MRI Prostate — multiparametric (PI-RADS)
Whole prostate and seminal vesicles at high resolution, with a large field-of-view sequence covering the pelvis to the aortic bifurcation for nodal and bone assessment when staging.
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Clinical suspicion of prostate cancer before biopsy, to direct or avoid biopsy.
- Prior negative biopsy with persistent suspicion.
- Active surveillance monitoring.
- Local staging of biopsy-proven disease, including extraprostatic extension and seminal vesicle invasion.
- Planning for focal therapy or targeted biopsy.
Technique
- High-resolution T2 turbo spin-echo in the axial plane plus at least one additional plane, with the axial plane angled to the prostate.
- Diffusion-weighted imaging with a low b value of roughly 0-100 s/mm² (50-100 preferred), an intermediate b value of about 800-1000 s/mm² for the ADC calculation, and a high b value of at least 1400 s/mm² either acquired separately or extrapolated.
- Dynamic contrast-enhanced 3D T1 gradient-echo with a temporal resolution of 15 seconds or better; earlier guidance argued for under 10 seconds, and both targets remain in circulation.
- Field strength of 1.5 T or 3 T with a multichannel external array; an endorectal coil is optional and its use varies widely.
Where it goes wrong
- High b-value imaging obtained by extrapolation when image quality at the acquired b values is already poor — the extrapolation inherits the noise.
- ADC computed from the wrong pair of b values, which shifts the numbers and undermines comparison across studies.
- Dynamic series too slow to resolve early focal enhancement, which defeats the only role the contrast sequence has.
- Rectal gas causing susceptibility distortion on echo-planar diffusion, misregistering the peripheral zone.
- Scanning too soon after biopsy, when haemorrhage mimics and masks tumour.
- Field of view too large or slice thickness too great to resolve capsular contact.
Clinical questions that reach this study
Contrast
Macrocyclic gadolinium agent at a typical single dose of about 0.1 mmol/kg by power injector at roughly 2-3 mL/s with saline chaser, with the dynamic series started before injection.
Acquisition
- Breathing
- Free breathing. Rectal peristalsis and gas are the dominant sources of artefact, not respiration.
- Preparation
- Where the study follows a biopsy, an interval of several weeks is conventional to let post-biopsy haemorrhage settle; confirm the local interval. Antiperistaltic agents and instructions to empty the rectum and avoid ejaculation before the scan vary between centres and are genuinely not standardised. Supply PSA, digital examination findings and prior biopsy history — they determine whether staging nodal coverage is needed.
Phases
Each phase is authored once and shared across every protocol that uses it, so the physiology below is the same wherever you meet it.
- Non-contrast (unenhanced)No injection. Acquired before any contrast is given.
Shows intrinsic tissue attenuation, and nothing else. The transferable principle is that contrast is anti-signal for anything that is already dense: calcification, acute haemorrhage, urinary and biliary calculi, iodine-containing or haemorrhagic fluid, and intrinsic fat all lose conspicuity, or become uninterpretable, once surrounding tissue enhances. It is also the only baseline against which enhancement can be measured, so any protocol that quantifies enhancement or washout (a lesion "enhances by X HU", adrenal absolute washout, renal mass characterisation) is arithmetically impossible without it. Conversely, an unenhanced series adds dose and no information whenever the question is purely about vascularity or perfusion.
- Dynamic contrast-enhanced series (multiphase gadolinium)A late arterial acquisition timed to about 15–20 s after contrast reaches the target artery (fluoroscopically triggered or test-bolus timed), a portal venous/early venous acquisition roughly 15–30 s later, and a delayed or transitional acquisition at about 2–3 min. Confirm locally.
The same volume is imaged repeatedly across the passage of a gadolinium bolus, so enhancement is read as a curve rather than as a single value. The transferable principle is that MR sees T1 shortening rather than photon attenuation, which removes the dose penalty for repeating an acquisition and therefore makes the TEMPORAL PATTERN the primary datum: rapid arterial uptake followed by relative fall-off, progressive centripetal fill-in, and persistent late enhancement are three different diagnoses that can share an identical single-timepoint appearance. Because everything downstream depends on hitting the arterial peak within a few seconds, the phase is unusually sensitive to circulation time and to breath-hold failure, and a mistimed arterial acquisition cannot be recovered by post-processing.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Prior contrast reaction and elective premedication· nurse pre scan
- Kidney function and gadolinium-based contrast· radiographer at scan
- Intravenous access adequate for the planned injection· radiographer at scan
- MR safety screening for implants and foreign bodies· radiographer at scan