Axial accuracy and signal enhancement in acoustic-resolution photoacoustic microscopy by laser jitter effect correction and pulse energy compensation.

Amir Asadollahi,Hamed Nikbakht,Ali Rezaei,Hamed Qazvini,Manojit Pramanik,Abolfazl Abedi,Hamid Latifi

doi:10.1364/boe.419564

Abstract

In recent years, photoacoustic imaging has found vast applications in biomedical imaging. Photoacoustic imaging has high optical contrast and high ultrasound resolution allowing deep tissue non-invasive imaging beyond the optical diffusion limit. Q-switched lasers are extensively used in photoacoustic imaging due to the availability of high energy and short laser pulses, which are essential for high-resolution photoacoustic imaging. In most cases, this type of light source suffers from pulse peak-power energy variations and timing jitter noise, resulting in uncertainty in the output power and arrival time of the laser pulses. These problems cause intensity degradation and temporal displacement of generated photoacoustic signals which in turn deteriorate the quality of the acquired photoacoustic images. In this study, we used a high-speed data acquisition system in combination with a fast photodetector and a software-based approach to capture laser pulses precisely in order to reduce the effect of timing jitter and normalization of the photoacoustic signals based on pulse peak-powers simultaneously. In the experiments, maximum axial accuracy enhancement of 14 µm was achieved in maximum-amplitude projected images on XZ and YZ planes with ±13.5 ns laser timing jitter. Furthermore, photoacoustic signal enhancement of 77% was obtained for 75% laser pulses peak-power stability.

Highlights

The photoacoustic (PA) effect was first discovered by Alexander Graham Bell over a century ago; this effect has attracted more attention and had applications in recent decades due to the availability of advanced short pulsed lasers, fast data acquisition (DAQ) devices, and computing capabilities
We proposed and experimentally demonstrated direct and simultaneous measurement of laser pulses’ PP variation and their temporal location using a fast PD and custom-built high sampling-rate DAQ in an acoustic-resolution photoacoustic microscopy (AR-PAM) system
The effect of timing jitter effect correction (TJEC) and peak-power compensation (PPC) was verified by imaging different samples in different conditions in terms of timing jitters, peak-powers, and systems focus

Summary

Introduction

The photoacoustic (PA) effect was first discovered by Alexander Graham Bell over a century ago; this effect has attracted more attention and had applications in recent decades due to the availability of advanced short pulsed lasers, fast data acquisition (DAQ) devices, and computing capabilities. One of the major applications of using the PA effect is photoacoustic imaging (PAI), in which a light absorbing specimen is illuminated by the short laser pulse. The detection of generated waves provides the possibility of locating initial PA wave sources, i.e., the spatial distribution of light absorbers. These absorbers could be microvasculature in tissue. In PAM, the 3D images of absorbers can be directly captured by scanning the sample in confined optical illumination and acoustic detection conditions [8] without further reconstruction algorithms as used in PAT systems [9,10,11,12,13]. In OR-PAM, tightly focused laser light is utilized to generate acoustic waves detected by a focused or unfocused high-frequency, broadband ultrasound transducer (UT). AR-PAM has been used for many biomedical imaging applications [17,18,19,20]

Methods

Results

Conclusion