Measurement of Grüneisen parameter of tissue by photoacoustic spectrometry

The Grüneisen parameter of tissue is a constitutive parameter in photoacoustic tomography. Here, we applied photoacoustic spectrometry (PAS) to directly measure the Grüneisen parameter. In our PAS system, laser pulses at wavelengths between 460 and 1600 nm were delivered to tissue samples, and photoacoustic signals were detected by a 20 MHz flat water-immersion ultrasonic transducer. By fitting photoacoustic spectra to light absorption spectra, we found that the Grüneisen parameter was 0.73 for porcine subcutaneous fat tissue, and 0.15 for oxygenated bovine red blood cells at room temperature (24°C)

Photoacoustic measurement of the Grüneisen parameter of tissue

The Grüneisen parameter, a constitutive parameter in photoacoustics, is usually measured from isobaric thermal expansion, which may not be valid for a biological medium due to its heterogeneity. Here, we directly measured the Grüneisen parameter by applying photoacoustic spectroscopy. Laser pulses at wavelengths between 460 and 1800 nm were delivered to tissue samples, and photoacoustic signals were detected by flat water-immersion ultrasonic transducers. Least-squares fitting photoacoustic spectra to molar optical absorption spectra showed that the Grüneisen parameter was 0.81±0.05 (mean±SD) for porcine subcutaneous fat tissue and 0.69±0.02 for porcine lipid at room temperature (22°C). The Grüneisen parameter of a red blood cell suspension was linearly related to hemoglobin concentration, and the parameter of bovine serum was 9% greater than that of water at room temperature

Quantitative imaging of bilirubin by photoacoustic microscopy

Noninvasive detection of both bilirubin concentration and its distribution is important for disease diagnosis. Here we implemented photoacoustic microscopy (PAM) to detect bilirubin distribution. We first demonstrate that our PAM system can measure the absorption spectra of bilirubin and blood. We also image bilirubin distributions in tissue-mimicking samples, both without and with blood mixed. Our results show that PAM has the potential to quantitatively image bilirubin in vivo for clinical applications

In vivo imaging of cell nuclei by photoacoustic microscopy without staining

Ultraviolet photoacoustic microscopy (UVPAM) can image cell nuclei in vivo with high contrast and resolution noninvasively without staining. Here, we used UV light at wavelengths of 210-310 nm for excitation of DNA and RNA to produce photoacoustic waves. We applied the UVPAM to in vivo imaging of cell nuclei in mouse skin, and obtained UVPAM images of the unstained cell nuclei at wavelengths of 245-282 nm as ultrasound gel was used for acoustic coupling. The largest ratio of contrast to noise was found for the images of cell nuclei at a 250 nm wavelength

Optimal ultraviolet wavelength for in vivo photoacoustic imaging of cell nuclei

In order to image noninvasively cell nuclei in vivo without staining, we have developed ultraviolet photoacoustic microscopy (UV-PAM), in which ultraviolet light excites nucleic acids in cell nuclei to produce photoacoustic waves. Equipped with a tunable laser system, the UV-PAM was applied to in vivo imaging of cell nuclei in small animals. We found that 250 nm was the optimal wavelength for in vivo photoacoustic imaging of cell nuclei. The optimal wavelength enables UV-PAM to image cell nuclei using as little as 2 nJ laser pulse energy. Besides the optimal wavelength, application of a wavelength between 245 and 275 nm can produce in vivo images of cell nuclei with specific, positive, and high optical contrast

Label-free photoacoustic microscopy of cytochrome c in cells

Cytochrome c is a heme protein normally bound to mitochondria and is important for mitochondrial electron transport and apoptosis initiation. Since cytochrome c is nonfluorescent, it is always labeled with fluorescent molecules for imaging, which, however, may affect normal cellular functions. Here, label-free photoacoustic microscopy (PAM) of mitochondrial cytochrome c was realized for the first time by utilizing the optical absorption around the Soret peak. PAM was demonstrated to be sensitive enough to image mitochondrial cytochrome c at 422 nm wavelength. Mitochondrial cytochrome c in the cytoplasm of fixed fibroblasts was clearly imaged by PAM as confirmed by fluorescent labeling. By showing mitochondrial cytochrome c in various cells, we demonstrated the feasibility of PAM for label-free histology of mouse ear sections. Therefore, PAM can sensitively image cytochrome c in unstained cells at 422 nm wavelength and has great potential for functional imaging of cytochrome c in live cells or in vivo

5-Methyl-1,2,3,3a-tetra­hydro­benzo[e]pyrrolo­[2,1-b][1,3]oxazepin-10(5H)-one

The asymmetric unit of the title compound, C13H15NO2, the main product of a photoreaction, contains two crystallographically independent mol­ecules. In both mol­ecules, the conformation of the seven-membered ring is twist sofa and that of the five-membered rings is envelope. In the crystal, mol­ecules are linked by weak inter­molecular C—H⋯O hydrogen bonds

Measurement of Grüneisen parameter of tissue by photoacoustic spectrometry

The Grüneisen parameter of tissue is a constitutive parameter in photoacoustic tomography. Here, we applied photoacoustic spectrometry (PAS) to directly measure the Grüneisen parameter. In our PAS system, laser pulses at wavelengths between 460 and 1600 nm were delivered to tissue samples, and photoacoustic signals were detected by a 20 MHz flat water-immersion ultrasonic transducer. By fitting photoacoustic spectra to light absorption spectra, we found that the Grüneisen parameter was 0.73 for porcine subcutaneous fat tissue, and 0.15 for oxygenated bovine red blood cells at room temperature (24°C)

Photoacoustic microscopy of myocardial sheet architecture in unfixed and unstained mammalian hearts

The laminar myocardial sheet architecture and its dynamic change play a key role in myocardial wall thickening. Histology, confocal optical microscopy (COM), and diffusion tensor MRI (DTI) have been used to unveil the structures and functions of the myocardial sheets. However, histology and COM require fixation, sectioning, and staining processes, which dehydrate and deform the sheet architecture. Although DTI can delineate sheet architecture nondestructively in viable hearts, it cannot provide cellular-level resolution. Here we show that photoacoustic microscopy (PAM), with high resolution (~1 μm) and label-free detection, is appropriate for imaging 3D myocardial architecture. Perfused half-split mouse hearts were also imaged by PAM in vitro without fixation, dehydration, nor staining. The laminar myocardial sheet architecture was clearly visualized within a 0.15 mm depth range. Two populations of oppositely signed sheet angles were observed. Therefore, PAM promises to access dynamic changes of myocardial architectures in ex vivo perfused-viable hearts