Miniaturized acoustic focus tunable photoacoustic transmitter probe

Aiming to provide dynamically adjustable acoustic field for in vivo ultrasound application scenarios, a miniaturized optical fiber photoacoustic (PA) transmitter is presented. Different from the existing laser generated focused ultrasound probes with fixed acoustic focal length, its focus can be continuously adjusted from infinity to 2.166 mm by deforming the PA conversion film using pneumatic actuation method. The PA film is designed into a circular suspending elastic membrane structure with clamped boundary, which consists of a PDMS/candle soot nanoparticles (CSNPs) mixture layer sandwiched between two pure poly-dimethylsiloxane (PDMS) layers. Using soft lithography strategy, the PA film together with a structured PDMS substrate and a multimode fiber (MMF) are assembled together to construct the final PA probe with 2.68 mm aperture. For a proof-of-concept demonstration, three different focusing statuses (with 5.196 mm, 3.246 mm and 2.166 mm focal lengths) are provided and their axial acoustic field distributions are characterized as well. Under the excitation condition with the laser fluence of 13.26 mJ/cm(2), acoustic signal with 9 MHz center frequency, 92.91% fractional bandwidth at - 6 dB and peak negative pressure (PNP) amplitude up to 8.91 MPa at the 2.166 mm focal point can be achieved, resulting in mechanical index (MI) of 2.97. Referring to the reported data, the current PA transmitter probe demonstrates excellent application potential. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

A miniaturized optical fiber photoacoustic transmitter is proposed to provide dynamically adjustable acoustic field for in vivo ultrasound applications. By using pneumatic actuation, the focus can be continuously adjusted to achieve three different focusing statuses for ultrasound output.