Three-D ultrasound enters the brain

Neurosurgery depends heavily on the ability of the surgeon to navigate through what can be seen as well as what cannot. MR- and CT-guided neuronavigational tools lately have done much to fill in the blanks with 3D maps that provide the context for interventions. Now biomedical engineers at Duke University are researching how ultrasound might provide a real-time guide to such surgeries.

Researchers working at Duke's Pratt School of Engineering have adapted a miniaturized ultrasound scanner to generate 3D real-time models of the brain during neurological interventions. Inserted into a dime-sized hole in the skull, the device could provide the means for tracking the excision of a brain tumor from one moment to the next.

Although the only research results so far have come from neurointerventions in dogs, they have been sufficient to prove the technology's potential. In one test, similar to the procedure for draining cerebrospinal fluid in human surgery, Dr. Srinivasan Mukundan Jr., anassistant professor of radiology at the Duke University Medical School, used the device as a guide to direct a needle into a particular region of an animal's brain. In a second animal test, the researchers used a contrast agent to enhance ultrasound images of blood vessels in the brain. The research findings will be published in Ultrasound in Medicine & Biology.

The transducer used by the investigators consisted of a 36 by 36 array with

interelement spacing of 0.18 mm. It included 504 transmitting and 252 receive channels operating at a frequency of 4.5 MHz.

In preclinical testing, the burr hole was drilled to avoid the sagittal sinus with the transducer placed against the intact dura mater. Images of the lateral ventricles included real-time 3D guidance of a needle puncture of one ventricle. The contrast-enhanced 3D color-flow Doppler images depicted cerebral vessels, including the complete circle of Willis.

The development of this device is the latest from Stephen Smith, Ph.D., a professor of biomedical engineering at Duke. His work over the past several years has demonstrated the use of tailored 3D ultrasound devices for specific clinical applications.

"Wherever there is a commercial 2D niche now, we are working to put a 3D tool in there," Smith said.

Earlier this year, Smith reported the development of a 3D system that might be used to image the heart and other organs during endoscopic interventions. These interventions would be performed through "keyhole" incisions about 3 cm in diameter ( Miniature ultrasound transducers open 3D windows on heart. Smith and colleagues further miniaturized this technology to fit through a 10-mm hole in the skull.

"The earlier device required a hole bigger than a quarter," said Edward Light, a research and development engineer in the biomedical engineering department at Duke. "Now it's closer to a dime."

Other adaptations included the orientation of the ultrasound beam, which the engineers switched from side-scan mode to forward looking.