Oxygen Measurement
Lara Wijayasiri, Kate McCombe, Paul Hatton, David Bogod in The Primary FRCA Structured Oral Examination Study Guide 1, 2017
Photoacoustic spectroscopy: Based on the photoacoustic effect, which was discovered by Alexander Graham Bell in his search for a means of wireless communication.Photoacoustic effect is the conversion between light and sound waves.Materials exposed to non-visible portions of the light spectrum (i.e. infrared and ultraviolet light) can produce acoustic waves.By measuring the sound at different wavelengths, a photoacoustic spectrum of a gas sample can be recorded and used to identify the components within that sample.This effect can be used to study solids, liquids and gases.
Photoacoustic Neuroimaging
Yu Chen, Babak Kateb in Neurophotonics and Brain Mapping, 2017
The photoacoustic effect, first discovered by Alexander Bell in 1880 (Bell 1880), refers to the formation of sound waves following light absorption in an object. The conversion of optical energy to acoustic energy allows visualization of deep tissue optical absorption with acoustically defined spatial resolution. Starting in the 1990s, with the advent of short-pulsed lasers and high-sensitivity ultrasound transducers, the photoacoustic effect began to be utilized for biomedical imaging (Kruger 1994, Karabutov et al. 1996, Oraevsky et al. 1997, Wang et al. 2002). In 2003, Wang et al. (2003a,b) reported the first functional photoacoustic tomography (PAT), which imaged hemodynamic response noninvasively in the rat brain. Since then, the field has been growing rapidly, and PAT is now becoming an important neuroimaging modality (Wang 2009, Hu and Wang 2010, Wang and Hu 2012, Xia and Wang 2013).
Facilitated coronary interventions: Adjuncts to balloon dilatation
John Edward Boland, David W. M. Muller in Interventional Cardiology and Cardiac Catheterisation, 2019
Devices designed to deliver laser energy to a catheter tip are largely of historical interest. The systems were expensive, cumbersome and of doubtful efficacy. Laser energy is typically generated by stimulation of a liquid, solid or gaseous medium. This results in excitation of atoms and subsequent release of photons with specific wavelengths ranging from approximately 300 nm to >10,000 nm. The characteristics of the electromagnetic energy generated by these devices depend on its wavelength, pulse repetition rate, and duration of the pulse (pulse width). Excimer lasers produce energy from a gaseous medium (xenon-chlorine) with a wavelength of 308 nm, have a relatively small penetration depth (30–50 µm), and produce little thermal injury. The dominant mechanism of action is via the formation of a vapour bubble that implodes, generating a photoacoustic effect on surrounding tissues. Solid-state lasers in the mid-infrared range, such as the holmium:YAG laser, have a higher ablation threshold and penetration depth than excimer lasers.
Treatment of gingival pigmentation with a 755-nm alexandrite picosecond laser
Published in Journal of Cosmetic and Laser Therapy, 2020
Cristina Pindado-Ortega, Adrián Alegre-Sánchez, Aitana Robledo-Sánchez, Ignacio Tormo-Alfaro, Pablo Boixeda
The use of picoseconds lasers to treat pigmented disorders has become popular in recent years. These lasers were initially developed with the aim of removal tattoo inks (4), but they have proved great efficacy in different pigmentary disorders (3,5). There are different picosecond lasers with different wavelengths. In our study, we used an alexandrite 755-nm picosecond laser which is optimal for the treatment of dark (black, brown) targets based on the principle of selective photothermolysis but also in a photoacoustic effect that pulverizes the pigment (3,5). The use of 755-nm alexandrite picoseconds laser to treat skin pigmented disorders was described in 2018 by Alegre et al. (3) with clearance rates of 61% for pigmentary flat disorders and 67% for elevated lesions. Histologic examination comparing before and after alexandrite picoseconds treatment of a purpuric pigmented dermatosis showed a reduction of the hemosiderin deposits that were present before treatment (3).
A randomized, single-blind, study evaluating a 755-nm picosecond pulsed Alexandrite laser vs. a non-ablative 1927-nm fractionated thulium laser for the treatment of facial photopigmentation and aging
Published in Journal of Cosmetic and Laser Therapy, 2018
Monica Serra, Krista Bohnert, Neil Sadick
While the number of subjects was limited, and the 755 nm group received double the amount of treatments compared to the 1927 nm group, the data indicate that the new generation picosecond lasers can effectively target and treat photopigmentation and signs of aging, with minimal downtime. As picosecond laser energy results in a combined photothermal/photoacoustic effect to the tissue, the overall thermal damage to the tissue is reduced, accounting for less side effects. At the same time the energy absorption is great enough to stimulate pigment degradation and stimulation of neocollagenesis, which leads to its clinical effects (17).
Recent advances in ultrasound-triggered therapy
Published in Journal of Drug Targeting, 2019
Chaopin Yang, Yue Li, Meng Du, Zhiyi Chen
Photoacoustic imaging (PAI), a novel imaging modality based on photoacoustic effect, also shows great promise in biomedical applications. By converting pulsed laser excitation into ultrasonic emission, PAI combines the advantages of optical imaging and ultrasound imaging, which benefits rich contrast, high resolution and deep tissue penetration [132].
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