Check out the name of this type of prostate imaging: microultrasonography. It’s a mouthful, and if you have trouble pronouncing it, you’re not alone. Let me break it down:

• Micro = very small. You may know words like micrometer or micromanage, same idea.
• Ultrasono = ultrasound.
• Graphy = graphics.

Put it all together and it means higher frequency ultrasound (US) that gives prostate pictures with high resolution, depicting fine details in tissue. It beats conventional prostate US in performance, since traditional US can’t tell the difference between normal tissue vs. prostate cancer.

Microultrasonography (MUS, also called micro-ultrasound) is becoming the new darling of urologists. The reason for their hope is its significantly better image resolution, which gives details of 1) prostate anatomy and 2) tissue density. These two key factors give important clues suggesting prostate cancer (PCa). In turn, this helps urologists target areas to biopsy using potentially fewer biopsy needles. As one research team puts it, “Preliminary evidence has shown comparable sensitivity to magnetic resonance imaging (MRI)…”^[i] Whoa, let’s slow down. Are they claiming that MUS is as good as MRI?

Well, no, not exactly. Formal research studies use words like comparable or noninferior when pitting one performance against another. For example, using Artificial Intelligence (AI) to diagnose PCa based on tissue samples might be described as comparable to experienced radiologists, meaning it’s roughly equal. Or, it might be termed noninferior to human readers—but saying that it’s not worse than human radiologists is not meant to imply it’s better than humans.

Today’s performance of MRI for prostate imaging is enviable, so it’s natural to want to get its detailed prostate portraiture into urologists’ hands. Currently, urologists have to refer their patients to a radiology center or hospital equipped with a large, specialized magnet. Urologists have been on board with referrals because what’s not to love about the unequalled the visual information of MRI?

The first effort to incorporate MRI scans directly into a urology office was another technology called fusion. Fusion is a two-step process. First, the patient goes to a radiology center for an MRI, and those images are read (interpreted) by a radiologist who writes a report that accompanies a copy of the MRI scan results back to the urologist. Second, the patient returns to the urologist for a real-time transrectal ultrasound (TRUS). The urologist has special software that “fuses” the MRI images (not real-time) with the real-time TRUS using a point-by-point system. The urologist thus uses the fusion images to, say, perform a targeted biopsy or plan a treatment because fusion allows visual identification of tumor location—something that ordinary US can’t do. Fusion is proven to be superior to conventional US, and published studies have demonstrated that when it comes to detecting clinically PCa it is either comparable or noninferior to real-time MRI. Fusion contains MRI information but it is not superior in sensitivity, which is why a fusion-guided biopsy is often not only targeted to the “known” tumor, but additional random needles may be taken as a precaution against fusion having missed some PCa. In fact, due to slight distortions, fusion can compromise the precision of real-time MRI. I cannot emphasize enough that fusion-guided biopsies should never be called MRI-guided biopsies. This is very misleading. Fusion is indeed more accurate than TRUS alone, but compared to real-time MRI? Close, but no cigar.

So, what about MUS? So far, I’ve talked about MUS, and fusion of MRI with real-time TRUS. There’s also a third type of imaging, fusion of MRI with real-time MUS. A new study reported comparisons among the three for targeted prostate biopsy, with detection of clinically significant PCa (Grade Group 2 or higher) as the goal.^[ii] Here’s a table summarizing differences in detecting clinically significant PCa:

	MUS alone	Fusion (TRUS + MRI)	Fusion (MUS + MRI)
Detecting Grade Group 1	11.6%	15.4%	17.3%
Detecting Grade Group ≥2	38%	34%	40%

According to the authors, since conventional TRUS isn’t for targeted biopsies (it doesn’t show tissue differences), MUS alone is a cheaper alternative to fusion because it uses portable, inexpensive US equipment. Its diagnostic performance is statistically comparable with TRUS + MRI fusion. You notice, however, that when MUS is fused with non-real time MRI, it performs even better, because MRI has functional imaging that provides more characteristics of tumor behavior than MUS can offer.

But let’s be perfectly clear. Let’s skip the fusion middleman. There is no excuse for adding the extra step, and diluting previous multiparametric MRI by marrying it to ultrasound imaging. MUS may show a suspicious tumor, but it can’t offer the spectrum of visual analysis gained during customized imaging sequences in real time that show anatomy, motion of water molecules in tissue, and tumor blood flow.

Understandably, 3T multiparametric MRI (mpMRI) may not yet be accessible to all potential PCa patients in all regions. Also, insurance coverage may limit availability. For patients in these circumstances, MUS is a better alternative than TRUS alone. But for patients who can access it, real-time MRI detection and in-bore MRI-guided targeted biopsy is unequaled by any other approach to prostate imaging. The patient who wants the best, and the urologist who wants the best for his patients, both know that mpMRI is the winner and still champion.

NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.

References

[i] Zhou SR, Choi MH, Vesal S, Kinnaird A et al. Inter-reader Agreement for Prostate Cancer Detection Using Micro-
ultrasound: A Multi-institutional Study. Eur Urol Open Sci. 2024 Jul 13;66:93-100.
[ii] Kinnaird A, Luger F, Cash H, et al. Microultrasonography-Guided vs MRI-Guided Biopsy for Prostate Cancer
Diagnosis: The OPTIMUM Randomized Clinical Trial. JAMA.