Prostate mpMRI & PI-RADS — What It Shows and When It’s Used

Prostate mpMRI & PI-RADS

Multiparametric MRI now sits before biopsy in prostate cancer pathways — finding significant disease and safely sparing many men an unnecessary biopsy.

The three parameters

T2-weighted: anatomy and zonal detail; the dominant sequence for the transition zone.
Diffusion (DWI/ADC): the dominant sequence for the peripheral zone; restricted diffusion (low ADC) flags cellular tumour.
Dynamic contrast (DCE): a secondary/tie-breaker showing early enhancement.

PI-RADS v2.1 combines these into a 1–5 score of the likelihood of clinically significant cancer — with a dominant sequence per zone (DWI in peripheral, T2 in transition).

PI-RADS at a glance

Score	Meaning
1–2	Clinically significant cancer very unlikely / unlikely
3	Equivocal — individualise (PSA density, follow-up)
4–5	Likely / highly likely — targeted biopsy indicated

MRI also enables MR-targeted (often MRI–ultrasound fusion) biopsy of the suspicious lesion, improving detection of significant disease over systematic biopsy alone.

Practical notes

Quality depends on protocol and reader experience; bowel gas and hip prostheses degrade DWI. PSA density complements PI-RADS 3 decisions. Post-biopsy haemorrhage can mimic tumour — timing matters.

Reference: Turkbey B et al. PI-RADS v2.1. Eur Urol 2019;76:340–9. Kasivisvanathan V et al. PRECISION trial. N Engl J Med 2018;378:1767–77.

Educational summary for clinicians; local pathways and guidelines take precedence. Not medical advice.