Magnetic resonance imaging (MRI) is the outstanding game changer in the world of detecting and diagnosing prostate cancer (PCa). MRI does what ordinary ultrasound cannot do, since a standard scan uses three imaging sequences (parameters) to characterize prostate tissues. When the parameters are integrated, it provides a 3-D portrait of the anatomy of the gland, revealing specific areas that are suspicious for PCa. Ultrasound simply is not at a point where such definition is possible.
Likewise, MRI guidance is superior over ultrasound for targeting biopsy needles into suspicious area(s). Here are the three MRI-targeted methods commonly used to diagnose PCa:
- MRI-targeted TRUS-guided cognitive biopsy – Cognitive means the doctor, based on a previously captured MRI scan as a reference, is mentally planning where to place biopsy needles. This is not real-time MRI guidance.
- MRI/ultrasound fusion-guided targeted biopsy – A recent development is MRI/ultrasound fusion, which relies on specialized software for a point-by-point “co-registration” of previously captured MRI plus real-time TRUS. This merger generates a 3-D pixar-like picture of the patient’s gland, with the MRI-detected tumor area highlighted. The software calculates a map of needle placement for targeting the suspicious area, and real-time TRUS guides corresponding placement to target the area. Generally, systemic TRUS biopsy is also done at the same time (concurrent systematic biopsy). This is not real-time MRI guidance.
- In-bore MRI-guided targeted biopsy – This biopsy is conducted while the patient is in the tunnel (bore) of the magnet, so the suspicious area is viewed in real time. Biopsy needles are directed into the suspicious area while the doctor is actually seeing it. This is real-time MRI guidance.
All three methods can be performed transrectally or transperineally.
Which method is best for a prostate biopsy? The criteria include accuracy, number of needles used, length of procedure, healthcare dollars spent, and widest availability for patients. Also, from the perspective of the doctor, “best” includes ease of learning and performing the biopsy. So, which is best?
Comparing biopsy methods
This blog reports a comparison of the three methods that was written by a distinguished multinational panel of experts.[i] Their analysis, based on nearly 20 previously published studies, addresses all of the criteria listed above. Due to complex differences in study size, definitions and designs, apples-to-apples comparisons were not always possible. While the authors did their best to level the playing field, in some ways their ranking of least favorable to most favorable is based on a forced fit among statistics. However, their guiding principle was that the detection of clinically significant PCa is most important.
Here are key points from their paper:
- MRI targeted biopsies are all more accurate, with fewer needles, than conventional TRUS-guided systematic biopsy at detecting and diagnosing clinically significant PCa. However, some authors point out that there is not enough evidence to warrant dropping concurrent systematic biopsy at the time of a targeted biopsy.
- MRI-targeted cognitive biopsy is the least expensive, since it does not require special equipment or software. It more accurately detects clinically significant PCa than systematic TRUS biopsies. However, its performance depends on the experience-based skill and knowledge of the doctor. It may be more challenging in large glands with small targets.
- MRI/US fusion-targeted biopsy appears to be more accurate than cognitive biopsy, especially when performed transperineally rather than transrectally. Concurrent systematic biopsies can be done in the same biopsy session, and an advantage of fusion over cognitive is that all needle locations can be recorded by software. Disadvantages include costs of the system, longer procedure time due to multiple steps and MRI segmentation of the prostate and lesions prior to the biopsy, and co-registration time. Operator error is a risk for registration errors, and there is a learning curve involved. It is becoming more widely available in urology offices.
- In-bore MRI-targeted biopsy, on average, appears to more accurately detect clinically significant PCa than fusion, and with fewer needles. However, some studies found no difference in detection between in-bore vs. fusion coupled with concurrent systematic biopsy (note that in-bore biopsies do not typically include concurrent systematic biopsy, but additional samples can be taken during in-bore biopsy if warranted). Needle sites can be recorded. On the other hand, in-bore biopsy is considered more expensive and time-consuming than the other two methods, and since it is not performed in a urology office, it may be less available to patients. As with fusion guidance, there is a learning curve, and the greater the physician experience, the more accurate the results.
Naturally, at the Sperling Prostate Center we are biased in favor of in-bore MRI-targeted biopsy. For us, it takes no longer than fusion because we have fewer steps. It is becoming increasingly available, though many patients are unable to travel to locations that are very inconvenient for them. However, given our leading experience in prostate MRI and the excellence of our staff, the accuracy of our targeted biopsy with minimal needles has a tremendous advantage for informed treatment planning. Thus, our own patients find any extra cost or inconvenience is offset by the fact that it’s not possible to put a dollar value on human life and quality of lifestyle. We confidently feel that our clinical services, grounded in our state-of-the-art 3T magnet’s powerful detection, and amplified by Artificial Intelligence, are in each patient’s best interest. While we recognize the appeal of fusion from the perspective of urologists, we know that in-bore targeted prostate biopsy, as we perform it, is in an incomparable class of its own. Simply put, it is more accurate than all other biopsy methods—including fusion.[ii]
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] Chang S, Ghai S, Kim CK, Oto A et al. MRI Targeted Prostate Biopsy Techniques: AJR Expert Panel Narrative Review. AJR Am J Roentgenol. 2021 Oct 13;1-19.
[ii] Prince M, Foster BR, Kaempf A, Liu JJ et al. In-Bore Versus Fusion MRI-Targeted Biopsy of PI-RADS Category 4 and 5 Lesions: A Retrospective Comparative Analysis Using Propensity Score Weighting. AJR Am J Roentgenol. 2021 Sep 9;1-8.