MRI for Biopsy: MRI-US Fusion vs. In-Bore

MRI for Targeted Biopsies

Multiparametric magnetic resonance imaging (mpMRI) can accurately visualize the inner workings of the prostate, including tumor location and volume, by incorporating anatomic and functional imaging techniques. A positive mpMRI allows lesions to be localized and targeted, whereas negative results can prevent unnecessary biopsy. This addresses the “uncertainty” of standard ultrasound, and as such, it is becoming a highly utilized tool in diagnostic imaging.1 Established organizations like the European Association of Urology (EAU), American Urology Association (AUA), Society of Abdominal Radiation (SAR) and the National Comprehensive Cancer Network (NCCN) strongly advise performing mpMRI on men who have an initial negative biopsy with continued suspicion of cancer, and those undergoing a repeat biopsy.2 Compared to the systematic approach, MRI-targeted biopsies are better at detecting clinically significant cancer and reduce the detection of insignificant lesions. However, the diagnostic capability of an mpMRI and consequent targeted biopsy is not foolproof; the average false negative rate of an mpMRI is around 10%.1 The technical acquisition of the MRI, the expertise of the radiologist interpreting the image and the threshold used to define a lesion are factors that can affect diagnostic accuracy.2 MRI-targeted biopsies may be performed via visual (cognitive) registration, MRI-US fusion (software-assisted fusion) or direct in-bore (in-gantry). In any event, mpMRI can prevent unnecessary biopsies and reduce overtreatment, which would lower the cost of follow-ups and lead to an overall improved quality of life.3

MRI-US Fusion

MRI-US fusion, also referred to as software-assisted fusion, combines the superior image resolution of mpMRI with the real-time capabilities and availability of ultrasound.1 It is the most commonly studied and practiced type of MRI-targeted biopsy. An MRI-US fusion biopsy conforms to existing workflows and may be performed in-office, under local anesthesia in 10-20 minutes.4 Prior to biopsy, an mpMRI scan is performed and then annotated by the radiologist. The fusion software platform fuses (registers) this image set with live ultrasound images to create a 3D reconstruction of the prostate.2 Registration may be rigid, elastic or a combination of both.2 The probe is spatially tracked and visualized in relation to the 3D model, which allows real time tracking of the needle path. The targeting accuracy of the fusion platform depends on the quality of registration. Inaccurate auto segmentation of the prostate and poor manual registration can cause indeterminable discrepancies between the visualized and actual target location.4 Generally two spatially distributed cores are taken from each target to account for any potential registration errors. Most fusion platforms keep a record of core locations, which can aid in active surveillance biopsies and resampling if the results are inconclusive.1

Direct In-Bore Biopsy

In-bore, also referred to as in-gantry, like MRI-US fusion uses a pre-biopsy mpMRI to identify lesions, but instead of ultrasound, the biopsy is guided by MRI. The procedure is carried out in the MRI scanner, under local or intrarectal gel anesthetics and may be performed in 30 minutes (1 target), with an additional 15 minutes per target. With the patient lying in the prone position, a needle guide is inserted into the rectum. To confirm the position of the needle path, a series of scans are taken and fused (registered) to the annotated mpMRI throughout the procedure. Once the needle guide is correctly aligned, the target is sampled and a final scan documents the needle tip location. Typically only one core is taken per target, since the MRI can confirm the lesion was accurately sampled. Although additional samples can be taken, its benefit is minimal with respect to detection rate and Gleason score upgrading.1 The targeting accuracy of the procedure is less likely to be affected by the quality of registration. This is because the patient is in the same position for both the pre-biopsy mpMRI and the procedure, which makes the image sets easier to match up. The absence of the ultrasound probe also minimizes potential for prostate deformation.2

MRI-US vs In-Bore

Both approaches outperform standard transrectal ultrasound guided biopsies, but which one is better? Comparing common measures such as detection rate, accessibility, procedure length, cost and uptake, MRI-US fusion is more advantageous than in-bore. Although limited, studies show no significant difference in detection rates between MRI-US fusion in conjunction with and without a systematic biopsy and in-bore.1,4 Both approaches require specialized equipment, like the fusion system and MRI-compatible tools, but the accessibility of in-bore relies on the limited availability of an MRI scanner. In addition, the procedure must be carried out by both a trained urologist and radiologist. Whereas an MRI-US fusion can be performed in-office by a urologist with or without an assistant. Although a very efficient and experienced operator can perform an in-bore biopsy in 30 minutes, studies show an average of 40- 60 minutes.1,4 MRI-US fusion is significantly shorter, with average procedure times of 10-20 minutes for a standalone biopsy4 and less than 30 minutes to perform an MRI-US fusion biopsy in conjunction with a systematic biopsy.1 MRI-US may have higher upfront costs for the fusion system, but in-bore has the continuing expense of the radiologist, MRI “slot-time”, and MRI-compatible needles. In 2017, a Dutch study evaluated the cost-effectiveness of implementing MRI-US fusion or in-bore biopsy over standard systematic. Cost-effectiveness was calculated using a plethora of models and values, but basically it boiled down to differences in procedure cost, the number of years lived and the quality of health per patient post intervention. The cost accounted for unit maintenance, staff, material cost, MRI slot time, potential complications and follow up. The average cost for each procedure was $2,941 USD and $3,592 USD, respectively. The results showed that compared to systematic, MRI-US is cost-effective, inexpensive to implement and leads to improved health outcomes. Whereas compared to MRI-US, in-bore is not considered cost-effective because it is significantly more expensive to implement and is not significantly more accurate.5 The comparable detection rate, accessibility, procedure length and cost all support the popularity of MRI-US fusion. Its uptake is more practical than in-bore, as it conforms to existing workflows, maybe performed with a systematic biopsy and provides real-time feedback. Since mpMRI could potentially miss 10% of clinically significant cancers, the ability to perform concomitant systematic biopsies may be considered warranted to reduce the chance of missing anything, compared to a lesion only biopsy.1 Overall, MRI-US fusion biopsies are considered as effective, cheaper and more practical than in-bore.

MRI-US Fusion Biopsies with Focal Healthcare’s Fusion Bx

In addition to the advantages of accuracy, accessibility, procedure length and cost, Focal Healthcare’s fusion biopsy system easily integrates with existing workflows by addressing some of the potential drawbacks like extensive training, registration complications and additional staff.

The Fusion MR Viewer software is used exclusively to view and contour MRIs. This allows radiologists to first interpret MRIs using their preferred software, which reduces training and cost to a minimum. The contoured MRIs are sent to the Fusion Bx device and fused with live ultrasound using a combination of elastic and rigid registration. This approach can more accurately address positional changes and potential prostate deformation. The auto motion compensation feature helps maintain registration by accounting for patient movement during the procedure. The workflow is broken down into 4 guided steps, which can be performed by one person using buttons on the stepper. During biopsy, the Fusion Bx software also records every core location using screen captures with the option to add notes. Upon follow-up, the patient’s pathology results, biopsy history and any additional information can be conveniently accessed on the study page. For more information about Focal Healthcare’s Fusion MR and/or Fusion Bx, contact us at [email protected].

1 Verma, S., Choyke, P. L., Eberhardt, S. C., Oto, A., Tempany, C. M., Turkbey, B., & Rosenkrantz, A. B. (2017). The Current State of MR Imaging–targeted Biopsy Techniques for Detection of Prostate Cancer. Radiology, 285(2), 343–356.

2 Giganti, F., & Moore, C. M. (2017). A critical comparison of techniques for MRI-targeted biopsy of the prostate. Translational Andrology and Urology, 6(3), 432–443.

3 D’agostino, D., Romagnoli, D., Giampaoli, M., Bianchi, F. M., Corsi, P., Rosso, A. D., … Porreca, A. (2020). “In-Bore” MRI-Guided Prostate Biopsy for Prostate Cancer Diagnosis: Results from 140 Consecutive Patients. Current Urology, 14(1), 22–31.

4 Venderink, W., van der Leest, M., van Luijtelaar, A., van de Ven, W. J. M., Fütterer, J. J., Sedelaar, J. P. M., & Huisman, H. J. (2017). Retrospective comparison of direct in-bore magnetic resonance imaging (MRI)-guided biopsy and fusion-guided biopsy in patients with MRI lesions which are likely or highly likely to be clinically significant prostate cancer. World Journal of Urology, 35(12), 1849–1855.

5 Venderink, W., Govers, T. M., de Rooij, M., Fütterer, J. J., & Sedelaar, J. P. M. (2017). Cost-Effectiveness Comparison of Imaging-Guided Prostate Biopsy Techniques: Systematic Transrectal Ultrasound, Direct In-Bore MRI, and Image Fusion. American Journal of Roentgenology, 208(5), 1058–1063.