Heart and blood vessels called the cardiovascular system closely interact with each other to control cardiac output and maintain vital activities. To observe heartbeat and vascular changes, high-resolution high-speed photoacoustic microscopy (PAM) and/or photoplethysmography (PPG) that are applied technologies of optics have been utilized in preclinical and clinical studies. Herein, we have embedded PPG sensing functionality in a high-speed PAM system to simultaneously perform microvascular imaging and heart rate measurement. In human fingers, we observed capillaries’ movements in blood vessel images from PAM, and moreover found that this phenomenon is due to pulsation by directly comparing between the capillaries’ movements and pulsation-dominant PPG signals. Further, the cardiac cycle could be extracted by quantifying the capillaries’ movements in consecutive blood vessel images, and this periodicity from PAM agreed with that from that of PPG sensing. From these results, the high-speed PAM with PPG could be potentially used as clinical tools for monitoring the changes in multiple cardiovascular information in response to internal and/or external circumstances.
Photoacoustic imaging is a promising biomedical imaging technology that can provide the biological information of animals and humans in vivo. Taking advantages of both optics and ultrasound simultaneously, the photoacoustic imaging has rich optical contrast and high ultrasonic resolution in deep tissues. Especially, the optical-resolution photoacoustic microscopy (OR-PAM), the major implementation of the photoacoustic imaging, achieves sharp spatial resolution with focused optical beams. However, developed OR-PAM systems are disadvantaged by limited temporal and/or spatial resolutions by hardware parts. Here, we introduce a high speed super-resolution localization OR-PAM that overcomes the limited resolutions. First, to improve a temporal resolution, we equipped a galvanometer scanner, which has been used in many optical microscopies. Previously, due to the vulnerability of the scanner to water, the PAM system using the scanner scanned only light, not ultrasound. However, our system overcame the weakness by immersing only a scanning part except to a galvanometer part, leading to scanning light and ultrasound simultaneously. Steering both laser beams and ultrasound waves with a scanner’s mirror immersed in the water, our system achieves a wide scanning range and a high signal-to-noise ratio as well as the B-mode imaging speed of 500 Hz. Furthermore, we acquired a super-resolved microvascular image in vivo using an agent-free localization imaging technology based on the fast scanning speed. These results show that our super-resolution high-speed OR-PAM can be used in a variety of fields, including neurology, oncology, and pathology.
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