Parallel Acoustic Delay Line (PADL) Arrays for Photoacoustic Imaging Applications

Micromachining process, such as laser micromachining and IC microfabrication process, allows production of complex structures in limited space, which reduces both the size and cost of hardware. In this research, using the advantages of micromachining processes, parallel acoustic delay line (PADL) arrays made of optical fibers and single-crystalline silicon (SCS) have been developed to reduce the number of ultrasonic transducers and data acquisition (DAQ) electronics for real-time photoacoustic tomography (PAT). The PADL arrays allow real-time PAT with the significantly reduced number of ultrasonic transducers and DAQs. Handheld optical PADL array enables more practical operation for photoacoustic imaging applications by miniaturizing previously developed optical PADL array. Sixteen channels of optical fiber PADLs were fabricated and assembled with laser micromachined acrylic housing for the compact structure. By conducting ultrasonic transmission testing, acoustic properties of optical fibers have been characterized. PA imaging capability of optical fiber PADL array has been evaluated by PA imaging experiment. Microfabrication process makes it possible to use single-crystalline silicon as a material for acoustic delay lines. Acoustic properties of silicon were characterized by ultrasonic transmission testing. Based on the characterization result, silicon acoustic delay line was designed into a spiral coil shape to minimize the overall size. Silicon PADLs are better than optical fiber PADL for miniaturization due to the advantages of microfabrication process. Silicon PADL array achieved a channel reduction ratio of 16:1, which is twice the ratio of optical fiber PADL. The PA imaging experiment has demonstrated the PA imaging capability of silicon PADL array. For fast imaging speed and good spatial resolution, silicon PADL array has been improved by applying 3D-printed linker structures and tapered input terminal. Linker structure design has been evaluated by both structural and acoustic simulation. The final design of linker structure is 3D-printed polymer linker to securely hold silicon delay lines with minimal contacts. Tapered input terminal was designed to reduce acoustic acceptance angle for better spatial resolution. Tapered input terminal was evaluated by acoustic simulation with different designs. Those designs and techniques are expected to provide new solutions to reduce the cost and complexity of ultrasonic receiving systems for photoacoustic imaging applications