Skin architecture and its underlying vascular structure could be used to assess the health status of skin. A non-invasive, high resolution and deep imaging modality able to visualize skin subcutaneous layers and vasculature structures could be useful for determining and characterizing skin disease and trauma. In this study, a multispectral high-frequency, linear array-based photoacoustic/ultrasound (PAUS) probe is developed and implemented for the imaging of rat skin in vivo. The study seeks to demonstrate the probe capabilities for visualizing the skin and its underlying structures, and for monitoring changes in skin structure and composition during a 5-day course of a chemical burn. We analayze composition of lipids, water, oxy-hemoglobin, and deoxy-hemoglobin (for determination of oxygen saturation) in the skin tissue. The study successfully demonstrated the high-frequency PAUS imaging probe was able to provide 3D images of the rat skin architecture, underlying vasculature structures, and oxygen saturation, water, lipids and total hemoglobin.

UNASSIGNED: We developed a novel photoacoustic needle, which emits ultrasound produced by the photoacoustic effect. This study focused on the most common \"pitfall\" associated with placement during ultrasound-guided vascular access, which is misidentification of the needle tip.
UNASSIGNED: The study was conducted as a prospective cohort study using a questionnaire. The authors intentionally created two successful and one failed ultrasound-guided central venous catheterization videos using the photoacoustic needle on a simulator. Each of these three videos was then split into two movies for viewing, one with standard ultrasound images only and the second including the images from the photoacoustic needle, for a total of six movies.
UNASSIGNED: Participants who were 18 anesthesiologists, 12 residents, and 10 medical students, watched each of the six movies and completed a survey whether the puncture was successful or not. In the results, there was a significant difference in the percentage of correct answers whether the movie depicted successful or failed puncture with and without the photoacoustic ultrasound (p = 0.0001).
UNASSIGNED: The novel photoacoustic needle improved the ability to identify the needle tip on recorded videos. It may have efficacy to prevent serious mechanical complication during the ultrasound-guided vascular access in clinical practice.

BACKGROUND: Chronic kidney disease (CKD) is a global burden affecting both children and adults. Novel imaging modalities hold great promise to visualize and quantify structural, functional, and molecular organ damage. The aim of the study was to visualize and quantify murine renal vasculature using label-free raster scanning optoacoustic mesoscopy (RSOM) in explanted organs from mice with renal injury.
METHODS: For the experiments, freshly bisected kidneys of alpha 8 integrin knock-out (KO) and wildtype mice (WT) were used. A total of n=7 female (n=4 KO, n=3 WT) and n=6 male animals (n=2 KO, n=4 WT) aged 6 weeks were examined with RSOM optoacoustic imaging systems (RSOM Explorer P50 at SWL 532nm and/or ms-P50 imaging system at 532 nm, 555 nm, 579 nm, and 606 nm). Images were reconstructed using a dedicated software, analyzed for size and vascular area and compared to standard histologic sections.
RESULTS: RSOM enabled mapping of murine kidney size and vascular area, revealing differences between kidney sizes of male (m) and female (f) mice (merged frequencies (MF) f vs. m: 52.42±6.24 mm2 vs. 69.18±15.96 mm2, p=0.0156) and absolute vascular area (MF f vs. m: 35.67±4.22 mm2 vs. 49.07±13.48 mm2, p=0.0036). Without respect to sex, the absolute kidney area was found to be smaller in knock-out (KO) than in wildtype (WT) mice (WT vs. KO: MF: p=0.0255) and showed a similar trend for the relative vessel area (WT vs. KO: MF p=0.0031). Also the absolute vessel areas of KO compared to WT were found significantly different (MF p=0.0089). A significant decrease in absolute vessel area was found in KO compared to WT male mice (MF WT vs. KO: 54.37±9.35 mm2 vs. 34.93±13.82 mm2, p=0.0232). In addition, multispectral RSOM allowed visualization of oxygenated and deoxygenated parenchymal regions by spectral unmixing.
CONCLUSIONS: This study demonstrates the capability of RSOM for label-free visualization of differences in vascular morphology in ex vivo murine renal tissue at high resolution. Due to its scalability optoacoustic imaging provides an emerging modality with potential for further preclinical and clinical imaging applications.

Endovenous laser ablation (EVLA) is a minimally invasive surgical procedure, often guided by ultrasound (US) imaging, for treating venous insufficiencies. US imaging limitations in accurately visualizing the catheter and the lack of a temperature monitoring system can lead to sub-optimal outcomes. An integrated photoacoustic (PA)-guided EVLA system has been previously developed and reported to overcome the shortcomings of US-guided procedure. In this study, we further characterized the system and tested the in vivo utility. In addition, PA thermometry was further explored by compensating the variation of PA signal with temperature with respect to the temperature-dependent absorption of blood and water. In vivo imaging results indicated that the PA-guided EVLA system can provide high contrast and accurate images of the ablation catheter tip overlaid on US images of the background tissue. Additionally, absorption-compensated PA signal amplitudes over a relevant range of temperature were measured and demonstrated.

Although transcranial photoacoustic imaging (TCPAI) has been used in small animal brain imaging, in animals with thicker skull bones or in humans both light illumination and ultrasound propagation paths are affected. Hence, the PA image is largely degraded and in some cases completely distorted. This study aims to investigate and determine the maximum thickness of the skull through which photoacoustic imaging is feasible in terms of retaining the imaging target structure without incorporating any post processing. We identify the effect of the skull on both the illumination path and acoustic propagation path separately and combined. In the experimental phase, the distorting effect of ex vivo sheep skull bones with thicknesses in the range of 0.7~1.3 mm are explored. We believe that the findings in this study facilitate the clinical translation of TCPAI.

Insects can provide clues in a variety of ways to assist in criminal investigations. The FTIR-PAS technique has been successfully used to assess the cuticular chemical profiles of insect samples from different groups and for several goals. However, until now, it has never been used to evaluate samples of forensic interest, despite providing faster results, compared to the methods currently used. In this study, mid-infrared photoacoustic spectroscopy was employed to assess the cuticular chemical profiles of different stages of development of the blow fly Chrysomya megacephala sampled from two distinct populations. The results showed that this technique enabled detection of significant differences between the main vibrational modes of the chemical bonds present in the cuticles of the two populations and the different stages of development of the fly. The method enables identification of the age of individuals collected at the crime scene, as well as the distinction of different populations. Therefore, this methodology could assist in forensic investigations, in both estimating the Postmortem Interval and determining the location where the crime occurred, or whether the body had suffered some type of translocation. The technique provides high reproducibility and fast analysis, so its application for analysis of C. megacephala is a viable option in forensic crime investigations.

Objective/Purpose: In order to study the effects of hyperthermia and other temperature-related effects on cells and tissues, determining the precise time/temperature course is crucial. Here we present a non-contact optoacoustic technique, which provides temperatures during heating of cultured cells with scalable temporal and spatial resolution.
A thulium laser (1.94 µm) with a maximum power of 15 W quickly and efficiently heats cells in a culture dish because of low penetration depth (1/e penetration depths of 78 µm) of the radiation in water. A repetitively Q-switched holmium laser (2.1 µm) is used simultaneously to probe temperatures at different locations in the dish by using the photoacoustic effect. Due to thermoelastic expansion of water, pressure waves are emitted and measured with an ultrasonic hydrophone at the side of the dish. The amplitudes of the waves are temperature dependent and can be used to calculate the temperature/time course at any location of probing.
We measured temperatures of up to 55 °C with a heating power of 6 W after 10 s, and subsequent lateral temperature profiles over time. Within this profile, temperature fluctuations were found, likely owing to thermal convection and water circulation. By using cultured retinal pigment epithelial cells, it is shown that the probe laser pulses alone cause no biological damage, while immediate cell damage occurs when heating for 10 s at temperatures exceeding 45 °C.
This method shows great potential not only as a noninvasive, non-contact method to determine temperature/time responses of cells in culture, but also for complex tissue and other materials.

The paper reports the potential use of UV based pulsed photoacoustic spectroscopy to study the thermal stability of some well-known premier explosives such as TNT, RDX, CL20, and ANTA between 30 and 350 °C range. The thermal PA spectra of samples were recorded using fourth harmonic wavelength i.e. 266 nm of pulse duration 7 ns and repetition rate 10 Hz obtained from Q-switched Nd: YAG laser system. Under the influence of UV radiation, the explosive molecules in vapor phase follow the photodissociation process and converted into their byproducts such as NO, NO2 and N2O etc. due to π* ← n transitions, which are responsible for the generation resultant PA signal at 266 nm wavelength. The results obtained from PA spectra as a function of temperature are cross verified with Thermo gravimetric-differential thermal analysis (TG-DTA) to ascertain the thermal stability of these samples. The comparative PA spectra of samples were analyzed and shown the behavior of acoustic modes with respect to incident laser energy, and data acquisition time. Finally, the thermal quality factor \"Q\" is measured to test the stability of reported explosives.

High-frequency ultrasound imaging can provide exquisite visualizations of tissue to guide minimally invasive procedures. Here, we demonstrate that an all-optical ultrasound transducer, through which light guided by optical fibers is used to generate and receive ultrasound, is suitable for real-time invasive medical imaging in vivo. Broad-bandwidth ultrasound generation was achieved through the photoacoustic excitation of a multiwalled carbon nanotube-polydimethylsiloxane composite coating on the distal end of a 300-μm multi-mode optical fiber by a pulsed laser. The interrogation of a high-finesse Fabry-Pérot cavity on a single-mode optical fiber by a wavelength-tunable continuous-wave laser was applied for ultrasound reception. This transducer was integrated within a custom inner transseptal needle (diameter 1.08 mm; length 78 cm) that included a metallic septum to acoustically isolate the two optical fibers. The use of this needle within the beating heart of a pig provided unprecedented real-time views (50 Hz scan rate) of cardiac tissue (depth: 2.5 cm; axial resolution: 64 μm) and revealed the critical anatomical structures required to safely perform a transseptal crossing: the right and left atrial walls, the right atrial appendage, and the limbus fossae ovalis. This new paradigm will allow ultrasound imaging to be integrated into a broad range of minimally invasive devices in different clinical contexts.

Photoacoustic (PA) and thermoacoustic (TA) effects have been explored in many applications, such as bio-imaging, laser-induced ultrasound generator, and sensitive electromagnetic (EM) wave film sensor. In this paper, we propose a compact analytical PA/TA generation model to incorporate EM, thermal and mechanical parameters, etc. From the derived analytical model, both intuitive predictions and quantitative simulations are performed. It shows that beyond the EM absorption improvement, there are many other physical parameters that deserve careful consideration when designing contrast agents or film composites, followed by simulation study. Lastly, several sets of experimental results are presented to prove the feasibility of the proposed analytical model. Overall, the proposed compact model could work as a clear guidance and predication for improved PA/TA contrast agents and film generator/sensor designs in the domain area.