Frank Robinson is remembered for a successful career as a Major League outfielder (14-time All Star) and manager. He is less remembered as the originator of common proverb, “Close only counts in horseshoes and hand grenades.” According to ESPN Classic, in the July 31, 1973 issue of Time magazine Robinson uttered these words with respect to baseball. It’s a colorful way to say that being almost accurate is simply not good enough.

At the Sperling Prostate Center, Robinson’s saying applies to prostate imaging. “Almost close” is not good enough when a patient has prostate cancer (PCa). The more precise the imaging, the more successful his treatment plan will be. Today’s patients want both effective cancer control and preservation of their urinary and sexual quality of life. The degree to which we generate an accurate portrait of a tumor’s aggression level, size, shape and location can make all the difference in the outcome. Thus, imaging accuracy matters.

For over a decade, multiparametric MRI (mpMRI) has been the reigning king of PCa imaging. With its multiple sequences, it not only reveals the suspicious lesion, but it also characterizes the danger level of the tissues. Furthermore, by distinguishing insignificant from significant (Gleason grade group ≥ 2) PCa, mpMRI can determine the need for a biopsy. If it proves to be necessary, a real time in-bore MRI-guided targeted biopsy offers the best diagnostic ability with the fewest needles.

mpMRI vs. Ultrasound (US)

When mpMRI became the star of PCa imaging, it put competitive pressure on standard ultrasound (US). Conventional US does not discriminate cancer from healthy tissue, so using it to guide biopsy needles means taking 12 or more random needle samples; it’s been likened to playing darts with a blindfold on. A new type of US called micro-ultrasound (micro-US) is a definite improvement over standard US. According to one user, “A standard ultrasound is about 6 to 12 MHz, whereas this one goes up to 29 MHz. With the increase in resolution, changes in the prostate architecture are easily identified that correspond to potential prostate cancer sites, which allows for real-time targeted biopsy.” But is it the same quality as mpMRI?

This question has led to head-to-head comparisons between mpMRI and micro-US. Here are a couple of recently published studies:

1. Ghai, et al. (Jul 2022) assembled data on 94 biopsy-naïve patients who had mpMRI followed by micro-US. The objective was to compare detection of clinically significant PCa, and the identification of MRI nodules visible at micro-US for real-time targeted biopsy. The authors concluded, “Multiparametric MRI and micro-US showed similar prostate cancer detection rates in biopsy-naive men; although micro-US was inferior to multiparametric MRI for biopsy avoidance, most MRI lesions were visible at micro-US.” Micro-US was also significantly inferior for preventing biopsies, as it tends to overdetect insignificant PCa. ^[i]
2. Results of a 2019 clinical study of micro-US guided targeted biopsies vs. mpMRI-guided targeted biopsies describe micro-US as “quite accurate in excluding clinically significant prostate cancer, however, many abnormalities detected on micro-US were not clinically significant cancer. Whether this modality is able to supplant mpMRI or serve as an adjunct to guide fusion biopsies remains to be ascertained in future studies.”^[ii]

This is not to say that micro-US is without merit. In situations where mpMRI is simply not available, micro-US at least offers better imaging fidelity than conventional US. However, it may have an inherent weakness in detecting anterior PCa, which conventional ultrasound also frequently misses:

Unlike its low frequency precursor, micro-ultrasound struggles with the phenomena of signal loss deep in the anterior, especially with larger prostates. … This neglects the anterior region which accounts for 20%-30% of all prostate cancers. Anterior tumors often require multiple standard biopsies for diagnosis and yield smaller areas of cancer on core biopsies, which can lead to an undergrading of disease and delayed treatment. Unfortunately, supporting “targeted” micro-ultrasound with the standard TRUS biopsy is unlikely to address the issue.^[iii]

To sum up, published studies of micro-US vs. mpMRI describe the performance of micro-US as “similar”, “comparable”, and “quite accurate” when compared with mpMRI. As far as our Center is concerned, those adjectives only count in horseshoes and hand grenades. In the world of urology, the search for in office imaging that performs as well as mpMRI will continue. Will any novel ultrasound technology be on a true par with mpMRI accuracy? Only time will tell. This much is true, however: there is currently no equal, no substitute, for the caliber of information provided by mpMRI of the prostate.

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] Ghai S, Perlis N, Atallah C, Jokhu S et al. Comparison of Micro-US and Multiparametric MRI for Prostate Cancer
Detection in Biopsy-Naive Men. Radiology. 2022 Nov;305(2):390-398.
[ii] Diagnostic Accuracy of Targeted Prostate Biopsies: Comparing Micro-Ultrasound with Multiparametric MRI for the Detection of Prostate Cancer. https://www.urotoday.com/conference-highlights/aua-2019-annual meeting/aua-2019-prostate-cancer/112321-aua-2019-diagnostic-accuracy-of-targeted-prostate-biopsies comparing-micro-ultrasound-with-multiparametric-mri-for-the-detection-of-prostate-cancer.html
[iii] “Micro-Ultrasound vs MRI for Prostate Cancer Diagnosis.” Sep. 2, 2020. https://focalhealthcare.com/micro ultrasound-vs-mri-for-prostate-cancer-diagnosis/.