officially endorsed by the ACR.
Peripheral Zone Calculator
Transition Zone Calculator
PI-RADS 2.1 Assessment Categories
PI-RADS 2.1 employs a 5-point scale based on the likelihood that mpMRI findings correlate with clinically significant cancer.
Clinically significant cancer is highly unlikely to be present. These lesions typically require no further follow-up.
Clinically significant cancer is unlikely. These findings generally do not warrant immediate biopsy in the absence of other risk factors.
The presence of clinically significant cancer is equivocal. Management should incorporate additional clinical factors such as PSA density.
Clinically significant cancer is likely. Biopsy is strongly recommended, with MRI-targeted approaches preferred.
Clinically significant cancer is highly likely. These lesions mandate tissue diagnosis and expedited clinical management.
Peripheral Zone – DWI Dominant
Peripheral Zone Scoring Algorithm:
- DWI=1 or 2: Direct PI-RADS 1 or 2 (no DCE needed)
- DWI=3: Requires DCE: negative→PI-RADS 3; positive→PI-RADS 4
- DWI=4 or 5: Direct PI-RADS 4 or 5 (no DCE needed)
Transition Zone – T2W Dominant
Transition Zone Scoring Algorithm:
- T2W=1: PI-RADS 1 (no DWI needed)
- T2W=2: DWI ≤3 → PI-RADS 2; DWI ≥4 → PI-RADS 3 (upgrade)
- T2W=3: DWI ≤4 → PI-RADS 3; DWI=5 → PI-RADS 4 (upgrade)
- T2W=4 or 5: Direct PI-RADS 4 or 5 (no DWI needed)
Clinical Decision-Making
PI-RADS 1-2 (Low Suspicion): Biopsy not recommended absent other compelling factors. Negative predictive value is high.
PI-RADS 3 (Equivocal): Management varies by location and clinical factors. Consider PSA density, follow-up MRI, or risk-stratified approaches.
PI-RADS 4-5 (High Suspicion): Biopsy recommended. MRI-targeted approaches show superior detection compared to systematic biopsies alone.
Key Technical Parameters
- Field Strength: Both 1.5T and 3.0T acceptable; 3.0T preferred for superior SNR
- DWI b-values: ADC with b=0-100 and b=800-1000 s/mm²; high b-value DWI at b=1400-2000 s/mm²
- DCE Temporal Resolution: <15 seconds to capture early enhancement
- Post-biopsy Interval: ≥6 weeks for staging purposes
Version 2.1 Updates from 2.0
Version 2.1 clarified several ambiguities from version 2.0:
- Improved transition zone scoring with explicit upgrading rules (2+1 and 3+1)
- More precise DWI criteria distinguishing focal from linear/wedge-shaped abnormalities
- Clarified measurement standardization and prostate volume calculation
- Enhanced peripheral and transition zone morphologic descriptions
Diagnostic Performance
Clinically Significant Cancer Detection (PI-RADS ≥4):
- Sensitivity: 0.83-0.90
- Specificity: 0.48-0.66
- Area Under Curve: 0.86-0.90
Inter-reader Agreement (Kappa): 0.40-0.60 (moderate to good). PI-RADS 3 has greatest variability.
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