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The present work determined the band gap energy of PbI₂ equal to 2.31 eV by amplitude measurement of the photoacoustic (PA) signal using the front side detection configuration. Furthermore, the thermal properties were obtained from the phase recording of the PA signal at the characteristic frequency 55 Hz of the single crystal (250 μm). These properties have also been compared with the earlier reported values under identical experimental conditions by amplitude recording of the PA signal on the same PA spectrometer.

Thermoacoustic computed tomography (TACT) is an emerging hybrid imaging method for non-invasive medical diagnosis and fully three-dimensional visualization of biological probes. Within this modality electromagnetic illumination is used to induce acoustic waves inside an object of interest. In this paper, we assume that a cylindrical array of line detectors is used to record the acoustical data. This leads to the mathematical problem of inverting the circular Radon transform.

The circular Radon transform arises in several other up-to-date imaging modalities, such as RADAR imaging or ultrasound tomography. In this paper we prove a novel stable formula for recovering a planar function from its circular Radon transform. We apply this formula to obtain an exact three-dimensional imaging algorithm for TACT. Numerical reconstructions from real and synthetic data demonstrate the potential and robustness of our algorithm.

We applied photoluminescence (PL) and photoacoustic techniques on erbium-doped porous silicon nanostructured (Er-doped-PSN) to study the influences of weight percent (%) of erbium-doped in PSN. Erbium-doped PSN has been intensively studied due their potentiality for optical devices such as waveguide and optical amplifier. Electrochemical technique was used to prepare the PSN samples. Polished p-type [100] c-Si was used as based material. Erbium doping process was carried out by electrodeposition technique using Erbium Chloride (ErCl₃) and ethanol composition as electrolyte. The weight percent of Er concentration is varied to get the optimum effect on PL. The doping process improves PL intensity and changing in peak position. Photoluminescence measurements were performed in the visible light range and excited with the 380 nm line a Xenon (Xe) light source. Photoacoustic (PA) measurements is useful to obtain the optical absorption characteristic for strongly scattering media such as PSN and it helps to confirm the possibility of a strong quantum confinement effect.

Photoacoustic molecular imaging, combined with the reporter-gene technique, can provide a valuable tool for cancer research. The expression of the lacZ reporter gene can be imaged using photoacoustic imaging following the injection of X-gal, a colorimetric assay for the lacZ-encoded enzyme β-galactosidase. Dual-wavelength photoacoustic microscopy was used to non-invasively image the detailed morphology of a lacZ-marked 9L gliosarcoma and its surrounding microvasculature simultaneously in vivo, with a superior resolution on the order of 10 μm. Tumor-feeding vessels were found, and the expression level of lacZ in tumor was estimated. With future development of new absorption-enhancing reporter-gene systems, we anticipate this strategy can lead to a better understanding of the role of tumor metabolism in cancer initiation, progression, and metastasis, and in its response to therapy.

In this paper, we consider the use of blind deconvolution for optoacoustic (photoacoustic) imaging and investigate the performance of the method as means for increasing the resolution of the reconstructed image beyond the physical restrictions of the system. The method is demonstrated with optoacoustic measurement obtained from six-day-old mice, imaged in the near-infrared using a broadband hydrophone in a circular scanning configuration. We find that estimates of the unknown point spread function, achieved by blind deconvolution, improve the resolution and contrast in the images and show promise for enhancing optoacoustic images.

In this paper, a novel photoacoustic viscoelasticity imaging (PAVEI) technique that provides viscoelastic information of biological tissues is presented. We deduced the process of photoacoustic (PA) effect on the basis of thermal viscoelasticity theory and established the relationship between the PA phase delay and the viscoelasticity for soft solids. By detecting the phase delay of PA signal, the viscoelasticity distribution of absorbers can be mapped. Gelatin phantoms with different densities and different absorption coefficients were used to verify the dependence of PAVEI measurements. Moreover, tissue mimicking phantoms mixed with fat and collagen at different concentrations were used to testify the feasibility of this technique with reliable contrast. Finally, the PAVEI was successfully applied to discrimination between biological tissue constituents. Our experimental results demonstrate that this novel technique has the potential for visualizing the anatomical and biomechanical properties of biological tissues.

Here, we report a new method using combined magnetic resonance (MR)–Photoacoustic (PA)–Thermoacoustic (TA) imaging techniques, and demonstrate its unique ability for in vivo cancer detection using tumor-bearing mice. Circular scanning TA and PA imaging systems were used to recover the dielectric and optical property distributions of three colon carcinoma bearing mice While a 7.0-T magnetic resonance imaging (MRI) unit with a mouse body volume coil was utilized for high resolution structural imaging of the same mice. Three plastic tubes filled with soybean sauce were used as fiducial markers for the co-registration of MR, PA and TA images. The resulting fused images provided both enhanced tumor margin and contrast relative to the surrounding normal tissues. In particular, some finger-like protrusions extending into the surrounding tissues were revealed in the MR/TA infused images. These results show that the tissue functional optical and dielectric properties provided by PA and TA images along with the anatomical structure by MRI in one picture make accurate tumor identification easier. This combined MR–PA–TA-imaging strategy has the potential to offer a clinically useful triple-modality tool for accurate cancer detection and for intraoperative surgical navigation.

All-optically integrated photoacoustic (PA) and optical coherence tomography (OCT) dual-mode imaging technology that could offer comprehensive pathological information for accurate diagnosis in clinic has gradually become a promising imaging technology in the aspect of biomedical imaging during the recent years. This review refers to the technology aspects of all-optical PA detection and system evolution of optically integrated PA and OCT, including Michelson interferometer dual-mode imaging system, Fabry–Perot (FP) interferometer dual-mode imaging system and Mach–Zehnder interferometer dual-mode imaging system. It is believed that the optically integrated PA and OCT has great potential applications in biomedical imaging.

Detection and visualization of $\beta$-galactosidase ($\beta$-gal) is essential to reflect its physiological and pathological effects on human health and disease, but it is still challenging to precisely track $\beta$-gal in vivo owing to the limitation of current analytical methods. In our work, we reported a photoacoustic (PA) nanoprobe for selective imaging of the endogenous $\beta$-gal in vivo. Our nanoprobe Cy7-$\beta$-gal-LP was constructed by encapsulation of a near-infra red (NIR) dye Cy7-$\beta$-gal within a liposome (LP, DSPE-PEG2000-COOH). The dye Cy7-$\beta$-gal was synthesized based on a dye Cy-OH where the hydroxyl group was replaced by a $\beta$-D-galactopyranoside residue, which can be recognized by $\beta$-gal as an enzyme hydrolytic site. With the addition of $\beta$-gal, the absorbance of Cy7-$\beta$-gal exhibited a significant red shift with the absorption peak moved from 600nm to 680nm, which should generate a switch-on PA signal at 680nm in the presence of $\beta$-gal. In addition, as the fluorescence of the dye was totally quenched due to aggregation within the liposome, Cy7-$\beta$-gal-LP exhibited high PA conversion efficiency. With the nanoprobe, we achieved the selective PA detection and imaging of $\beta$-gal in the tumor-bearing mice.

Early detection of vulnerable plaques is the critical step in the prevention of acute coronary events. Morphology, composition, and mechanical property of a coronary artery have been demonstrated to be the key characteristics for the identification of vulnerable plaques. Several intravascular multimodal imaging technologies providing co-registered simultaneous images have been developed and applied in clinical studies to improve the characterization of atherosclerosis. In this paper, the authors review the present system and probe designs of representative intravascular multimodal techniques. In addition, the scientific innovations, potential limitations, and future directions of these technologies are also discussed.

Bioprobe based on fluorescence is widely used in biological and medical research due to its high sensitivity and selectivity. Yet, its quantification in vivo is complicated and often compromised by the interaction between the fluorophore with the environmental factors, as well as the optical scattering and absorption by the tissue. A high florescence quantum yield and minimal interference by the environment are key requirements for designing an effective bioprobe, and the pre-requisitions severely limit the available options. We propose that a comprehensive evaluation of potential bioprobe can be achieved by simultaneously measuring both radiative and non-radiative transitions, the two fundamental and complementary pathways for the energy de-excitation. This approach will not only improve the accuracy of the quantification by catching the information from a broader spectrum of the energy, but also provide additional information of the probe environment that often impacts the balance between the two forms of the energy transition. This work first analyzes the underlying mechanism of the hypothesis. The practical feasibility is then tested by means of simultaneous measurements of photoacoustic signal for the non-radiative and fluorescence for the radiative energy processes, respectively. It is demonstrated that the systematic evaluation of the probe energy de-excitation results in an improved quantitative tracing of a bioprobe in complex environment.

Elastography can be used as a diagnostic method for quantitative characterization of tissue hardness information and thus, differential changes in pathophysiological states of tissues. In this study, we propose a new method for shear wave elastography (SWE) based on laser-excited shear wave, called photoacoustic shear wave elastography (PASWE), which combines photoacoustic (PA) technology with ultrafast ultrasound imaging. By using a focused laser to excite shear waves and ultrafast ultrasonic imaging for detection, high-frequency excitation of shear waves and noncontact elastic imaging can be realized. The laser can stimulate the tissue with the light absorption characteristic to produce the thermal expansion, thus producing the shear wave. The frequency of shear wave induced by laser is higher and the frequency band is wider. By tracking the propagation of shear wave, Young’s modulus of tissue is reconstructed in the whole shear wave propagation region to further evaluate the elastic information of tissue. The feasibility of the method is verified by experiments. Compared with the experimental results of supersonic shear imaging (SSI), it is proved that the method can be used for quantitative elastic imaging of the phantoms. In addition, compared with the SSI method, this method can realize the noncontact excitation of the shear wave, and the frequency of the shear wave excited by the laser is higher than that of the acoustic radiation force (ARF), so the spatial resolution is higher. Compared to the traditional PA elastic imaging method, this method can obtain a larger imaging depth under the premise of ensuring the imaging resolution, and it has potential application value in the clinical diagnosis of diseases requiring noncontact quantitative elasticity.

Near-infrared photoacoustic (PA) imaging usually employs near-infrared light-absorbing agents to detect cancer cells/tissue by generating acoustic energy from optical energy. Here, a class of near-infrared dyes, pyrene derivatives with different substitutes, was characterized by PA technology. Interestingly, the click reagents F4-TCNQ could cause the redshift of peaks of the PA intensity of pyrene derivatives. Besides, the symmetric pyrene derivatives had a better PA effect, pyrene accumulation of benzene ring structure also had a certain influence on the PA effect. The systematical study of the near-infrared dyes not only showed the high potential of pyrene derivatives as PA contrast agents but also gave guidelines for designing near-infrared absorbing dyes for high PA intensity in the future.