Rationale and Objectives
This study compares the performance of T2 maps in the detection of prostate cancer (PCa) in comparison to T2-weighted (T2W) magnetic resonance images.
Materials and Methods
The prospective study was institutional review board approved. Consenting patients ( n = 45) with histologic confirmed PCa underwent preoperative 3-T magnetic resonance imaging with or without endorectal coil. Two radiologists, working independently, marked regions of interests (ROIs) on PCa lesions separately on T2W images and T2 maps. Each ROI was assigned a score of 1–5 based on the confidence in accurately detecting cancer, with 5 being the highest confidence. Subsequently, the histologically confirmed PCa lesions ( n = 112) on whole-mount sections were matched with ROIs to calculate sensitivity, positive predictive value (PPV), and radiologist confidence score. Quantitative T2 values of PCa and benign tissue ROIs were measured.
Results
Sensitivity and confidence score for PCa detection were similar for T2W images (51%, 4.5 ± 0.8) and T2 maps (52%, 4.5 ± 0.6). However, PPV was significantly higher ( P = .001) for T2 maps (88%) compared to T2W (72%) images. The use of endorectal coils nominally improved sensitivity (T2W: 55 vs 47%, T2 map: 54% vs 48%) compared to the use of no endorectal coils, but not the PPV and the confidence score. Quantitative T2 values for PCa (105 ± 28 milliseconds) were significantly ( P = 9.3 × 10 −14 ) lower than benign peripheral zone tissue (211 ± 71 milliseconds), with moderate significant correlation with Gleason score ( ρ = −0.284).
Conclusions
Our study shows that review of T2 maps by radiologists has similar sensitivity but higher PPV compared to T2W images. Additional quantitative information obtained from T2 maps is helpful in differentiating cancer from normal prostate tissue and determining its aggressiveness.
Introduction
Prostate cancer (PCa) is the most common noncutaneous cancer and the second leading cause of death among men in the United States . Conventional prostate-specific antigen (PSA) screening and transrectal ultrasound-guided biopsies have low sensitivity in PCa detection . In addition, distinguishing low-risk tumors from potentially life-threatening tumors using PSA and transrectal ultrasound is inadequate, and many patients with low-risk tumors elect to undergo radical prostatectomy, a major procedure with potential quality of life-altering complications. These limitations emphasize the need for noninvasive imaging techniques for detection, staging, and risk stratification of PCa, which may enable better choice of treatment and reduce the overtreatment of indolent diseases .
Multiparametric magnetic resonance imaging (mpMRI) is increasingly being used for PCa diagnosis and guiding biopsies, and has high sensitivity, negative predictive value, and specificity in PCa diagnosis . mpMRI has the potential to provide reliable information about the cancer grade, location, and volume for the selection of optimum therapy . T2-weighted (T2W) imaging is an integral part of mpMRI protocol recommended by the American College of Radiology and the European Society of Urogenital Radiology in the consensus guidelines, Prostate Imaging Reporting and Data System (PI-RADS) . PCa shows hypointensity in T2W images compared to benign tissue and has a sensitivity of around 50%–70% for PCa detection . T2 mapping techniques require acquisition of multiple T2W images at various echo times (TEs). The signal from various TEs is then fitted an exponential magnetic resonance (MR) signal decay model to generate an estimate of the quantitative T2 values. Numerous studies have found that quantitative T2 values are significantly lower in PCa compared to benign prostate tissue . The interpretation of conventional T2W images is subjective as signal intensities in T2W images are not comparable between patients and contrast is highly dependent on imaging parameters. However, quantitative T2 values from T2 maps are absolute and comparable. The use of T2 maps may help mitigate the subjective nature of T2W image interpretation and allow improved PCa detection based on a subtle difference in T2 values between different tissues.
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Materials and Methods
Study Patients
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Magnetic Resonance Imaging
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TABLE 1
Magnetic Resonance Imaging Parameters
Imaging Sequence Pulse Sequence FOV (mm) Matrix Size In-plane Resolution (mm) TE (ms) TR (s) Group A: TSE without endorectal coil TSE (T2W) 180 240 × 240 0.75 × 0.75 115 4.5 TSE (T2 map) 200 250 × 250 0.8 × 0.8 38, 88, 138, 188, 238, 288 8.6 Group B: TSE with endorectal coil TSE (T2W) 160 400 × 400 0.4 × 0.4 115 4.2 TSE (T2 map) 160 212 × 212 0.75 × 0.75 30, 60, 90, 120, 150, 180, 210, 240, 270 8.8 Group C: TSE (T2W) and k - t -T2 (T2 map) with endorectal coil TSE (T2W) 160 400 × 400 0.4 × 0.4 115 4.2k - t -T2 (T2 map) 160 160 × 160 1.0 × 1.0 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 144, 156, 168, 180, 192, 204, 216, 228, 240, 252, 264, 276, 288, 300, 312, 324, 336, 348, 360, 382, 396 3.3
FOV, field of view; T2W, T2-weighted; TE, echo time; TR, repetition time; TSE, turbo spin echo.
Slice thickness = 3 mm, flip angle = 90°.
Scan time for T2 mapping using TSE sequence = 492 seconds (without endorectal coil) and 436 seconds (with endorectal coil), k - t -T2 sequence = 316 seconds.
Scan time for T2W imaging using TSE sequence = 270 seconds (without endorectal coil) and 381 seconds (with endorectal coil).
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MR Image Analysis
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Results
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TABLE 2
Histologic Confirmed Cancers
Overall Group A: TSE without Endorectal Coil Group B: TSE with Endorectal Coil Group C: TSE (T2W) and k - t -T2 (T2 Map) with Endorectal Coil_n_ 112 43 32 37 Gleason score 3 + 3 54 19 13 22 3 + 4 42 19 13 10 4 + 3 15 4 6 5 4 + 5 1 1 — — Stage T2 87 38 20 29 T2c 8 1 2 5 T3 1 1 — — T3a 14 1 10 3 T3b 2 2 — — Mean tumor size (range) (cm 2 ) 1.6 × 0.8 (0.5–5.3 × 0.2–3.5) 1.5 × 0.8 (0.5–4.3 × 0.2–3.5) 1.7 × 0.9 (0.5–5.3 × 0.2–2.0) 1.5 × 0.7 (0.5–3.5 × 0.2–1.7)
T2W, T2-weighted; TSE, turbo spin echo.
TABLE 3
Radiologist Performance Statistics
Magnetic Resonance Imaging Sequence Sensitivity (%) Positive Predictive Value (%) Confidence Score T2W vs T2 maps T2W Overall 51 72 4.5 ± 0.8 Radiologist 1 52 81 4.5 ± 0.8 Radiologist 2 51 65 4.5 ± 0.9 T2 map Overall 52 88 4.5 ± 0.6 Radiologist 1 57 88 4.7 ± 0.5 Radiologist 2 47 88 4.2 ± 0.5 Endorectal coil usage T2W No endorectal coil Overall 47 71 4.4 ± 1.0 Radiologist 1 47 80 4.4 ± 0.9 Radiologist 2 47 65 4.3 ± 1.0 Endorectal coil Overall 54 72 4.5 ± 0.8 Radiologist 1 55 81 4.6 ± 0.7 Radiologist 2 54 65 4.5 ± 0.8 T2 map No endorectal coil Overall 48 89 4.4 ± 0.9 Radiologist 1 53 88 4.8 ± 0.4 Radiologist 2 44 90 4.2 ± 0.5 Endorectal coil Overall 54 87 4.4 ± 0.5 Radiologist 1 59 87 4.8 ± 0.5 Radiologist 2 49 87 4.2 ± 0.5
T2W, T2-weighted.
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Qualitative Results
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Use of Endorectal Coil
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Interobserver Agreement
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Quantitative Results
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Discussion
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Conclusions
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