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rad6608midterm2
| Question | Answer |
|---|---|
| where do electron interactions occur? and what do the result in? | occur in the xray tube, and results in photons. |
| where do photon interactions occur??? how are they absorbed, and what do they result in? | occur from tube to infinity, are differentially absorbed, and can result in ionization of matter. |
| what controls the characterisitcs of the electron beam? | kVp and mAs |
| what controls the characteristics of the xray beam? | electron beam (therefore kVp and mAs control it) |
| what affect does kVp have on the electron beam? | the quality and quantity. |
| what effect does mAs have on the electron beam? | quantity (quantity of photons produced) |
| in the cannon analogy what is the kvp and mas? | kvp = powder, and mas = shot |
| what does kvp balance with each exam? | penetration, contrast, and pt dose. |
| if mas is too low what happens to the film? | underexposed |
| if mas too high what happens to the film? | overexpressed |
| what are projectile electrons? | electrons expelled by the cathode. |
| where is the kinetic energy of the projectile electrons transferred to? | to the target. |
| what 3 products does the transfer of kinetic energy have? | heat (>99%), electromagnetic energy (1. bremsstraglung radiation, and characteristic radiation). |
| efficiency of electron transfer increases with an increased? | kVp |
| 60 kvp = ___% efficiency, 100 kvp = __% efficiency, 20 mVp = ___% efficiency | 60=.5%, 100 = 1%, 20MVp = 70% |
| what are the two types of electromagnetic energy(radiation) made when the electron beam hits the target? | Bremsstrahlung, and characterisitc radiation |
| what are the other names for bremsstralung radiation? | braking, slowed down, white |
| where does the projectile electron passs in bremsstrahlung radiation? | near the nucleus |
| what happens to the kintetic energy and course of bremsstrahlung radiaton? | losses ke and changes course |
| in bremmstrahlung radiation minimal deviation creastes what vs maximal deviation? | minimal creates low energy photons, while max releases high energy photons |
| what is the same thing as the maximum photon energy produced in bremmstahlung rad? | the kVp set on the control panel = maximum photon energy |
| with characterisitic rad where does the projectile electron strike? | strikes the inner shell electron (k or L) |
| characeristic radiation does what to the target atom, with ejection of what? | characteristic rad IONIZES the target atom with ejection of the inner shell electron. |
| instability of the ejection of the inner shell in characteristic rad leads to what? | an outer sheel electron (m, n, o ,p) filling the inner shell, which results in xray photon formation |
| in characteristic radiation what results in xray photon formation? | outer shell electron filling the inner shell which was ejected. |
| in characteristic rad the photon has energy _____ of the target atom | characteristic of the target atom |
| in characteristic rad what is the energy = to? | to the difference in shell binding energy (k energy - l energy = photon energy) |
| which shells are most energetic in characteristic rad? | k ejections are most energetic, l less so and m n o p are insignificant |
| what is the target made of? | tungsten (W) |
| what are the electron binding energies of k l and m | k = 69 l = 12 m = 3 |
| m n and o shell to k shell = ? | 69 kEv |
| l shell to k shell = ? | 57 kEv |
| m shell to l shell = ? | 9 kEv |
| what must the kvp be at least for tungsten? | 69 kVp |
| majority of the beam is ____ | bremsstahlung |
| what is the bremmstrahlung spectrum peak at? | 1/3 the kVp (most photons made here) |
| maximum photon energy is equal to the? | max photon energy is = to the kVp setting. |
| At 100 kVp, ___% characteristic | 15% |
| what happens to the radiation spectrum curve with an inc in kvp/ | stays the same |
| how does the curve shift with an increase in kvp? | right shift of curve (increased efficiency) |
| what happens to the amplitude and quality with an increae in kvp? | increased amplitude (quantity), and increased quality (harder) beam. |
| increasing mAs does what to amplitude and photon quantity? | increases the amplitude (larger area under the curve) and directly increases the photon quantity, but the curve is identical. |
| ___% increase in kvp is = to ___ the mAs | 15% inc in kVp is = to DOUBLING the mas |
| 15% increase in kVp ___optical density of the film | doubles optical density of the film |
| small vs large changes in kvp and mas on film density | small changes in kvp = drastic effect on film density, and large mas changes needed to change density |
| what is the minimum % needed to change mAs to see a change in density? | 25%! |
| when changing factors on the fly should you change kvp or mas? | mas!! |
| what part types are kvp and mas based on? | kvp is type, and mas is thickness. |
| what is added to filter the beam which removes weaker photons? | aluminum |
| what does aluminum do in regards to filtering the beam? | hardens the beam, right shifs the spectrum, decreases wasted pt dose, and removes weaker photons. |
| inherent filtration is from? | glass of the tube. .5mm aluminum. (increases with use d/t tungsten deposition) |
| added filtration is? | al between tube and collimator, with 1.0mm al |
| filtration of collimator mirror? | 1.0mm al |
| what is the total filtration? | 2.5mm Al |
| what are the 4 various types of compenstion filters? | simple wedge (100$), supertech, nolan, and larsen. |
| what does aluminum do to the beam? | hardens it |
| what does aluminum do to the photons? | removes lower energy photons |
| what does al do in regards to quanity and quality | increases qual and dec quantity |
| what are four filtration typse? | inherent, added, collimator mirror, and compensation filters. |
| increase mas ___ photon quantity | increase (directly proportional) |
| doubling mas does _____ optical density | doubles optical density |
| inc kvp, ____ photon quantity | inc |
| photon quanity of kvp is proptional to? | to the square of the kvp change |
| doubling the kvp _____ the optical density | quadruples the optical density |
| inc distance ____ photon quantity | dec photon quantity (inverse square law) |
| doubing the distance ___ optical density | doubling th dist dec optical density 4x |
| inc filtration, ____ photon quantity | dec photon quantity |
| how does higher energy affect penetration? | increases it |
| Half value layer... uses what? increases with what? amount of al added decreases photons by what? | HVL - uses step wedge, increases with increase in kvp, amount of al that decreases number of photons by half. |
| primary control of xray quality, inc kvp = ___ | increase quality |
| secondary control of xray quality by? | added filtration, inc filtration inc quality |
| what do photons interact with in the tube? | tube, filtration, collimator |
| what are the 5 interactions of photons? | coherent scatter, compton effect, photoelectrif effect, pair production, photodisintegration |
| which interactions of photons are in the dx range? | coherent, compton, and photoelectric, but only compton and photoelectric matter. |
| coherent scatter aka? | classic scatter, thompson scatter. |
| what does compton effect do with photons on the electron shell? | photon ejects an OUTER shell electron which changes the course of the original photon. |
| compton ___ photon energy | dec |
| compton: photon can be deflected from ____ to __ degrees | 0 10 180 |
| @ 180 degree deflection, ____ energy loss | 1/3rd energy loss |
| what is backscatter radiation seen with | compton effect |
| backscatter radiation is what? | photons deflected back toward the operate, greatest reason for technician shielding. |
| what is the #1 source of radiation exposure of technician | backscatter radiation (compton) |
| weaker compton photons are absorbed by what? | photoelectric effect |
| any remaining compton photons do what? | degrade film quality by decreasing the contrast. (essentially fogs the film, homogenous exposure to entire film) |
| what helps to dec the compton effect due to overall interactions? | inc kvp |
| if mass density inc of pt what does it do to compton effect | increases it, obsese and overwt pts have lower contrast films. |
| what happens with photons in photoeectric effect? | photon ejects a shell electron, photon is completely absorbed. |
| what are the 2 products of photoelectric effect? | photoelectron and charactristic photon |
| what can the photoelectron do? | go on to interact with matter and create another photon (photoelectric effect) |
| what produces the characteristic photon in photoelectric effect? | by the tissue hit. |
| what are three facts about characterisitc photon ? (photone effect) | can go in any direction, typically only weak photons are produced, will be absorbed byfore making it to the film. |
| if incident photon strikes low atomic # atom inner shell (fat/mm) what happens in photoelec effect/ | resultant characteristic photon is almost as strong as the incident photon therefre can darken the film |
| if incidcent photon strikes mid or high atoomic number outer shell (bone, metal hardware) what happens in photoelec effect? | resultant characteristic photon is very weak, and will likely be absorbed before getting thru the pt. |
| photoelectric effect proportional to? | the atomic # cubed. (small changes in atomic # = large photoelectric rxn) |
| what two things can characteristic photons do? | be absorbed, or act as scatter radiation and contribute little to the image. |
| what does inc in kvp do to photoelectric effect? | dec photoelectric effect, fewer relative photoelectric effect relative to compton. |
| what does an inc in mass density do to the photoelectric effect? | increase in photoelectric absorption |
| less than ___% of the xray emitted from the tube result in the image = differential absorpotion | .5% |
| what are 3 important interactions for differential absorption? | transmitted xrays (dark radiolucent areas), photoelectric effect (absorbed photons - results in light areas), compton scatter (general noise, dec image quality.) |
| xray quality is dependent on proper ___ selection | kVp (results in balance of differential absorption) |
| what three things happen if kvp is too high? | greater transmission, dec photoelectric effect, dec contrast. |
| what 3 things happens if kvp is too low? | not enough photons make it thru pt, dec density, inc pt dose. |
| what is the probability of photoelectric and compton rxns directly proportinal to? | mass densiy of the object |
| what is attenuation? | result of absorption and scatter. |
| reducation of the #s of photons from pre-pt to post-pt | attenuation (photoelectric + compton) |
| absorption (photoelectric) of attenuation | removal of photon from the field |
| scatter (compton) or attenuation | photon is partially absorbed, travels a dif path. |
| attenuation: exponential based on ______ | tissue thickness. |
| what contains intensifying screens? | cassettes (screens flow which intensifies film) |
| 4 facts about old school cassettes | direct exposure film, cardboard cassettes just to keep light off film, slow exposure with high dose, potential for incredible detial. |
| modern cassettes - 1 screen on each side for what? | double emulsion films |
| what do modern cassettes protect? | film and screens. |
| in modern cassettes what exposes the film? | the screens, not the xrays!! (xray photons <1% of darkening, remainder from screen. |
| what % of xray beam interacts with the screens? | 30% |
| pros of screens? | dec pt dose, and dec in exposure time dc pt motion artifact. |
| cons to screens | image is blurred by using screens |
| cassette front covers must have a ___ atomic # | low |
| back cover of cassette must have ___ atomic # t prvent backscatter from reaching the film | high atomic # |
| what would backscatter do to the film? | dec photons getting to the screens, therefore underexposed xrays, and seeing the cassette hinges on the film |
| what is phosphor? | any material that emits light in response to an outside stimulus |
| what are the two types of luminescence? | fluorescence and phophoresence |
| fluorescence used in? | light bulbs and xrays |
| fluorescence mechanism | visibile light is emitted only when phosphor is stimulated |
| phosphorescence used in? | watch dials |
| phosphoresnce mech? | the phosphor continues to emit light after the sitmulus |
| some phosphorescence exists even in fluorescent materials... exs? | afterglow of fluorescent tubes and tvs, and screen lag in xray screens (bad) |
| why are there screens on both sides of the cassette? | to activate both smulsions. |
| what is the base layer of the screen? | polyester backing material (very durable) |
| what is the phospor layer of the screen responsible for? | for the emitted light |
| what hits the phosphor layer of the screen? | photons |
| what two things does phosphor layer of the screen dec? | dec pt dose, and dec tube load. |
| phosphor layer of screen emits what? | thousands of visible light photons |
| phosphor layer of screen recduces what? | shielding requirements. |
| what was screen phsophor originally made up of? | calcium tungstate (CaWO4) |
| in 1970s what was screen phosphor made of? | rare earth screens - gadolinium, lanthanum, yttrium oxysuflits. Higher efficiency and cuts dose from 50-75% |
| how do phosphors emit light | isotropically |
| what does the reflective layer of the screen do? | enhances the efficacy of the screen about two times. |
| what is the problem with isotropic light formation? | dec resolution |
| what is the solution to the dec resolution of isotropic light formation? | dyes in the phosphor layer absorb photons with steeply angled path (dec soeed and inc resolution) |
| what does the protective coating of the screen do? | prevents the mechanical damage to the phosphor layer, dec static electriculty build up.... it's an exposed surface. |
| what are 3 speed characteristics? | speed, image noise, spatial resolution. |
| what is the intensification factor | comparison of optical density with screens vs without screens. Measures screen speed. |
| 100 speed aka? | PAR SPEED, based off the old CaWO4 screens. |
| what increases image noise? | fast screens, high kVp, low mAs |
| what is quantum mottle? | grainy apperance d/t image noise d/t fast screens and or high kvp technique with a low mAs. |
| what is spatial resolution a similar concept to? | 2 point discrim. |
| what is spatial resolution? | amount of detail available on the film, how small of an object can be seen. |
| faster the screen ___ the resolution | lower |
| highest resolution is seen with ___ exporsure film | direct |
| two screen pros | dec pt dose, and dec xray system workload |
| con of screen | dec resolution |
| how is spatiral resolution measured? | in LINE PAIRS PER MILLIMETER. |
| what lp/mm are fast(spinal) screens at? | 7 lp/mm. |
| what lp/mm are detail (extremity) screens at? | 15 lp/mm |
| what 4 things affect spatial resolution? | ***focal spot size, film emulsion thickness, screen phosphor layer thickness, phosphor size. |
| over all is directly proportinal to what? and inversely proportinal to what 2 things? | direct proptional to noise, inversely to resolution and pt dose. |
| if you have slow speed you have __noise, ____ resolution and ___ pt dose | low noise, high resolution and high pt dose |
| system speed is the combo of what? | film speed and screen speed |
| film speed is usually? | 100 par speed film |
| what sets the system speed? | cassettes |
| what is the system speed of spinal rad | 100 speed film, 400 speed cassettes = 400 speed |
| what is obese pt spinal speed? | 100 speed flm, 800 speed cassettes |
| what is small extremity rad system speed | 100 speed film, 100 speed cassette = 100 speed |
| screens do not wear of from? | radiation |
| how do screens die? | mechanical wear and or misuse |
| never use what to take out a film | fingernails |
| always keep cassettes ___ | closed |
| xray films have emulsion on ____ | both sides of the base |
| original xrays used ___plates | glass |
| what are films made of? | polyester |
| what are 4 good qualities to using polyester? | rigid struc for emulsion, felxy water & damage resistant, dimensionally stable (doesnt change size during process), and transparent*** (faint blue tint to dec eyestrain) |
| emulsion done in? | gelatin base with silver halide crystals (98% silver bromide, and 2% silver iodide) |
| what is the gurney mott hypothesis of emulsion? | atoms & ions free to move within the silver halid crystal dt frankel defect. Photon hits sens speck. Photoelectron is captured by sens speck, Photoelectric effect results in photon absorption and photoelectron production. |
| what is frankel defect in emulsion? | allows Ag and Br ion movt. |
| what is sensitivity speack | sulfur based small imperfection in silver halide crystal |
| what captures the photoelectron ? | the sensitivity speck |
| what does the neg charge of the sens speck attract? | Ag+ ions which concert to metallic silver (4-10 atomsof Ag formed) |
| Latent image created by? | metallic silver created by sens speck drawing in Ag+, and freed Br and I mirgrate into the gelatin. |
| unexposed film appears ____ to the film with a latent image | identical (dif can only be seen with electron microscope_ |
| more than ____ dif types of film | 500 |
| what are 3 major catergories of film types | direct exposure film, screen film, and duplication (copy) film |
| direct exposure film.. uses ___ cassette., speed (in comparison to screen film)?, ___detail, ____ pt dose, used in what med setting? | uses cardboard cassette, VERY slow (10-100x longer than screen film), high detail, massive pt dose, used in dentistry for bitewings. |
| what film type do we use? | screen film |
| screen film - uses what, with what inside? what creates the latent image? | uses metal or plastic cassettes wth light emitting intensifying screens inside..... xray photons dont create the latent iamge, the light from the screen does. |
| Duplication film - ___ emulsion film for what? film is what? what are the color changes? | single emulsion film for copying originals.... film is solarized, starts black, turns clear when exposued. |
| what are 5 film characteristics? | speed, contrast, crossover, spectral sensitivity, safelight requirements. |
| what does speed of film describe? | sensitivity to light |
| what is the mc speed of film? | 200 speed |
| what is 100 speed aka? | full speed or par speed |
| what does a higher speed number mean? | faster, more sens to light requireing less exposure (lower mAs) |
| what 3 factors makes speed vary? | # of silver halide crystals, size & shape of crystals, thickness of emulsion |
| emulsion efficiency = ? | covering power |
| what is double emulsion? | emulsion on both sides to cut exposure time in half. |
| what is film contrast | the dif bw black and white |
| what is lattitude | range of exposure techniques that result in an acceptable image. |
| contrast and lattitude are ____ proprotional | inversely |
| what is made with high contrast/narrow lattitude? | sharp black and whites... smaller & uniform crystals |
| what is made with low conteast/wide latitude | lots of grays, larger, non uniform crystals. |
| H & D curve describes what? | film reactivity and inherent film contrast |
| what are the 3 parts to the H & D curve? | toe, slope/straight line, shoulder. |
| toe? | minimal density of film |
| slope/linear region =? | latitude |
| steep slope = ? | high contrast/ narrow latitude |
| low slope? | low contrast wide latitude |
| what is the shouder? | area of overexposure, black film |
| what is crossover? | light crosses from one emulsion to the other |
| what does crossover create? | bluriness |
| what does crossover control layer prevent>? | light from transmitting thru |
| when is crossover removed? | during processing |
| filsm are sensitive to what spectra of light? | blue or green |
| ORTHOCHROMATIC = ? | green spectra |
| what wavelengths do screens emit? | either blue or green |
| mixing film and casette colors = ___ pt dose | 4x pt dose |
| spectral mismatch? | mixing film and cassette colors |
| what does spectral sensitivity allow for? | light in the darkroom |
| what emits light that films is not sens to? | safelights |
| what are the mc filters of safelighs? | amber and red |
| which filter works for both safelights? | red! |
| What is the max bulb wattage of safelight? | 15W |
| what is the min distance of safelights? | 5 ft |
| how should you store the film>? | upright |
| store films away from? | heat light and radiation |
| what is film processing? | chem process which converts the LATENT image to the visibile image |
| in hx hand tanks took how long to make film? | more than an hr |
| who created the first automatic processor with rollers in 1956? | kodak |
| what is current industry standard for automatic processing times? | 90-120 sec |
| when can film be viewed after manual processing? | after fixing |
| when can flm be viewed during automatic processing? | after drying |
| developing film converts ___ silver to ___ silver | ionic silver to metallic silver |
| what does the developer act as? | a wetting agent (softens the gelatin and allows chem penetration) |
| the developer is a ____ agent | reducing agent (contributes e-) |
Created by:
margaretrhager
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