Overcoming optical attenuation in tissue imaging

Optical photoacoustic microscopy, an in vivo imaging technique that leverages the photoacoustic effect to detect optical contrasts at the optical-diffraction limit, is used to probe physiological and pathological mechanisms at the cellular level. Its imaging capabilities for deep microvasculature are limited by a narrow depth of field, however. While wavefront engineering has been used to shape beam profiles, efforts have mainly been made to lengthen the propagation distance of the beam, neglecting optical attenuation characteristics in tissue imaging.

To achieve high-quality imaging across all tissue depths, Yang et al. engineered a customized diffractive optical element in photoacoustic microscopy, compensating for signal loss in deeper microvasculature.

“By modeling the optical attenuation distribution within tissue across the extended depth, we used wavefront modulation to design an inverse-compensated extended focusing field,” said author Chao Tao. “The resulting wavefront phase produces a depth-compensated needle-shaped beam.”

The team tested the ability of the depth-compensated diffractive optical element photoacoustic microscope (DC-DOE-PAM) to uniformly excite vasculature over an extended depth of field. Results showed an extended axial profile with increased axial intensity — in other words, greater depth range and stronger signal, respectively — enabling researchers to simultaneously acquire both superficial and deep tissue images with consistent signal-to-noise ratio. In vivo imaging of a mouse ear and brain confirmed the adaptability of DC-DOE-PAM in complex scattering environments.

The team next looks to apply DC-DOE-PAM to hemodynamic studies.

“We plan to extend the technique to additional optical wavelengths, which will enrich the biological targets we can examine and support functional photoacoustic imaging studies, such as imaging blood oxygen saturation in deep tissue,” said Tao. “Building on this, we will further investigate microcirculation in living tissue and how it changes under pathological conditions.”

Source: “Depth-compensated needle-shaped beam for in vivo photoacoustic microvascular imaging,” by Yifan Yang, Chao Tao, Wei Song, and Xiaojun Liu, APL Photonics (2026). The article can be accessed at https://doi.org/10.1063/5.0332017 .