The days of poke and hope are over! For decades, prostate biopsies have been performed in a random, systematic fashion. An ultrasound probe is inserted into the patient’s rectum and an image of the shape of the prostate gland is obtained. Random, systematic cores are taken out at the apex level (bottom), the mid-gland level and the base (top). This is conventionally known as transrectal ultrasound guided biopsy or TRUS biopsy and has been the standard for decades. This procedure is usually performed in an outpatient setting.
MRI-Guided Biopsy improves diagnostic performance
With the advent of multiparametric MRI, we are now able to look at detailed images of the prostate gland and aim the biopsy needle toward a specific target rather than systematically sampling 10, 12 or 18 cores or more. MRI allows us to see anatomic and morphologic features as well as functional information like perfusion, or blood flow and diffusion, movement of water molecules between cells. These functional sequences add great value and improve diagnostic performance.
Benefits of diffusion-weighted imaging
A special attribute of diffusion-weighted imaging (DWI) is that we can mathematically calculate something called apparent diffusion coefficient value or ADC. This number is derived from the diffusion sequence and reflects the amount of restriction of water movement. This is referred to as “restricted diffusion.” The lower the ADC value, the more likely malignancy is present – there is an inverse, linear relationship between ADC value and tumor aggressiveness. This relationship has been well-published in the radiology and urology literature. It is important to note there are other things besides cancer that can cause a low ADC, for example infection or inflammation.
More accurate scoring
The best part about MRI-guided biopsy is we are able to aim at a target within a target; in other words, if a lesion has one particular area that looks most suspicious, we can take aim at that part of the tumor with pinpoint precision. The benefit is more accurate Gleason scoring and better tissue-based genomics. If a random biopsy is performed, there can be misclassification of disease, especially if the tumor is far toward the front of the prostate gland, which can be missed with TRUS biopsy.
High accuracy, very low infection rate
For the patient, the procedure is very straightforward. He lies on the MRI scan table on his stomach. A needle guide smaller than an adult’s index finger is inserted into the rectum. The needle guide functions two ways: it is both a receptacle for instruments to be inserted and it functions as a fiducial marker. Our specialized computer software allows us to see the needle guide and its relationship to the target area. The software gives us coordinates that allow us to aim at the area of interest with a high degree of accuracy. We can angle left, right, front, back and insert or retract the device to aim squarely at the target. Once the needle has been deployed the technologist takes an image of it in the fired position. We have our pathologist include this image in our report so the location of the tissue is indisputable. The procedure takes only about a half hour and does not require anesthesia. Numbing gel is used to ease any possible discomfort and patients tolerate the procedure extremely well. There is also an extremely low risk of infection of 0.6 percent. We presented this finding at the annual American Urological Association meeting in San Francisco in 2018.
Another important role of MRI is its use by urologists who adopt high-tech MRI/ultrasound fusion biopsy. This targeted technique is performed in-office by the urologist using ultrasound imaging in real-time overlapped onto MRI images obtained previously. This technique has the benefit of targeting the biopsy and taking additional core biopsies if indicated.
Genomic testing valuable for assessing metastatic risk
Once the biopsy specimens are collected, they are sent to a specialized laboratory for the pathologist to evaluate them and generate a report of findings. Our pathologist is specifically trained in prostate cancer evaluation. In many cases we send the specimens to another laboratory for genomic testing. This test looks at 22 genes known to be associated with prostate cancer. The report will designate the patient as low, intermediate or high risk as it relates to potential for metastasis or spread of cancer outside the prostate gland to lymph nodes or skeletal structures. This information can be a valuable piece of a complicated jigsaw puzzle.
Better PSA density measurement
Another important piece of the puzzle is PSA density. This is the patient’s PSA divided by their prostate gland volume. This prognostic indicator combined with imaging findings and genomics can be very helpful. For example, if one man has a prostate the size of an apricot and another man has a prostate the size of a grapefruit and they both possess a PSA level of 4 ng/mL, the one with the smaller gland will have a higher PSA density then the man with the larger gland. MRI allows us to measure the prostate gland In order to accurately calculate PSA density.
New MRI-first guidelines adopted in US
The functional MRI sequences also allow us to monitor response to treatment over time so we can tell if a patient is responding well to whichever therapy they choose. Even if they are on active surveillance also called watchful waiting, the MRI allows us to monitor the patient and keep them safe. In the United Kingdom and the European Union, guidelines have been published mandating MRI prior to biopsy and recently the American Urological Association published their policy statement agreeing with those guidelines and implementing it in the United States. We tell our patients to never allow anyone to put a finger, a needle or a scalpel anywhere near your prostate gland unless they have done an MRI first.
Bernadette M. Greenwood is Chief Research Officer at Halo Diagnostics and a Clinical Instructor at UC Riverside School of Medicine. For more information about MRI-guided biopsy and tissue-based genomics, contact Halo Dx at (760) 776.8989 or visit www.DesertMedicalImaging.com.