Backward-Mode Photoacoustic Imaging Using Illumination Through a CMUT With Improved Transparency

Area of Science:

• Biomedical Engineering
• Acoustic Imaging
• Optical Physics

Background:

• Photoacoustic imaging (PAI) combines optical absorption and ultrasound detection for high-resolution imaging.
• Capacitive micromachined ultrasonic transducers (CMUTs) are crucial for ultrasound detection in PAI.
• Existing CMUT designs can limit optical penetration, especially for backside illumination techniques.

Purpose of the Study:

• To develop and characterize a novel CMUT with improved optical transparency for PAI.
• To evaluate the performance of the transparent CMUT for backside illumination PAI.
• To demonstrate the feasibility of the CMUT for in vivo PAI applications.

Main Methods:

• Fabrication of a CMUT on a glass substrate using indium-tin oxide electrodes and a silicon plate via anodic bonding.
• Characterization of the CMUT's optical transmission in the 700-900 nm wavelength range.
• Performance evaluation using two PAI experiments: imaging a pencil lead and a polyethylene tube phantom.

Main Results:

• The fabricated CMUT exhibited 30%-40% transmission at 700-800 nm and 40%-60% at 800-900 nm.
• The CMUT successfully reconstructed 2-D and 3-D images of imaging targets.
• Spurious signals from silicon layer absorption were found to be significantly lower than the photoacoustic signals of interest.

Conclusions:

• The developed transparent CMUT is suitable for photoacoustic imaging with backside illumination.
• The fabrication method and device structure show promise for advanced PAI applications.
• This CMUT design offers improved optical transparency for enhanced PAI performance.