PI-RADS v2.1
Assign a PI-RADS v2.1 category to a prostate MRI lesion. Choose the zone, grade DWI and T2, add size and DCE, and the calculator applies the dominant-sequence and upgrade rules.
Lesion
PI-RADS
4
DWI
4
T2
3
PI-RADS 4 · PZ · DWI 4, T2 3 · 12 mm
PI-RADS 4. Clinically significant cancer is likely. In the peripheral zone, DWI is the dominant sequence: DWI 4, T2 3.
At this score, also describe extent: capsular breach, seminal vesicle invasion and the distance to the neurovascular bundle change the surgical plan more than the score itself.
PI-RADS grades one lesion. Report at most four and name the index lesion: the one with the highest score, and where scores tie, the one with extraprostatic extension or the largest diameter.
How to read the result
The category expresses the probability of clinically significant cancer, not its presence. Categories 1 and 2 close the question, 4 and 5 lead to targeted biopsy, and 3 hands the decision to information the MRI does not contain.
How the category is assigned
Peripheral zone: DWI decides. Transition zone: T2 decides.
PZ only: a DWI of 3 becomes PI-RADS 4 when DCE is positive. This is the sole remaining role of dynamic contrast in v2.1.
TZ, two upgrades with different thresholds: a T2 of 2 becomes PI-RADS 3 when DWI is 4 or 5, and a T2 of 3 becomes PI-RADS 4 only when DWI is 5.
For both sequences, the difference between 4 and 5 is size: 15 mm or more, or definite extraprostatic extension or invasive behaviour.
When to use it
- Assigning a category to a lesion on multiparametric prostate MRI.
- Checking whether the dominant sequence for this zone is the one you actually scored on.
- Working out whether DCE changes anything, which in v2.1 it rarely does.
- Settling a 4 versus 5 where the lesion sits close to 15 mm.
⚠️ Pitfalls
- Scoring the transition zone on DWI is the commonest error. In the TZ, T2 leads and DWI only upgrades.
- The two transitional upgrades use different thresholds: T2 2 lifts at DWI 4, but T2 3 lifts only at DWI 5. Upgrading a T2 3 at DWI 4 is the proposed v2.1-B variant from the literature, not v2.1.
- DCE does nothing in the transition zone, and nothing in the peripheral zone unless DWI is exactly 3. An enhancing lesion is not thereby a PI-RADS 4.
- Measure the largest diameter on the sequence where the lesion is most conspicuous, usually the ADC map in the peripheral zone. Measuring on T2 alone shifts lesions across the 15 mm boundary.
- PI-RADS grades lesions, not patients. Report at most four and name the index lesion explicitly.
- The category does not include PSA, prior biopsy or family history. Those belong in the conclusion, not in the score.
Frequently asked questions
How is a PI-RADS v2.1 category assigned?
By the dominant sequence for the zone: DWI in the peripheral zone and T2 in the transition zone. A peripheral DWI 3 becomes a 4 with positive DCE, and a transitional T2 3 becomes a 4 when DWI is 4 or 5.
What separates PI-RADS 4 from 5?
Size and behaviour. The same appearance scores 4 below 15 mm and 5 at 15 mm or more, or whenever there is definite extraprostatic extension or invasive behaviour.
When does dynamic contrast matter?
Only in the peripheral zone, and only when DWI is exactly 3. In every other situation, including the whole transition zone, DCE does not change the category.
What should be done with a PI-RADS 3?
The MRI has said what it can. PSA density typically decides: around 0.15 and certainly from 0.20 upward it tips toward biopsy, and below that toward surveillance.
What changed between PI-RADS v2 and v2.1?
The transition zone gained an upgrade: a T2 of 2 becomes PI-RADS 3 when DWI is 4 or 5. The DWI descriptors were rewritten, with score 2 becoming linear or wedge-shaped and score 3 dropping the terms mildly and moderately in favour of focal, discrete and different from background, marked on one sequence but not both. “Marked” itself was defined as a more pronounced signal change than any other focus in the same zone. A negative DCE now explicitly includes an enhancing extruded BPH nodule.
Which lesion is the index lesion?
The one with the highest PI-RADS category. Where categories tie, the lesion with extraprostatic extension, and failing that the largest one.
References
📄Turkbey B, Rosenkrantz AB, Haider MA, et al. Prostate Imaging Reporting and Data System Version 2.1: 2019 Update of PI-RADS Version 2. Eur Urol. 2019;76(3):340–351.
📄Weinreb JC, et al. PI-RADS Prostate Imaging – Reporting and Data System: 2015, Version 2. Eur Urol. 2016;69(1):16–40.
📄ACR PI-RADS resources.↗This calculator supports clinical judgement and does not replace it. Always check the result against your own measurements and the guideline in force.
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