Post-Treatment MRI Assistant
A prostate MRI recurrence helper that routes cases to PI-RR after radiation/prostatectomy or PI-FAB after focal ablation.
Educational tool · PI-RR / PI-FAB
Quick reference
PI-FAB after focal ablation: what the score means
PI-FAB is meant for suspected residual or recurrent tumor at the focal therapy treatment zone or treatment margin. It is not meant to score a separate lesion in untreated prostate tissue. Those out-of-field lesions should be assessed with PI-RADS v2.1 while the ablation zone is described separately.
1PI-FAB is DCE driven.
Start with enhancement at or near the treatment zone, then use DWI/ADC and T2W as supporting features.
Start with enhancement at or near the treatment zone, then use DWI/ADC and T2W as supporting features.
2The practical question is local recurrence.
The score is asking whether the ablation zone or margin looks benign, equivocal, or suspicious.
The score is asking whether the ablation zone or margin looks benign, equivocal, or suspicious.
3Out-of-field findings are different.
Do not force an untreated gland lesion into PI-FAB. Use PI-RADS and describe the ablation zone separately.
Do not force an untreated gland lesion into PI-FAB. Use PI-RADS and describe the ablation zone separately.
PI-FAB decision logic
| Score | Typical pattern | Practical interpretation |
|---|---|---|
| PI-FAB 1 | No suspicious enhancement, or linear/non-masslike enhancement favoring fibrosis, vessel, or inflammation. | Low suspicion for in-field or marginal recurrence. |
| PI-FAB 2 | Tiny enhancing focus measuring 3 mm or less at the original tumor site. | Equivocal. Correlate with PSA kinetics and prior MRI; biopsy may be considered if concern is rising. |
| PI-FAB 3 | Enhancing focus greater than 3 mm within/at the treatment margin, interval growth of a prior PI-FAB 2 focus, or focal enhancement with suspicious DWI/T2 correlate. | Suspicious for residual or recurrent disease; targeted biopsy is usually the next step. |
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How this assistant uses PI-FAB
The focal ablation pathway first asks whether the finding is in-field or at the ablation margin. It then uses the DCE pattern to assign the primary PI-FAB score. DWI/ADC and T2W morphology are included because they can increase confidence, especially when a focal enhancing abnormality also restricts diffusion or has a masslike T2 correlate.
DCE
Primary driver after focal therapy. Look for focal enhancement at the treated site or margin.
Primary driver after focal therapy. Look for focal enhancement at the treated site or margin.
DWI / ADC
Supportive. Matched high b-value DWI signal and low ADC at the enhancing focus increases concern.
Supportive. Matched high b-value DWI signal and low ADC at the enhancing focus increases concern.
T2W
Supportive. Helpful for morphology, ablation cavity/scar, masslike tissue, and comparison with the original tumor site.
Supportive. Helpful for morphology, ablation cavity/scar, masslike tissue, and comparison with the original tumor site.
PI-RR reminder
Radiation therapy and radical prostatectomy use PI-RR logic rather than PI-FAB. After radiation, DWI and DCE drive the score. After prostatectomy, DCE is the dominant sequence, with DWI used as an upgrade pathway when reliable. T2W remains important for localization and morphology, but it is usually descriptive rather than the main score driver. Read the Understanding PI-RR article.
All about PI-RR A short guide to local recurrence scoring after radiation therapy or radical prostatectomy.
About this article
This educational article was written by Nicholas H. Shaheen, MD for the Prostate MRI Toolkit. It is intended for teaching and reference, is not peer reviewed, and should not replace local practice standards, institutional protocols, or formal society guidelines.
Last updated: June 2026
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Created by Nick Shaheen. PI-RR pathway for radiation therapy/radical prostatectomy. PI-FAB pathway for focal ablation in-field/marginal recurrence. Out-of-field lesions in untreated prostate should be assessed with PI-RADS v2.1. Not medical advice; verify with the source standard and local practice.