Overview of PI-RADS Version 2.1

PI-RADS (Prostate Imaging Reporting and Data System) version 2.1 represents the current standard for reporting multiparametric MRI (mpMRI) of the prostate, jointly developed by the American College of Radiology (ACR), European Society of Urogenital Radiology (ESUR), and AdMeTech Foundation in 2019.

This system provides a structured framework for detecting, localizing, characterizing, and risk-stratifying clinically significant prostate cancer through standardized imaging interpretation.​

The primary objective of PI-RADS 2.1 is to improve patient outcomes by establishing minimum technical parameters for prostate mpMRI, standardizing terminology and reporting content, facilitating MRI-targeted biopsies, developing assessment categories that summarize suspicion levels, and reducing variability in imaging interpretations.

Unlike its predecessor PI-RADS v2.0, version 2.1 addresses ambiguities and limitations identified through clinical experience, particularly regarding inter-reader reproducibility and specific assessment criteria.​

The PI-RADS Assessment Categories

PI-RADS 2.1 employs a 5-point scale based on the likelihood that mpMRI findings correlate with clinically significant cancer, defined as Gleason score ≥7 (including 3+4 with prominent Gleason 4 component), volume >0.5cc, and/or extraprostatic extension.

Each category carries specific clinical implications and associated malignancy rates derived from meta-analyses:​

PI-RADS Category	Description	Cancer Detection Rate
PI-RADS 1 – Very Low Risk	Clinically significant cancer is highly unlikely to be present. These lesions typically require no further follow-up unless clinical examination or PSA levels change significantly.	Approximately 2%
PI-RADS 2 – Low Risk	Clinically significant cancer is unlikely. Similar to PI-RADS 1, these findings generally do not warrant immediate biopsy in the absence of other clinical risk factors.	Approximately 4%
PI-RADS 3 – Intermediate Risk	The presence of clinically significant cancer is equivocal, representing the most challenging category for clinical decision-making. Management remains flexible and should incorporate additional clinical factors such as PSA density, digital rectal examination findings, and patient preferences.	Approximately 20%
PI-RADS 4 – High Risk	Clinically significant cancer is likely to be present. Biopsy is strongly recommended for these lesions, with MRI-targeted approaches demonstrating superior detection compared to systematic biopsies alone.	Approximately 52%
PI-RADS 5 – Very High Risk	Clinically significant cancer is highly likely. These lesions mandate tissue diagnosis and typically require expedited clinical management.	Approaching 89%

Anatomic Considerations and Scoring Logic

The prostate is divided into distinct anatomic zones with different cancer predilections and MRI characteristics.

Approximately 70-75% of prostate cancers originate in the peripheral zone (PZ), while 20-30% arise in the transition zone (TZ). This zonal anatomy forms the foundation for PI-RADS scoring, as different MRI sequences serve as the dominant determinant depending on lesion location.​

Peripheral Zone Assessment

For peripheral zone lesions, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps serves as the primary sequence for determining the PI-RADS score.

The scoring follows this algorithm:​

• DWI score 1 or 2: Final PI-RADS equals the DWI score (1 or 2), regardless of other sequences
• DWI score 3: The lesion remains PI-RADS 3 if dynamic contrast-enhanced (DCE) imaging is negative, but is upgraded to PI-RADS 4 if DCE shows positive focal enhancement​
• DWI score 4 or 5: Final PI-RADS equals the DWI score (4 or 5), with DCE and T2-weighted imaging providing supplementary information but not changing the category

The DWI scoring criteria for peripheral zone lesions incorporate both the ADC map and high b-value images (typically b=1400-2000 s/mm²):​

• DWI Score 1: No abnormality visible on ADC and high b-value DWI, representing normal tissue.​
• DWI Score 2: Linear or wedge-shaped hypointensity on ADC and/or linear/wedge-shaped hyperintensity on high b-value DWI, typically associated with benign conditions such as prostatitis or atrophy.​
• DWI Score 3: Focal (discrete and different from background) hypointensity on ADC and/or focal hyperintensity on high b-value DWI. Critically, the lesion may be markedly hypointense on ADC or markedly hyperintense on high b-value, but not both. This distinction separates equivocal from clearly suspicious lesions.​
• DWI Score 4: Focal markedly hypointense on ADC and markedly hyperintense on high b-value DWI, measuring <1.5 cm in greatest dimension. Both criteria must be present simultaneously, indicating substantial restricted diffusion characteristic of malignancy.​
• DWI Score 5: Same imaging characteristics as DWI score 4 but ≥1.5 cm in greatest dimension, or demonstrating definite extraprostatic extension or invasive behavior. Size and extension are critical staging factors that elevate risk.​

T2-weighted imaging in the peripheral zone primarily provides anatomic context and helps identify extraprostatic extension, seminal vesicle invasion, and neurovascular bundle involvement.

While T2WI characteristics are described for completeness, they do not modify the final PI-RADS score in peripheral zone lesions when DWI is adequate.​

Transition Zone Assessment

For transition zone lesions, T2-weighted imaging serves as the primary sequence, reflecting the greater challenge of distinguishing cancer from the heterogeneous background of benign prostatic hyperplasia (BPH) nodules.

The scoring algorithm is more complex than for peripheral zone:​

• T2W score 1: PI-RADS 1 regardless of DWI score
• T2W score 2 with DWI ≤3: PI-RADS 2
• T2W score 2 with DWI ≥4: Upgraded to PI-RADS 3​
• T2W score 3 with DWI ≤4: PI-RADS 3
• T2W score 3 with DWI 5: Upgraded to PI-RADS 4​
• T2W score 4 or 5: Final PI-RADS equals T2W score (4 or 5)

This upgrading mechanism in version 2.1 represents a significant refinement from version 2.0, particularly for the “2+1” upgrade (T2W=2, DWI≥4 → PI-RADS 3) and “3+1” upgrade (T2W=3, DWI=5 → PI-RADS 4).

Recent meta-analyses demonstrate that these upgraded transition zone lesions perform as intended: the 2+1 category shows a cancer detection rate of 13% (versus 6% for T2W=2 alone), while the 3+1 category shows 37% (versus 19% for T2W=3 alone).​

The T2-weighted scoring criteria for transition zone lesions emphasize morphologic features that distinguish cancer from BPH:​

• T2W Score 1: Normal appearing transition zone (rare in older men) or a round, completely encapsulated nodule, termed a “typical nodule”. This represents classic BPH without suspicious features.​
• T2W Score 2: A mostly encapsulated nodule or a homogeneous circumscribed nodule without encapsulation (termed “atypical nodule”) or a homogeneous mildly hypointense area between nodules. These remain predominantly benign but lack the complete encapsulation of score 1.​
• T2W Score 3: Heterogeneous signal intensity with obscured margins, encompassing lesions that do not qualify as scores 2, 4, or 5. This represents the equivocal category where additional DWI information becomes critical.​
• T2W Score 4: Lenticular or non-circumscribed, homogeneous, moderately hypointense lesion measuring <1.5 cm in greatest dimension. The lenticular shape and lack of circumscription distinguish these from benign nodules.​
• T2W Score 5: Same characteristics as score 4 but ≥1.5 cm in greatest dimension or demonstrating definite extraprostatic extension or invasive behavior.​

Dynamic Contrast-Enhanced Imaging

DCE imaging plays a limited but specific role in PI-RADS 2.1, primarily serving to upgrade peripheral zone lesions from category 3 to 4.

DCE is considered positive when enhancement is focal, earlier than or contemporaneous with adjacent normal prostatic tissue, and corresponds to a suspicious finding on T2W and/or DWI.

DCE is negative when there is no early enhancement, diffuse multifocal enhancement not corresponding to a focal finding, or focal enhancement corresponding to features of BPH.​

Importantly, DCE does not contribute to scoring when lesions already demonstrate low (PI-RADS 1-2) or high (PI-RADS 4-5) suspicion.

The PI-RADS steering committee deliberately minimized DCE’s role to simplify interpretation and acknowledge that when T2W and DWI are of diagnostic quality, DCE adds limited incremental value.​

Technical Specifications for mpMRI Acquisition

PI-RADS 2.1 establishes minimum technical standards to ensure diagnostic quality across institutions.

While the document does not prescribe optimal parameters, it defines acceptable thresholds that should produce reliable results.​

Field Strength and Coil Configuration

Both 1.5 Tesla and 3.0 Tesla scanners can provide adequate diagnostic examinations when acquisition parameters are optimized.

However, most PI-RADS steering committee members prefer and recommend 3.0T due to increased signal-to-noise ratio, which can be exploited for higher spatial resolution, temporal resolution, or both.

The fundamental advantage of 3T lies in superior image quality, particularly for inherently low signal-to-noise sequences like DWI.​

Endorectal coils, when integrated with external phased array coils, increase signal-to-noise ratio at any field strength.

While they may be considered indispensable for some older 1.5T systems for achieving staging-quality imaging, their use at 3T is optional and based on institutional preference.

Contemporary phased array coils with 16 or more elements and RF channels may achieve adequate signal-to-noise ratio without endorectal coils at both 1.5T and 3T.

The decision involves balancing image quality benefits against increased examination time, patient discomfort, gland distortion, and potential artifacts.​

Sequence Parameters

T2-weighted imaging should be acquired in at least two orthogonal planes, with the axial plane perpendicular to the long axis of the prostate.

High-resolution images with small field-of-view provide optimal anatomic detail for assessing zonal anatomy, lesion morphology, and extraprostatic extension.​

Diffusion-weighted imaging parameters underwent clarification in version 2.1.

ADC map calculation should use a low b-value of 0-100 s/mm² (preferably 50-100 s/mm²) and an intermediate b-value of 800-1000 s/mm².

Additional b-values between 100-1000 s/mm² may be acquired.

High b-value images for visual assessment should use b=1400-2000 s/mm², with higher values showing improved tumor conspicuity in some studies.​

DCE imaging should achieve temporal resolution <15 seconds to adequately capture early focal enhancement.

3D T1-weighted gradient echo sequences are preferred.

The entire prostate should be covered for at least 2 minutes following intravenous gadolinium administration.​

Patient Preparation and Timing

PI-RADS 2.1 addresses several practical considerations for examination quality.

Post-biopsy hemorrhage, manifested as T1-hyperintense signal in the peripheral zone, may confound assessment.

However, when the primary purpose is cancer detection rather than staging, delaying MRI may not be necessary, as clinically significant cancer is unlikely at the site of hemorrhage without corresponding suspicious MRI findings.

For staging purposes, an interval of at least 6 weeks between biopsy and MRI should be considered.​

The presence of stool or air in the rectum may induce artifacts compromising DWI quality, particularly when an endorectal coil is not used.

Some form of minimal preparation enema administered by the patient hours prior to the examination may be beneficial, though it may also promote peristalsis.

Use of antispasmodic agents to reduce motion artifact from bowel peristalsis may be beneficial in some patients, but is not universally necessary.​

Clinical Decision-Making and Management

PI-RADS scores guide but do not dictate clinical management, which must incorporate PSA levels, digital rectal examination findings, prior biopsy history, patient comorbidities, and individual preferences.

The system explicitly avoids prescriptive management algorithms to allow flexibility for local standards of care.​

High-Suspicion Lesions (PI-RADS 4-5)

Biopsy should be considered for PI-RADS 4 or 5 lesions, with the standard management recommendation being referral to MRI-targeted biopsy.

These lesions demonstrate cancer detection rates of 52% and 89% respectively, justifying the invasiveness and cost of tissue sampling.

MRI-targeted biopsies show superior detection of clinically significant cancer compared to systematic approaches alone, with additional benefit from combined protocols.​

Low-Suspicion Lesions (PI-RADS 1-2)

Biopsy is generally not recommended for PI-RADS 1 or 2 lesions absent other compelling clinical factors.

The negative predictive value of mpMRI for clinically significant cancer is high, supporting observation strategies in this population.

However, systematic biopsy may still be performed based on clinical judgment, particularly with elevated PSA density or concerning digital rectal examination.​

Equivocal Lesions (PI-RADS 3)

PI-RADS 3 represents the most challenging category for clinical decision-making, with no universal management consensus.

Management strategies vary based on anatomic location, patient characteristics, and institutional protocols.​

For peripheral zone PI-RADS 3 lesions, several approaches merit consideration:​

• Immediate targeted biopsy: Captures the 20% of cases harboring clinically significant cancer but results in unnecessary biopsies in 80% of cases.​
• Risk stratification with PSA density: PSA density thresholds (commonly ≥0.15 ng/mL/mL) can stratify biopsy necessity, with higher PSA density associated with increased likelihood of clinically significant cancer.​
• Short-interval follow-up MRI: Monitoring lesion characteristics with repeat imaging at 6-12 months provides a pragmatic alternative, particularly when PSA density and digital rectal examination remain stable. Stable or regressing lesions suggest benign etiology, while progression warrants biopsy.​
• Active surveillance without biopsy: May be appropriate in select patients with low PSA density, favorable clinical characteristics, and limited life expectancy.​

For transition zone PI-RADS 3 lesions, the cancer detection rate is notably lower than peripheral zone, and high-grade cancers (Gleason ≥8) are rarely detected.

Active surveillance may be optimal, especially for patients without high-risk factors such as PSA <10 ng/mL or PSA density <0.15 ng/mL/mL.

The challenge of distinguishing cancer from BPH and the higher rate of false positives support conservative management in many cases.​

Recent evidence suggests that the DWI upgrading rules in version 2.1 effectively stratify risk within the PI-RADS 3 category.

Transition zone lesions upgraded from score 2 to 3 based on DWI ≥4 (“2+1” lesions) show 13% cancer detection rate, while those upgraded from score 3 to 4 based on DWI=5 (“3+1” lesions) show 37% detection rate, approaching that of conventional PI-RADS 4 lesions.

This suggests “3+1” transition zone lesions warrant biopsy consideration similar to PI-RADS 4, while “2+1” lesions may be candidates for observation or risk-stratified approaches.​

Key Changes from PI-RADS Version 2.0 to 2.1

Version 2.1 maintains the fundamental framework of version 2.0 while addressing identified ambiguities and limitations:​

• Technical Specifications: Clarified b-values for DWI acquisition and ADC calculation, specified temporal resolution <15 seconds for DCE, and clarified preference for 3D T1-weighted gradient echo DCE sequences.​
• Transition Zone Scoring: Round, fully encapsulated nodules now explicitly assigned PI-RADS 1, with more precise criteria for category 2 lesions (atypical nodules). The introduction of upgrading rules based on DWI scores represents a significant refinement.​
• DWI Criteria Refinement: More precise descriptions distinguish linear/wedge-shaped (score 2) from focal (score 3) abnormalities. Score 3 lesions may be markedly hypointense on ADC or markedly hyperintense on high b-value, but not both—clarifying the boundary between equivocal and suspicious.​
• Peripheral Zone Clarification: Enhanced descriptive criteria for distinguishing categories 2 and 3, reducing ambiguity in this critical determination.​
• Measurement Standardization: Lesions in peripheral zone should be measured on ADC, while transition zone lesions should be measured on T2W. The minimum requirement is reporting the largest dimension on axial images.​
• Prostate Volume Calculation: Clarified methods using manual/automated segmentation or ellipsoid formula (AP × longitudinal × transverse × 0.52). Volume reporting enables PSA density calculation, an important adjunct risk factor.​
• Sector Map Refinement: Updated segmentation model employing 41 sectors/regions for standardized lesion localization. Up to four lesions with PI-RADS ≥3 may be mapped, with the index (dominant) lesion identified based on highest PI-RADS score, presence of extraprostatic extension, or largest size.​

Despite these refinements, studies comparing PI-RADS 2.0 and 2.1 have shown comparable diagnostic performance and inter-reader agreement, with no statistically significant differences in area under the curve for detecting clinically significant cancer.

This suggests version 2.1 successfully maintains diagnostic accuracy while clarifying ambiguous criteria.​

Diagnostic Performance and Validation

Multiple systematic reviews and meta-analyses have validated PI-RADS 2.1 performance.

A comprehensive meta-analysis by Oerther et al. including studies through 2022 provided benchmark diagnostic accuracy estimates:​

For clinically significant prostate cancer detection using a PI-RADS ≥4 threshold, pooled sensitivity ranged from 0.83-0.90 and specificity from 0.48-0.66 across different studies.

When using a PI-RADS ≥3 threshold, sensitivity increased to 0.92-0.98 at the expense of lower specificity (0.33-0.51).​

Area under the curve values demonstrate excellent discriminatory ability, typically ranging from 0.86-0.90 for detection of clinically significant cancer.

Reader experience influences performance, with more experienced readers achieving higher sensitivity and specificity even when applying identical PI-RADS criteria.​

Inter-reader agreement for PI-RADS 2.1 shows moderate to good reliability, with weighted kappa values typically ranging from 0.40-0.60.

Agreement is generally higher for peripheral zone lesions than transition zone lesions, and better for PI-RADS ≥4 compared to ≥3 thresholds.

The equivocal PI-RADS 3 category demonstrates the greatest inter-reader variability, highlighting the inherent challenge of indeterminate findings.​

Transition zone lesion performance merits special attention, as this represents a more challenging diagnostic scenario.

The upgrading rules introduced in version 2.1 show appropriate risk stratification: lesions remaining at baseline T2W scores without DWI upgrade show lower cancer detection rates compared to those upgraded by DWI criteria.

This validates the algorithmic approach to combining T2W and DWI information.​

Limitations and Future Directions

Several important limitations of PI-RADS 2.1 warrant acknowledgment:

• Size-based criteria rely on subjective measurement and may be influenced by sequence selection and measurement plane. The 1.5 cm threshold distinguishing scores 4 from 5 provides a simple dichotomous rule but does not capture the continuous relationship between size and aggressiveness.​
• Inter-reader variability persists despite standardization efforts, particularly for equivocal findings and transition zone lesions. Quantitative measurements, including ADC values, prostate volume, and lesion dimensions, may reduce subjectivity but are not currently integrated into scoring algorithms.​
• Overlap with benign conditions creates diagnostic challenges, particularly for PI-RADS 3 lesions. Prostatitis, benign prostatic hyperplasia, atrophy, and post-biopsy changes can mimic malignancy on mpMRI. The presence of chronic prostatitis in 34% of benign cases in some series underscores this confounding factor.​
• Lack of management algorithms for each PI-RADS category, particularly category 3, results in heterogeneous clinical approaches. While this flexibility accommodates local practice patterns, it also reduces standardization of patient care. Future versions of PI-RADS may incorporate evidence-based management recommendations.​
• Multifocal disease presents challenges for the index lesion concept, as smaller high-grade lesions may be clinically more significant than larger low-grade foci. The recommendation to report up to four lesions with PI-RADS ≥3 helps address this but may not capture all clinically relevant disease.​
• Emerging technologies not yet incorporated into PI-RADS include advanced diffusion techniques (diffusion tensor imaging, diffusion kurtosis imaging, intravoxel incoherent motion), MR spectroscopic imaging, blood oxygenation level-dependent imaging, and ultra-small superparamagnetic iron oxide agents. Artificial intelligence applications show promise for automated lesion detection, segmentation, and PI-RADS scoring, with moderate agreement with expert radiologists in preliminary studies. The PI-RADS steering committee has issued requirements for AI development and reporting to guide this evolving field.​

Future versions of PI-RADS will likely incorporate quantitative biomarkers, refined criteria based on accumulating evidence, specific management algorithms for each category, and potentially integration of validated artificial intelligence tools.

The system remains a “living document” intended to evolve as clinical experience and scientific data accrue.​

Educational and Research Applications

Beyond clinical practice, the PI-RADS 2.1 calculator serves important educational and research functions.

For radiology residents and fellows, structured scoring systems provide a framework for learning prostate MRI interpretation, ensuring systematic assessment of all relevant sequences and anatomic regions.

The explicit criteria and decision trees facilitate competency development.​

For research applications, standardized PI-RADS scoring ensures consistency across institutions and readers, enabling meaningful pooling of data for meta-analyses and multicenter trials.

The system supports reproducible outcome assessment, particularly when combined with standardized definitions of clinically significant cancer.​

Multidisciplinary communication benefits substantially from PI-RADS standardization, as urologists, oncologists, and radiation therapists can reliably interpret risk categories without reviewing images.

This facilitates tumor board discussions, treatment planning, and coordination of targeted biopsies.​

Conclusion

The PI-RADS 2.1 calculator provides a clinically validated, evidence-based tool for standardizing prostate MRI interpretation and guiding management of suspected prostate cancer.

By implementing the official ACR/ESUR criteria in an interactive format, the calculator reduces cognitive burden, minimizes interpretation variability, and ensures adherence to current best practices.

While clinical judgment remains paramount and must integrate mpMRI findings with other risk factors, PI-RADS 2.1 provides a robust framework for risk stratification that improves early diagnosis, reduces unnecessary biopsies for low-suspicion findings, and facilitates targeted biopsies for high-suspicion lesions.

As the field continues to evolve with advancing technology and accumulating evidence, PI-RADS will adapt accordingly, maintaining its role as the international standard for prostate cancer imaging.

References

1. Turkbey B, Rosenkrantz AB, Haider MA, Padhani AR, Villeirs G, Macura KJ, et al. Prostate Imaging Reporting and Data System Version 2.1: 2019 Update of Prostate Imaging Reporting and Data System Version 2. Eur Urol. 2019;76(3):340–351. doi:10.1016/j.eururo.2019.02.033.
2. Purysko AS, Rosenkrantz AB, Baroni RH, Verma S, Turkbey B, Shoji S, et al. PI-RADS Version 2.1: A Critical Review, From the AJR Special Series on Radiology Reporting and Data Systems. AJR Am J Roentgenol. 2021;216(5):—. doi:—.
3. Oerther B, Engelhard K, Hübner M, Gawlitza J, Linker R, Zöllner FG, et al. Cancer detection rates of the PI-RADSv2.1 assessment categories: a systematic review and meta-analysis. Sci Rep. 2021;11(1):—. doi:10.1038/s41598-021-93411-2.
4. Oerther B, Engelhard K, Hübner M, Linker R, Zöllner FG, Linsenmaier U, et al. Update on PI-RADS Version 2.1 diagnostic performance of prostate MRI for the detection of prostate cancer: living systematic review and meta-analysis. AJR Am J Roentgenol. 2024;—:—. doi:—.
5. Agrotis G, de Rooij M, Tzortzis V, Vos PC, Span PN, Fütterer JJ, et al. Detection rates for prostate cancer using PI-RADS 2.1 upgrading rules (“2+1” and “3+1”): a meta-analysis. 2025;—:—. Available from: https://pmc.ncbi.nlm.nih.gov/ (open-access).
6. Walker SM, Gallagher FA, Barrett T. PI-RADSv2.1: Current status. Urology Research and Practice. 2020;—:—. Available from: https://pmc.ncbi.nlm.nih.gov/ (open-access).
7. Oerther B, Zöllner FG, Engelhard K, Linker R, Linsenmaier U, Armbruster M, et al. Living systematic review and meta-analysis of the prostate MRI diagnostic test with PI-RADS assessment: protocol. BMJ Open. 2022;12(9):—. Available from: https://bmjopen.bmj.com/.
8. American College of Radiology. ACR Prostate Imaging Reporting & Data System (PI-RADS) resources. 2024. Available from: https://www.acr.org/Clinical-Resources/PI-RADS.
9. The Radiology Assistant. Prostate Cancer – PI-RADS v2.1. 2020. Available from: https://radiologyassistant.nl/abdomen/prostate/prostate-cancer-pi-rads-v2-1.
10. Lei Y, Wang Z, Chen J, Zhang Y, Zhang L, Wang R, et al. Combining prostate-specific antigen density with PI-RADS v2.1 to optimize biopsy decisions. Front Oncol. 2022;12:—. Available from: https://www.frontiersin.org/.

What is PI-RADS v2.1 and who developed it?

PI-RADS v2.1 is the 2019 update of the Prostate Imaging Reporting and Data System that standardizes mpMRI acquisition and interpretation for prostate cancer, developed by the ACR, ESUR, and AdMeTech Foundation.

How does the 5-point PI-RADS scale relate to cancer risk?

The scale reflects increasing likelihood of clinically significant cancer, with typical patient-level cancer detection rates around PI-RADS 1: ~3%, 2: ~6%, 3: ~20%, 4: ~53%, and 5: ~83%.

Which MRI sequences are dominant in the peripheral and transition zones?

Diffusion-weighted imaging with ADC maps is dominant for peripheral zone assessment, while T2-weighted imaging is dominant for transition zone assessment; DCE acts primarily as a tie-breaker.

When does DCE change the PI-RADS score?

In v2.1, DCE can upgrade a peripheral zone lesion from PI-RADS 3 to 4 if there is positive focal early enhancement matching the suspicious finding; it does not change scores when findings are clearly low (1–2) or high (4–5).

What defines DWI scores 3, 4, and 5 in the peripheral zone?

Score 3 is a focal abnormality that is markedly abnormal on either ADC or high b-value DWI, but not both; score 4 is markedly abnormal on both ADC and high b-value DWI with size <1.5 cm; score 5 meets score 4 imaging but is ≥1.5 cm or shows definite extraprostatic extension.

How are transition zone lesions upgraded in PI-RADS v2.1?

v2.1 allows T2W 2 lesions to be upgraded to final PI-RADS 3 when DWI ≥4 (the “2+1” rule), and T2W 3 lesions to be upgraded to final PI-RADS 4 when DWI = 5 (the “3+1” rule); studies report cancer detection rates of ~13% for 2+1 and ~37% for 3+1.

What are the key technical parameters recommended in v2.1?

ADC should be calculated using a low b-value of 0–100 s/mm² (preferably 50–100) and an intermediate b-value of 800–1000 s/mm²; visual high b-value images of ~1400–2000 s/mm² are recommended; DCE should achieve temporal resolution under 15 seconds using 3D T1-weighted gradient-echo.

Is 3T preferred and is an endorectal coil necessary?

Both 1.5T and 3T can be diagnostic when optimized, but 3T offers higher SNR that can be traded for resolution; endorectal coils may be helpful at 1.5T but are generally optional at 3T depending on site preference and image quality.

How should PI-RADS 3 lesions be managed regarding PSA density?

Management is individualized; PSA density thresholds near 0.15 ng/mL/mL are commonly used to stratify risk and guide biopsy decisions for PI-RADS 3, though PSA density should not be used in isolation.

What is the diagnostic performance of PI-RADS v2.1 at common thresholds?

Using a PI-RADS ≥3 threshold yields high sensitivity with lower specificity, while a ≥4 threshold balances sensitivity and specificity better; recent meta-analyses report ~96%/43% (≥3) and ~88–89%/66% (≥4) for sensitivity/specificity at the patient level.