Multifrequency Interlaced CMUTs for Photoacoustic Imaging

Multifrequency capacitive micromachined ultrasound transducers (CMUTs) are introduced consisting of interlaced 82-μm (low frequency) and 36-μm (high frequency) membranes. The membranes have been interlaced on a scale smaller than the shortest wavelength of operation allowing several advantages over other multifrequency transducer designs including aligned beam profiles, optimal imaging resolution, and minimal grating lobes. The low- and high-frequency CMUTs operate at 1.74 and 5.04 MHz in immersion, respectively. Multifrequency transducers have applications in wideband photoacoustic (PA) imaging where multifrequency transducers are better able to detect both high- and low-frequency PA frequency content. The PA frequency content is target size dependent, which means traditional high-frequency transducers have less sensitivity to larger objects such as diffuse contrast agents. We demonstrate that the low-frequency subarrays are able to better visualize diffuse agent distributions, while the high-frequency subarrays offer fine-resolution imaging important for microvascular imaging and structural navigation. Spectroscopically unmixed images superimpose high sensitivity images of agent concentrations (acquired using low-frequency subarrays) onto high-resolution images of microvessel-mimicking phantoms (acquired using high-frequency subarrays).