We all know how consumer demand spawns knockoffs of high-end goods, and how inferior the resulting imitations are. For instance, there’s a huge quality gap between a flea market “Rolex” vs. the original Swiss superstar. But a Rolex watch is not accessible for everyone, so in the interest of maintaining one’s image, compromise comes easily. After all, there’s not much at stake except a status symbol.
When it comes to detecting prostate cancer (PCa), however, we’re talking about an image where one’s life may be at stake. It’s the image of the disease itself within the gland. Today, we have a superstar technology that’s like the Swiss watch of imaging. It’s called multiparametric MRI (mpMRI) because it uses 3 parameters, or functional imaging sequences, to detect abnormal prostate tissue function:
- T2-weighted (T2) is about anatomy and suspicious areas (regions of interest or ROIs)
- Diffusion-weighted imaging (DWI) is about the motion of water molecules in tissues. Dense tumor cells restrict water motion within and between them, which stands out using DWI MRI.
- Dynamic contrast-enhancement (DCE or CE) can add further definition by highlighting the blood flow in the tumor’s chaotic blood vessels.
When these three imaging sequences are combined into a 3-D portrait of a man’s prostate, an experienced reader is able to evaluate even a very small ROI, and assign it a numeric “danger” value from 1 to 5 based on its appearance. This is called the Prostate Imaging Reporting and Data System (PI-RADS), a 5-point scale from 1 (most likely not cancer) to 5 (most likely cancer). And, when mpMRI is done with a powerful 3 Tesla (3T) magnet, and the results are read by an experienced prostate radiologist, it gives detection/diagnostic precision to MRI the same way Rolex does to telling time.
Men want mpMRI
Roughly a million ultrasound-guided biopsies are done annually in the U.S. Alternatively, men whose PSA blood test comes back high, or rising, are now more aware that rushing into a conventional biopsy can lead to overdiagnosis of insignificant PCa, and overly aggressive treatment with risks of urinary and sexual side effects. They much prefer the intermediary step of a high resolution, noninvasive mpMRI.
The problem is, there aren’t enough powerful magnets and highly experienced readers to meet the demand. But compromise is unacceptable. According to an international Committee of PI-RADS experts,
The steadily increasing demand for diagnostic prostate MRI has led to concerns regarding the lack of access to, and the availability of qualified MRI scanners, and sufficiently experienced radiologists and radiographers/technologists to meet the demand. Solutions must enhance operational benefits without compromising diagnostic performance, quality and delivery of service.[i]
In short, how can 3T mpMRI be adapted to make it more efficient and less expensive without sacrificing accuracy, readability, and patient safety?
One proposed model weighed by the Committee is biparametric MRI (bpMRI) using only 2 parameters, T2 and DWI. Excluding DCE shortens the scan time, which requires IV administration of a contrast agent called gadolinium. In fact, for years bpMRI has been the workhorse of prostate MRI, with evidence that DCE does not add incremental value.[ii] There are peer-reviewed studies documenting the high degree of confidence in detecting PCa using these T2 and DWI combined. Thus, it’s reasonable for the Committee to consider bpMRI to make prostate imaging more efficient, less expensive and more widely available.
Of course, in the interests of both excellence of patient care and good science, the committee specifies certain conditions, like having expert readers, that should be taken into account before issuing broad guidance on bpMRI. A key factor is how to determine which patients most need the addition of DCE.
An excellent 2019 retrospective study (analyzing previous patient records) compared the diagnostic accuracy of bpMRI and mpMRI for clinically insignificant and significant PCa, and examined when bpMRI would gain the most advantage from adding DCE to turn it into mpMRI[iii]. For this study, all patients had both bp and mp MRI, and biopsy-confirmed PCa for correlating with imaging results. The authors found that bpMRI and mpMRI are quite equal in accuracy, so which cases need extra definition from DCE? Here’s where PI-RADS scores come in. Those who had bpMRI PI-RADS scores ≥3, especially 4, were more likely to have clinically significant PCa, which DCE would be valuable for confirming.
This is exactly what the Committee wants to know, but they are not satisfied with a backward-looking analysis. They write, “There is a need for prospective [designed in advance to be forward-looking] studies where biopsy decisions are based upon MRI without contrast. Such studies must define clinical and operational benefits and identify which patient groups can be scanned successfully without contrast.” Such caution may be warranted, but it takes many years and dollars to plan such studies, recruit patients, and follow them.
This does not mean that men have to wait for bpMRI, but it does mean that the Committee won’t issue formal recommendations without the prospective research evidence “about MRI without contrast as an initial diagnostic approach for prostate cancer work-up.”These higher quality data are needed before the PI-RADS Committee will publish guidance about MRI without contrast as an initial diagnostic approach for prostate cancer work-up.”[iv] These higher quality data are needed before the PI-RADS Committee will publish guidance about MRI without contrast as an initial diagnostic approach for prostate cancer work-up.
Meanwhile, if you are at risk for PCa, or have a suspicious PSA result, contact Sperling Prostate Center for excellence in prostate imaging and compassionate care. As with all cancer, the earlier you know, the better your outcomes.
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.
[i] Schoots IG, Barentsz JO, Bittencourt LK, Haider M et al. PI-RADS Committee Position on MRI Without Contrast Medium in Biopsy Naive Men with Suspected Prostate Cancer: A Narrative Review. AJR Am J Roentgenol. 2020 Aug 19.
[ii] Donati OF, Jung SI, Vargas HA, Gultekin DH et al. Multiparametric prostate MR imaging with T2-weighted, diffusion-weighted, and dynamic contrast-enhanced sequences: are all pulse sequences necessary to detect locally recurrent prostate cancer after radiation therapy? Radiology. 2013 Aug;268(2):440-50.
[iii] Xu L, Zhang G, Shi B, Liu Y et al. Comparison of biparametric and multiparametric MRI in the diagnosis of prostate cancer. Cancer Imaging. 2019 Dec 21;19(1):90.
[iv] Schoots et al. Ibid