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The Photoacoustic Spectral Reconstruction Method | OMICS International
ISSN: 2155-6210
Journal of Biosensors & Bioelectronics

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The Photoacoustic Spectral Reconstruction Method

Zhen Yuan*

Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611-6131, USA

*Corresponding Author:
Zhan Yuan
Department of Biomedical Engineering
University of Florida, Gainesville
FL 32611-6131, USA
E-mail: [email protected]

Received Date: March 11, 2012; Accepted Date: March 12, 2012; Published Date: March 15, 2012

Citation: Yuan Z (2012) The Photoacoustic Spectral Reconstruction Method. J Biosens Bioelectron 3:e102. doi: 10.4172/2155-6210.1000e102

Copyright: © 2012 Dhyani H, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Keywords

PAT; Multi-spectral optical imaging; Reconstruction methods; Transducers

Introduction

Biomedical PAT is a potentially powerful modality that can offer high resolution structural and functional imaging of tissues [1-6]. In PAT, a short-pulsed laser source is used to irradiate the tissue of interest. The laser-produced temperature rise and subsequent thermo elastic expansion of tissues generate acoustic wave which is detected by ultrasound transducers along multiple boundary positions. A reconstruction algorithm is used to recover the photoacoustic (PA) images. In this study, we describe a new spectral approach that allows for direct simultaneous reconstruction of tissue chromophores and acoustic velocity using multiple-wavelength laser illumination. Due to the use of multiple laser wavelengths, this approach provides more accurate physiological parameter reconstruction, especially for acoustic velocity and direct recovery of functional parameters. We will demonstrate this multispectral PAT approach using in vivo experiments.

Photoacoustic Spectral Reconstruction Method

In multi-spectral PAT, frequency-domain Helmholtz wave equation in an acoustically heterogeneous medium is written in consideration of Beer’s law equation, [4-7]

equation   (1)

where ci is the concentration and εi(λ) is the extinction coefficient of the ith chromophore (HBO2, HbR and H2O) at wavelength λ. And the inverse solution can be obtained by solving the following equation:

equation   (2)

in which equationis the update vector for chromophores and acoustic velocity; ξ is the regularization parameter determined by combined Marquardt and Tikhonov regularization schemes; equationand equationare measured and calculated data for i=1,2,…M boundary locations and are written as for each acoustic frequency ω within each incident optical wavelength λ,

equation   (3)

The Jacobian matrix, J is denoted as equation, where equation and equation represent the Jacobian submatrix for acoustic velocity and different chromophores, respectively.

Results and Discussion

In this section, we evaluate the multi-spectral PAT approach using small animal experiments. Multispectral PAT was performed on a mouse with an implanted subcutaneous tumor (see Figure 1). The PAT imaging setup has been described elsewhere. Five optical wavelengths (755, 800, 860, 900 and 930 nm) were used from the Ti: Sapphire laser source. Figures 2a-2d present the reconstructed in vivo HbR, HbO2, H2O and acoustic velocity images. We see that he tumor is remarkably imaged with the highest contrast in HbR and HbO2 images.

biosensors-bioelectronics-beam-splitter-computer

Figure 1: Schematic demonstration of our PAT system. BS: beam splitter; PC: personal computer (left); photograph showing the imaging region for a mouse with an implanted subcutaneous tumor (right).

biosensors-bioelectronics-reconstructed-acoustic-velocity

Figure 2: Reconstructed in vivo images of Hb (a), HbO2 (b), H2O (c) and acoustic velocity (d) from a mouse with a subcutaneous tumor.

The multi-spectral PAT approach presented provides an efficient means of concurrent reconstruction of multiple parameters including different chromophore concentrations and acoustic velocity. Nonetheless, the ability of reconstructing multiple parameter images may provide us a convenient tool to quantify physiological function, disease progression, or response to intervention.

References

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