Key Technology of Multi-array Phased Array for Transcranial Focused Ultrasound

Transcranial focused ultrasound is an effective neuromodulation technique that can deliver mechanical force in the form of sound waves non-invasively to specific areas of brain tissue to achieve the modulation and treatment of intracranial target areas, with the advantages of non-invasive, focused targets and adjustable focus. The earliest research on transcranial focused ultrasound can be traced back to the 1950s when the pioneering research of Lynn et al. laid the foundation for ultrasound research in the field of brain science. However, due to the strong acoustic attenuation and non-homogeneous nature of the skull, focused ultrasound suffers from focus shift, insufficient energy in the focal domain, and skull burns after transcranial. Early focused transcranial ultrasound studies would remove part of the cranial bone in the path of the acoustic beam. With the development of magnetic resonance imaging, electron computed tomography and multi-array phased array technology, noninvasive transcranial focusing of transcranial focused ultrasound is gradually becoming possible. Multi-array ultrasound phased arrays can correct the phase deviation and amplitude attenuation of ultrasound after transcranial, and achieve accurate and effective intracranial focusing. This paper first introduces the array arrangement of transducer elements, including periodic arrays, random arrays and spiral arrays. Periodic arrays include line arrays, rectangular surface arrays, curved surface arrays, and concentric ring arrays. Spiral arrays include the Fermat spiral, sixteen-arm spiral and Archimedean spiral. This paper summarizes the modulation methods of the phased array excitation signal, including phase correction methods and amplitude correction methods. Finally, this paper reviews and outlooks the basic research based on the self-researched phased array system and the clinical applications based on the Exablate system.