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Photoacoustic Doppler Effect and Flow Sensing
Published in Lihong V. Wang, Photoacoustic Imaging and Spectroscopy, 2017
The photoacoustic effect and Doppler effect involve two independent physical principles. The photoacoustic effect, the process of energy transformation from intensity-modulated optical radiation to acoustic waves, was first described in 1880 by Bell in his photophone research [1]. The Doppler effect, frequency shift of a wave when the wave source is moving with respect to an observer, was discovered in 1840 by Doppler while he was analyzing the colored light of stars [2]. The photoacoustic Doppler (PAD) effect is the combination of these two effects. By means of the photoacoustic effect, an acoustic wave is produced from a light-absorbing medium. From the Doppler effect, the acoustic wave undergoes a Doppler shift when the photoacoustic source, the part of the light-absorbing medium generating the acoustic wave at a given moment, has motion relative to a detector. While both the photoacoustic effect and Doppler effect are well understood, the combined photoacoustic Doppler effect and its applications have not been studied extensively.
Elastic Constants of Wood Material
Published in Voichita Bucur, Acoustics of Wood, 2017
Photoacoustics (optoacoustics) was developed as the result of the effect observed when a modulated light beam was focused on the surface of an absorbing solid, which produced a local temperature modulation. In Figure 5.13 illustrates this effect. The light beam intensity modulated at the frequency (ú)) produces a temperature modulation, AT, on the solid. The temperature of the air adjacent to the solid also changes, and a pressure modulation is achieved. This pressure modulation can be detected with a microphone as a sound at the modulation frequency a). This is the photoacoustic effect associated with three fundamental processes: the absorption of the incident energy, the generation and propagation of thermal waves, and the generation and propagation of acoustic waves. The intensity of the detected sound depends on optical input power, the modulation frequency, and the thermal and acoustical properties of the specimen. The success of the technique is related also to the efficiency of the “photoacoustic cell”; containing the microphone and the sample.
Nanomaterial-Antibody Hybrids
Published in Feng Chen, Weibo Cai, Hybrid Nanomaterials, 2017
Jyothi U. Menon, Lei Song, Nadia Falzone, Katherine A. Vallis
GNP-antibody hybrids have been applied to other detection techniques such as photoacoustic imaging (Agarwal et al. 2007; Joshi et al. 2013) and surfaceenhanced Raman spectroscopy (SERS) and imaging (Lee et al. 2009; Qian et al. 2008). Photoacoustic imaging is a non-invasive technique based on the photoacoustic effect, a process of converting absorbed light into acoustic waves that can be recorded by ultrasonic transducers to form images with high resolution. GNPs can absorb light very efficiently due to SPR and the resonance wavelength can also be tuned to the range of 700-900 nm (tissue transparent window) to maximize light penetration depth in tissues. Thus, GNP-antibody hybrids are good candidates for targeting cancer cells for high contrast photoacoustic imaging. GNPs can significantly amplify the SERS efficiency of Raman reporters by 14-15 orders of magnitude. Qian and others have exploited this property, demonstrating that small Raman reporter molecules (e.g., malachite green) can be incorporated into and stabilized by GNP-ScFv B10 antibody hybrids for in vivo tumor detection by SERS (Qian et al. 2008). Furthermore, GNP-antibody hybrids have been applied to PET and SPECT by incorporating radioactive isotopes such as Zr89 and In111 (Kao et al. 2013; Karmani et al. 2014), to fluorescence imaging by exploiting the native fluorescence from GNPs (He et al. 2008) and to two-photon luminescence imaging by taking advantage of the highly efficient two-photon-induced luminescence by GNPs (Durr et al. 2007; Zhang et al. 2013).
Performance of near-infrared dyes as effective contrast agents for breast cancer detection through simulation of photoacoustic imaging
Published in Journal of Modern Optics, 2020
A. Prabhakara Rao, Saugata Sinha
Photoacoustic Imaging is based on the principle of the photoacoustic effect. In the PA effect, light absorbing fluid elements absorb nanosecond duration laser pulses and convert the absorbed light energy into heat energy which produces pressure increments. These pressure increments are released in the form of high frequency U.S. waves, which are also known as PA waves [12]. These PA waves are recorded using a single element or multi element U.S. transducer. Finally, the greyscale PA images, which provide the PA signal amplitudes at different locations inside the tissue, are reconstructed using the time dependent PA signal values captured by the U.S. transducer elements. In this study, a comprehensive model that had three primary aspects was used to simulate the PA images of the human breast. The first part of the model was required to accurately propagate the pulsed laser light through multi-layered human breast tissue to provide an accurate distribution of light fluence inside the breast tissue. The initial pressure increment, generated at different locations inside the breast tissue was found using light fluence, optical absorption coefficient and Grüneisen coefficient of the tissue. Considering the spatially varying initial pressure increment as the source, the second part of the model was used to accurately propagate the PA waves through the tissue and find out the time dependent PA signal values recorded by each element of the U.S. transducer array. Finally, the third part of the model reconstructed the initial pressure distribution from the data acquired by the U.S. transducer array.
Photoacoustic analysis and imaging techniques: Sound of light
Published in Particulate Science and Technology, 2018
The photoacoustic effect is actually a conversion between light and acoustic waves generated by local thermal expansion as a result of the absorption of light. Serial light pulses falling on a substance sample is absorbed by this substance (Figure 3).