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RAD 121
Unit 1 - words/concepts
| Question | Answer |
|---|---|
| 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 current | mA OUTPUT IS DIRECTLY PROPORTIONAL TO mA |
| 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
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