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X-ray Vision: Diagnostic X-rays and CT Scans
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
One of these wave properties is refraction, which is the change in the direction of propagation as the wave travels through different media. In Chapter 2, we discussed refraction of light in transparent matter. The simplest case is the refraction of light at a sharp boundary between two homogeneous materials (air and water, or air and glass for example). Snell's law gives the relation between the angle of incidence and the angle of refraction (Equation 2.2). The refractive properties of matter are determined by an index of refraction, n. Similarly, in the x-ray phase-contrast method, an image is created using the variation of refractive indices for x-rays between different soft tissues.
Optics and refractive errors
Published in Mostafa Khalil, Omar Kouli, The Duke Elder Exam of Ophthalmology, 2019
Nemat Ahmed, Omar Kouli, Mostafa Khalil, Obaid Kousha
The angle of incidence is the angle the light travels as it hits the boundary of another medium. The angle of refraction is dependent on the angle of incidence and is the angle the light travels as it crosses the boundary.
Basic Principles of Ultrasonic Imaging
Published in Asim Kurjak, CRC Handbook of Ultrasound in Obstetrics and Gynecology, 2019
As illustrated in Figure 5, part of the wave energy is reflected and part is transmitted through the boundary. In effect, the sound wave is divided into two waves with different intensities and directions. The angle of refraction depends on the ratio of propagation speeds in the two respective media and is described by the following equation:
Null strain analysis of submerged aneurysm analogues using a novel 3D stereomicroscopy device
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Brooks A. Lane, Susan M. Lessner, Narendra R. Vyavahare, Michael A. Sutton, John F. Eberth
Two CMOS cameras (EO-1312M; 1280 × 1024 pixels) with VZM 200i Zoom Imaging Lenses capable of 0.5-2X zoom (Edmund Optics; #37-553 and #54-715) are mounted on a 3-axis translation stage (Thorlabs; PT3) positioned along a radial line from the center of the specimen stage. The stereo-rig mounting hardware contains dual stereo angle adjustment screws and a locking mechanism to prevent unintentional shifting. The cameras are fixed at individual pan angles 7°-8° above and below the normal plane, providing a stereo angle (φ) of ∼15°. This stereo angle has been shown to enable adequate sensitivity to out-of-plane motion while maintaining minimal perspective differences between imaging subsets (Schreier et al. 2009). Moreover, the small angle reduces refraction-related image distortions so that image correction algorithms can be implemented in the commercial VIC-3D software (Correlated Solutions I).
The Effect of Gender on Visual Field Sensitivity: The Singapore Chinese Eye Study
Published in Ophthalmic Epidemiology, 2019
Nicholas Y. Q. Tan, Yih-Chung Tham, Victor Koh, Carol Y. Cheung, Tin Aung, Tien Yin Wong, Ching-Yu Cheng
All subjects underwent a standardised and comprehensive interview and ophthalmic examination, including measurement of best-corrected visual acuity (BCVA) in logarithmic minimal-angle resolution, refraction, axial length measurement, intraocular pressure (IOP) measurement, and fundus examination. IOP was measured with a Goldmann applanation tonometer (Haag-Streit, Bern, Switzerland) before pupil dilation. Fundus examination included the evaluation of the optic disc with a 78-diopter (D) lens at x16 magnification with a measuring graticule during dilated ophthalmoscopy for the calculation of the vertical cup-disc ratio. The refraction of each eye was measured using an autorefractor (Canon RK 5 Auto Ref-Keratometer; Canon Inc., Ltd., Tochigiken, Japan). Axial length was measured with a noncontact partial coherence laser interferometry (IOLMaster Version 3.01; Carl Zeiss Meditec AG, Jena, Germany), and the mean of five measurements was used in the analysis. Lens opacity was assessed from lens photographs using the Wisconsin Cataract Grading System.13 In addition, participants also underwent VF assessment, which is further described below.