35.2 A Spatial-Domain Compressive-Sensing Photoacoustic Imager with Matrix-Multiplying SAR ADC

Wearable deep-tissue imaging technologies promise a paradigm shift to preventive, proactive, and accessible health care. Real-time and long-term imaging offers unprecedented insights into one's body conditions, enabling constant monitoring of high-risk patients (e.g., cardiovascular [1] and musculoskeletal [2]), tracking fetal development [3], and overseeing recovery after surgeries. These devices also make medical imaging more accessible and affordable in low-income countries. Ultrasound and photoacoustic (PA) imaging modalities are well suited for such applications because of their high resolution for imaging deep tissue and fewer safety concerns. Compared to the well-known ultrasound, emerging PA technology [4], [5] employs optical excitation and ultrasonic readout, governed by PA effects, to achieve higher molecular contrast and sensitivity based on the agents' optical absorption properties while offering similar depth and resolution. Thus, this work targets a compact and low-power PA RX with data compression as a key enabler of the envisioned wireless wearable PA imager. It is worth noting that PA and ultrasound RX share similar sensor arrays and readout circuits, except that the amplitude of received PA signals is roughly ten times smaller than that of ultrasound due to an extra stage of energy transduction and light exposure limits. Thus, we discuss and compare ultrasound and PA RX designs together in this paper.