The power of MR and MR/US biopsy to aid in prostate cancer diagnosis

Particularly when a patient with clinically significant prostate carcinoma has had multiple negative transrectal ultrasound (TRUS) biopsies before, this targeted procedure can assist urologists to quickly make a confident diagnosis and allows patients to start therapy as soon as possible. This may be life-changing for the patient.

The use of MR imaging has significantly improved capabilities in prostate cancer diagnosis, according to Dr. Steiner. “Multi-parametric prostate MR allows us to look at three parameters to build our diagnosis on: conventional T1 and T2 signal intensity, diffusion-weighted imaging and ADC map, as well as dynamic flow imaging, to define the highest probability of prostate carcinoma.”

The standard PI-RADS¹ system is then used to grade lesions based on the MRI findings. For PI-RADS 1 and 2, clinically significant cancer is (highly) unlikely. Intermediate PI-RADS 3 lesions represent a kind of diagnostic “gray area” – these lesions may become PI-RADS 4 lesions if they demonstrate a hypervascular tumor flow pattern or depending upon index of suspicion. PI-RADS 4 and 5 lesions have a statistically high chance of being a clinically significant prostate carcinoma and should be biopsied. Once biopsy is performed, the pathologists characterize the biopsy samples with either a Gleason score or an ISUP grade group.²

Depending upon the Gleason score and prior therapies, prostate carcinoma has a certain predictable pattern on multi-parametric MR, according to Dr. Steiner. “In general, lesions in the peripheral zone have decreased T2-weighted signal and are relatively focal,” he says. “In the transitional zone, these lesions are more difficult to evaluate on T1 and T2 but are generally non-encapsulated.”

“We also look at diffusion-weighted images and the ADC map. Prostate neoplasms generally have diffusion restriction, so they are bright on diffusion-weighted imaging and dark on an ADC map, which is one of the most important characteristics of neoplasms.”

“The third characteristic we look at, flow, is somewhat less specific but may be quite important in deciding whether a lesion is significant or insignificant. Prostate neoplasms often have a hypervascular tumor flow pattern, meaning that there is rapid inflow of blood into the lesion and then rapid outflow due to a disrupted capillary bed. This can be graphed on multi-parametric images, allowing us to define regions of interest and look at the actual flow within these regions.”

“I perform this interrogation using DynaCAD prostate, which also provides an easy way to determine the PI-RADS score and create the report for the urologist.”

Images from multi-parametric MR of a classic peripheral zone lesion in the prostate

Dr. Steiner describes this case: “For lesions in the peripheral zone of the prostate, the DWI (diffusion weighted imaging) and ADC map are most helpful for diagnosis. In this case, the DWI shows a very bright signal, which indicates diffusion restriction. The arcuate area with significant signal drop out (arrow) on the ADC map is recognized as highly suspect for tumor. On the axial T2-weighted image the capsule contour looks a little irregular (arrow), which we interpret as capsular disruption, and I usually give a measurement: this lesion shows larger than 1.5 cm capsular disruption. I don’t see any signs of lymphadenopathy but interpret this lesion as PI-RADS 5. The hypervascular flow pattern in the bottom images adds to the diagnostic confidence.”

Dr. Steiner explains how a “blind” ultrasound biopsy may lead to a negative result, even when a tumor is present. “In a non-targeted biopsy guided by ultrasound, you see the needle and the confines of the prostate but cannot see the tumor. So, when trying to get 12 cores as evenly distributed as possible, the tumor may still be missed, particularly when it is in the anterior gland, low in the apex or in other regions generally not easily biopsied by ultrasound.”

This is why Dr. Steiner has implemented a pathway where the MR images can also be used to guide the biopsy. He uses an MR/ultrasound fusion guided biopsy device, UroNav, which fuses pre-biopsy MR images of the prostate with real-time ultrasound images during transrectal biopsy, for excellent delineation of the prostate and suspicious lesions, as well as clear visualization of the biopsy needle path.

“I felt strongly that urologists are used to doing free-hand biopsies – their brain and hand are very used to manipulating the probe,” says Dr. Steiner. “What UroNav offers is no change in that workflow; it takes the diagnostic MR images and the localized, segmented lesions and adds tracking and navigation to fuse that with the live ultrasound images. In this way, the MR images can be used for targeting the lesion when performing the biopsy. The UroNav navigation sensor is mounted on the TRUS probe*, so for urologists the manipulation is similar to what they were used to.”

“This process allows us to perform focal biopsies of suspicious areas based on PI-RADS categories that indicate the probability of an underlying potential malignancy,” says Dr. Steiner.

For Dr. Steiner, DynaCAD Prostate is essential as a diagnostic tool for the interpretation of multi-parametric prostate MR. “I have a custom layout that I’m comfortable with. It allows me to link all of the images and shows the T1, T2, diffusion-weighted images and ADC map on one screen. It also shows me the flow patterns on a second screen so that I can actually cross-link and read all of the images at the same time; I just scroll through the depth of the image,” says Dr. Steiner. “DynaCAD also has a PI-RADS module, and I can actually annotate anything I dictate and have that as a report to show to the patient or the urologist.”

"Most people interpret prostate MIs in a zonal manner, so we need a program such as DynaCAD that allows us to look at the flow pattern in basically one dataset.”

If a urologist determines that a biopsy is necessary, Dr. Steiner uses the DynaCAD Prostate segmentation feature to define the prostate contour and any suspicious lesions in 3D. “This data is then sent to the UroNav, and my technologist literally combines the real-time ultrasound image with the MR data, so that the actual MR image is the live image that I’m seeing during the biopsy,” says Dr. Steiner.

“I partnered with one of our local urology groups and we jointly did the first ten MRI fusion biopsies in our operating room, which gave us both experience as well as leadership. Having the UroNav capability added ‘GPS navigation’ to the urologist’s normal workflow and we could perform targeted biopsy. And I already owned DynaCAD, from which data could directly be imported to UroNav. It was a great win-win,” Dr. Steiner says.

“DynaCAD allows me to easily import the images into UroNav for eventual biopsy,” he says. “The decision for biopsy is taken after interpreting the MRI. So, if I don’t use DynaCAD/UroNav I would have to import the data into another modality and literally need to redo all of my work.”

Says Dr. Steiner “In our first 13 cases of repeat fusion biopsy following negative TRUS biopsy, 11 patients yielded positive tissue for clinically significant carcinoma; 92% of 48 targeted cores were positive in PI-RADS 4 and 5 lesions. The entire procedure takes less than 20 to 30 minutes, and patients who have previously experienced a conventional transrectal ultrasound-guided biopsy often remark at how easy this procedure is.”

Dr. Steiner emphasizes that the power of MR is now recognized not only for multi-parametric examinations to identify suspicious lesions, but also expands into guiding biopsies to inform a definitive diagnosis.

“Patients that have PI-RADS 4 and 5 lesions on MRI have a high risk for clinically significant carcinoma. Such lesions are often in the anterior gland, low in the apex, or near regions generally not easily biopsied by ultrasound. These patients now receive MRI/ultrasound fusion biopsies, and this has been our standard of practice now for a year,” says Dr. Steiner. “In my opinion, the combination of MRI and ultrasound fusion biopsy is extremely powerful. We will be doing more and more of these biopsies and scans for the future.”