A GP guide to understanding prostate MRI – the PI-RADS scoring system

April 2018, Dr Chee L Khoo

Forget about whether PSA screening saves lives or not. What is the next step when a PSA level comes back elevated. Obviously if the PSA is >10 or much higher, they need referral to a urologist for biopsies. What if it is trending high or is significantly higher than the age related reference range? Patients are increasingly having prostate MRIs performed the results are reported as PI-RADS scores. Do you understand those scores?

An elevated PSA (>3-4 ng/ml) or if DRE indicates suspected tumour, a TRUS is indicated to clarify and if cancer is detected, to assess its extent, volume and aggressiveness. The only problem is that an elevated PSA is neither terribly specific nor sensitive. A biopsy is invasive and may underestimate the extent and grade of cancer. Advances in MRI show promise for improved detection and characterisation of prostate cancer.

The PROMIS study lived up to its promise (pun intended). It informed us of the sensitivities and specificities of multi-parametric prostate MRIs using template prostate mapping biopsies (i.e. pretty much sampling the whole prostate) as a reference test. We now have an investigation algorithm for patients with elevated PSA. The PROMIS was reviewed in my article in February 2017 here.

Rather than reporting prostate MRI as being “normal” or “abnormal”, it now have a scoring system to inform us as to the likelihood of prostate based on the characteristics of the MRI lesions. In 2012, the European Society of Urogenital Radiology produced a set of guidelines for prostate MRI. So that everyone is talking the same language, a structured reporting scheme, the PI-RADS scoring system was developed.

The MRI performed is a multi-parametric MRI meaning the four commonly used parameters are:

  • T2 weighted images (T2W) give excellent anatomic detail and thus show the location of a suspicious area.
  • Diffusion-weighted imaging (DWI) gives functional information about the movement of water molecules, which is different in healthy tissue than in tumours.
  • Dynamic contrast-enhancement (DCE) can point to a tumour by revealing abnormal blood flow from network of abnormal blood vessels that feed the tumour (angiogenesis)
  • MRI spectroscopy (MRS) is used to show concentrations of biochemicals called metabolites, since the presence of certain metabolites characterizes prostate cancer.

From the multiple parameters, a score is derived.

PI-RADS score Definition
1 Very low (clinically significant cancer is highly unlikely to be present)
2 Low (clinically significant cancer is unlikely to be present)
3 Intermediate (the presence of clinically significant cancer is equivocal)
4 High (clinically significant cancer is likely to be present)
5 Very high (clinically significant cancer is highly likely to be present)


A PI-RADS score of 3 or above will probably require further investigations subject to a discussion with the patient.

We are quite lucky in South West Sydney. Dr Daniel Mosses at Spectrum Medical Imaging, Liverpool is our local expert on prostate MRI and have a special interest on the subject. Have a look at this month’s case history on the topic courtesy from our friends from Spectrum Medical Imaging.


Barentsz, j et al. ESUR prostate MR guidelines 2012. Eur Radiol 10 Feb 2012.