Medical Device Daily Senior Staff Writer
Imagine for a moment you suffer from dystonia – a disorder that causes involuntary contraction of muscles, resulting in twisting and repetitive movements that can cause discomfort. You've been told there is an operation that could help you, but you'll have to be awake during the entire procedure – which could take up to eight hours – with a stereotactic frame bolted to your head.
About eight or nine years ago two neurosurgeons at the University of California, San Francisco (UCSF) who had been performing these deep brain stimulation (DBS) procedures on patients with dystonia decided there must be a better way to do it.
And they were right. Philip Starr, MD, PhD, co-director of the Functional Neurosurgery programs at the UCSF, and Paul Larson, MD, an associate clinical professor of neurological surgery at UCSF, with help from Alastair Martin, PhD, an associate adjunct professor in the UCSF Department of Radiology, developed a better way of doing the DBS surgery for patients with dystonia. The new method, which involves the use of a new generation of MRI scanners known as interventional MRI units, offers many benefits over the traditional method including one major benefit for the patient - they no longer have to be awake for it.
To explain the genesis behind the development, Larson told Medical Device Daily that DBS requires a process known as brain mapping to help the surgeon implant the electrodes in the most ideal location in the brain. The brain has areas of white matter, he explained, which are "fairly silent," and it also has areas of gray matter where there is a lot of electrical activity. "The different parts of the brain have their own characteristic pattern of electrical activity. So we do this mapping process where we put little listening electrodes, or recording electrodes, into the brain and we listen to the brain cell activity and we know what the brain activity in the area that we want to implant is, we know what that activity should look like, what it should sound like, and so that's how we make sure that we're putting the electrodes in the best possible spot," he said.
The problem is that this is a lengthy process – it takes hours to do – and requires a lot of technical expertise on the part of the surgeon and implanting team. Not to mention the fact that it requires the patient to be awake the entire time. "It also relies on [MRI] images of the brain that we obtain before we actually go into the operating room," Larson said. "We use those images to try to guide us during the surgery, but once you actually make a hole in someone's head the spinal fluid will come out and air gets in and the brain will shift, it will move inside the skull, so where you think you are based on the images you got before surgery is not necessarily where you really are."
So for all of those reasons, Larson and Starr began to wonder if there was a better way to do these operations. Starr had trained in Boston where they had developed a technique called intraoperative MRI, Larson explained, which allowed the surgeon to perform neurosurgical procedures inside an MRI scanner and obtain MRI scans during surgery "and really see where you were in the brain in real time."
Larson had trained at the University of Louisville (Kentucky) with a similar system. "So both of us sort of grew up, if you will, taking brain tumors out of people in these intraoperative MRI scanners," he said.
When the two became partners at UCSF in 2001 they began to put that experience to work in an effort to improve DBS procedures.
A small startup company, SurgiVision (Memphis, Tennessee), has developed the ClearPoint Neuro Intervention System designed to allow neurosurgical procedures like DBS to be performed inside an MRI scanner, which the FDA approved in June. UCSF also developed ClearPoint software so that any neurosurgeon can perform the new procedure using any MRI scanner. In the beginning, they worked with existing technology and "actually started with sort of a home-grown technique" that they started doing on patients in 2004, Larson said.
At that time the team was using a commercially available device from Medtronic (Minneapolis) that was actually designed for "sort of a different way of doing DBS," Larson said, but the team adapted it for use in the MRI scanner. He explained that MRI scanners have their own computers that drive them and that he and Starr were using Martin, "a very smart MR physicist," to do the procedures using Medtronic's device. "Dr. Martin figured out a way to manipulate the inherent software in the MRI scanner itself to sort of drive the procedure," Larson explained.
Using this "home-grown technique," the team implanted more than 80 electrodes over the years. "It was very successful, but it had significant limitations," Larson said.
For starters, the aiming device the team was using was not really designed for DBS implantation and it was not designed for use in an MRI scanner. "We literally had to have a PhD in MR physics running the software . . . a lot of other centers were interested in trying this but they didn't have a Dr. Martin-type person sitting at the scanner."
So in about 2007 the team started working with SurgiVision, a company that expressed interest in developing a second-generation system specifically to do neurosurgical procedures like DBS, as well as other things like brain biopsy or electrode implantation for epilepsy, inside an MRI scanner.
"The need to develop something from the ground up was the motivation for teaming up with SurgiVision," Larson said.
The ClearPoint software runs on a laptop. Larson explained that every MR scanner operates on its own software. So the MRI scanner takes the images in real time, then that data is immediately imported into ClearPoint, and ClearPoint "literally walks the implant team through the implant procedure step-by-step and it helps you decide where you should enter the skull, it lets you pick the pathway down to the area that you want to implant, it lets you decide what kinds of pictures you want to take so you can see the area optimally, and then it steps you through aiming the device so that the aiming device is aimed right where you want it to be," he said, adding that it is "very simple," and there is even a "little remote that attaches to this aiming device that mounts on the skull" that has color-coded knobs.
"It's gone from someone needing a PhD to run the machine, to literally any surgeon with 10 to 15 minutes of training can do a case," Larson said.
To test the learning curve of this new technique, the team took one of the UCSF residents who had never seen the software before and showed him the equipment in "literally a 15 minute training session" then had him do a mock procedure on a plastic head. "His time was only about four minutes longer to do a procedure than my time to do a procedure and I've been involved with the design of this thing since the beginning. So it's pretty straight forward," Larson said.
He added that the software is designed to have a very similar look and feel to the navigation software that most neurosurgeons already use on a daily basis so it's a familiar working environment for them.
Another benefit of this new procedure compared to traditional DBS, Larson said, is that it requires fewer brain penetrations. With the traditional method, surgeons have to penetrate the brain multiple times, even on the most ideal cases. For example, Larson said he did a regular DBS implantation last Wednesday and it was "a very good day," but even in that best-case scenario he had to make four brain penetrations. On a typical day, if the surgeon is not in the right spot the first time, it requires "easily six or eight brain penetrations to get the electrodes in the right spot."
The procedure time of the new technique is also significantly reduced, Larson said, by about a half or a third and the recovery is easier.
Being able to see MRI scans in real time also makes it easier for the surgeon to account for complications, such as if the brain shifts during the procedure, which can happen.
"The functional neurosurgeon community has been anticipating this for quite some time and surgeons that do things like DBS, as one example, have been very excited to have this come out because they don't need a Dr. Martin at their place," Larson said. He added that the other nice thing about the procedure is that it is done in a standard MRI scanner in the radiology department rather than in a "specialized super-custom operating room with an ultra expensive MRI scanner."
"The technology does a couple of things; I think it opens the door for surgeons who are very good at what they do but don't have the physiology expertise or the time investment that it takes to really build a big DBS program, this offers an alternative for a group like that," Larson said. Also, he added, it might encourage more patients who are good candidates for DBS to actually get the procedure because many are – understandably – too intimidated by the idea of being awake to undergo the traditional procedure.
Amanda Pedersen, 309-351-7774;