Focused Ultrasound for Non-invasive Neuromodulation

The development of effective therapies to treat central nervous system (CNS) disorders and diseases has historically been a challenging problem due, in part, to the invasiveness of interventional surgical procedures and to the presence of the blood–brain barrier (BBB) that restricts passage of most therapeutic drugs from the circulation into the brain. Furthermore, existing CNS drug therapies often have undesirable systemic side effects, while effective neurosurgical approaches are not applicable to large patient populations. To circumvent these limitations, there is great research interest in designing non-invasive CNS therapies. It has been hypothesized that ultrasound, with proper tuning and focusing of ultrasonic energies, can be delivered from outside the head to targeted regions in the brain to induce alterations in neuronal conduction, connectivity of regions, neurotransmitter release, and to induce transient opening of the BBB to facilitate drug delivery. These potential uses of ultrasound to modulate cellular and molecular functions at the micro- and nanoscale in the CNS have provided the stimulus for collaborative research among biomedical engineers, neuroscientists, psychiatrists, and neurosurgeons that is necessary to advance this novel therapy to the clinic. The objective of this chapter is to introduce ultrasound interactions with tissue and bone and to present examples of potential CNS applications of focused ultrasound (FUS).