A handheld 1D transparent CMUT array probe for photoacoustic imaging: Preliminary results

A transparent transducer array is desired in backward-mode photoacoustic imaging (PAI). CMUT technology is especially suitable for this application because of its wide bandwidth and a wide selection of processing materials. We have previously demonstrated a single-element CMUT with an ITO bottom electrode for improved transparency. The device showed 40% to 70% optical transmission from 700 nm to 900 nm, which is the wavelength range commonly used for in-vivo PAI. In this work, we present a 1D PAI probe that integrates a 1D CMUT array, a fiber bundle, in-probe optics, and low-noise amplifiers which interface with a real-time imaging system. We also demonstrate the PAI capability of a single transparent CMUT element. In this experiment, the phantom was a polyethylene tube filled with indocyanine green (ICG) solution embedded in a tissue-mimicking material. In this setup, the light introduced from the back side of the CMUT enabled direct illumination of the imaging field. We are currently developing 1D arrays for use in PAI with high Vis-NIR transmission. As a proof of principle, we built a 128-channel handheld probe which integrates light from the back side and allows for in-probe front-end amplifiers. The center of the probe houses a compact optical design for the illuminator based on cylindrical lenses. The probe electronics consists of two printed circuit boards, each with 64 channels of low-noise amplifiers with integrated transmit/receive switching and biasing circuitry. This handheld probe has been used in initial tests with a standard nontransparent 1D CMUT array to show the basic electrical functionality.