Prostate cancer diagnosis has long relied on imaging to help clinicians identify suspicious lesions and guide tissue sampling. While magnetic resonance imaging (MRI) has become an important tool for detecting clinically significant prostate cancer, its cost, availability, and workflow requirements can present challenges.
Could high-resolution ultrasound offer a comparable alternative?
A randomized clinical trial published in JAMA, titled “Microultrasonography-Guided vs MRI-Guided Biopsy for Prostate Cancer Diagnosis: The OPTIMUM Randomized Clinical Trial”, suggests that it may.
The study found that micro-ultrasound-guided prostate biopsy was noninferior to MRI fusion-guided biopsy in detecting clinically significant prostate cancer in biopsy-naive men (when combined with standard systematic biopsy), highlighting a potentially important advancement in image-guided diagnosis.
What Is Micro-Ultrasound, and How Does It Compare to MRI?
Traditional transrectal ultrasound has been widely used to guide prostate biopsies, but conventional ultrasound may not clearly distinguish suspicious cancerous tissue from surrounding healthy tissue.
Multiparametric MRI helps address this limitation by identifying suspicious regions before biopsy. Clinicians can then combine MRI findings with real-time ultrasound guidance to target these areas during tissue sampling.
Micro-ultrasound takes a different approach.
Using high-frequency imaging at approximately 29 MHz, micro-ultrasound provides substantially greater spatial resolution than conventional ultrasound. This allows clinicians to examine prostate tissue in greater detail and identify suspicious regions during the biopsy procedure itself.
Unlike MRI fusion-guided biopsy, which typically requires a separate MRI examination, micro-ultrasound can potentially combine lesion identification and biopsy guidance into a single appointment.
The question is whether this approach can detect clinically significant prostate cancer as reliably as MRI-guided techniques.
What the OPTIMUM Trial Examined
The OPTIMUM trial was an international, multicenter, randomized clinical trial conducted across 20 centers in eight countries between December 2021 and September 2024.
Researchers enrolled biopsy-naive men with suspected prostate cancer, based on elevated prostate-specific antigen (PSA) levels and/or abnormal digital rectal examination findings. Men with contraindications to MRI or biopsy were not eligible.
Of the 802 randomized participants, 678 underwent prostate biopsy and were included in the primary analysis.
Participants were assigned to one of three imaging approaches:
- Micro-ultrasound-guided biopsy: Suspicious prostate regions were identified and targeted using high-resolution micro-ultrasound, without a prebiopsy MRI.
- MRI/conventional ultrasound fusion-guided biopsy: Prebiopsy MRI findings were combined with conventional ultrasound to guide tissue sampling.
- Combined micro-ultrasound/MRI-guided biopsy: Micro-ultrasound targets were sampled first while the operator was blinded to the MRI; MRI targets were then revealed and sampled.
In all three arms, targeted biopsies were followed by standard systematic biopsy in the same session, so the headline detection rates reflect targeted plus systematic sampling rather than image-targeted sampling alone.
The primary objective was to determine whether micro-ultrasound-guided biopsy was noninferior to MRI fusion-guided biopsy for detecting clinically significant prostate cancer, defined as Gleason Grade Group 2 or higher. The prespecified noninferiority margin was 10 percentage points.
Key Findings: Micro-Ultrasound Meets the Noninferiority Threshold
The trial found that micro-ultrasound-guided biopsy achieved detection rates comparable to MRI fusion-guided biopsy, with both approaches combined with systematic biopsy.
For clinically significant prostate cancer, the researchers reported:
- 46% detection with micro-ultrasound-guided biopsy in the primary comparison, which pooled the micro-ultrasound-only arm (47%) with micro-ultrasound samples from the combined arm obtained before MRI information was available.
- 43% detection with MRI/conventional ultrasound fusion-guided biopsy.
- 47% detection with combined micro-ultrasound/MRI-guided biopsy.
The primary comparison demonstrated that micro-ultrasound-guided biopsy was statistically noninferior to MRI fusion-guided biopsy, with an absolute detection difference of 3.52 percentage points (95% CI, -3.95% to 10.92%; P < .001 for noninferiority).
Importantly, noninferiority does not establish superiority. Rather, it indicates that micro-ultrasound met the study's predefined criteria for not being meaningfully less effective than the MRI-guided approach. The lower bound of the confidence interval means the data remain compatible with micro-ultrasound detecting up to about 4 percentage points fewer clinically significant cancers than MRI fusion biopsy.
The researchers also examined targeted biopsy samples separately. Detection rates for clinically significant prostate cancer were 38% with micro-ultrasound, 34% with MRI fusion guidance, and 40% with the combined approach. These differences were not statistically significant.
Together, the findings suggest that micro-ultrasound may provide a viable alternative to MRI fusion guidance for prostate biopsy for biopsy-naive men when performed by trained, experienced operators alongside systematic biopsy.
Why These Findings Matter for Prostate Cancer Diagnosis
The OPTIMUM trial raises important questions about how prostate cancer diagnostic pathways could evolve.
Greater accessibility: MRI availability varies across healthcare settings. Micro-ultrasound may offer an additional imaging option for patients who face limited access to MRI services or have contraindications to MRI. However, men with MRI contraindications were excluded from OPTIMUM, so this use was not tested in the trial.
More streamlined workflows: Because micro-ultrasound can identify suspicious lesions and guide biopsy during the same procedure, it may reduce the need for separate imaging appointments. The trade-off is that micro-ultrasound assessment happens during the biopsy session itself. In MRI-first pathways, many men with low-suspicion MRI findings and a favorable PSA density currently avoid biopsy altogether. OPTIMUM did not test that kind of triage, because every participant underwent biopsy regardless of imaging findings.
Potential resource savings: Reducing reliance on prebiopsy MRI could help lower imaging-related costs and waiting times, although additional research is needed to establish these benefits across different healthcare systems.
However, the findings do not suggest that MRI should be universally replaced. Current guidelines recommend MRI before biopsy for men at risk of prostate cancer, and a single trial does not change that on its own. MRI also supports local staging and treatment planning, which OPTIMUM did not assess.
The study focused on biopsy-naive men with suspected prostate cancer and evaluated cancer detection rather than long-term patient outcomes. Further research is needed to understand how micro-ultrasound performs across different clinical populations, operator experience levels, and healthcare environments.
The Importance of Ultrasound Training in Image-Guided Diagnosis
As ultrasound technology becomes increasingly sophisticated, the ability to acquire, interpret, and act on imaging findings remains essential.
High-resolution imaging can provide additional anatomical detail, but clinicians must still recognize relevant structures, distinguish suspicious findings, and accurately guide procedures.
Micro-ultrasound also requires specialized imaging interpretation, reinforcing the importance of appropriate training and clinical experience before adopting new diagnostic techniques. In OPTIMUM, micro-ultrasound findings were scored with PRI-MUS, a dedicated risk scoring system that is still in its first version, and every operator had completed a formal micro-ultrasound training program before enrolling patients.
These considerations extend beyond prostate imaging. Across medical specialties, effective ultrasound use depends on a strong foundation in sonographic anatomy, image acquisition, and interpretation.
Building Foundational Ultrasound Skills with SonoSim
As research continues to expand the clinical applications of ultrasound, accessible and structured education remains an important part of preparing healthcare professionals to use imaging effectively.
The SonoSim Ultrasound Training Ecosystem combines expert-led educational content with hands-on virtual scanning using real patient ultrasound imagery, helping learners build foundational imaging and interpretation skills through repeatable practice.
For clinicians and educators interested in genitourinary ultrasound, SonoSim offers dedicated resources, including the Prostate Anatomy & Physiology Ultrasound Training Module, which covers prostate anatomy, sonographic imaging techniques, transducer selection, and common imaging pitfalls.
Learners can also explore SonoSim's broader Urology Ultrasound Training Modules to strengthen their understanding of genitourinary anatomy and ultrasound applications.
While these resources do not provide specialized micro-ultrasound-guided prostate biopsy training, they support the foundational ultrasound knowledge and scanning skills relevant to this evolving field.
As the OPTIMUM trial demonstrates, advances in ultrasound technology continue to create new possibilities for image-guided care. Developing the skills to interpret and apply ultrasound findings remains essential to translating those advances into clinical practice.
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):1679-1687.
Read the full study in JAMA.