On the importance of low-frequency signals in functional and molecular photoacoustic computed tomography

TL;DR

This paper demonstrates that low-frequency signals in photoacoustic computed tomography contain valuable functional and molecular information, enhancing imaging accuracy and reducing artifacts across various biomedical applications.

Contribution

It provides a theoretical framework and experimental evidence showing the significance of low-frequency signals in improving PACT imaging of biological tissues.

Findings

Low-frequency signals improve structural visibility.

They enhance quantitative accuracy in functional imaging.

They help reduce sampling artifacts.

Abstract

In photoacoustic computed tomography (PACT) with short-pulsed laser excitation, wideband acoustic signals are generated in biological tissues with frequencies related to the effective shapes and sizes of the optically absorbing targets. Low-frequency photoacoustic signal components correspond to slowly varying spatial features and are often omitted during imaging due to the limited detection bandwidth of the ultrasound transducer, or during image reconstruction as undesired background that degrades image contrast. Here we demonstrate that low-frequency photoacoustic signals, in fact, contain functional and molecular information, and can be used to enhance structural visibility, improve quantitative accuracy, and reduce spare-sampling artifacts. We provide an in-depth theoretical analysis of low-frequency signals in PACT, and experimentally evaluate their impact on several representative PACT applications, such as mapping temperature in photothermal treatment, measuring blood oxygenation in a hypoxia challenge, and detecting photoswitchable molecular probes in deep organs. Our results strongly suggest that low-frequency signals are important for functional and molecular PACT.