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Emerging Biomedical Imaging
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
In this session, the physics of the signal generation will be explained through several condensed mathematical equations based on recent publications (Xia et al. 2014, Kim et al. 2015, Zhou et al. 2016). More detailed explanation of this principle is available through a recently published textbook (Wang 2017). According to experts of the field of photoacoustic imaging, the signal generation involves three sequential steps. First, the object receives and absorbs an intense light (and the accompanied optical energy). Next, the absorbed optical energy is then converted into heat, leading to a temperature increase. Lastly, the thermoelastic expansion as a result of temperature rise leads to a pressure rise. And this change of pressure then propagates to an emission of acoustic waves (Xia et al. 2014, Zhou et al. 2016). Since the generation of acoustic wave requires that the thermoelastic expansion to be in a “time variant” form, i.e., it changes with time, the most common light energy source nowadays is the pulsed laser, which fulfills the time variant requirement. Other light sources include continuous-wave laser with intensity modulation at a constant or variable frequency. Pulsed laser is preferred since it has a higher signal to noise ratio if maximum allowable fluence or power set by the American National Standards Institute is used (Xia et al. 2014).
Lasers in Photomedicine
Published in Henry W. Lim, Nicholas A. Soter, Clinical Photomedicine, 2018
Roy G. Geronemus, Robin Ashinoff
The dye utilized in the dye laser is an alcohol in a fluorescent base that can be excited by a flashlamp or an argon laser. The argon-pumped dye laser is a continuous-wave laser that does not produce optimal vascular damage. However, some clinicians have found that by using a very small spot size and low energy, one can achieve good clinical results in treating port wine stains with the argon-pumped tunable dye laser (27).
Laser Principles in Otolaryngology, Head and Neck Surgery
Published in John C Watkinson, Raymond W Clarke, Louise Jayne Clark, Adam J Donne, R James A England, Hisham M Mehanna, Gerald William McGarry, Sean Carrie, Basic Sciences Endocrine Surgery Rhinology, 2018
The configuration of the resonator cavity and the method in which an energy source is applied to the ‘active laser medium’ will determine the pattern of a laser output. The output may be continuous wave or pulsed. A continuous wave laser operates with a constant intensity. A laser that operates with a continuous output for longer than 0.1 seconds is considered a continuous wave laser. A pulsed laser produces a single or train of pulses with each individual pulse less than 0.1 seconds. A Q-switch is an electro-optical component that facilitates the production of a very short (less than 1 microsecond) but high intensity pulse of laser energy.
Hysteroscopy Combined with Laser Vaporesection for Endometrial Polyps
Published in Journal of Investigative Surgery, 2022
Hongyan Ren, Hua Duan, Sha Wang, Yanan Chang
2 μm laser is a kind of high energy laser. The maximum absorption peak of water on the laser is 1.94 μm, which can be absorbed by the human tissue water efficiently. And it can also achieve high tissue ablation rate. Moreover, the operation effect is not dependent on the color of vascularization or organization change [26]. It has the advantage of continuous wave laser beam [27]. In clinical application, it can achieve efficient tissue vaporization by moving the laser fiber quickly and tangentially to the tissue surface. The thermal damage to the tissue during tissue cutting is relatively superficial, so as to reduce the occurrence of intraoperative bleeding. Due to the shallow penetration of laser to tissue, the coagulation zone had almost no effect on specimen pathology [28]. However, in electrosurgical operation, high-frequency electric heating can be used to cut the tissue. And the temperature is high, and it is easy to produce scab on the section surface of the tissue. After the eschar falls off, it usually causes bleeding.
A three-dimensional transient computational study of 532-nm laser thermal ablation in a geometrical model representing prostate tissue
Published in International Journal of Hyperthermia, 2018
Hossam Elkhalil, Aiman Alshare, Gal Shafirstein, John Bischof
The one-dimensional steady-state analytical model developed by Venugopalan et al. (see Table 1) was chosen [20]. The tissue was assumed a one-dimensional pure absorbing medium with a length of 10 mm and an absorption coefficient (µa) of 1 mm−1. The thermo-physical tissue properties summarized in Table 2 were used. Thermal ablation simulation was induced by continuous wave laser with laser irradiance of 100 W/mm2. Spatial grid size (Δx) was refined until discretization error became negligible. Temporal grid size (Δt) was refined in compliance with the stability condition of the employed explicit numerical scheme. Another condition imposed while refining Δt was that the accumulated energy within a control volume during the time step should not exceed the heat of ablation threshold. Adiabatic boundary conditions were imposed. The simulation was stopped when ∼70% of the tissue was ablated. The comparison with the analytical solution was carried out in terms of steady-state temperature profile and tissue front position, whose rate of change is the ablation velocity.
Intravitreal chemotherapy and laser for newly visible subretinal seeds in retinoblastoma
Published in Ophthalmic Genetics, 2018
David H. Abramson, Federica Catalanotti, Scott E. Brodie, Michael G. Kellick, Jasmine H. Francis
Single center, Institutional Review Board (IRB) approved retrospective series of patients with “new” SRS (newly seen SRS that were not previously noted in an eye that received OAC) managed with combined intravitreal chemotherapy (melphalan 30 ug or melphalan 30 ug plus topotecan 20 ug) and 810 nm indirect laser (continuous wave). Filtered melphalan (30 ug/0.07 mL) was injected 3 mm from the limbus in an area devoid of active seeding after lowering intraocular pressure with digital massage and ultrasonic biomicroscopic exam, done prior to lowering the pressure, showed no tumor in the needle path. Before removing the needle, cryotherapy was applied to seal and sterilize the needle site. Indirect 810 nm laser was done (usually at the same session just before the intravitreal injection) with a 20-diopter lens on continuous wave laser and titrated till visible burns were evident.