By: Dan Sperling, MD

Standard transrectal ultrasound (TRUS) guided prostate biopsies generally involve taking 12-14 needle samples according to a systematic template consisting of 50% of the needles from each side of the gland. Such biopsies are essentially blind and random, because ultrasound does not show enough tissue difference to discriminate tumor from healthy tissue. Therefore, the physician cannot “see” what to aim at. The disadvantages of such biopsies are well documented:

False-negative rates of up to 30% (biopsy needles missed the tumor(s) resulting in a report of no prostate cancer present)

Under-grading the aggression level of the tumor because the samples did not include the most dangerous cells)

Overdetection of prostate cancer that is not significant (also called indolent prostate cancer)

The need for repeat biopsies when PSA continues to rise despite negative biopsies.

On the other hand, multiparametric MRI (mpMRI) is able to produce high resolution 3-dimensional images of the prostate gland that reveal not only the location, shape and size of cancer-suspicious areas, but also allow experienced readers to interpret the aggression level of such areas. Although there is no substitute for a biopsy to obtain tissue samples, new evidence suggests that multiparametric MRI (mpMRI) guided targeted biopsies increase the yield and accuracy of diagnosis over standard TRUS biopsies. Targeting needles directly into the suspicious lesions increase the probability of capturing a higher percentage of cancer per needle core as well as the most aggressive cells, and generally allows a procedure using fewer needles than the conventional 12-14 of TRUS biopsies.

While many urologists continue to employ standard TRUS biopsies, others recognize the merits of mpMRI detection of prostate cancer and seek to incorporate MRI results to help better direct biopsies into targeted lesions. There are three types of MRI guided targeted biopsies:

Cognitive fusion (or co-registration) – Can be done in a urology practice. Based on the images, the physician mentally calculates where to place TRUS-guided biopsy needles; although ultrasound cannot depict the tissue differences within the gland, it confirms needle placement as the doctor mentally calculates a pathway into the target. The problem is that the prostate seen by the doctor on real-time ultrasound will never exactly match the MRI scan, since different angles and patient movement will confound accuracy.

MRI/ultrasound fusion (MR/US fusion or co-registration) – Can be done in a urology practice. Previously capture MRI images are “fused” with real-time ultrasound images of the gland; software generates of 3-D image of the patient’s gland, and depicts the reconstructed location, shape and size of the suspicious area. Planning needle placement is accomplished by the software, with physician ability to override it. As with cognitive fusion, however, there will always be a degree of mismatch between the live ultrasound image of the prostate and the previously captured, static MRI image.

In-bore MRI guidance – Can be done only in a radiology setting equipped with a magnet. As the MRI captures scans of a patient’s prostate while at least two different parametric sequences are used to reveal suspected tumor(s), planning needle pathways into the tumor occurs in real time, with immediate confirmation of location.

Is one of these biopsy approaches better than another? A research team from Turkey conducted a study to address that question, and their results suggest that in-bore MRI-guided targeted biopsy outperforms each of the other two.

Acar et al (2015) designed a study with the objective of comparing the diagnostic accuracy of standard TRUS biopsy (not targeted), cognitive fusion targeted biopsy, and real-time in-bore mpMRI targeted biopsy in patients with positive screening indications for cancer but no previous biopsy. They retrospectively analyzed the clinical charts of 140 patients, all of whom had mpMRI prior to any biopsy. The imaging sequences included T2-weighted MRI, diffusion weighted MRI, and dynamic contrast-enhanced imaging. According to the authors, “Cognitive fusion biopsies were performed after a review of mp-MRI data, whereas TRUS-guided biopsies were performed blinded to MRI information. In-bore biopsies were conducted by means of real-time targeting under MRI guidance.” All men were treated by radical prostatectomy, and the pathology reports on the gland specimens were available for comparison with biopsy results. Diagnosis rates of prostate cancer (PCa) were as follows:

Analysis of the data did not identify a statistically significant difference among the three biopsy types. However, the authors clarify: “Although the detection rate of clinically significant disease was not significantly different between the groups, it is evident that there is a trend towards improved diagnostic efficiency with the adoption of image-guided sampling techniques. Perhaps, with a larger patient population or prospective randomization into all available biopsy techniques, including cognitive fusion, it would have been possible to achieve more solid outcomes in favor of MRI-guided prostate biopsies.”

Indeed, larger clinical studies involving randomization of patients are needed. Still, the preliminary evidence from this study provides early confirmation that mpMRI, especially when done on a powerful 3 Tesla magnet, can guide a minimum number of biopsy needles into the most relevant areas of the prostate, based on imaging detection. Interested readers are directed to the full article at  HYPERLINK “http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4498421/” http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4498421/

Bjurlin M, Meng X, Le Nobin J, Wysock J et al. Optimization of prostate biopsy: the role of magnetic resonance imaging targeted biopsy in detection, localization and risk assessment.  HYPERLINK “http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=24769030” t “pmc_ext” J Urol. 2014 Sep; 192(3): 648–658.

Acar Ö, Esen T,  HYPERLINK “http://www.ncbi.nlm.nih.gov/pubmed/?term=%C3%87olako%C4%9Flu%20B%5BAuthor%5D&cauthor=true&cauthor_uid=26027768” Çolako?lu B, Vural M et al. Multiparametric MRI guidance in first-time prostate biopsies: what is the real benefit?  HYPERLINK “http://www.ncbi.nlm.nih.gov/pubmed/26027768” o “Diagnostic and interventional radiology (Ankara, Turkey).” Diagn Interv Radiol. 2015 Jul-Aug;21(4):271-6. doi: 10.5152/dir.2015.46014.