Micro-ultrasound in the Canadian prostate cancer diagnostic pathway

Recent Canadian data further reinforce the utility of micro-ultrasound (US) within our diagnostic ecosystem for prostate cancer. In a retrospective cohort, Black et al reported their experience with micro-US-guided transperineal (TP) biopsy.¹ They compared it to a cohort who underwent magnetic resonance imaging (MRI)–US fusion transrectal (TR) biopsy, showing a similar clinically significant prostate cancer (csPCa) detection, despite fewer biopsy cores, and demonstrating no cases of post-biopsy sepsis.¹

Their findings mirror broader international evidence that micro-US offers high diagnostic accuracy and that using the TP approach reduces/eliminates the risk of infection. Notably, the study highlights that micro-US lesion targeting — performed without radiology involvement or MRI-compatible fusion equipment — can deliver outcomes comparable to those of software-based MRI–US fusion systems. Micro-US employs a 29-MHz transducer that provides real-time visualization with a 70-μm resolution, enabling identification of suspicious lesions with spatial resolution far superior to conventional US.²

Prospective cohort data summarized in a recent Nature review corroborate the conclusions made in the current study. In a large, single-center series involving over 1400 men, micro-US demonstrated an 85% sensitivity and 79% negative predictive value for csPCa. With a concordance between modalities of >95%, micro-US identified 25 cases of csPCa missed by multiparametric (mp)MRI, while multiparametric (mp) MRI identified only four missed by micro-US.³

Additional data show that when mpMRI and micro-US findings are discordant, micro-US-guided targeted biopsy detects more csPCa than MRI-targeted biopsy alone, and also suggest that combination targeted biopsies may support elimination of the systematic biopsy.⁴ Meanwhile, whole-mount pathology co-registration work suggests that micro-US not only effectively detects index lesions but may also better characterize tumor extent than mpMRI.⁵

The OPTIMUM randomized controlled trial provides us with robust, prospective, randomized evidence supporting the use of micro-US in prostate cancer diagnosis.⁶ In biopsy-naive men, micro-US-guided biopsy was non-inferior to MRI/conventional-US fusion biopsy for detecting csPCa. Detection rates were virtually identical, and targeted biopsy performance was comparable across modalities. Importantly, every patient still received a systematic biopsy, reflecting real-world practice. OPTIMUM provides evidence that micro-US can function confidently as a primary imaging modality — a critical finding for Canada, where MRI access still poses significant challenges.

Canadian implementation must also consider workflow advantages. Unlike mpMRI, micro-US is performed at the point of care by urologists, eliminating delays associated with MRI availability, reporting queues, and MRI-US fusion registration challenges, though the ExactVu™ platform does include fusion software, FusionVu™. Because micro-US integrates directly into the biopsy procedure, patients can undergo imaging and targeted sampling in the same session, removing the diagnostic uncertainty associated with the historical systematic prostate biopsy. In a public system, the marginal cost of micro-US is minimal once capital equipment has been acquired.

Micro-US is not without limitations, however. Operator expertise matters; interpretation requires structured training, and image quality attenuates with increasing depth, which may limit evaluation of large prostates or transition-zone lesions. Micro-US is not yet a replacement for mpMRI in all contexts. For local staging, specifically the pelvic lymph nodes and assessing extraprostatic extension (EPE), mpMRI retains value, although emerging micro-US-based nomograms show promise, with predictive accuracy of 85.9% for EPE on final pathology.⁷

Systematic, in addition to targeted, biopsies remain the standard of care; multiple studies demonstrate that targeted approaches alone would miss 20–25% of csPCa cases, though this was without the use of micro-US.⁸ We must also consider that the diagnosis of csPCa is a surrogate endpoint in these studies, and we are still working on ways to improve prostate cancer outcomes while reducing the harms of overtreatment.

Nevertheless, micro-US should not be viewed as a competitor to mpMRI and should be considered a practical complement that has the potential to address Canada’s most significant diagnostic bottleneck: MRI access (Figure 1). A micro-US-first pathway, with selective MRI reserved for equivocal cases, prior negative biopsies, staging considerations, and surgical planning, would dramatically improve diagnostic efficiency while maintaining oncologic safety.

Figure 1.

Rationale and potential impact of a micro-ultrasound first imaging strategy in prostate cancer diagnostics. csPCa: clinically significant prostate cancer; mpMRI: multiparametric magnetic resonance imaging; US: ultrasound.