Rationale and Objectives
To evaluate interobserver agreement with the use of and the positive predictive value (PPV) of Prostate Imaging Reporting and Data System version 2 (PI-RADS v2) for the localization of intermediate- and high-grade prostate cancers on multiparametric magnetic resonance imaging (mpMRI).
Materials and Methods
In this retrospective, institutional review board-approved study, 131 consecutive patients who had mpMRI followed by transrectal ultrasound-MR imaging fusion-guided biopsy of the prostate were included. Two readers who were blinded to initial mpMRI reports, clinical data, and pathologic outcomes reviewed the MR images, identified all prostate lesions, and scored each lesion based on the PI-RADS v2. Interobserver agreement was assessed by intraclass correlation coefficient (ICC), and PPV was calculated for each PI-RADS category.
Results
PI-RADS v2 was found to have a moderate level of interobserver agreement between two readers of varying experience, with ICC of 0.74, 0.72, and 0.67 for all lesions, peripheral zone lesions, and transitional zone lesions, respectively. Despite only moderate interobserver agreement, the calculated PPV in the detection of intermediate- and high-grade prostate cancers for each PI-RADS category was very similar between the two readers, with approximate PPV of 0%, 12%, 64%, and 87% for PI-RADS categories 2, 3, 4, and 5, respectively.
Conclusions
In our study, PI-RADS v2 has only moderate interobserver agreement, a similar finding in studies of the original PI-RADS and in initial studies of PI-RADS v2. Despite this, PI-RADS v2 appears to be a useful system to predict significant prostate cancer, with PI-RADS scores correlating well with the likelihood of intermediate- and high-grade cancers.
Introduction
In an attempt to standardize image interpretation and reporting of multiparametric magnetic resonance imaging (mpMRI) of the prostate, the European Society of Urogenital Radiology published the first Prostate Imaging Reporting and Data System (PI-RADS 1.0) in 2012. PI-RADS 1.0 is based on assessment of T2-weighted MRI, diffusion weighted imaging (DWI), and dynamic contrast enhanced-MRI (DCE-MRI) with or without MR spectroscopy for each lesion according to a 5-point scale and assigning a sum score ranging from 3 to 15 without MR spectroscopy (MRS) and from 4 to 20 with MRS . Several studies have validated the original PI-RADS in terms of accuracy; however, interobserver agreement was only moderate . Recent studies also suggest that assigning a score for T2-weighted imaging (T2WI) to transitional zone lesions and for DWI to peripheral zone lesion is adequate for stratification of patients for further diagnostic workup . On the other hand, MRS was rarely used in recent studies, and DCE-MRI curve-type analysis does not seem to add significant value in the characterization of prostate lesions .
Based on these new data, the PI-RADS steering committee of the American College of Radiology and the European Society of Urogenital Radiology prostate MRI working group revised PI-RADS and published PI-RADS version 2.0 in early 2015 . In this new version of PI-RADS, a primary determinant MRI sequence is used to evaluate each prostate lesion based on location. For peripheral zone lesions, DWI is the dominant sequence, and for transitional zone lesions, T2-weighted sequence is the dominant sequence. On DCE-MRI, results are scored as positive or negative based on the presence or absence of focal early enhancement, and the previously used curve-type analysis was abandoned. DCE-MRI is used strictly for characterization of peripheral zone lesions and is applied only if it makes a clinically relevant difference in cases where a lesion is upgraded from PI-RADS 3 to 4. Finally, a final score of 1–5 is assigned to each prostate lesion based on the revised rules.
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Materials and Methods
Study Design and Patient Population
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MR Imaging Protocol
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TABLE 1
Magnetic Resonance Imaging Sequence Parameters
Parameter Repetition Time (ms) Echo Time (ms) Flip Angle (°) Slice Thickness (mm) Acquisition Matrix Imaging Time FOV (cm) NEX Scan Mode No. of Repetitions Repetition Time (s) T2WI 3427 102 180 4 320 × 320 5:11 20 4 Zoom – – T1WI 500 Minimum full 180 4 224 × 256 4:56 20 1 Zoom – – DWI 3800 Minimum full 180 4 128 × 128 2:24 20 1 (b value of 0)
12 (b value of 600)
1 (b value of 1000) Zoom – – DCE 3 Minimum full 15 4 160 × 160 6:07 20 1 Zoom 53 7
DCE, dynamic contrast-enhanced; DWI, diffusion weighted imaging; FOV, field of view; T1WI, T1-weighted imaging; T2WI, T2-weighted imaging.
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Prostate Biopsy
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MR Analysis
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Radiologic-Pathologic Correlation
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Statistical Analysis
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Results
Lesion Characteristics
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Interobserver Agreement
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TABLE 2
Interobserver Agreement—Intraclass Correlation Coefficient Based on Lesion Type
Lesion Type Intraclass Correlation Coefficient All 0.74 (95% CI: 0.60, 0.83) All PZ lesions 0.72 (95% CI: 0.56, 0.83) All TZ lesions 0.67 (95% CI: 0.22, 0.89) All intermediate- and high-grade lesions 0.60 (95% CI: 0.34, 0.78)
CI, confidence interval; PZ, peripheral zone; TZ, transitional zone.
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Positive Predictive Value
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TABLE 3
Positive Predictive Value for Each PI-RADS Score
PI-RADS Score PPV (%) Reader 1 2 0 3 13.0 (95% CI: 6.5, 23.8) 4 64.9 (95% CI: 47.4, 79.3) 5 88.9 (95% CI: 50.7, 99.4) Reader 2 2 0 3 11.9 (95% CI: 5.3, 23.5) 4 62.2 (95% CI: 44.8, 77.1) 5 84.6 (95% CI: 53.7, 97.3)
CI, confidence interval; PI-RADS, Prostate Imaging Reporting and Data System; PPV, positive predictive value.
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Discussion
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