Three-dimensional handheld LED-based photoacoustic/ultrasound imaging: A potential point-of-care tool for diagnosing peripheral arterial disease

Peripheral arterial disease (PAD) is a common, important condition, affecting a large population globally. It is of paramount importance to identify and treat PAD at an early stage to avoid further clinical problems. Even though large arteries can be visualized using techniques like ultrasound imaging and magnetic resonance imaging, spatial resolution precludes accurate assessment of smaller blood vessels (microvasculature). Photoacoustic imaging has shown good potential in label-free assessment of microvasculature non-invasively. However, clinical translation of this promising technique has not been fast mainly because of the requirement of bulky and expensive pulsed lasers for tissue illumination. In this work, we demonstrate handheld 3D LED-based photoacoustic and ultrasound imaging of human peripheral vasculature with high spatial and temporal resolution. We used high power LED arrays (wavelength : 850 nm, pulse energy: 400 mu J) for optical illumination and 10 MHz linear array ultrasound probe (128 elements, 80% bandwidth) for acoustic detection. Utilizing the high pulse repetition frequency of the LED arrays (4 KHz), our system is capable of combined 2D photoacoustic and ultrasound imaging at a maximum frame rate of 30 Hz. Handheld dual-mode probe can be scanned linearly to generate multiple 2D slices and can be further rendered to 3D volumes using the high-speed GPU processing available. We used the system to image micro-vasculature networks in palm and foot of a human volunteer. Also, we performed human volunteer imaging experiments to evaluate the efficacy of 3D LED-based photoacoustic and ultrasound imaging in assessing the constriction of microvasculature in response to cold exposure and to study the impact of occlusion in peripheral microvasculature. 3D photoacoustic and ultrasound images generated by the system demonstrate its potential in becoming an affordable point-of-care tool for PAD diagnosis and treatment monitoring.