In vivo spatial-spectral photoacoustic microscopy enabled by optical evanescent wave sensing

Abstract

In addition to offering morphological visualizations via capture of the spatial distributions of optical absorption, photoacoustic imaging technology can reveal abundant physical information about biological particles, including their orientation, density, and viscoelasticity, through analysis of the pressure transients in the spectral domain. However, the low-amplitude wideband photoacoustic signals of intrinsic microscopic optically-absorbing objects under the action of confined photoacoustic excitation power continue to hinder simultaneous photoacoustic structural imaging and spectroscopic analysis of the nonfluorescent chromophores in living biological tissues because of the inadequate responses to photoacoustic impulses observed in most photoacoustic imaging setups that include piezoelectric transducers. Building upon a recently-developed optical evanescent wave sensor that can respond to ultrasound with high sensitivity over a broad frequency range, we propose in vivo spatial-spectral photoacoustic microscopy for recovery of structural imaging in three dimensions and characterization of anatomical features in the acoustic frequency domain. Label-free photoacoustic images of a living zebrafish are acquired in which spectroscopically-resolved differentiation of the microarchitecture is accessed, along with isometric micrometer-scale volumetric visualizations. The proposed imaging technology could potentially provide more comprehensive evaluations of the physiopathological status of living small animals.

Keywords

• Photoacoustic microscopy
• Optical evanescent wave sensing
• Spatial-spectral imaging
• In vivo imaging