Magnetic System Promises to Improve Brain Surgery

An interdisciplinary team of scientists from institutions throughout the U.S. reported development of a computer-controlled magnetic system for delivering therapeutic agents to the brain in an IMSTG session at the March APS Meeting. Known as the Magnetic Stereotaxis System (MSS), it is intended improve treatments for brain tumors, Parkinson's disease, and other neurological disorders. The technology is currently being tested in gel models of the brain and should be ready for human trials by the end of the year.

"The technology will be a minimally invasive, more efficient and safer way of doing brain surgery for certain indications," said Ralph G. Dacey, Jr., of Washington University School of Medicine in St. Louis. The research team includes collaborators from the University of Iowa, the Medical College of Virginia, and the University of Washington, as well as Stereotaxis, Inc., which contracted the first full-scale prototype for human use.

According to Dacey, when neurosurgeons perform conventional stereotactic surgery, they use a computer and MRI or CT scans to locate the diseased part of the brain in three-dimensional space and to determine the best straight line path to that target. Reaching the target could possibly damage structures en route.

The primary advantage of the magnetic system is that it will allow neurosurgeons to move precisely through the brain in any direction, avoiding sensitive areas that may lie between the surface and the area to be treated. Nonlinear movement is possible because magnetic fields guide a magnet the size of a grain of rice, which in turn pulls a small implant containing drugs or sources of radiation.

The system can also reposition an implant over time, permitting surgeons to perform multiple treatments without successive surgeries. "The MSS represent the optimal fulfillment of a minimally invasive concept that will cause the least amount of tissue damage in accessing targets to the brain and other parts of the body," said Matthew Howard III, University of Iowa, who co-invented the system.

After creating a small opening in the skull, the neurosurgeon places the magnet on the surface of the brain and places the patient's head in a "helmet." Superconducting magnets in the helmet generate gradients that direct the tiny magnet through the brain with great accuracy and minimal tissue disruption. The neurosurgeon monitors the movement of the magnet by watching fluoroscopic images superimposed on an anatomical, pre-operative MRI image. Over the next few days or weeks, the therapeutic agent interacts with the surrounding brain tissue.

The research will focus initially on improving treatments for malignant brain tumors, which are typically excised by placing the patient under general anesthesia, shaving the head, temporarily removing a portion of the skull to expose a large part of the brain, and the manually cutting out the tumor under direct visualization. In contrast, magnetic tumor surgery could allow a flexible radioactive catheter to be coiled into the tumor so that gamma rays can kill the tumor cells. The insertion may only take one or two hours, and could possibly be performed on an outpatient basis.

Despite the recent development of an imaging navigational system, which was a key element in refining the MSS technique, it remains difficult to navigate in a live brain with the necessary high precision. The researchers are working on refining the technique and demonstrating the safety and effectiveness of the MSS machine allowing commercialization of the system and development of other applications.

Magnetic drug delivery, to treat disabling neurologic conditions, will be tested during the second phase of the research. By placing drugs directly into the affected part of the brain, the magnetic surgery will bypass the blood brain barrier, which normally prevents many compounds from reaching their destination. Direct delivery will also avoid the side effects that occur when drugs targeted to one part of the brain interact with receptors in other parts of the brain or body.

For example, the system could improve treatment for Parkinson's Disease by delivering implants of dopamine — a neurotransmitter that is depleted in this disorder — or substances that boost dopamine production to an area deep in the brain called the striatum. Applications for other parts of the body will follow the neurological treatments.