Low Temperature-Mediated Enhancement of Photoacoustic Imaging Depth

Mohammad A. Ansari,Hossein Z. Jooya,Qiuyun Xu,Sadreddin Mahmoodkalayeh,Ali Hariri,Mohammad R. N. Avanaki,Yang Zhou

doi:10.1038/s41598-018-22898-2

Abstract

We study the temperature dependence of the underlying mechanisms related to the signal strength and imaging depth in photoacoustic imaging. The presented theoretical and experimental results indicate that imaging depth can be improved by lowering the temperature of the intermediate medium that the laser passes through to reach the imaging target. We discuss the temperature dependency of optical and acoustic properties of the intermediate medium and their changes due to cooling. We demonstrate that the SNR improvement of the photoacoustic signal is mainly due to the reduction of Grüneisen parameter of the intermediate medium which leads to a lower level of background noise. These findings may open new possibilities toward the application of biomedical laser refrigeration.

Highlights

The temperature dependency of the Grüneisen parameter has previously been explored in several studies[9,10,11,12,13,14,15,16,17,18,19]
In biological tissues due to multiple scattering, the fluence is significantly affected and the photons are greatly scattered especially after they reach the diffusion limit (i.e., ~1 mm). Such scattered photons generate background PA signals which reduce the signal-to-noise ratio (SNR) of the PA signal generated from the imaging target
Through several sets of simulation and experiment, that the SNR of the photoacoustic signal generated from a black wire as an imaging target at different depths, is improved by lowering the temperature of the intermediate medium between the PA sensor and the target

Summary

Introduction

The temperature dependency of the Grüneisen parameter has previously been explored in several studies[9,10,11,12,13,14,15,16,17,18,19]. Wang et al, developed a Grüneisen relaxation photoacoustic microscopy (GR-PAM) system in which two laser pulses with a specified time delay were employed, one for thermal tagging, the other one for signal generation[9]. They showed that when the second laser pulse excites the tagged absorbers within the thermal relaxation time, a stronger photoacoustic signal than the initial one is obtained In another configuration, they used a continuous wave (CW) laser for thermal tagging and observed that the performance of their method is diminished. The proposed cooling mechanism opens up the possibility of using the laser refrigeration technology in the future This approach creates an efficient channel through the biological tissue layers, which in turn, can significantly improve the penetration depth in photoacoustic imaging

Methods

Results

Conclusion