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SAMJ: South African Medical Journal

On-line version ISSN 2078-5135
Print version ISSN 0256-9574

SAMJ, S. Afr. med. j. vol.99 n.6 Pretoria Jun. 2009

 

Multiparametric magnetic resonance imaging (mpMRI) of the prostate has an important role in the diagnostic work-up and staging of patients with suspected prostate cancer.1 Prostate imaging and interpretation up until 2019 was based on Prostate Imaging-Reporting and Data System version 2 (PI-RADS v2) which provided clinical guidelines for mpMRI of the prostate. The aim of PI-RADS v2 was to create a global standard in the acquisition, interpretation, and reporting of prostate mpMRI examinations, as well as to enhance the detection, localisation and risk stratification in patients with treatment-naïve prostate glands.2 Numerous studies have ratified the value of PI-RADS v2 but have also shown inconsistencies and limitations especially relating to inter-observer variability for evaluation of the Transition Zone (TZ).3 In an attempt to reduce inter-observer subjectivity, the PI-RADS steering committee, recommended multiple modifications to PI-RADS v2 by employing a consensus based system. The system maintains the same framework of assigning scores to individual sequences, and using these scores, to calculate an overall assessment category for each patient. The updated version is termed PI-RADS v2.1 and provides an approach to interpretation and reporting.

 

Introduction

Prostate cancer (PCa) is the second most common cancer in men worldwide. Two thirds of PCa cases are diagnosed in the more developed regions in the world.2,4 In South Africa the age-adjusted risk of being diagnosed with PCa is 30.96/100 000 and the lifetime risk in men is 1:2.5 Traditional diagnostic tests for detecting PCa, namely prostate-specific antigen (PSA) and transrectal ultrasound-guided (TRUS) biopsy, lack both sensitivity and specificity. Prostate-specific antigen is specific to the prostate gland but not to PCa. Transrectal ultrasound-guided biopsy can miss up to 30% of tumours and in approximately 30% of cases underestimates tumour aggressiveness.2,6,7

Imaging with MRI was initially used for loco-regional staging and computed tomography (CT) or bone scintigraphy for distant staging in patients with biopsy-proven cancer. Recent advantages in MR technology that allows both anatomical and functional imaging to be performed simultaneously, mpMRI, has improved our ability to both detect and characterise prostate tumours.1

In 2012 the European Society of Urogenital Radiology (ESUR) released a standardised prostate MRI assessment called PI-RADS. This was PI-RADS version 1 (v1). This established clinical guidelines for the acquisition, interpretation and reporting of mpMRI of the prostate in order to facilitate a greater level of standardisation and consistency.1 These guidelines were based on the calculation of points for the evaluation of each focal lesion with different sequences, namely T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI), dynamic contrast enhanced (DCE) and selective spectroscopy.1

In 2015 these guidelines were updated (PI-RADS v2) by the American College of Radiology (ACR) and EAU Section of Urological Research (ESUR). In the updated version, spectroscopy assessment was not included and DCE imaging was rated less significant. Prostate Imaging-Reporting and Data System v2 introduced two important changes to PI-RADS v1: the concept of a dominant sequence for each prostate zone (DWI for the periphery and T2W imaging for the transitional gland) and the relegation of DCE to a tie-breaker role when a lesion remains indeterminate.8 It is important to note that PI-RADS only indicates the 'probability' of a clinically significant cancer with a 5-point evaluation for a focal lesion. Prostate Imaging-Reporting and Data System v2 led to a more cogent scoring system for assigning an overall score (1-5) for a lesion - with a score of 1 indicating a low chance of significant disease, and a score of 5 indicating a high likelihood of significant disease.

Although PI-RADS v2 has been taken up and used broadly worldwide, experience has highlighted ambiguities in the scoring and limitations in relation to inter-reader reproducibility. Prostate Imaging-Reporting and Data System v2.1 recommends several minor adjustments to try and simplify assessment and reduce inter-reader variability without changing the overall scope and principle of v2.1

 

What PI-RADS v2.1 aims to do3

In patients with suspected PCa, PI-RADS v2.1 is configured to improve detection, accurately localise, characterise and risk stratify lesions in treatment-naïve prostate glands.

There are a number of aims of the PI-RADS v2.1 update. The basic acceptable technical parameters to perform prostate mpMRI have been defined. Simple and standardised terminology for concise reporting have been devised. This will assist radiologists in prostate MRI reporting and help reduce inter-observer interpretative variability. Assessment categories, summarising the level or suspicion of risk of a lesion have been calculated. The guidelines will stratify patients who would benefit from biopsy and management intervention versus an observation strategy of management. The use of data obtained from mpMRI can be used to guide and perform MRI biopsy of suspicious lesions. The streamlined and updated v2.1 will facilitate multi-disciplinary meetings and afford more effective communication between clinicians and radiologists.

 

Major revisions in PI-RADS v2.13

Image data acquisition Technical specifications:

  • T2WI: It is recommended to perform a T2W sequence in the axial plane and at least one additional orthogonal plane.

  • DWI: clarification of b-values to use for purposes of DWI acquisition and for apparent diffusion coefficient (ADC).

  • DCE MRI: Temporal resolution < 15 s is advised to show early focal enhancement. 3D T1W gradient echo (GE) sequences are preferred.

Clarifications in interpretation criteria:

  • Further description of assessment of lesions in the central zone (CZ) and the anterior fibromuscular stroma (AFMS).

  • Revision in criteria for T2WI scores of 1 and 2 in TZ.

  • Revision in determination of overall assessment category in TZ.

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