Deep brain stimulation – the implantation of electrodes in specific brain areas to regulate abnormal impulses – is used to treat a number of movement disorders, though determining the exact target areas for the electrodes can prove tricky. Now, researchers from Duke Medicine have created a high-resolution 3D map of the human brain stem that they say could aid surgeons when performing the procedure, making it safer for patients.
Image credit: Duke Medicine
Dr. Nandan Lad, of the NeuroOutcomes Center at Duke, and colleagues publish the details of their map in the journal Human Brain Mapping.
Deep brain stimulation (DBS) is a procedure used to treat Parkinson’s disease, dystonia, essential tremor and some other neurological conditions that affect an individual’s movement. It is normally given to patients who are unable to control their symptoms with medication.
During the procedure, a surgeon will implant thin metal electrodes into areas of the patient’s thalamus – the region that controls motor functions – believed to be involved in triggering the patient’s symptoms. The implanted electrodes produce electrical impulses that either regulate abnormal ones or stimulate certain cells or chemicals to relieve symptoms.
In order to find brain targets for the electrodes during DBS, many neurosurgeons rely on lower-resolution computed tomography (CT) and magnetic resonance imaging (MRI) scans, combined with geographic coordinates that guide them to the dentatorubrothalamic tract (DRT) of the thalamus.
However, Dr. Lad and colleagues note that neurosurgeons often have to remove and reinsert the electrodes during DBS in order to test impulse frequencies and find the exact areas responsible for patients’ symptoms.
Repeated removal and reinsertion of electrodes can be risky; each time an electrode is moved, a neurosurgeon must navigate through delicate brain tissue. This may raise the risk of complications for the patient, including hemorrhage, seizures and impaired memory.
The Duke team says their novel map, however, could help eradicate these risks. “This map will potentially help us reach the optimal target the first time,” says Dr. Lad. “It could eliminate trial and error and make the surgery safer.”
To create the map, the researchers used a 10-day scan of a postmortem brain stem from a healthy donor. The scan was taken using a 7-Tesla MRI system.
Next, the team used an MRI technique called diffusion tractography to convert the scan into a 3D map of the human brain stem, which can be scaled to each individual’s brain anatomy using a “high-performance computing cluster.”
According to senior study author G. Allan Johnson, director of the Duke Center for In Vivo Microscopy, the map produces images that are 1,000 times more detailed than a clinical MRI.
“You can actually see the nerve fibers in the brain,” he adds, “how they’re crossing, and the subtleties of contrast between gray and white matter in the brain far beyond what a clinical scan could offer.”
The team tested the map on 12 patients who had already undergone successful DBS for tremors. They used the map to pinpoint the target areas for electrode placement in each patient, comparing the identified areas with those where the electrodes had already been placed.
Over all subjects, the electrode placement predictions taken from the map matched 22 of the 24 electrodes that had been successfully placed.
The team believes their findings hold promise for improving outcomes for patients undergoing DBS, and they plan to conduct a prospective study to further investigate the effectiveness of the 3D model in guiding DBS surgery.
What is more, they say their study could open the door to new treatments for a number of other conditions. Lead study author Dr. Evan Calabrese explains:
“We now have a guide to be able to visualize these complex neuronal connections that would otherwise be impossible to see. This will help us continue to explore applications for treatments of Alzheimer’s disease, neuropathic pain, depression and even obsessive-compulsive disorders.”
In September 2014, Medical News Today reported on a clinical guideline published in the journal Neurosurgery, in which experts recommend DBS for patients with obsessive-compulsive disorder (OCD) who do not respond to medication.