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Principle of microstructure evaluation. (a) Geometry for analysis of PA imaging. (b) Power spectra of PA signal from microspheres with diameters of 50 μm and 200 μm, respectively. (c) Relationship between the spectral slope and the diameter of spherical absorbers, where the solid and dashed lines correspond to the calibration objects with an infinite small diameter and 200 μm diameter, respectively.
Procedure of photoacoustic tomography using the spectrum parameter. (a) Schematic diagram of the imaging system. (b) The detected PA field. (c)The PA signal recorded by the 90th detector. The inset is the PA signal from the calibration object. (d) Power spectra of PA signals during 20.82–22.48 μs, where the three solid lines from bottom to top correspond to the calibration object and the sample with 49 μm microspheres before/after calibration. The dotted lines from bottom to top represent the power spectra of the sample with 199 μm microspheres before/after calibration. The dashed line is the best linear fit of the calibrated power spectra within the window 1-5 MHz (gray region). (e) Spectral slope series of the PA signal in (c).
Comparison of spectral parameter images and B-mode PAT images, where (a-b) are B-mode PAT images and (c-d) are spectral parameter images. The left and right columns correspond to the samples with 49 μm and 199 μm microspheres, respectively.
Statistical discrepancy of spectral parameter between two artificial tumors at various working frequency, where the five horizontal lines of the box chart are determined by the 5th, 25th, 50th, 75th, and 95th percentiles, respectively. The circles represent the mean value. The usable bandwidth is 4 MHz and the axis represents the central frequency of the usable band.
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