  Photoacoustic computed tomography (PACT) is emerging as a new technique for
functional brain imaging, primarily due to its capabilities in label-free
hemodynamic imaging. Despite its potential, the transcranial application of
PACT has encountered hurdles, such as acoustic attenuations and distortions by
the skull and limited light penetration through the skull. To overcome these
challenges, we have engineered a PACT system that features a densely packed
hemispherical ultrasonic transducer array with 3072 channels, operating at a
central frequency of 1 MHz. This system allows for single-shot 3D imaging at a
rate equal to the laser repetition rate, such as 20 Hz. We have achieved a
single-shot light penetration depth of approximately 9 cm in chicken breast
tissue utilizing a 750 nm laser (withstanding 3295-fold light attenuation and
still retaining an SNR of 74) and successfully performed transcranial imaging
through an ex vivo human skull using a 1064 nm laser. Moreover, we have proven
the capacity of our system to perform single-shot 3D PACT imaging in both
tissue phantoms and human subjects. These results suggest that our PACT system
is poised to unlock potential for real-time, in vivo transcranial functional
imaging in humans.
