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Advancements in Focused Ultrasound Promise Cost-Effective Brain Treatment

Focused ultrasound, often with MR guidance, has shown promise for treating brain diseases. Currently, it is FDA approved to treat essential tremor, and work is ongoing to expand its range of possibilities. There is hope that focused ultrasound may become more useful for other brain diseases, as well, including cancer. One of the main drawbacks of MR-guided focused ultrasound, however, is that MR is an expensive, time-consuming test. To address this challenge, a group of interdisciplinary researchers at Georgia Institute of Technology (Georgia Tech) are testing the parameters of delivering focused ultrasound to the brain without MR guidance.

The projects, which are sponsored by the National Science Foundation, use ultrasound-based methods to measure the contours and density of the skull and focus ultrasound beams precisely in the brain. Because distances as small as 1 mm are significant in brain anatomy, precise focus is essential. Four different labs are conducting research to improve the process.

The lab of Brooks Lindsey, PhD, an assistant professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University, is investigating the effects of bone microstructure, specifically the porosity of the trabecular bone layer, on ultrasound imaging. The lab has recently characterized the effect of skull microstructure and angle of incidence on transcranial ultrasound imaging, including ultrafast plane wave Doppler imaging, which can be used for imaging blood flow in large cerebral arteries in stroke patients.

The lab of Costas D. Arvanitis, PhD, an assistant professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech, is exploring new and faster methods of focusing ultrasound through the skull to promote and evaluate the therapeutic potential of linear and nonlinear effects from high-frequency ultrasound fields in the brain. Arvanitis’ lab has derived a general solution for sound propagation that can effectively correct for skull aberrations, providing a computationally efficient and accurate method for trans-skull focusing.

The lab of Alper Erturk, PhD, FASME, FSPIE, the Woodruff Professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech, is studying low-frequency vibrations and suture dynamics of the skull to facilitate modeling and elastic parameter identification. Erturk's lab has modeled and experimentally validated vibration characteristics of various cranial bone regions, by accounting for high-resolution bone porosity, and demonstrated the accuracy of the identified elastic parameters via ultrasound experiments.

Finally, the lab of Massimo Ruzzene, PhD, the Slade Professor of Mechanical Engineering, the associate dean for graduate programs in the College of Engineering and Applied Sciences at the University of Colorado Boulder, and a former Georgia Tech colleague, is delving into the use of guided waves in the skull and their radiation characteristics into the brain. The lab has used numerical and semianalytical methods to simulate guided waves in the skull and identified their radiation conditions, which were validated experimentally.

Taken together, these advances offer the possibility of expanded focused ultrasound use in the brain. The researchers believe an improved understanding of skull-brain system dynamics will lead to improvements in imaging, diagnosis, and therapy.

“The ultimate goal in these studies is to stimulate the development of novel medical imaging and therapy techniques that may have profound impact in areas such as diagnosis and treatment of brain tumors, detection of traumas and skull-related defects, mapping of the brain function, and neurostimulation,” Erturk says. “The research could also have implications on ultrasound-based blood-brain barrier openings for drug delivery, which may be critical for the management and treatment of diseases such as Alzheimer’s.”

A Radiology Today staff report