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Implementing the probe beam deflection technique for acoustic sensing in photoacoustic and ultrasound imaging Ronald A. Barnes Jr. The University of Texas at San Antonio This work is a collaboration between The University of Texas at San Antonio and The University of Texas Health Science Center.
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Implementing the probe beam deflection technique for acoustic sensing in photoacoustic and ultrasound imaging Ronald A. Barnes Jr. The University of Texas.

Jan 18, 2016

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Modeling, Simulation and Application of the Probe Beam Deflection Technique for Photoacoustic and Ultrasound Imaging

Implementing the probe beam deflection technique for acoustic sensing in photoacoustic and ultrasound imagingRonald A. Barnes Jr.The University of Texas at San Antonio

This work is a collaboration between The University of Texas at San Antonio and The University of Texas Health Science Center.OutlineIntroductionBackgroundModeling (MATLAB)Acoustic Wave PropagationRay TracingSimulation (MATLAB)Optimum Sensor TopologyOptimum Beam TopologyQuadrant Photodiode SimulationAcoustic Wave Directionality MeasurementSensor Frequency ResponseVisualization (ParaView and MATLAB)ConclusionIntroductionWhat is Photoacoustic Tomography?Photoacoustic Tomography (PAT) is accomplished by measuring the propagating acoustic energy radiated from a sample of tissue whose thermal expansion is invoked by a pulse laser. An image of the tissue composition is reconstructed based on the measurement of the of this acoustic energy.What is the Probe Beam Deflection Technique?The Probe Beam Deflection Technique (PBDT) is sensing topology that uses probe beam lasers and there deflection and refraction to measure the properties of the propagating acoustic wave, through the implementation of a Quadrant Photodiode (QPD).Why is Modeling and Simulation important for this project?To develop an efficient algorithm for reconstruction of a tissue composition image, one must understand the interaction between probe beam and propagating acoustic wave front. A ray tracing simulation in combination with an acoustic wave simulation will allow for the prediction of beam deflection or refraction for various experimental topologies and implementations.Background (PAT)Light enters a scattering medium (Ex. Tissue Phantom) where a portion of the energy is absorbed by the tissue in the form of heat, this produces thermal expansion.

If the temperature increase inside the phantom occurs at a faster rate then the thermal relaxation time of the tissue, an acoustic wave will propagate as a result of the photo-acoustic effect.

This acoustic wave produced is a wideband ultrasonic transmission and to date is measured with piezoelectric transducers.PAT ApplicationsMelanoma detectionPhotoacoustic tomography of gene expression.Doppler photoacoustic tomography for flow measurement.Photoacoustic and thermoacoustic tomography of the brainLow-background thermoacoustic molecular imaging.[2]. Prospects of photoacoustic tomography, Lihong V. WangPhotoacoustic vs. Other Contrast MethodsContrast MethodBandwidth (Hz)Primary ContrastPenetration Depth (mm)Axial Resolution (um)Lateral Resolution (um)Photoacoustic microscopy 50 M Optical absorption 31545Photoacoustic microscopy 5 M Optical absorption 50700700Confocal microscopy Fluorescence, scattering 0.2200.3-3 Two-photon microscopy Fluorescence 0.5-1.0 100.3-3 Optical coherence tomography 50 T Optical scattering 20.5-10 10Scanning Laser Acoustic Microscopy 300 M Ultrasonic scattering 22020Acoustic microscopy 50 M Ultrasonic scattering 2020-100 80-160 Ultrasonography 5 M Ultrasonic scattering 60300300[1] Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis.Background (PBDT)PBDT is implemented by focusing probe beams through an enclosure filled with a propagation medium. As an acoustic wave travels through the medium the refractive index is changed relative to the pressure gradient produced by the wave. The probe beam deflects and refracts as it interacts with the refractive index profile along its beam path.

The probe beam deflection technique offers various advantages when compared to transducers, these include: Wave front directionality measurement, passive sensing, and low implementation cost.Development of a ModelStep 1: Produce a model of acoustic wave propagation in homogeneous and heterogeneous mediums based on the 2nd order PDE governing acoustic wave propagation.Step 2: Modify this model in such a way that all parameters are adjustable. This includes: Initial acoustic wave magnitude, propagation medium properties, acoustic wave frequency, etc.Step 3: Convert the pressure values in the four dimensional dataset (3 dim. for space and 1 for time) to refractive index using the lorentz-lorenz relation.Step 4: Develop a ray tracing simulation to trace a bundle of rays through the previously created dataset using the vector form of Snells law. This simulation should have adjustable parameters which include: initial ray origin (for all rays that make up beam), initial ray intensity, and initial ray direction. Model Setup

MATLAB Visualization

MATLAB Visualization

Method for Ray Trace Simulation (PBDT)The nature of Snells law allows the PBDT method to determine the propagation direction of the wavefront in relation to the probe beam. This is a distinct advantage over piezoelectrics whose measurement ability is limited to distance from transducer to acoustic wave source.

Visual Example of Ray Trace

Probe Beam Orientations

Quadrant Photodiode Concept

Beam Intersection on QPD Surface(Simulation)

MATLAB Visualization

MATLAB Visualization

QPD X SIGNALQPD Y SIGNALExperimental Implementation

Probe Beam Orientations(Experiment)

Experimental ResultsABC

Future WorkDefine optimum beam and sensor topologies for experimental implementation of PBDT derived from simulation.Define the frequency response of PBDT and compare to the frequency response to commercially available transducers.Develop reconstruction algorithm based on integrating line detectors as proposed by G. Paltauf but with added angular information. AcknowledgmentsNSF grant (HRD-0932339), Drs. Demetris Kazakos and Richard Smith, project managers.PREM Grant # DMR- 0934218. ReferencesAndr Conjusteau, Saher Maswadi, Sergey Ermilov, Hans-Peter Brecht, Norman Barsalou, Randolph D. Glickman and Alexander A. Oraevsky, "Detection of gold-nanorod targeted pathogens using optical and piezoelectric optoacoustic sensors: comparative study", Proc. SPIE 7177, 71771P (2009); doi:10.1117/12.813434 B. E. Treeby and B. T. Cox, "A k-space Green's function solution for acoustic initial value problems in homogeneous media with power law absorption," J. Acoust. Soc. Am., vol. 129, no. 6, pp. 3652-3660, 2011. B. E. Treeby, E. Z. Zhang, and B. T. Cox, "Photoacoustic tomography in absorbing acoustic media using time reversal," Inverse Prob., vol. 26, no. 11, p. 115003, 2010. B. E. Treeby and B. T. Cox, "Modeling power law absorption and dispersion for acoustic propagation using the fractional Laplacian," J. Acoust. Soc. Am., vol. 127, no. 5, pp. 2741-2748, 2010B. E. Treeby and B. T. Cox, "k-Wave: MATLAB toolbox for the simulation and reconstruction of photoacoustic wave-fields," J. Biomed. Opt., vol. 15, no. 2, p. 021314, 2010. B. T. Cox and B. E. Treeby, "Artifact trapping during time reversal photoacoustic imaging for acoustically heterogeneous media," IEEE Trans. Med. Imaging, vol. 29, no. 2, pp. 387-396, 2010. B. T. Cox, S. Kara, S. R. Arridge, and P. C. Beard, "k-space propagation models for acoustically heterogeneous media: Application to biomedical photoacoustics," J. Acoust. Soc. Am., vol. 121, no. 6, pp. 3453-3464, 2007 B. T. Cox and P. C. Beard, "Fast calculation of pulsed photoacoustic fields in fluids using k-space methods," J. Acoust. Soc. Am., vol. 177, no. 6, pp. 3616-3627, 2005. Wang, L. V., Ed. . Photoacoustic Imaging and Spectroscopy. Taylor & Francis, 2009.

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Acoustic Wave Front (H)

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