New Interventional MRI System Developed to Improve Surgery for Movement Disorders
Deep brain stimulation (DBS) has been used for over a decade to treat movement disorders such as Parkinson’s disease, essential tremor, and dystonia. It has become the gold standard for surgical care of these diseases; over 40,000 patients have had DBS devices implanted worldwide. DBS uses a pulse generator implanted in the chest, similar to a pacemaker, to deliver pulses to specific regions of the brain via a permanently implanted electrode. The traditional method of surgical implantation involves placement of a stereotactic head frame and an awake implantation procedure using a technique known as microelectrode recording (MER). During MER, the surgeon passes small microelectrodes into the region of the intended target and observes the pattern of neuronal activity to physiologically confirm accurate placement of the stimulating electrode. Although this technique is widely used, it is technically demanding, time consuming, and often difficult for patients to tolerate.
Interventional MRI (or iMRI) allows surgeons to take advantage of MR imaging in real time by performing procedures inside the scanner itself. Paul Larson MD, assistant professor of neurological surgery, and Philip Starr MD, PhD, Dolores Cakebread Endowed Chair and associate professor of neurological surgery, were both involved with this technology during its development in the 1990s. In 2002, they began to think about how to perform DBS using this technique at UCSF. The subthalamic nucleus (STN) is by far the most common brain target for DBS in Parkinson’s disease and is visible on 1.5T MR images. In traditional DBS surgery, MER is used to map the STN and locate the center of its motor region, the area which has been shown to be effective in reducing symptoms when stimulated. With iMRI, the surgeons can see this region directly and can place the DBS electrode without the need for MER.
In conjunction with Alastair Martin PhD in the Department of Radiology, Jill Ostrem MD in the Department of Neurology, and others, Starr and Larson developed a technique of implantation using a modified but commercially available skull-mounted aiming device and custom-made, MR-compatible surgical instruments. After validating the techniques with numerous phantom studies, they began performing iMRI implantations in patients in 2004. To date they have implanted 67 electrodes in 36 patients using this technique. iMRI DBS has several distinct advantages over traditional implantation methods. There is no need for a stereotactic frame and no need for the patients to be awake and off of their Parkinson’s medications, so patients tolerate the procedure well. The procedure time is half that of traditional MER guided implantation, and since MER is not necessary there is only one brain penetration needed in the vast majority of cases. The shorter operative times and fewer brain penetrations may lead to less confusion postoperatively, particularly in older patients. It may ultimately result in a lower hemorrhage risk as well, but this remains to be established.
In 2008, Larson, Starr, and Martin partnered with the medical device company SurgiVision to develop new technologies for the iMRI DBS technique. This includes an MRI-compatible, skull-mounted aiming device and MR coils specifically designed to provide optimal imaging during surgery. They have also developed a software environment that will standardize the implantation procedure on different MRI platforms. The new software environment will stream data from any manufacturer’s 1.5T MRI scanner and guide the surgeon through the implantation procedure using a specially designed graphical interface. The software will also improve accuracy by automating some steps that were previously dependent on the user. The UCSF group and SurgiVision will be testing and validating the new system this spring and summer.