Calibration-free absolute quantification of particle concentration by statistical analyses of photoacoustic signals in vivo
ABSTRACT Currently, laser fluence calibration is typically required for quantitative measurement of particle concentration in photoacoustic imaging. Here, we present a calibration-free method to quantify the absolute particle concentration by statistically analyzing photoacoustic signals. The proposed method is based on the fact that Brownian motion induces particle count fluctuation in the detection volume. If the count of particles in the detection volume is assumed to follow the Poisson distribution, its expected value can be calculated by the photoacoustic signal mean and variance. We first derived a theoretical model for photoacoustic signals. Then, we applied our method to quantitative measurement of different concentrations of various particles, including red blood cells. Finally, we performed in vivo experiments to demonstrate the potential of our method in biological applications. The experimental results agreed well with the predictions from the theoretical model suggesting that our method can be used for noninvasive measurement of absolute particle concentrations in deep tissue without fluence calibration.
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ABSTRACT: We developed handheld photoacoustic microscopy (PAM) to detect melanoma and determine tumor depth in nude mice in vivo. Compared to our previous PAM system for melanoma imaging, a new light delivery mechanism is introduced to improve light penetration. We show that melanomas with 4.1 and 3.7 mm thicknesses can be successfully detected in phantom and in in vivo experiments, respectively. With its deep melanoma imaging ability and handheld design, this system can be tested for clinical melanoma diagnosis, prognosis, and surgical planning for patients at the bedside.Optics Letters 08/2014; 39(16). DOI:10.1364/OL.39.004731 · 3.18 Impact Factor
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ABSTRACT: Photoacoustic tomography (PAT) is a hybrid imaging modality that takes advantage of high optical contrast brought by optical imaging and high spatial resolution brought by ultrasound imaging. However, the quantification in photoacoustic imaging is challenging. Multiple optical illumination approach has proven to achieve uncoupling of diffusion and absorption effects. In this paper, this protocol is adopted and synthetic photoacoustic data, blurred with some noise, were generated. The influence of the distribution of optical sources and transducers on the reconstruction of the absorption and diffusion coefficients maps is studied. Specific situations with limited view angles were examined. The results show multiple illuminations with a wide field improve the reconstructions.Biomedical Optics Express 11/2014; 5(11). DOI:10.1364/BOE.5.003960 · 3.50 Impact Factor
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ABSTRACT: We applied a linear-array-based photoacoustic probe to detect melanin-containing melanoma tumor depth and volume in nude mice in vivo. This system can image melanomas at five frames per second (fps), which is much faster than our previous handheld single transducer system (0.1 fps). We first theoretically show that, in addition to the higher frame rate, almost the entire boundary of the melanoma can be detected by the linear-array-based probe, while only the horizontal boundary could be detected by the previous system. Then we demonstrate the ability of this linear-array-based system in measuring both the depth and volume of melanoma through phantom, ex vivo, and in vivo experiments. The volume detection ability also enables us to accurately calculate the rate of growth of the tumor, which is an important parameter in quantifying the tumor activity. Our results show that this system can be used for clinical melanoma diagnosis and treatment in humans at the bedside. Linear-array-based PA images of melanoma acquired in vivo on day 3 (a) and day 6 (b). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Journal of Biophotonics 03/2015; 9999(9999). DOI:10.1002/jbio.201400143 · 3.86 Impact Factor