Characterizing cellular morphology by photoacoustic spectrum analysis with an ultra-broadband optical ultrasonic detector.

Ting Feng,Qiaochu Li,Cheng Zhang,Xueding Wang,Jie Yuan,L. Jay Guo,Guan Xu

doi:10.1364/oe.24.019853

Abstract

Photoacoustic spectrum analysis (PASA) has been demonstrated as a new method for quantitative tissue imaging and characterization. The ability of PASA in evaluating micro-size tissue features was limited by the bandwidth of detectors for photoacoustic (PA) signal acquisition. We improve upon such a limit, and report on developments of PASA facilitated by an optical ultrasonic detector based on micro-ring resonator. The detector's broad and flat frequency response significantly improves the performance of PASA and extents its characterization capability from the tissue level to cellular level. The performance of the system in characterizing cellular level (a few microns) stochastic objects was first shown via a study on size-controlled optically absorbing phantoms. As a further demonstration of PASA's potential clinical application, it was employed to characterize the morphological changes of red blood cells (RBCs) from a biconcave shape to a spherical shape as a result of aging. This work demonstrates that PASA equipped with the micro-ring ultrasonic detectors is an effective technique in characterizing cellular-level micro-features of biological samples.

Highlights

Photoacoustic Imaging (PAI) is a hybrid medical imaging modality based on laser-induced thermo-acoustic effect in biological tissues
Recent studies have demonstrated that the power spectrum of the broadband radio frequency (RF) PA signal contains the micro-structural information of the tissue [1,2,3,4,5,6,7,8,9]
Similar to ultrasound spectral analysis (USSA), photoacoustic spectral analysis (PASA) uses the slope, mid-band fit, and intercept of the linear regression model to characterize the main features of the signal power spectrum [4]

Summary

Introduction

Photoacoustic Imaging (PAI) is a hybrid medical imaging modality based on laser-induced thermo-acoustic effect in biological tissues. Aiming at quantitative imaging and tissue characterization, a technique termed ‘photoacoustic spectral analysis (PASA)’ has been developed. PASA is based on the fact that the frequency components of the PA signals are closely correlated to the morphological properties of optically absorbing objects in tissues, including their sizes, shapes, and densities [4, 10]. Quantitative analysis of the PA signals in the frequency domain would enable an objective evaluation of the morphologies of optically absorbing objects stochastically distributed in biological tissues [3, 11]. The averaged power spectrum provides a robust method of quickly characterizing the stochastic nature of tissue microstructures, and can lead to measurements that are more repeatable. PASA minimizes the contributions of system components, and leads to measurements that are more objective and quantitative

Methods

Results

Conclusion