Journal
IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS
Volume 13, Issue 5, Pages 835-847Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TBCAS.2019.2922027
Keywords
Transducers; Ultrasonic imaging; Acoustics; Spatial resolution; Acoustic beams; Neuromodulation; Energy efficiency; Brain; figure-of-merit; microscopic ultrasound stimulation; neuromodulation; spatial resolution; transcranial focused ultrasound stimulation; ultrasound transducer
Funding
- National Institutes of Health [1R21EY029424, R00EB017729-04]
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In order to improve the spatial resolution of transcranial focused ultrasound stimulation (tFUS), we have recently proposed microscopic ultrasound stimulation (US). In US, either an electronically phased array of ultrasound transducers or several millimeter-sized focused transducers are placed on the brain surface or sub-millimeter-sized transducers are implanted inside the brain tissue to steer and deliver a focused ultrasound pressure directly to the neural target. A key element in both tFUS and US is the ultrasound transducer that converts electrical power to acoustic pressure. The literature lacks a comprehensive study (in a quantitative manner) of the transducer characteristics, such as dimension, focusing, acoustic matching, backing material, and sonication frequency (f(p)), in the US. This paper studies the impact of these design parameters on the acoustic beam profile of millimeter-sized transducers with the emphasis on the stimulation spatial resolution and energy efficiency, which is defined as the US figure-of-merit (FoM). For this purpose, disc-shaped focused and unfocused piezoelectric (PZT-5A) transducers with different dimension (diameter, thickness), backing material (PCB, air) and acoustic matching in the frequency range of 2.2-9.56MHz were fabricated. Our experimental studies with both water and sheep brain phantom medium demonstrate that acoustically matched focused transducers with high quality factor are desirable for US, as they provide fine spatial resolution and high acoustic intensities with low input electrical power levels (i.e., high FoM).
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