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RAD PHYSICS
TEST WEEK #3
| Question | Answer |
|---|---|
| What is the # of protons in the nucleus? | atomic # (Z) |
| What is the electron binding energy? | The force in which an electron is are held in their orbital shells |
| What is the strength of the binding energy dependent upon? | Location (closeness to nucleus) & complexity of atom (higher Z #) |
| When electrons are sent from the cathode to the anode what 3 things take place? | anode heat, bremsstrahlung radiation, & characteristic radiation |
| As the electrons from the cathode strike the anode, only the ___ ___ electrons on the anode get excited & drop back into place, thus the target is not ___. | outer shell ; ionized. |
| How much of the projected electron is converted to heat? | 99% |
| How much of the projected electron is converted to xray? | 1% |
| When is characteristic xrays produced? | When the projectiled electron interacts with an inner shell electron of the atom. |
| How is the xray emitted in characteristic rays? | As the inner (K) shell electron is knocked out, an outer (L) shell electron fills its place (cascade effect)an xray photon is then created that is eaual in power to the difference in binding energy between the 2 shells. |
| Is characteristic xrays homo or hetero geneous? And why? | Homogeneous, all photons have same energy |
| How is xrays emitted in Brems rays? | The projectiled electron passes completely thru orbital electrons, slows from force field of nucleus and changes direction and the energy the photon loses is relaeased as an xray. |
| Is brems hetero or homo geneous? | heterogeneous |
| What are most xrays? | Brems |
| What kind of radiation do characterisitic and brems emit? | primary radiation |
| As kV goes up what does brems and characteristic do? | Brems down; charac up |
| Define prime factors | Factors affecting xray emission under direct control of the radiographer |
| What are the 3 prime factors? | mAs, kV, & distance |
| What is quantity? | Measure of # of photons in the beam. |
| What is quantity also known as? | Output, intensity, exposure, & density |
| What is the unit of measurement for quantity? | roentgen |
| What factors directly affect quantity? | mAs, kV, distance, & filtration |
| What is the measurement of an xray tubes current? | mAs |
| Is mA directly proportional to tube current? | yes |
| What is the primary controller of film density? | mAs |
| Increasing kV will cause an increase in the ____ & ____ of the electrons applied across the tube. | speed & energy |
| How does kV affect the quantity? | more interactions occur at the target when kV is increased |
| How does kV affect the quality? | each electron has more energy (greater penetrability) |
| What does kV determine? | penetrating ability |
| As kV increases, the wavelength _____ and xrays become ______ penetrating. | decreses; more |
| What formula do you use to describe the relationship between distance and quantity? | Inverses Square Law |
| As distance increases, intensity _____, and exposure to the IR ______. | decreases; decreases |
| What formula is used to compensate for film density changes when distance is changed? | Exposure Maintenance Formula (direct square law) |
| What is xray emission spectrum? | The photons in an xray beam seperated according to their energy. |
| Which way is the energy, curve, and quantity higher in the spectrum? | Right |
| What are the 4 image quality factors? | contrast, density, detail, and distortion |
| Define density | the degree of blackening on a film |
| When deciding between the film being too dark or too light which is better? | dark |
| what is the reciprocity law? | any combo of mA and time will produce the same mAs will produce the same destiny mAs=mAs ex. 1x12=12 3x4=12 |
| What is the minimum change necessary to have any effect on density? | shift mAs by 30% |
| As mAs increases, density _____. | increases |
| How does kV affect density? | when the potential difference is higher, the electrons strike the anode in greater numbers and with greater energy thus producing more xrays |
| What rule is used in density when using kV? And explain it. | an increase in kV bt 15% (keeping all other factors the same) will double density and a 15% decrease will half the density |
| Explain anode heel affect | intensity of the beam is greater at the cathode |
| Where should the greater tissue density be laced in relation to the tube? | under cathode |
| What is another name for the exposure maintenance law? | New mAs Law |
| Define the NML | If u increase your distance, you must increase your exposure factors to maintain the same density (exposure) |
| What is the NML formula? | mAs1=(D1)2 ---------- mAs2=(D2)2 |
| Define Inverse Square Law | The intensity of the beam is inversely proportional to the square distance |
| What is the inverse square law formula? | I1=(D2)2 -------- I2=(D1)2 |
| As filtration increases, density _____. | decreases |
| How does beam restriction affect density? | Collimation reduces the total number of photons , this reduces scatter, reducing density on the film |
| As tissue thickness increases, density _____. | decreases |
| How do grids affect density? | Grids absorb scatter, which would add exposure and density to the IR |
| The higher the grid ratio, the ____ the density | less |
| How does the IR affect density? | the faster the IR speed the more density the IR will receive |
| As processing increases, density _____ | increases |
| What is contrast? and what controls it? | the difference in adjacent densities. Shades of gray to the film. ; kV |
| High contrast=____ kV=___scale | low; short |
| Low contrast=___kV=___scale | high; long |
| which has more shades of gray low or high contrast? | Low |
| As kV increase, contrast ______ | decreases |
| How does OID affect contrast? | As OID increases there is less chance of scatter reaching the IR increasing contrast |
| Filtration changes the average energy of the beam which is the same as raising kV which raises the chance for ____ interactions, thus _____ contrast | compton; reducing |
| Increasing collimation means | makes window smaller |
| Collimation up= contrast __. | up |
| tissue density up= contrast ___. | down |
| How do grids help contrast? | by removing scatter before it hits the IR |
| Grids up= contrast ___. | up |
| What is detail? | degree of geometrical sharpness or accuracy of the structural lines actually recorded on the image |
| What are other terms also known as detail? | definition, sharpness, spatial resolution, recorded detail |
| Unit of resolution is... | line pairs per millimeter |
| For optimal detail you should... | eliminate motion, reduce OID, reduce focal spot size, slower screens, increase SID |
| What is SOD? | subject to object distance |
| SOD + OID = _____ | SID |
| SID/SOD= | magnification |
| As OID decreases, detail _____ | increases |
| As SID decreases, detail ____ | decreases |
| Give an example when you should use a large SID to compensate for a large OID | c-spine |
| What is a sharp shadow around object? | umbra |
| What is an unsharp shadow around onject? | penumbra |
| As focal spot increases, penumbra increases, detail _____ | decreases |
| As file/screen speed increases, detail _____ | decreases |
| Why use a large focal when always wanting detail? | overheating of the filament |
| What is it called if the total number of incident photons reaching the IR screen are insufficient to activate enough phosphors to emit light over the entire radiograph? | quantum mottle |
| What is quantum mottle caused by? | low mAs |
| What appearance does quantum mottle produce? | grainy |
| Why do we perform the wire mesh test? | good contact is needed between the film and intensifying screen poor contact makes bad resolution |
| What are the 3 types of motion? | 1.pt motion 2.tube motion 3.excessive grid motion (reciprocating) |
| What are 2 kinds of pt motion? | 1.voluntary 2.involuntary |
| Give an example of voluntary motion and how is it best resolved? | breathing; communication |
| Give and example of involuntary motion and how is it best maintained? | heartbeat; short exposure time and increased mA for more density |
| What is distortion? | misrepresentation of the size or shape of the structures being examined |
| 2 kinds of distortion? | size and shape |
| As size magnification decreases, detail ____ | increases |
| To minimize size distortion maximize ____ and minimize ______ | SID; OID |
| What is the magnification factor? | SID/SOD=M |
| What is shape distortion? | Elongation or foreshortening |
| What is elongation caused by? | tube angle, or IR improperly aligned |
| What is foreshortening caused by? | By the pt being improperly aligned |
| What is the atomic # of an element? | The number of protons in the nucleus |
| Describe binding energy | The force in which the electrons are in thier orbital shells |
| List the 3 possible interactions at the target | heat, brems, characteristic |
| What electron shell is used for production of characteristic xrays? | k shell |
| what percent of the energy used for xray production is heat loss? | 99% |
| The primary beam is composed of a ____ mixture of energy. | heterogeneous |
| _______ is also known as breaking or white radiation | Brems |
| What force does the projectile electron interact with to create breaking radiation? | The force field around the nucleus |
| What type of radiation comprises most of the primary beam? | Brems |
| What is the definition of density? | Blackness on the film |
| ____ is the controlling factor for density | mAs |
| List some influencing factors for density | filtration, grids, collimation, SID, OID |
| What are the prime factors used in a radiographic exposure? | mAs, kV, & distance |
| Changing the mAs up by 30% will do what to the film? | 1 shade darker |
| Explain how collimation affects the density on the film | As collimation increases density decreases |
| A cxr uses _____ kV, _____scale, _____latitude and _____ contrast | high; long; wide; low |
| What si the controlling factor of contrast? | kV |
| The relationship between contrast and kV is direct or indirect? | indirect |
| What technique can be used to reduce scatter by increasing OID? | Air gap technique |
| As filtration decrease, contrast _____ | increases |
| As collimation increases, contrast_____ | increases |
| As anatomical part decreases, contrast _____ | increases |
| As grid ratio decreases, contrast _____ | decreases |
| What is the formula for the contrast improvement factor? | k= contrast w/grid------------------contrast w/out grid |
| kVp controls the quantity or quality of the xray beam. | quality |
Created by:
miss4o7
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