Photoacoustic imaging of sub-diffraction objects with spectral contrast

Label-free photoacoustic imaging guided sclerotherapy for vascular malformations: a feasibility study

We used high-resolution photoacoustic imaging (PAI) to guide sclerotherapy of vascular malformations in an in vivo animal model. A focus-adjustable PAI system was developed. It can adapt to the imaging needs of different depths by adjusting the focus. Blood samples drawn before and after sclerosis were examined with PAI, which could distinguish whether or not the blood had been exposed to a sclerosing agent. Superficial and deep vessels in the animal model were examined in vivo to prove the feasibility of guiding sclerotherapy. We found that PAI can distinguish sclerotic vessels from normal vessels within a certain depth range. Our findings suggest the potential of PAI to find accurate injection points and to localize thrombi, making it possible to reduce the dosage of sclerosing agents.

Overcoming the acoustic diffraction limit in photoacoustic imaging by the localization of flowing absorbers

The resolution of photoacoustic imaging deep inside scattering media is limited by the acoustic diffraction limit. In this Letter, taking inspiration from super-resolution imaging techniques developed to beat the optical diffraction limit, we demonstrate that the localization of individual optical absorbers can provide super-resolution photoacoustic imaging well beyond the acoustic diffraction limit. As a proof-of-principle experiment, photoacoustic cross-sectional images of microfluidic channels were obtained with a 15 MHz linear capacitive micromachined ultrasonic transducer array, while absorbing beads were flown through the channels. The localization of individual absorbers allowed us to obtain a super-resolved cross-sectional image of the channels by reconstructing both the channel width and position with an accuracy better than λ/10. Given the discrete nature of endogenous absorbers such as red blood cells, or that of exogenous particular contrast agents, localization is a promising approach to push the current resolution limits of photoacoustic imaging.