Tens of thousands of people who experience movement disorders associated with Parkinson's and a variety of other neurological conditions stand to benefit from a new guidance system that uses computerized brain-mapping techniques to significantly improve an increasingly popular procedure called deep brain stimulation.
DBS has proven to be highly effective in the treatment of movement disorders when standard drug therapies either do not work or have lost their effectiveness. However, the fact that it is an extremely long, difficult and expensive operation, which involves implanting electrodes deep in the brain, has limited its availability.
Since the procedure's approval in 1998, the number of DBS operations performed has grown gradually to about 3,000 annually, although more than 100,000 people a year could stand to benefit from it as a way of treating the tremor, rigidity, stiffness and slowed movement they experience as a result of neurological disorders ranging from dystonia to multiple sclerosis, to Parkinson's disease, to obsessive-compulsive disease.
To improve the procedure further, a team of electrical engineers and neuroscientists at Vanderbilt University has developed a pilot guidance system that automates the most difficult part of the operation: identifying the proper location to insert the electrodes. To work, the electrodes must pass through small nuclei deep in the brain that are about the size of a pea and are not visible in brain scans or to the naked eye. The researchers – writing in a special issue of the journal IEEE Transactions on Medical Imaging published this month – report that the new system can do a better job of identifying the initial location to insert the electrodes than an experienced neurosurgeon.
"The biggest problem with the procedure is that the surgeons cannot see the structure where they have to put the electrode and, as a result, they must spend a considerable amount of time searching for it," says Benoit Dawant, professor of electrical engineering, computer engineering and radiological sciences at Vanderbilt University, who is developing the guidance system in collaboration with Peter Konrad, associate professor of neurological surgery and biomedical engineering.
The only way that the target region can be identified is by its electrical characteristics. So the surgeons must first insert a recording electrode and monitor the electrical activity of the neurons that it touches. Sometimes they have to remove and reinsert the electrode two or more times. Sometimes they have to insert three or four electrodes at the same time in order to find the elusive spot.
"I tell patients that it is something like playing a big game of Battleship," says Konrad, who helped pioneer the procedure. "Like the game, you don't know where the target is until you've made a hit."
Each time the surgeons are forced to reinsert the electrode, it increases the risk of damage to the brain and the length of the operation. When surgeons decide that they have hit the right spot, they implant a stimulating electrode and test it to determine if it reduces the patient's symptoms. Because muscle disorders typically occur only while a person is awake, the patient must remain conscious through the entire procedure.
The operation can take as long as eight to 12 hours to properly place one electrode. (Most patients require two, one in each hemisphere.) "This is extremely rough on patients, who have to be awake through the surgery and have to be locked to the bed," says Konrad. "Anybody who performs this surgery quickly appreciates the need to trim the procedure down to a shorter process."