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Medical Physics > Key Words > Flashcards

Key Words Flashcards

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1
Q

Accommodation

A

The ability of the eye to adjust its focal length.

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2
Q

Acoustic impedance (Z)

A

The product of the density, r, and the speed of sound, c, in that material.

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3
Q

Action potential

A

The change in electrical potential that occurs across a cell membrane during the passage of a nerve impulse.

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4
Q

A-scan (amplitude scan)

A

A range-measuring system, which records the time taken for an ultrasonic pulse to travel to an interface in the body and be re ected back.

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5
Q

Astigmatism

A

A defect in the eye or in a lens caused by a deviation from spherical curvature, which results in distorted images.

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6
Q

Attenuation

A

The reduction of intensity as a wave travels through a material.

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7
Q

Auditory nerve

A

Carries auditory sensory information from the cochlea of the inner ear directly to the brain.

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8
Q

Biological half-life (TB)

A

The time required for the body to eliminate half of an administered dose of any substance by regular physiological processes.

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9
Q

Bremsstrahlung (‘braking’ radiation)

A

Electromagnetic radiation produced by the acceleration or especially the deceleration of a charged particle after passing through the electric and magnetic elds of a nucleus.

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10
Q

B-scan (brightness scan)

A

A diagnostic test used in optometry and ophthalmology to produce a two-dimensional, cross-sectional view of the eye and the orbit

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11
Q

Characteristic X-rays

A

Emitted when outer-shell electrons ll

a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is ‘characteristic’ to each element.

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12
Q

Ciliary muscle

A

One of the muscles around the lens of the eye that can change the shape of the lens in order to produce a clear image.

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13
Q

Cladding

A

The outer covering of an optical fibre, which confines light to the core.

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14
Q

Coherent bundle

A

An ordered collection of optical bres that can carry images.

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15
Q

Cochlea

A

Part of the inner ear where sound vibrations are converted into electrical signals.

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16
Q

Computed tomography

CT

A

Radiography in which a three-dimensional image of a

body structure is constructed by computer from a series of plane cross-sectional images made along an axis.

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17
Q

concave lens

A

A lens that spreads a parallel beam into a divergent emergent beam.

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18
Q

cones

A

Light-sensitive cells in the retina, responsible for colour vision.

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19
Q

Contrast

A

In X-ray image: the variation in brightness of the image due to differential absorption of X-rays in the patient

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20
Q

Contrast medium

A

A material of high density and atomic number put into the body to enable soft organs to be visualised on an X-ray image.

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21
Q

convex lens

A

A lens that causes a parallel beam to converge to a point called the focus.

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22
Q

cornea

A

The outer covering of the front of the eye, where most of the refraction of light takes place.

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23
Q

CT scanner

A

Medical scanner

that uses beams of X-rays to produce high-contrast images of a cross-section through the body.

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24
Q

dBA

A

dBA-weighted decibels are
a measurement of the relative loudness of sounds in air as perceived by the human ear. In
the A-weighted system, the decibel values of sounds at low frequencies are weighted in such a way that they are reduced compared with unweighted decibels (dB). This weighting is applied because the human ear is less sensitive at low and high audio frequencies and the A weighting matches more closely the human ears frequency response to sound levels.

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25
Q

dB scale

A

The logarithmic scale used to measure intensity of sound.

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26
Q

Decibel (dB)

A

The unit used to measure the intensity of a sound

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27
Q

Depolarisation

A

A sudden change within a cell, during which the cell undergoes a dramatic electrical change.

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28
Q

Eardrum

A

The membrane of the middle ear, which vibrates in response to sound waves.

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29
Q

Electrocardiograph (ECG)

A

An instrument used in the

detection and diagnosis of heart abnormalities that measures the electrical activity of the heart.

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30
Q

Endoscope

A

An instrument that can be introduced into the body to give a view of its internal parts.

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31
Q

excited

A

Being at an energy level higher than the ground state.

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32
Q

Far point

A

the farthest point from the eye at which images are clear

33
Q

Flat-panel (FPD) detectors

A

A class of solid-state X-ray digital radiography devices similar in principle to the image sensors used in digital photography and video.

34
Q

Focal length (f)

A

The distance between the principal focus of a lens and its centre.

35
Q

Focus

A

The point where light rays originating from a point on the object converge.

36
Q

Fovea

A

A region on the retina with a high concentration of cone cells.

37
Q

Gamma camera

A

A device used to image gamma radiation emitting radioisotopes.

38
Q

Image intensifier

A

A device used in the X-ray technique uoroscopy to produce a visible image using a lower dose of X-rays.

39
Q

Incoherent bundle

A

A bundle of laments of optical glass or other transparent materials that transmit only light, not optical images.

40
Q

Intensifying screen

A

Absorbs the energy in the X-ray beam that has penetrated the patient and converts this energy into a light pattern.

41
Q

Intensity

A

The power of a wave transmitted through unit area perpendicular to the direction of travel of the wave; unit: watts per square metre, Wm-1

42
Q

Intensity attenuation coef cient (μ)

A

The fraction of a beam of X-rays or gamma rays that is absorbed or scattered per unit thickness of the absorbing material.

43
Q

Intensity level

A

The relative sound intensity at any point in a sound eld as compared with a speci ed standard intensity.

44
Q

Iris

A

A thin, circular structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina

45
Q

Lens

A

A transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina.

46
Q

Linear attenuation coefficient

μ

A

A measure of a material’s ability to attenuate X-rays

47
Q

Magnetic resonance (MR)

A

The excitation of particles (as atomic nuclei or electrons) in a magnetic field by exposure to electromagnetic radiation of a specific frequency.

48
Q

Mass attenuation coefficient (μm)

A

a measure of a material’s ability to attenuate X-rays that is independent of the material’s density; equal to the linear attenuation coef cient divided by the density

49
Q

Myopia

A

Short-sightedness: the inability to focus on objects at large distances from the eye.

50
Q

Near point

A

The closest distance from the eye at which an object can be brought into focus.

51
Q

Nuclear magnetic resonance (NMR)

A

The absorption of electromagnetic radiation at a precise frequency by a nucleus in an external magnetic eld.

52
Q

Optic nerve

A

A paired nerve that transmits visual information from the retina to the brain

53
Q

Optical fibres

A

Thin transparent fibres of glass or plastic that transmit light throughout their length by internal reflections; used in medical instruments to view otherwise inaccessible parts of
the body.

54
Q

Ossicles

A

Three bones in the middle ear, malleus, incus and stapes, that are among the smallest bones in the human body.

55
Q

Photocathode

A

A negatively charged electrode in a light-detection device such
as a photomultiplier or phototube that is coated with a photosensitive compound.

56
Q

Photodetector

A

A device that detects or responds to incident light by using the electrical effect of individual photons.

57
Q

Photodiode

A

A semiconductor diode that, when exposed to light, generates a potential difference or changes its electrical resistance

58
Q

Photomultiplier

A

An instrument containing a photoelectric cell and a series of electrodes, used to detect and amplify the light from very
faint sources.

59
Q

Piezoelectric effect

A

The ability of certain materials to generate an electric charge in response to applied mechanical stress.

60
Q

Piezoelectric transducer

A

A device that generates a potential difference when it is compressed
or expanded; used to generate and detect ultrasound.

61
Q

Polarised

A

A transverse wave is polarised when the vibration of the wave is con ned to one direction.

62
Q

Power

A

The rate at which energy is transferred or at which work is done, measured in joules per second, or watts, W.

63
Q

Principal axis

A

An imaginary line drawn at right angles to a lens passing through the optical centre, used in constructing ray diagrams

64
Q

Principal focus

A

A particular point on the optical axis of a lens where light is focused.

65
Q

Pulse rate

A

The number of times your heart beats per minute.

66
Q

pupil

A

The aperture of the eye.

67
Q

Radioactive tracer

A

A radioactive isotope used for medical imaging and which is tracked and detected by an external radiation detector.

68
Q

real image

A

An image formed by the convergence of rays of light; it can be formed on a screen

69
Q

Repolarised

A

Describes the change in the cell membrane potential that returns it to a negative value just after the depolarisation phase of an action potential has changed the membrane potential to a positive value.

70
Q

Resonance

A

Occurs when a system accepts energy from a driving source at its natural frequency – the amplitude increases greatly.

71
Q

Retina

A

A tissue of light-sensitive cells lining the back of the eye.

72
Q

Rhodopsin

A

A photopigment present in rod cells, which disassociates when it absorbs a photon of light

73
Q

Rods

A

Light-sensitive cells in the retina, which respond well in low light conditions

74
Q

Scintillator

A

A material that uoresces when struck by a charged particle or high-energy photon

75
Q

Source focal spot

A

The small area of the target of an X-ray tube
on which the electron beam is focused; it is an important factor in the ability of an X-ray machine to produce a sharp image.

76
Q

Thermionic emission

A

The process by which electrons are released from the surface of a heated metal

77
Q

Threshold of hearing (I0)

A

The lowest sound intensity that can be detected by a healthy human ear, de ned as 1×10-12 W m-2.

78
Q

Ultrasound

A

Sound waves with a frequency above 20 kHz.

79
Q

Virtual image

A

An image caused by rays that do not converge; the image can be seen by the eye but not formed on a screen.

Medical Physics (9 decks)

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