Telescopes for Inner Space: Fiber Optics and Endoscopes
Suzanne Amador Kane, Boris A. Gelman in Introduction to Physics in Modern Medicine, 2020
Optics can be divided into two branches: geometrical optics and wave optics. Geometrical (or ray) optics describes how light travels within various materials, how it interacts with matter, and how light can be manipulated to perform various useful functions. Geometrical optics assumes that within a uniform medium, light travels (or propagates) along straight lines from its source to a distant point (Figure 2.3a). By medium, we mean any material, such as air, water, glass, blood, fat, or other human tissue. The straight lines along which light propagates are called light rays, or simply rays. A narrow shaft of sunlight breaking through a cloud, or a laser beam, are good approximations to a ray of light. In this chapter we will see that to draw rays we use the properties of parallel lines, angles, and other geometrical figures, hence the term geometrical optics. Wave optics, discussed in the next chapter, builds on the fact that light is an electromagnetic wave carrying energy through vacuum or matter. This alternative approach allows us to understand a wider variety of optical phenomena relevant to medical applications.
Theory of Tomographic Reconstruction
Bhagwat D. Ahluwalia in Tomographic Methods in Nuclear Medicine: Physical Principles, Instruments, and Clinical Applications, 2020
As illustrated in Figure 1, it is assumed that when an observation is made it is along some path which is normally termed a ray. In tomography, it is convenient to call this set of observations projections and to use the symbol p to represent them. Thus, one given observation p(ξ,θ) corresponds to some function of the values f(x,y) along the corresponding ray. The ray is categorized by a pair of values, θ its angle, and ξ its perpendicular distance from a line drawn through the center of rotation. (In 3-D the ray is categorized by three values, ξ, θ, and Φ, as was shown in Figure 2.) Normally, it is assumed that p(ξ,θ), or in 3-D p(ξ,θ,Φ), is the line integral, i.e., the sum of the values found along the ray. Thus where s is a variable directed along the ray. Thus, one projection line is the set of values of p(ξ,θ) for all values of ξ for a specific value of θ, as illustrated in Figure 3. Note the distinction between a projection line and a ray line. The Radon transform23-25 therefore converts the set of values f(x,y) into a set of projection values p(ξ,θ). Angle θ is defined in Figure 3.
Principles of the Laser and Applications
Sujoy K. Guba in Bioengineering in Reproductive Medicine, 2020
Laser is the abbreviated form of light amplification by stimulated emission of radiation. Now that the technique has become so widespread, the term “laser” has become a word by itself and represents the technology where energy is emitted by the transition of group of atoms in a media from a high energy level to a low energy level. The atoms have to be raised to the high energy state by means of an external source. This step of raising the energy level is known as “pumping”. Light and heat being both electromagnetic radiations differing only in their frequencies, by appropriate selection of the atomic energy levels and the energy gap through which they transcend the frequency of the emitted electromagnetic radiation can be determined to have a greater or lesser component of light or heat. Beams in the frequency band 0.75 × 1015 to 0.42 × 1015 Hz corresponding to wavelength 400 to 700 nm are sources of visible light and longer wavelengths up to 1.25 × 105 nm corresponding to frequency of 2.4 × 1012 Hz are predominantly heat waves and may be invisible. A special feature of the energy produced is that it has one single frequency component with ray segments being in time phase unlike energy from other sources which have a spectrum of frequencies. This character known as “coherence” helps in focusing of the beam into a small spot size to obtain high energy density. On account of the same property a laser beam will not disperse along its path.
Steering light in fiber-optic medical devices: a patent review
Published in Expert Review of Medical Devices, 2022
Merle S. Losch, Famke Kardux, Jenny Dankelman, Benno H. W. Hendriks
Another possible fiber core end design is a conical shape as described in seven patents [23,38–43]. The cone can be polished either positively [23,38–41] or negatively [42,43]. For a standard positively polished tip, the conical surface forms an interface between two media: fiberglass and tissue [23,38–40]. Most light rays that strike the cone wall for the first time reflect totally, as their incidence angle is greater than the critical angle. These reflected light rays then strike the opposing wall of the cone with an incident angle lower than the critical angle, causing radial refraction of the light beam into the tissue, see Figure 2e. The device of Scheller [41] describes a unique positively polished cone-shaped fiber tip design with four slanted surfaces that split the light into four separate beams that travel in individual directions. Two devices include a design for a negatively polished tip [42,43]. This surface always contains a reflective coating that ensures that all light that strikes the cone is reflected into the tissue [42,43] or collected from the tissue [43] in radial direction.
Preparation, characterization and dynamical mechanical properties of dextran-coated iron oxide nanoparticles (DIONPs)
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Hatice Kaplan Can, Serap Kavlak, Shahed ParviziKhosroshahi, Ali Güner
The X-ray diffraction, (XRD) patterns were obtained from a Rigaku D-Max 2200 powder diffractometer. The XRD diffractograms were measured at 2θ, in the range 2–50°, using a Cu-Kα incident beam λ = 1.54059 Α°), monochromated by a Ni-filter. The scanning speed was 1°/min, and the voltage and current of the X-ray tubes were 40 kV and 30 mA, respectively. The Bragg equation was used to calculate the interlayer spacing (d) nλ = (2d sinθ), where n is the order of reflection, and θ is the angle of reflection. Crystallinity of the nanocomposites was calculated using the Equations (1) and (2)s is the magnitude of the reciprocal-lattice vector which is given by s = (2sinθ)/λ (θ is one-half the angle of deviation of the diffracted rays from the incident X-rays, and λ is the wavelength); I(s) and Ic(s) are the intensities of coherent X-ray scattering from both crystalline and amorphous regions and from only crystalline region of polymer sample, respectively, Wc and Wa are the areas of the crystalline and amorphous portions in the X-ray patterns, respectively.
Two-stage classification of electromyogram signals from hand grasps in the transverse plane
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Nantarika Thiamchoo, Pornchai Phukpattaranont
In the experiment, the subject sat comfortably on a chair in front of a table as shown in Figure 1. The chair height was adjusted so that the elbow was at a right angle when the forearm and the hand were lying comfortably on the table. The subject was asked to grasp the five kinds of objects shown in Figure 3, as follows a sphere (diameter 8 cm), a cylinder (diameter 3.3 cm), a keycard (thickness 0.15 cm), an eraser (thickness 1.4 cm), and a pen (diameter 1 cm). These object grasps were selected to provoke three grip types, namely power, intermediate, and precision grips (Feix et al. 2016). They have been previously identified as being the most useful from a user’s perspective (Peerdeman et al. 2011). The object was placed at one of the nine alternative positions in 3 main directions, which were along a central ray (P1, P2, and P3) and along rays pointing 45-degrees to the left (P4, P5, and P6) or to the right (P7, P8, and P9) as shown in Figure 4. There was a distance of 10 cm between consecutive positions along a ray.
Related Knowledge Centers
- Ray Tracing
- Geometrical Optics
- Refractive Index
- Fermat'S Principle
- Angle of Incidence
- Reflection
- Snell'S Law
- Optical Axis
- Aperture
- Real Image