Trends: Real-time, MRI-guided, Minimally Invasive Neurosurgery in Your Standard Diagnostic MRI Suite

Real-time, MRI-guided, minimally invasive brain surgery constitutes a growing trend in the field of neurosurgery. New technology platforms developed by innovative young companies are enabling a range of neuro procedures to be performed under MRI-guidance. While the types of procedures enabled by these platforms vary, all real-time, MRI-guided, minimally invasive neurosurgeries share a number of key attributes: 1) the procedure is minimally invasive, performed through a burr hole ( ~14 mm diameter) or twist drill hole (~3mm in diameter); 2) the procedure is performed with the patient positioned within the bore of a MRI scanner; and 3) the procedure is visualized with near real-time, intraprocedural magnetic resonance imaging of both patient anatomy and surgical instruments.

MRI-guided, minimally invasive neurosurgery has experienced major momentum in recent years, propelled by technologies such as MRI Interventions’ neurosurgical navigation platform and MRI-guided laser ablation platforms developed by Visualase and Monteris. Collectively, these technologies have enabled more than 1,100 MRI-guided neurosurgical procedures across more than 70 hospitals in the United States to date, and procedure growth is accelerating. The vast majority of these MRIguided platforms are used within standard diagnostic MRI suites.

In a recent survey of neurosurgeons and neurologists, 80% of respondents expressed a belief that real-time MRI-guidance will or can become the future of functional neurosurgery.1

The utilization of these MRI-guided technologies is not limited to researchers and future applications. Today, clinicians are performing an increasing number of MRI-guided neuro procedures as part of their regular clinical practice.

Industry involvement in MRI-guided therapies is also growing. The MRI-guided approach is being used in the United States to place Medtronic deep brain stimulation (DBS) leads and NeuroPace responsive neurostimulation (RNS) leads, and in Europe to place St. Jude DBS leads. In August 2014, Medtronic acquired the laser ablation technology company Visualase for $105 million.2 Additionally, companies like Sanofi/Genzyme, Tocagen, UniQure, and Merrimack are involved in MRIguided drug delivery trials now underway.

The main driver for MRI-guided neurosurgery is intraprocedural visualization. Near real-time visualization enables neurosurgeons to see the placement of instruments and devices. It also enables surgeons to achieve a high rate of accuracy—approximately 0.68 mm in radial error across 500+ electrodes placed using MRI Interventions’ neuro navigation platform to date.3 Intraprocedural visualization also enables immediate feedback regarding delivery of a therapy, allowing surgeons to confirm desired coverage when delivering therapeutic agents directly to intracranial targets, or facilitating verification that target tissue has been destroyed in laser ablation procedures.

Patient benefits also cannot be overlooked. Visual anatomical targeting often means fewer passes into the patient’s brain, and intraprocedural visualization now supports some minimally invasive surgeries in place of traditional invasive procedures, such as laser ablation as an alternative to open craniotomy resection.

MRI-guidance is enabling a variety of minimally invasive procedures for a broad range of patients. For instance, MRI-guided electrode placement may be used for patients with Parkinson’s disease or primary dystonia. Likewise, MRI-guided laser ablation may be used for patients with epilepsy, brain tumors, and radiation necrosis. In clinical trials, MRI-guided direct drug delivery is being administered to patients with Parkinson’s disease and certain brain tumors. MRI-guidance technology has even been utilized to facilitate hybrid cases in which a combination of diagnostic and therapeutic procedures are performed in a single setting, such as a biopsy followed by cyst drainage followed by laser ablation of a brain tumor.

The overwhelming majority of hospitals performing MRI-guided, minimally invasive neurosurgery are doing so in one of their standard diagnostic MRI suites, and for good reason. Outfitting an existing standard diagnostic suite for minimally invasive procedures typically requires a relatively small investment and obviates the need for a multimillion-dollar intraoperative MRI capital purchase when initially evaluating the new approach. Current MRIguided technologies have been designed to enable procedures in existing diagnostic suites based on the fact that they far outnumber their MR-OR counterparts—more than 5,000 diagnostic MRI scanners to only around 75 intraoperative MRI suites across the United States. At certain institutions, performing initial MRI-guided neuro procedures in an existing diagnostic suite can serve as a stepping stone that ultimately does lead to a later investment in a MR-OR suite.

Of course, there are some concerns to performing neurosurgical interventions in the diagnostic MRI setting. Topics of specific interest include economics, sterility, procedure workflow, and hospital politics. To address economic questions, a comparison of the revenue per hour generated by diagnostic scans versus that generated by MRI-guided surgery in the MRI suite shows that MRI-guided procedures can produce more revenue per hour than diagnostic scans. For example, MRI Interventions estimates that MRI-guided procedures could generate up to $5,2754 per hour in reimbursement, whereas diagnostic MRI scans may only generate around $1,2005 per hour.

Sterility is a fair concern when moving a traditionally OR-based procedure into the MRI suite, and the solution is two-fold: specialized draping coupled with a thorough review of the suite with the infection control/sterility team to assess items such as positive air pressure, air exchanges, and the room prep procedure. Workflow concerns are addressed with detailed and thorough training of all team members who will participate in the procedures, establishing a tight protocol and maintaining a consistent team for MRI-guided surgeries.

Finally, political issues between the two main departments affected by this new surgical method, radiology and neurosurgery, are solved by listening to the concerns of all parties and building a mutually beneficial approach for both departments to account for these new procedures.

We are still early in the shift toward MRIguidance for neurosurgical procedures, but we have seen this scenario play out before. Real-time, image-guided, minimally invasive procedures dramatically transformed other medical specialties, such as cardiovascular surgery with the emergence of fluoroscopy in the 1970s, as well as orthopedic surgery with the advent of arthroscopy and abdominal surgery with the rise of laparoscopy in the 1980s.

Today, neurosurgery is undergoing its own paradigm shift toward real-time intraprocedural visualization, both for enhancing existing therapies and helping to enable new therapies as we move into the future.

References

  1. Interviews conducted by a third party on behalf of MRI Interventions (n=36).
  2. Medtronic, Inc. (2014). Medtronic Completes Acquisition of Visualase, Inc. [Press release]. Retrieved from http://newsroom.medtronic.com/phoenix. zhtml?c=251324&p=irol-newsArticle&id=1951904.
  3. Data on file with MRI Interventions, Inc.
  4. Based on a weighted average payment to MRI Interventions’ customers (as of September 2014) for an electrode placement procedure for Medicare and private insurance patients, calculated by MRI Interventions using a payor mix weighted 67% to average Medicare reimbursement and 33% to average private insurance reimbursement. Average Medicare reimbursement calculated as the weighted average Medicare payment for MRI Interventions’ customers (as of September 2014) for an electrode placement procedure under MS-DRGs 025, 026 and 027. Average private insurance reimbursement calculated as 1.5x Medicare reimbursement, based on published data. Hourly amount assumes 4.5 hour procedure duration. Excludes professional fees. Actual revenues will vary by hospital, procedure, and payor.
  5. Estimated average US hospital-based MRI suite revenue per hour for outpatient diagnostic scans, based on data gathered by MRI Interventions. Excludes professional fees. Actual revenues will vary by hospital, procedure, and payor.