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Wearable photoacoustic watch for humans

Ting Zhang, Heng Guo, Weizhi Qi, and Lei Xi

Open Access Open Access

Abstract

Longitudinal detection of hemodynamic changes based on wearable devices is imperative for monitoring human healthcare. Photoacoustic effect is extremely sensitive to variations in hemoglobin. Therefore, wearable photoacoustic devices are apt to monitor human healthcare via the observation of hemodynamics. However, the bulky system and difficulties in miniaturizing and optimizing the imaging interface restrict the development of wearable photoacoustic devices for human use. In this study, we developed a wearable photoacoustic watch with a fully integrated system in a backpack that has a size of 450 mm × 300 mm × 200 mm and an affordable weight of 7 kg for an adult to wear. The watch has a size of 43 mm × 30 mm × 24 mm, weighs 40 g, and features a lateral resolution of 8.7 µm, a field of view (FOV) of 3 mm in diameter, and a motorized adjustable focus for optimizing the imaging plane for different individuals. We recruited volunteers to wear the watch and the backpack and performed in vivo imaging of the vasculatures inside human wrists under the conditions of walking and human cuff occlusion to observe hemodynamic variations during different physiological states. The results suggest that the focus shifting capability of the watch makes it suitable for different individuals, and the compact and stable design of the entire system allows free movements of humans.

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Supplementary Material (2)

NameDescription
Visualization 1       A volunteer performs the vascular imaging of his wrist when wearing the entire system and walking in a room.
Visualization 2       The observed images at the same position during the entire movement of the optical focus.

Data availability

Data underlying the results presented in this Letter are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Figures (4)
Fig. 1.
Fig. 1. Schematic of the wearable photoacoustic watch system. (a) Photograph of the photoacoustic watch system. (b) Schematic of the system configuration. (c) Photograph of a volunteer wearing the backpack and imaging watch. (d) Detailed internal structure of the imaging watch. (e) Wrist of a volunteer wearing the well-assembled imaging watch. AMP, amplifier; MCU, micro controller unit; DAQ, data acquisition card; F&C, fiber and cable; PD, photodiode; PS, power supply; LC, laser controller; BS, beam splitter; L, lens; Obj, objective lens; FC, fiber coupler; SMF, single mode fiber; MDB, motor drive board; CL, collimate lens; DL, doublet lens; M, mirror; T, transducer; CG, cover glass. See Visualization 1.

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Fig. 2.
Fig. 2. Systematic performance of the imaging watch. (a) Line spread function of a sharp surgical blade with full sampling. The inserted image is the MAP image of the surgical blade. The position of the profile is denoted by a red dashed line. (b) MAP image of a grid plate to measure the effective FOV. (c) Line spread function of a sharp surgical blade with sparse sampling. (d) Sparsely sampled, interpolated, and fully sampled PA images of a skin vascular network, respectively. The bottom images are the close-up views of the areas indicated by the green dashed rectangles.

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Fig. 3.
Fig. 3. Assessment of the focus shifting capability of the watch. (a) Schematic of the optical excitation and acoustic generation inside a multilayered skin with an adjusted beam focus. (b) OR-PAM images of the human wrist with a shifted laser focus. (c) Quantitative analysis of 30 consecutive focus-adjusted images at the same position of the wrist. See Visualization 2.

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Fig. 4.
Fig. 4. Hemodynamic changes of vascular network during the cuff occlusion. (a) Photograph of in vivo cuff occlusion experiment using a tonometer. (b) OR-PAM image before the cuff occlusion. (c) Chronological sequence of the operations and OR-PAM images of two regions of interest (ROIs) indicated in Fig. 4(b) by yellow and white dashed circles. (d) Normalized PA signals within the ROIs indicated in Fig. 4(b). VO, venous occlusion; AO, arterial occlusion.

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