Abstract
Multiparametric magnetic resonance imaging has become an established method for evaluating the prostate for clinically significant prostate adenocarcinoma. Criteria have been developed for categorizing MRI findings, the most frequently used of which is the PI-RADS system. The PI-RADS V2 document provides separate image interpretation and clinical grading sections. Within this article we give an overview of the integrated, algorithmic way, we approach prostate MRI, show images corresponding to each PI-RADS category, and provide several illustrative cases.
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Multiparametric magnetic resonance imaging (mpMRI) has become an established technique for the detection and staging of clinically significant prostate adenocarcinoma. Recently, the American College of Radiology proposed and published the prostate imaging-reporting and data system (PI-RADS) V2 [1] as a synoptic reporting template for prostate cancer. Studies have since been completed validating the imaging parameters specified within this report [2], as well as mpMRI’s role in active surveillance and targeting biopsies, increasing the diagnostic yield for clinically significant cancers [3–7]. This article aims to provide a simplified algorithm and imaging atlas to reference with the assessment and reporting portion of the PI-RADS V2 document.
PI-RADS V2 changes in comparison to V1
PI-RADS V2 recommends the use of high b value images (≥1400) for diffusion-weighted imaging (DWI) in the multiparametric analysis of prostate MRI images. Increasing b values has been shown to increase lesion conspicuity and identify clinically significant prostate cancers [8]. The main differences in image interpretation are as follow:
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The primary assessment of the peripheral and transition zones is now different, with the designation of a dominant sequence for each.
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The dominant sequences in evaluating the peripheral zone are high b value DWI and apparent diffusion coefficient (ADC).
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T2-weighted images are now used in the peripheral zone only to confirm the mass-like appearance of the observed restricted diffusion, to evaluate for extracapsular extension, and to give a PI-RADS score when DWI is inadequate (such as when there is artifact from a hip prosthesis).
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T2-weighted sequences are now dominant in the evaluation of the transition zone. Diffusion restriction now only plays a role in upgrading what would be a PI-RADS 3 lesion to a PI-RADS 4 lesion in the transition zone.
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Dynamic contrast enhancement (DCE) evaluation has been simplified. The absence or presence of enhancement before or at the same time as the rest of the prostate now differentiates lesions with minimal diffusion restriction into PI-RADS 3 and 4 lesions instead of the more complex washout curve analysis.
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MR spectroscopy is no longer a factor involved in PI-RADS scoring.
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New size criteria have been added. Lesions are differentiated based on size as measured on ADC for the peripheral zone and T2-weighted images for the transition zone with lesions <1.5 cm being PI-RADS 4 and lesions ≥1.5 cm being PI-RADS 5. Other sequences can be used for measurement if the preferred dominant sequence is technically inadequate [1].
In the figures we provide an algorithmic approach to evaluate the prostate using the same method as PI-RADS V2 but in a simplified manner (Figs. 1, 2, 3). Additionally, images and illustrative cases are provided for each PI-RADS category (Figs. 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15).
References
PI-RADS™ Prostate Imaging-Reporting and Data System Version 2. (2015). http://www.acr.org/~/media/ACR/Documents/PDF/QualitySafety/Resources/PIRADS/PIRADS%20V2.pdf. Accessed 11/19/2015
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Horn, G.L., Hahn, P.F., Tabatabaei, S. et al. A practical primer on PI-RADS version 2: a pictorial essay. Abdom Radiol 41, 899–906 (2016). https://doi.org/10.1007/s00261-016-0705-z
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DOI: https://doi.org/10.1007/s00261-016-0705-z