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-space propagation models for acoustically heterogeneous media: Application to biomedical photoacoustics
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10.1121/1.2717409
/content/asa/journal/jasa/121/6/10.1121/1.2717409
http://aip.metastore.ingenta.com/content/asa/journal/jasa/121/6/10.1121/1.2717409
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

A collimated laser beam with a tophat profile, indicated with an arrow, is incident on an optically absorbing half-space, the surface of which is marked by a dotted line. The optical absorption coefficient . The absorbed energy distribution decays exponentially from the boundary according to the Beer-Lambert law. The laser fluence at the surface was (i.e., per cm into the plane of the paper). The sound speed and density were and , respectively, and the Grüneisen parameter . The evolution of this acoustic field is shown in Fig. 2.

Image of FIG. 2.
FIG. 2.

The evolution of the photoacoustic pressure field for the arrangement shown in Fig. 1. The acoustic pressure is shown at times , 0.33, 0.66, and following the laser pulse, calculated using the homogeneous model of Sec. III. The linear grey scale is from (white) to (black).

Image of FIG. 3.
FIG. 3.

Acoustic pressure off axis for an infinitely long impulsive heating source with a Gaussian radial profile. Analytic solution (solid line) which assumes instantaneous ( function) heat deposition, and -space model for a homogeneous medium (circles), which uses a Gaussian approximation to the temporal function. When the stress confinement condition holds, as in this case, this approximation gives good agreement. The Gaussian radial width .

Image of FIG. 4.
FIG. 4.

An example identical to Fig. 1, except for the circular heterogeneity with sound speed and density half that of the surrounding medium.

Image of FIG. 5.
FIG. 5.

The evolution of the photoacoustic pressure field for the arrangement shown in Fig. 4, including a circular heterogeneity. The acoustic pressure is shown at times , 0.33, 0.66, and following the laser pulse, calculated using the homogeneous model of Sec. III. The linear grey scale is from (white) to (black). The wave reflected from the heterogeneity, and the distorted wave front due to the reduced sound speed are clearly visible.

Image of FIG. 6.
FIG. 6.

Pressure time histories calculated for the point (see Figs. 2 and 5), for both the acoustically homogeneous (solid line) and heterogeneous (dashed line) cases. The additional wave, reflected from the acoustic inhomogeneity, is clear.

Image of FIG. 7.
FIG. 7.

The acoustic pressure field radiated from three circular photoacoustic sources is shown every following an excitation light pulse. The sound speed and density are and , respectively. The position of a rectangular acoustic heterogeneity (, ), which distorts the wavefront on the right of the image, is indicated by a dotted line. The periodic boundary conditions implicit in this model cause the acoustic waves to wrap around when it reaches the edge of the computational domain.

Image of FIG. 8.
FIG. 8.

The acoustic pressure field radiated from three circular photoacoustic sources, as shown in Fig. 7, at 2 and following an excitation light pulse. The sound speed and density are and , respectively. The position of a rectangular acoustic heterogeneity , which distorts the wave front on the right of the image, is indicated by a dotted line. In contrast to the final two frames of Fig. 7, the acoustic waves do not wrap around when they reach the edge of the computational domain, but are rather attenuated to almost zero, due to the absorbing boundary condition.

Image of FIG. 9.
FIG. 9.

The tissue properties for the example shown in Fig. 10. The sound speed and density of each region were set to: muscle, and , fat, and , marrow, and , and bone, and .

Image of FIG. 10.
FIG. 10.

Propagation of acoustic waves from a small, circular, photoacoustic source, through a heterogeneous medium with tissue-like properties (see Fig. 9). The frames are snapshots of the acoustic field at intervals of following the optical pulse. The boundaries between the regions with different acoustic properties are superimposed, to show how the wave fronts are distorted by the heterogeneities.

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/content/asa/journal/jasa/121/6/10.1121/1.2717409
2007-06-01
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: k-space propagation models for acoustically heterogeneous media: Application to biomedical photoacoustics
http://aip.metastore.ingenta.com/content/asa/journal/jasa/121/6/10.1121/1.2717409
10.1121/1.2717409
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