Rationale and Objectives
To compare prostate morphology, image quality, and diagnostic performance of 1.5-T endorectal coil magnetic resonance (MR) imaging (MRI) and 3.0-T nonendorectal coil MRI in patients with prostate cancer.
Materials and Methods
MR images obtained of 83 patients with prostate cancer using 1.5-T MRI systems with an endorectal coil were compared to images collected from 83 patients with a 3.0-T MRI system. Prostate diameters were measured, and image quality was evaluated by one American Board of Radiology (ABR)–certified radiologist (reader 1) and one ABR-certified diagnostic medical physicist (reader 2). The likelihood of the presence of peripheral zone cancer in each sextant and local extent was rated and compared to histopathologic findings.
Results
Prostate anterior–posterior diameter measured by both readers was significantly shorter with 1.5-T endorectal MRI than with 3.0-T MRI. The overall image quality score difference was significant only for reader 1. Both readers found that the two MRI systems provided a similar diagnostic accuracy in cancer localization, extraprostatic extension, and seminal vesicle involvement.
Conclusions
Nonendorectal coil 3.0-T MRI provides prostate images that are natural in shape and that have comparable image quality to those obtained at 1.5 T with an endorectal coil, but not superior diagnostic performance. These findings suggest an opportunity exists for improving technical aspects of the 3.0-T prostate MRI.
Prostate cancer is the second most common cause of cancer death among American men. The American Cancer Society estimated that 233,000 new cases of prostate cancer would be diagnosed in 2014, and approximately 29,480 men would die of the disease . Magnetic resonance (MR) imaging (MRI), with excellent soft-tissue contrast, provides high resolution images of the pelvis for use in prostate cancer management .
The use of an endorectal coil is an essential part of the prostate 1.5-T MRI protocol in the clinical diagnosis of prostate cancer . An endorectal coil is inserted tightly against the prostate during the MRI examination to increase image resolution and improve staging accuracy . However, the endorectal coil leads to deformity in the prostate contour, and the anatomic distortion resulting from it can potentially hinder the diagnosis and pathology correlation . The changes in prostate shape and volume after the introduction of an endorectal coil may cause difficulties in MRI–computed tomography fusion and radiotherapy planning . Another limitation is that patients with rectal stenosis or immediately after surgery or radiotherapy may not be good candidates for the use of the endorectal coil during MR examination .
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Materials and methods
Study Design and Population
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MR Imaging Protocol
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Table 1
Parameters for T2-weighted MR Imaging
Parameters Axial T2-weighted Fast Spin Echo Coronal T2-weighted Fast Spin Echo 1.5-T Endorectal 3.0 T 1.5-T Endorectal 3.0 T Coil Torso phased-array, endorectal 32-channel phased-array Torso phased-array, endorectal 32-channel phased-array TR (ms)/TE (ms) 4000–6600/90–150 3488–4400/100 4000–6500/90–150 2138–2685/100 Section thickness 3 3 3 3 Intersection gap (mm) 0–1 0.3 0–1 0.5 Field of view (mm) 100–142 140 100–140 260 Frequency direction Anteroposterior Anteroposterior Anteroposterior or superoinferior Superoinferior Matrix 256 × 192 192 × 154 256 × 192 304 × 294 Number of signals acquired 1.5–2 2 1.5–3 2 Echo train length 8–16 14 8–16 14
MR, magnetic resonance; TE, echo time; TR, repetition time.
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Image and Histopathology Analysis
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Table 2
Qualitative Evaluation of Image Quality
Visualization of Posterior Border Visualization of Seminal Vesicles 5. Well delineated 5. Margins and septations seen 4. 75%–100% of margin clearly seen 4. Margins seen, septations poorly defined 3. 50%–75% of margin clearly seen 3. Septations seen, margins poorly defined 2. 25%–50% of margin clearly seen 2. Poorly defined 1. <25% of margin clearly seen 1. Unreadable Visualization of Neurovascular Bundle Overall Image Quality Rating 4. Seen well on both sides 5. Excellent 3. Seen well on one side 4. Very good 2. Seen suboptimally on both sides 3. Good 1. Unreadable 2. Fair 1. Poor
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Statistical Analysis
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Results
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Table 3
Comparison of Prostate Diameter Measurement
Reader 1: Radiologist Reader 2: Physicist 1.5-T Endorectal 3.0 T_P_ Value ∗ 1.5-T Endorectal 3.0 T_P_ Value ∗ Prostate diameter measurement Left–right (mm) 48.0 ± 6.0 48.1 ± 7.6 .553 (NS) 47.5 ± 5.6 45.7 ± 7.1 .039 Cranial–caudal (mm) 38.3 ± 6.0 43.2 ± 6.9 <.001 40.3 ± 5.7 42.1 ± 7.6 .179 (NS) Anterior–posterior (mm) 26.2 ± 5.5 35.0 ± 5.9 <.001 25.5 ± 6.0 32.8 ± 6.3 <.001 LR/CC ratio 1.27 ± 0.18 1.13 ± 0.19 <.001 1.19 ± 0.17 1.10 ± 0.18 <.001 LR/AP ratio 1.88 ± 0.30 1.40 ± 0.23 <.001 1.93 ± 0.36 1.41 ± 0.19 <.001 Image quality scoring result Posterior border 4.48 ± 0.86 4.58 ± 1.04 .041 4.83 ± 0.38 4.81 ± 0.45 .946 (NS) SV 4.51 ± 1.03 4.34 ± 1.09 .069 (NS) 4.75 ± 0.58 4.28 ± 0.77 <.001 NVB † 3.49 ± 0.83 3.63 ± 0.82 .101 (NS) 3.70 ± 0.58 3.69 ± 0.58 .869 (NS) Overall image quality 4.19 ± 1.04 4.47 ± 1.04 .014 4.77 ± 0.48 4.64 ± 0.58 .107 (NS) AUCs for diagnostic performance Sextant tumor localization 0.5664 0.5521 .701 (NS) 0.6095 0.5932 .628 (NS) Extracapsular extension 0.7206 0.7250 .968 (NS) 0.6334 0.4475 .088 (NS) SV involvement 0.5112 0.7714 .133 (NS) 0.5577 0.5625 .975 (NS)
AP, anterior–posterior; AUCs, area under the receiver operating characteristic curves; CC, cranial–caudal; LR, left–right; NS, not significant; NVB, neurovascular bundle; SV, seminal vesicles.
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Discussion
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