Micro-Ultrasound (Micro-US), MRI, and PSMA PET in Prostate Cancer: Whole-Mount Correlation Study

Posted by Wayne G. Brisbane, MD

Overview
Following prior work (OPTIMUM trial), this study compares micro-ultrasound (Micro-US), multiparametric MRI (mpMRI), and PSMA PET for lesion detection and local staging in men undergoing prostatectomy, with whole-mount pathology as the reference. The goal was to assess whether high-resolution Micro-US can perform comparably to MRI—and whether combining modalities improves accuracy.

1. Background and Rationale

• Micro-Ultrasound (29 MHz) offers much higher spatial resolution than conventional ultrasound, enabling visualization of prostate architecture similar to MRI.
• The OPTIMUM trial (biopsy-based) established noninferiority of micro-ultrasound to MRI for detecting clinically significant prostate cancer (Grade Group ≥2).
• This current analysis extends that comparison to surgical (whole-mount) specimens to validate imaging accuracy against histopathology.

2. Methods

• Cohort: Surgical patients with available MRI, micro-ultrasound, and in a subset, PSMA PET imaging.
• Expert Reviewers: Radiologist (MRI), urologist (Micro-US), and nuclear medicine physician (PSMA) independently contoured lesions; a pathologist mapped whole-mount sections.
• All imaging and pathology were aligned to a 39-sector prostate map to enable sector-by-sector comparison.
• Endpoints:
  

   

  • Primary: Detection of Grade Group ≥2 lesions.
  • Secondary: Detection of extracapsular extension (ECE).

3. Results

• Sample: After exclusions, 68 evaluable patients; about one-third had ≥T3 disease—allowing ECE assessment.
• Lesion Detection:
  

   

  • Index Lesions: Micro-ultrasound and MRI both achieved ~90% detection, no statistical difference.
  • All Grade Group ≥2 Lesions: ~78% accuracy for both modalities.
  • Anterior Tumors: Slight numerical advantage for MRI, but not significant; small tumors also similar.
• ECE Detection: MRI outperformed micro-ultrasound.
• PSMA PET Subset: Showed similar index and Grade Group ≥2 detection (high 90s and 70s, respectively). PSMA performance for anterior and small lesions was unexpectedly modest, possibly due to sample variation.

4. Key Takeaways

• Micro-Ultrasound ≈ MRI for detecting clinically significant intraprostatic lesions — consistent with prior biopsy-based data (OPTIMUM trial).
• MRI remains superior for evaluating extraprostatic extension (ECE).
• PSMA PET adds complementary information but did not outperform MRI or MrUS in this surgical cohort.
• Clinical Implications:
  

   

  • Micro-US may serve as a real-time, lower-cost alternative to MRI for lesion targeting.
  • However, systematic biopsy remains essential—especially for anterior and small-volume disease.
  • For focal therapy planning, relying on imaging alone risks missing clinically significant cancers.