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Physics of Ultrasound
Published in Marvin C. Ziskin, Peter A. Lewin, Ultrasonic Exposimetry, 2020
The variations in density in a medium supporting an ultrasonic wave produce corresponding changes in optical refractive index if the medium is transparent. This phenomenon forms the basis of several methods for detecting ultrasonic waves. In the schlieren method, a beam of light is arranged to pass through a transparent medium (usually water) in which is established the ultrasonic field to be investigated.114 The light is then focused onto an obstruction, so that none reaches the observer (or TV camera) when the field is zero. When ultrasound changes the refractive index of the medium, the light that passes through the disturbed areas no longer necessarily passes through the occluded focal spot; that which is deviated produces a corresponding variation in brightness in the image. Thus, the “ultrasonic beam” becomes visible against the dark background. Moreover, pulsing the light synchronously with the ultrasonic pulse generator results in stroboscopic visualization, and an indication of the beam profile can be obtained by displaying the amplitude-time waveform of an appropriately selected transverse TV line.
Pediatric vitreoretinal surgery
Published in A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha, Vitreoretinal Surgical Techniques, 2019
TRD in ROP may exhibit a complex configuration (Figs 53.3–53.6). It is important to keep in mind the four main tractional vectors: ridge-to-lens, ridge–disc/posterior pole/ stalk, ridge-to-ridge (drum configuration), and ridge-to-eye-wall. Following the principles outlined above, the surgeon should address each of these vectors in a sequential fashion, except as detailed below. If a narrow peripheral trough exists between the TRD and the eyewall (Fig. 53.5), the traction between the ridge–disc/posterior pole/stalk should be released last, in order to allow the trough to open at the end of the case. The vector release is created by engaging vitreous with a pick or forceps, lifting it away from the retina, and then using the microvitrectomy handpiece to remove the excess. This process is repeated as often as necessary. Fine connections that are firmly adherent to the retina may be engaged with the pediatric MPC scissors, lifted away from the retina, and then cut free. Thermal energy to control hemostasis should be avoided, as it may induce a retinal break. Hemostasis should be controlled by elevation of IOP. If a retinal vessel is growing out of the retina into the vitreous cavity anteriorly and it is bleeding, rarely should diathermy be used to control hemostasis. When operating near the ridge, occasionally the ridge will be split into leaflets. These leaflets may be safely removed with the vitrectomy handpiece, although there is an increased risk of postoperative hemorrhage. It is not uncommon to notice schlieren during surgery; this does not necessarily indicate that there is a break,39,40 especially in children. Schlieren results from a viscous interface phenomenon and can represent an area of retina that has been separated from another area with lower or higher viscosity. One sign of relief of traction, aside from the obvious relaxation of the retina, is increased retinal perfusion. This is evidenced by obvious dilation of the retinal vessels in the affected area. Once the retina has been mobilized and all tractional vectors have been relieved, it is all right to proceed to air–fluid exchange. The microvitrectomy handpiece is used to set the posterior limit of air–fluid exchange (the depth of the microvitrectomy handpiece into the eye). Approximately 60–70% of air–fluid exchange is enough to accomplish these surgical goals. Blood, even a lot of blood, may be left on the retinal surface, as long as traction has been removed.
Aerosol release, distribution, and prevention during aerosol therapy: a simulated model for infection control
Published in Drug Delivery, 2022
Marc Mac Giolla Eain, Ronan Cahill, Ronan MacLoughlin, Kevin Nolan
The results of the Schlieren visualization are presented in Figure 3 and are compared to the PIV analysis of the laser visualization. As detailed in the ‘Materials and methods’ section, Schlieren visualization requires a change in the refractive index, typically in the form of local temperature or species variation. Schlieren is not capable of imaging aerosol, conversely laser imaging only detects aerosol. As a result, this allows the decoupling of the air flow and aerosol trajectories. In the case of the filtered mouthpiece tests, there was no such change due to the homogenization of the field by the filter. Similarly, due to the effectiveness of the filter, there is insufficient particle to perform PIV analysis on the data. As such, the images presented in Figure 3 are for the unfiltered mouthpiece only. It is apparent that the aerosol initially follows a very close path to the expiratory port of the mouthpiece. However, this fugitive aerosol plume quickly falls toward the ground, within 0.2 m of the exit of the mouthpiece.
An in vitro visual study of fugitive aerosols released during aerosol therapy to an invasively ventilated simulated patient
Published in Drug Delivery, 2021
Marc Mac Giolla Eain, Mary Joyce, Ronan MacLoughlin
The Schlieren optical system in this study used a 200 mm diameter spherical mirror with a 1 m focal length. An LED with a variable aperture was used as a light source to illuminate the spherical mirror and the image of the mirror was focused onto a knife edge. The light source and knife-edge were placed at the center of curvature of the spherical mirror, which was twice the focal length. 800 × 600-pixel videos were recorded using a monochromatic camera (Phantom v310, Vision Research, Wayne, NJ) with a Nikon Micro-Nikkor f105mm lens. Video files were recorded at a frame rate of 400 frames/second at an exposure of 1 ms. Post hoc processing was completed using the Phantom Cineviewer Software (Version 3.5, Vision Research, Wayne, NJ). In this study, the Schlieren optical system revealed the density gradients in the air and integrated this information in the direction of the optical axis in order to produce a planar image of the respective flow patterns. This flow visualization technique was chosen as it is well established in science and engineering, has been used in infection control research since the late 1960s (Lewis et al., 1969; Clark & Edholm, 1985; Clark & De Calcina-Goff, 2009), and allows 3D flow information to be integrated onto a single plane. Furthermore, the Schlieren optical method does not require the use of any tracer gasses or particles, or high-intensity lasers.