Prostate cancer diagnostics have undergone a major shift with the adoption of multiparametric MRI (mpMRI), improving detection of clinically significant disease while reducing unnecessary biopsies [1,2]. However, MRI-based pathways come with practical limitations: cost, access, delays and reliance on radiological expertise.
Micro-ultrasound (MicroUS), a high-frequency 29 MHz imaging modality, has emerged as a potential alternative or adjunct [3]. By enabling real-time visualisation of prostate microarchitecture and targeted biopsy using the PRI-MUS scoring system, MicroUS promises a streamlined, clinic-based diagnostic pathway [3].
But does it replace MRI or simply complement it?
What does MicroUS add in practice?
Unlike conventional transrectal ultrasound (TRUS), MicroUS provides significantly improved spatial resolution, allowing direct visualisation of suspicious lesions during biopsy. This removes the need for pre-acquired imaging or fusion platforms and enables targeted and systematic sampling in a single session. For clinicians, the appeal is clear:
- Real-time targeting without MRI
- Simpler workflow
- Outpatient feasibility
- Reduced dependence on radiology infrastructure.
However, these advantages come with trade-offs. MicroUS is operator-dependent, requires training and has limited penetration in larger or anterior prostates. Importantly, it lacks the whole-gland functional assessment provided by mpMRI.
All current clinical evidence pertains exclusively to the ExactVu 29 MHz system (Exact Imaging, Canada), the only commercially available MicroUS platform at the time of writing; findings cannot be assumed to generalise to future alternative platforms.
Clinically significant prostate cancer (csPCa); Prostate Risk Identification using Micro-Ultrasound (PRI-MUS); Prostate Imaging Reporting and Data System (PI-RADS). Data represent general trends across studies rather than pooled estimates.
What does the evidence show?
The strongest evidence comes from the OPTIMUM randomised trial, which demonstrated that MicroUS-guided biopsy is non-inferior to MRI-based pathways (47.1% vs 42.6% csPCa detection) for detecting clinically significant prostate cancer [4].
Meta-analyses reinforce this:
- Sensitivity is similar between MicroUS and mpMRI (pooled: 0.87 vs 0.88)
- Specificity is lower with MicroUS (pooled: 0.25 vs 0.30)
- Biopsy avoidance is inferior with MicroUS (10% vs 34% in biopsy-naïve men) [5–7].
This distinction is clinically important. While MicroUS detects a comparable number of significant cancers, it tends to generate more positive findings, leading to more biopsies.
Figure 1: Representative MicroUS imaging features across PRI-MUS scores 1–5.
Prospective studies highlight a key insight: MicroUS and mpMRI identify overlapping but not identical cancers. In a large prospective series, MicroUS-targeted biopsy exclusively identified 25 csPCa cases compared with only four for MRI-targeted biopsy [8]. Conversely, a combined MRI plus MicroUS pathway detected csPCa in 40% of men versus 35% with MicroUS alone, confirming that MRI captures a subset of disease not visible on ultrasound [7]. This is not redundancy. It is complementarity.
So where does MicroUS fit?
The question is no longer whether MicroUS “matches” MRI, but how it integrates into clinical pathways.
1. As an adjunct to MRI
This is currently the most defensible role. Combining MicroUS with mpMRI allows:
- Improved real-time targeting
- Detection of lesions missed by MRI
- More flexible biopsy workflows [8].
In practice, MicroUS acts as the “eyes” during biopsy, while MRI provides the roadmap.
2. As an alternative where MRI is limited
In settings where MRI is unavailable, contraindicated or delayed, MicroUS offers a credible alternative supported by randomised evidence from OPTIMUM trial [4].
However, this comes with a clear compromise, you lose MRI’s ability to safely avoid biopsy in low-risk patients. It should be noted that OPTIMUM was conducted at centres with certified MicroUS expertise; its results are not directly transferable to settings without equivalent operator training, irrespective of MRI availability.
3. In active surveillance
MicroUS has a potential role in repeat and confirmatory biopsy, where real-time targeting can simplify workflows [9]. However, MRI remains superior for ruling out progression; and MicroUS alone risks missing upgrading (sensitivity 94.1% vs 100% for mpMRI; NPV 88.9% vs 100% for mpMRI, with an overall upgrading rate of 34%) [9]. At present, MicroUS should be seen as an adjunct, not a replacement, in surveillance protocols.
From a guideline perspective, the NCCN Prostate Cancer Early Detection Guidelines (v2.2026) acknowledge MicroUS-guided biopsy at experienced centres as an alternative to MRI-targeted biopsy [10]. The EAU Guidelines formally acknowledge MicroUS within the diagnostic framework but stop short of designating it as a recommended alternative to MRI-based pathways [11].
The key limitation is specificity. Across studies, the consistent weakness of MicroUS is lower specificity. Clinically, this means:
- More false positives
- Higher biopsy rates
- Less ability to reassure and avoid intervention.
This is where mpMRI still holds a clear advantage, and why it remains central in modern pathways.
TAKE HOME MESSAGES
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MicroUS provides high-resolution, real-time prostate imaging using a 29 MHz transducer.
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Randomised evidence shows non-inferior detection of clinically significant cancer compared to MRI pathways.
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Sensitivity is similar to mpMRI, but specificity and biopsy avoidance are lower.
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icroUS and mpMRI detect overlapping but non-identical cancers.
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The strongest current role is complementary use alongside MRI.
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It may serve as an alternative where MRI is unavailable.
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In active surveillance, it is an adjunct – not a replacement.
References
1. Kasivisvanathan V, Rannikko AS, Borghi M, et al. MRI-Targeted or Standard Biopsy for Prostate-Cancer Diagnosis. N Engl J Med 2018;378(19):1767–77.
2. Ahmed HU, Bosaily AE, Brown LC, et al. Diagnostic accuracy of multi-parametric MRI and TRUS biopsy in prostate cancer (PROMIS): a paired validating confirmatory study. The Lancet 2017;389(10071):815–22.
3. Ghai S, Eure G, Fradet V, et al. Assessing Cancer Risk on Novel 29 MHz Micro-Ultrasound Images of the Prostate: Creation of the Micro-Ultrasound Protocol for Prostate Risk Identification. J Urol 2016;196(2):562–9.
4. Kinnaird A, Luger F, Cash H, et al. Microultrasonography-Guided vs MRI-Guided Biopsy for Prostate Cancer Diagnosis: The OPTIMUM Randomized Clinical Trial. JAMA 2025;333(19):1679–87.
5. Garcia-Becerra CA, Arias-Gallardo MI, Juarez-Garcia JE, et al. Comparative diagnostic accuracy of multiparametric-MRI and Micro-ultrasound for clinically significant prostate cancer-a bivariate meta-analysis of prospective studies. Prostate Cancer Prostatic Dis 2026. [ePub ahead of print]
6. Gawad AMA, Aboelsaad AY, Elsayed AF, et al. Standalone 29-MHz micro-ultrasound for classifying clinically significant prostate cancer: a systematic review and diagnostic test accuracy meta-analysis of prospective studies. Abdom Radiol (NY) 2025;51(6):2979–92.
7. Ghai S, Perlis N, Atallah C, et al. Comparison of Micro-US and Multiparametric MRI for Prostate Cancer Detection in Biopsy-Naive Men. Radiology 2022;305(2):390–8.
8. Avolio PP, Piccolini A, Saitta C, et al. Enhanced diagnostic accuracy of micro-ultrasound in prostate cancer detection: An updated series from a single-center prospective study. Urol Oncol 2025;43(8):470.e19–470.e26.
9. Maffei D, Fasulo V, Avolio PP, et al. Diagnostic performance of microUltrasound at MRI‐guided confirmatory biopsy in patients under active surveillance for low‐risk prostate cancer. Prostate 2023;83(9):886–95.
10. NCCN Clinical Practice Guidelines in Oncology: Prostate Cancer Early Detection; Version 2. National Comprehensive Cancer Network 2026.
https://www.nccn.org/guidelines/
guidelines-detail?category=2&id=1460
11. Cornford P, Tilki D, van den Bergh RCN, et al. EAU-EANM-ESTRO-ESUR-ISUP-SIOG Guidelines on Prostate Cancer. EAU 2026.
https://uroweb.org/guidelines/prostate-cancer
[All links last accessed April 2026].
Declaration of competing interest: None declared
