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RAD PHYSICS

TEST WEEK #3

QuestionAnswer
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 on 2008-11-12



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