What is the optimal magnetic resonance imaging (MRI) protocol to evaluate both the prostate and bladder?

Optimal MRI Protocol for Prostate and Bladder Evaluation

For simultaneous evaluation of both prostate and bladder, order a multiparametric MRI pelvis with and without IV contrast at 1.5T or 3T (preferably 3T) using a pelvic phased-array surface coil, including T2-weighted imaging, diffusion-weighted imaging (DWI) with ADC maps, and dynamic contrast-enhanced (DCE) imaging. 1, 2

Core Technical Specifications

Field Strength and Coil Selection

• Use 1.5T or 3T MRI scanner, with 3T preferred for improved signal-to-noise ratio and superior spatial resolution 2
• Employ a pelvic phased-array surface coil positioned over the pelvis—an endorectal coil is neither mandatory nor routinely recommended at either field strength 2
• 3T systems provide comparable performance to 1.5T with endorectal coil when using multichannel phased-array coils 1

Required Imaging Sequences

All three sequences below are mandatory and must be included:

1. T2-weighted imaging (axial, sagittal, and coronal planes):

   • Provides anatomic detail of prostate zones, seminal vesicles, ejaculatory ducts, and bladder wall layers 1, 2
   • Critical for assessing depth of bladder wall invasion and distinguishing superficial from deep muscle invasion 1
   • Superior to CT for detecting invasion of detrusor muscle and perivesical tissues 1

2. Diffusion-weighted imaging (DWI) with ADC mapping:

   • Use high b-values (b=1400-2000) for optimal cancer detection 2
   • Detects areas of restricted diffusion correlating with tumor cellularity 2, 3
   • Improves accuracy in distinguishing muscle-invasive from non-muscle-invasive bladder cancer (sensitivity 78-98%, specificity 82-100%) 1
   • Enhances detection of malignant lymph nodes (sensitivity 61-94%, specificity 90-99%) 1

3. Dynamic contrast-enhanced (DCE) imaging with IV gadolinium:

   • Mandatory—contrast administration significantly improves staging accuracy 1
   • Increases sensitivity to 88% and accuracy to 74% for distinguishing organ-confined from non-organ-confined bladder cancer 1
   • Provides 41% sensitivity and 92% specificity for detecting nodal disease 1

Multiparametric Approach: The Gold Standard

Multiparametric MRI combining T2-weighted imaging, DWI, and DCE is the most optimal technique for local staging of both bladder and prostate pathology. 1

• This combined approach achieves sensitivity 90-94% and specificity 60-94% for distinguishing organ-confined from non-organ-confined bladder tumors 1
• For bladder cancer, use the VI-RADS (Vesical Imaging-Reporting and Data System) 5-point scoring system to estimate likelihood of detrusor muscle invasion 1
• For prostate evaluation, follow PI-RADS version 2.1 standards 2

Field of View Considerations

• Small field-of-view images: High-resolution axial T1-weighted and multiplanar T2-weighted sequences for detailed prostate gland, seminal vesicles, ejaculatory ducts, and bladder wall evaluation 1
• Large field-of-view images: Extended coverage to assess pelvic lymphadenopathy and extravesical disease 1

Critical Timing and Clinical Context

Timing Considerations

• Perform MRI at least 6 weeks after prostate biopsy to avoid hemorrhage artifact that degrades image quality 2
• If evaluating post-focal therapy, obtain first MRI at 12 months after treatment to minimize treatment-induced artifacts 2

Essential Clinical Information to Provide

When ordering, include: 2

• Recent PSA values
• Gleason scores from any prior biopsies
• Details of any prior focal therapy or bladder procedures
• Specific indication for the study

Common Pitfalls to Avoid

1. Never accept incomplete protocols: If any required sequence is missing or of inadequate quality, repeat before making treatment decisions 2
2. Do not order MRI without contrast for bladder evaluation: Non-contrast protocols have insufficient accuracy for local staging 1
3. Ensure adequate radiologist experience: The interpreting radiologist should read at least 20 prostate MRI examinations annually 2
4. Always obtain comparison images: Essential for detecting interval changes, particularly in surveillance scenarios 2

Alternative Considerations

• MR urography (MRU) with and without contrast can be added if upper tract evaluation is needed, providing superior contrast resolution compared to CT urography for small tumor detection 1
• PSMA PET/CT may be considered as an adjunct in specific scenarios (high-risk disease, biochemical recurrence), though data for routine use remain limited 1