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RAD 121

Unit 1 - words/concepts

Bremsstrahlung interactions radiation produced when incident electrons are slowed down or decelerated in anode occur when incident negative electrons interact w/positive force field of nucleus, slowing electron, loses kinetic energy, energy is emitted as x-ray P 113/Orth
characteristic cascade transition of electrons between shells caused by characteristic interaction with tungsten anode
characteristic interactions Occur in anode when projectile electron passes near K shell orbital electron; negative energy from projectile electron ejects inner orbital electron, causing a vacancy, energy transitioned to ejected electron, original electron absorbed as heat in anode
incident electrons electrons from the thermionic cloud that bombard the target
inherent filtration filtration of useful x-ray photons provided by permanently installed components of x-ray tube housing assembly and glass window of x-ray tube
keV kiloelectron volts (energy of projectile electrons)
kVp kilovoltage peak (energy of x-ray photons)
x-ray beam quality penetrating ability of x-ray beam P 116 Orth/p 116 S controlled by kVp determined by their energy (more penetrating = high energy, high frequency, short wavelength)
x-ray beam quantity directly controlled by mAs; influenced by kVp
unit to measure frequency and wavelength frequency is hertz (Hz) wavelength is PERIOD
annihilation radiation The combination of the positron with a negative electron, resulting in the destruction of both and the creation of 2 photons, each with .511 keV energy, that move in opposite directions
backscatter radiation x-rays that have interacted with an object and are deflected backward; strongest type of scatter
coherent scatter P127 S Also known as Classical, Thompson, inelastic or unmodified scatter very low energy photon interacts with firmly bound orbital electron, setting the electron vibrating which sends out an identical photon in a DIFFERENT direction
Compton scatter p127 S Incident photon interacts w/loosely bound electron, ejecting it different direction (Compton/recoil electron) Energy of incident photon is decreased (recoil electron acquires difference in orig energy) Exposure hazard / scatter for image
pair production P 128 S Beyond realm of diagnostic x-rays photon (1.02 MeV energy) disappears and give birth to pair - negative electron & positive electron (positron) which cancel each other out converting mass to energy, 2 x-rays w/energy of .51MeV in opposite direct
photodisintegration an interaction between an x-ray photon and a nucleus of an atom where the nucleus absorbs all the photons' energy and emits a nuclear fragment
photoelectric effect complete absorption of incident photon by atom
photoelectron an electron ejected from an atom following a photoelectric interaction
radiopaque Any material that absorbs photons
radiolucent Any material that easily transmits photons
cathode ray tube a partially evacuated glass tube (Crookes Tube) TV monitor used to display the fluoroscopic image
fluorescence the production of light in the intensifying screen phosphor by x-ray photons
diaphragm device that restricts the x-ray beam to a fixed size
thermionic emission P 38 S Heating a metal to incandescence increases the kinetic energy of the outermost shell electrons, allowing them to escape into a cloud (allowing us to create x-rays)
inertia the tendency of a resting body to remain at rest and a body moving at a constant speed in a straight line to remain in motion
kinetic energy the energy of a moving body
potential energy stored energy in a non-moving body
contrast the difference in optical density between two areas of an image shades of gray (long scale or short scale) DIFFERENCE IN BRIGHTNESS LEVELS ON MONITOR/IMAGE improves recorded detail
alpha particle form of particulate radiation that consists of two protons and two neutrons (identical to a Helium atom). Emitted from the nucleus of very heavy elements. Very large and doesn't penetrate the skin. No application in diagnostic radiology
atomic mass number The total number of protons and neutrons in the nucleus of an atom designated by the letter A
atomic mass unit (AMU) 1/12 mass of carbon 12 nucleus Similar to atomic weight
atomic number the number of protons or positive charges in the nucleus of an atom designated by the letter Z
beta particle identical to an electron except for its origin - it is generated from the nucleus with a considerable amount of kinetic energy. used in Nuclear Med
covalent bonds When two ions SHARE an electron 2 types covalent bonding - equal sharing Polar covalent bonding - unequal sharing
electron binding energy describes how tightly the electron is held in its shell How much energy is required to remove the electron from its shell
half-life the time it takes for a radioisotope to decay to one half its activity
ion charged atoms an atom that has gained or lost an electron When the outer shell does not contain 8 electrons, it is able to accept or give an electron, causing attraction between two ions creating a compound.
ion pair two oppositely charged ions
ionic bonds the attraction between two ions is a chemical bond; one positive and one negative
ionization converting atoms to negative or positive charge through removal or addition of orbital electrons
Bohr model describes the atom as a central dense positive nucleus surrounded by electrons moving around the nucleus
spatial resolution recorded detail the ability of the system to image adjacent small structures such as the edges or borders of structures that appear in hairline fractures lp/mm
detail the smallest separation of 2 lines or edges that can be recognized as separate structures on the image. lp/mm
isotopes Atoms of the same element having different mass numbers Atoms that have the same number of nuclear protons but different numbers of nuclear neutrons (P30 S) IE (different numbers of neutrons)
nucleons types of particles contained in the nucleus PROTONS or neutrons NEUTRONS
radioactive decay the transformation of radioactive nuclei into a different element followed by the emission of particulate or electromagnetic radiation
radioisotopes an unstable isotope that spontaneously transforms into a more stable isotope with the emission of radiation
amplitude the maximum height of the peaks or valleys of a wave
electromagnetic spectrum describes the different forms of electromagnetic radiation
frequency the number of crests or cycles per second FREQUENCY IS INVERSELY PROPORTIONAL TO WAVELENGTH measured in hertz (Hz)
intensity measure of the energy of the x-ray beam; the quantity of radiant energy flowing per second through unit area of surface perpendicular of direction of beam at designated point OUTPUT R/min or mR/min
inverse square law p215 S the x-ray output or exposure rate at a given distance from a point source is INVERSELY proportional to the square of the distance I 1 / I 2 = D 2 squared / D1 squared
period the time required for one complete cycle of a waveform
photon A bit of electromagnetic energy that depends on the frequency of the wave It is preferable to designate x and gamma rays according to their photon energy rather than their wavelength.
wavelength The distance between two successive crests IE Peak to Peak, Trough to Trough
actual focal spot The physical area on the anode that is impacted by the electron stream
anode POSITIVE electrode target material in x-ray tube (tungsten W 74)
anode angle the angle between the anode surface and the central ray of the x-ray beam
anode heel effect differential intensity of the x-ray beam; phenomenon resulting from angling the anode target causes the intensity to be less on the anode side because photons are absorbed in the anode itself P 104 Orth fig 9.13
cathode negative electrode hot filament in x-ray tube
effective focal spot The area of the focal spot projected toward object being imaged
filament Source of electrons in Cathode
focal spot where the electron stream bombards a small area of the anode Area where projectile electrons strike, source of X-ray photons
focal track Area of anode where high voltage electrons will strike
focusing cup The negatively charged part of the x-ray tube that confines the electron stream to a very narrow beam The narrower the electron beam, the smaller the focal spot and the sharper the x-ray images
leakage radiation Radiation outside the primary X-ray beam emitted through tube housing
line focus principle Use the angle of the anode to maintain large actual FS yet reduce the effective area of focal spot
off-focus radiation Photons not produced at focal spot
rotating anode An anode that turns during an exposure
rotor Central rotating component of an electric motor, used to rotate anode
SID Source-to-image receptor distance
space-charge effect With buildup of electrons by filament, electrons’ negative charges begin to oppose the emission of additional electrons
15% rule changing the kVp by 15% will either double or halve the receptor exposure Increasing kV requires dropping mAs by a factor of 2 Decreasing kV requires increasing mAs by a factor of 2
brightness amount of luminance or light emission from a display monitor
direct square law maintains image brightness by changing mAs values to compensate for change in distance mAs1 / mAs2 = SID 1 squared / SID 2 squared
exposure time length of time required to end an exposure
involuntary motion motion not in control of the patient - heart beat, peristalsis, breathing (to a degree)
mAs/distance compensation formula a math calculation for adjusting mAs when adjusting SID mAs 1 / mAs 2 = SID 1 squared / SID 2 squared
kilovoltage peak (kVp) kilovoltage peak - a measure of voltage applied to the x-ray tube
milliampere stream or flow of electrons from cathode hot filament to anode target
milliampere-second (mAs) The total charge transferred in the process of production of high speed electrons
optical brightness a measure of the degree of blackness of the image expressed on a logarithmic scale Primarily controlled by mAs
quantum mottle also called noise occurs when not enough photons are transmitted to the IR, results in a grainy, speckled appearing image requires a REPEAT
radiographic density in film screen, the amount of overall blackness produced on the processed image
distortion the misrepresentation of an object size (magnification) or shape (elongation/foreshortening) distortion
technical factors kVp and mAs as selected for a given procedure
voluntary motion motion that the patient can control - moving fingers, raising shoulders
valence the combining ability of the outermost shell of the element - determined by the number of electrons 8 (octet) is most stable the chemical properties of an element depend on its valence
chemical bond The bond formed between two ions - also called ionic bond
Ionic Bond also known as chemical bond oppositely electrically charged atoms are attracted to each other enough to form a compound
electromagnetic radiation wavelike fluctuations of electric and magnetic fields set up in space by oscillating (vibrating) electrons
How are x-rays produced? 1) fast-moving electrons undergo rapid deceleration 2) electrons drop from outer shell to holes in inner shell
thermions the filament electrons liberated by incandescence
useful beam Only those x-rays that leave the x-ray tube via the small window
polyenergetic radiation xray photons are nonuniform in energy and wavelength due to differences in braking speed and how closely they approach the nucleus
characteristic x-ray x-ray with energy unique to its target element and involved shells (Tungsten W 74 - k shell energy is 69.5kev)
primary radiation x-rays emerging from the target General - polyenergetic radiation (Brems) 90% Characteristic - limited, discrete energies (and wavelengths) 10%
Target material Tungsten * withstands high heat (99% of interactions result in heat only) *has high atomic # (better penetrability of emitted x-ray)
tube potential kV increases output because electrons are speeded up and produce more photons at the target
filtration removal of low energy x-rays by placing a material in the primary beam (hardening the beam)
What is the equivalent monoenergetic quality for a 120kV x-ray beam? about 1/3 to 1/2 peak energy 50 keV monoenergetic xrays
off-focus radiation electrons that strike anode metal other than the focal spot, causing the emission of x-rays
relationship of photon energy and wavelength minimum wavelength is inversely related to maximum photon energy
Half value layer HVL that thickness of specified metal that reduces the radiation output to 1/2 its initial value
inherent filtration P122 S filtration due tube housing, inlcuding glass window, cooling oil and tube housing
attenuation p124 S progressive decrease in initial number of photons 2 processes Absorption - various kinds of interactions with atoms in the body in path of beam ending the travel of the photon Scattered/secondary radiation
Scattered radiation x-ray photons that change direction the photon interaction with an atom resulting in a change of direction and loss of energy
Secondary radiation characteristic x-rays emitted by atoms after having absorbed x-ray photons
binding energy the energy required to remove an electron from a particular shell and beyond the range of the nuclear positive field (each shell has specific energy unique to its level)
possible interactions with matter 1) photoelectric effect 2) coherent (classical/Thomson) scatter 3) Compton interaction with modified scatter 4) Pair production 5) Photodisintegration >10MeV
Photoelectric interaction incident photon gives up all its energy to K or L shell (truly absorbed), atom responds by ejecting K or L shell electron leaving a hole in that shell (photoelectron) which goes on to have more interactions w/other atoms. Results in a cascade to fill vac
annihilation reaction P 128 S Pair Production Positron combines with any negative electron, giving rise to two photons with energies of .511MeV, moving in opposite directions
Primary electrons a) photoelectrons b)Compton or recoil electrons c) Positron-negatron pairs
Secondary/Scattered x-rays a) Characteristic b) Coherent or unmodified scatter c) Modified scatter (Compton effect) d) Annihilation reaction
How does hardening of a primary x-ray beam with filter occur? mostly from photoelectric absorption of relatively more low energy than high energy photons
Photoelectric absorption - why is it important? It is about 4-6X greater in bone than soft tissue, resulting in much of the radiologic contrast between these tissues
Compton effect - why is it important? It is mainly scatter - accounts for 80-90% of the beam in soft tissues (patient dose). It degrades image quality requiring grids and collimators Increasing kV increases scatter, the scattered radiation is stronger and more direct
recorded detail spatial resolution the ability of the IR to produce separate images of closely spaced small objects
subject contrast the result of the absorption characteristics of the tissues that are seen as multiple shades of gray
differential absorption process where some x-ray photons are absorbed photoelectrically while others pass completely through patient
what is meant by Z number? atomic number - # of protons
air kerma Gy unit of measure for exposure
Gray Gy unit of measure for absorbed dose
Sievert Sv unit of measurement for dose equivalent
Becquerel Bq Unit of measure for radioactivity
five radiographic properties receptor exposure/exposure indicator Brightness contrast Spatial Resolution Distortion
PRIME Factors that govern receptor exposure mA Time kVp SID (filtration - not controlled by tech)
Photographic variables Visibility receptor exposure contrast
Geometric variables Sharpness spatial resolution distortion
exposure indicator (different ones and relationships) S - Fuji and Konica (inverse) EI - Carestream and Kodak (direct) decimal - Agfa (algorithm)
how does mA affect receptor exposure directly proportional to radiation quantity
how does kVp affect receptor exposure directly related to radiation quantity and quality (not proportional) inversely related to contrast
Recorded detail Radio graphic quality - definition, sharpness, and simply detail
Blur Opposite of sharpness
Resolution Measures ability of IR to produce separate images of closely spaced objects
Sharpness Measured by acutance (abruptness of a boundary between an image detail and its surroundings)
Visibility of detail Ability of observer to see recorded detail; can be obscured by NOISE or MOTION
Major causes of Image unsharpness P206 S Geometric- focal spot size Photographic - motion, nature IR, shape of part
Geometric blur Penumbra/focal spot blur/edge gradient Depends on Effective Focal Spot size, SID, OID
Created by: Larobbins