Acousto-Optic Imaging

Optical bioimaging provides rich contrast for probing tissue structure and function, but its performance degrades rapidly with depth due to strong scattering and absorption in biological media. Acousto-optic imaging (AOI) addresses this limitation by combining light with focused ultrasound, which locally modulates the optical field and enables depth-invariant resolution governed by acoustic focusing. By scanning tissue with ultrasound, AOI reconstructs depth-resolved optical fluence profiles that encode information about tissue absorption and scattering. However, conventional continuous-wave AOI requires slow mechanical scanning and performs poorly in vivo due to speckle decorrelation.

Time-of-Flight AOI (ToF-AOI) overcomes the need for mechanical scanning by using pulsed, line-focused ultrasound to obtain depth-resolved measurements. Despite this advantage, existing ToF-AOI implementations suffer from low signal-to-noise (SNR) ratio and typically rely on bulky photomultiplier detectors, limiting their practicality.

In this talk, we will overview the key optimizations introduced to our ToF-AOI system to improve signal-to-noise ratio and enable probing of local optical attenuation coefficients. Signal sensitivity is substantially improved using two complementary strategies. First, a coded ultrasound excitation scheme based on Hadamard pulse sequences increases the effective insonification without sacrificing depth resolution, yielding a 4.5-fold improvement in SNR. Second, a homodyne optical detection approach enables shot-noise-limited detection with high-efficiency silicon photodiodes, providing an additional 4.16-fold SNR enhancement.

Beyond sensitivity gains, the talk will demonstrates the feasibility of quantitative AOI by recovering depth-dependent optical attenuation in tissue-mimicking phantoms, and extends the method to multispectral measurements for chromophore concentration estimation.
Together, these advances significantly improve the speed, robustness, and quantitative potential of AOI, paving the way toward practical functional imaging and non-invasive tissue characterization in vivo.

Ph.D. student under the supervision of Prof. Amir Rosenthal.