Ultrafast photoacoustic computed tomography for in vivo visualization of respiratory and cardiac dynamics in mice

We present an ultrafast photoacoustic computed tomography (UPACT) system that combines a 1 kHz nanosecond laser, 256-channel high-speed data acquisition, and frequency-domain SNR-weighted reconstruction to enable single-shot, full-view tomography at up to 1000 frames per second with 100 μm in-plane resolution under ultralow surface fluence (∼0.226 mJ/cm²). Phantom experiments validate motion-freezing and quantitative tracking by imaging rapidly moving 100 μm-diameter microspheres. In vivo imaging of nude mice captures cardiopulmonary dynamics, yielding a diaphragm thickness of 0.6 mm, a diaphragm motion amplitude of 0.8 mm, and a respiratory rate of 75 breaths per minute. UPACT further resolves chamber-specific cardiac mechanics, revealing a dominant cardiac frequency of 4.55 Hz and an atrioventricular mechanical delay of 0.093 s. The system achieved an effective penetration depth of up to 14 mm along the short axis and 20 mm along the long axis of the mouse-body cross-section, enabling full visualization of internal organs such as the kidneys and spleen in vivo. These results suggest that UPACT might be a powerful platform for noninvasive monitoring of rapid physiological dynamics, offering new opportunities for research on cardiac function and related fields.