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Rad Imag. 2

Ch 8-11

Xrays in air are measured in grays
The number of xrays in the useful beam define xray quanitity, exposure, intensity
Xray quantity increases in direct proportion to increases in mAs
If SID is reduced by one half the intensity of the image intensity increases 4 times
If filter thickness is increased then xray intensity is reduced
If filter thickness is decreased then xray intensity is increased
Which has the greater effect on increasing density, a 10% increase in kVp or a 10% increase in mAs? kVp
If xray quantity is doubled, the optical density on the finished radiograph will be increased by a factor of doubled
A change from 200 mAs to 400 mAs will cause intensity to ___ and optical density to ___ double; double
An increase of 15% in kVp is equivalent to increasing mAs 100%
The penetrability of an xray beam is called xray quality
An xray that could pass through thick tissue would have high penetrability and quality
Beam quality is affected by kVp and filtration
Image contrast is affected by beam quality and kVp
Xray beam quality is increased by increasing filtration
A compensating filter is used to create uniform optical density
The two primary forms of xray interaction in diagnostic range are Compton scattering and photoelectric absorption
An xray interacts with an atom without ionization during coherent interaction
An outer shell electron is ejected and the atom ionized during Compton interation
Photoelectric absorption involves the ejection of K shell electrons
Compton scatter is directed at ___ angle from the incident beam any
There is compete absorption of the incident xray photon on photoelectric interaction
Only at energies above 10MeV can photodisintegration take place
K shell binding energy increases with increasing atomic number
Bone has greater mass density than fat, soft tissue, or air
Because of differential absorption about __% of incident beam contributes to the image .5
Differential absorption depends on the kVp of exposure, atomic number of absorber, and mass density of absorber
Attenuation is caused by absorption and scatter
Barium is a good contrast agent because of its high atomic number
A negative contrast agent is air
____ kVp techniques reduce patient dose high
If 5% of the incident beam are not attenuated then 95% were absorbed or scattered
A high quality radiograph should always demonstrate structures and tissues
Spatial resolution improves with decreased screen, motion, and geometric blur
The ability to image two separate objects and visually detect one from the other is called resolution
High speed IR generally produce images with increased noise
The slope of the straight line portion of the characteristic curve shows the film contrast
A transmission of 10% incident light corresponds to an optical density of 1
An IR with wide latitude can be used over a great range of exposures
The three primary geometric factors affecting quality are magnification, distortion, and focal spot blur
Way to minimize magnification long SID and small OID
Focal spot blur can be reduced by using a small focal spot, long SID, and small OID
Subject contrast is affected by patient thickness, atomic number, density, and kVp selection
The chest has high subject contrast because of the wide differences in ____ and ____ tissue mass density between air and bone. atomic number; greatest
Radiographic image quality is improved when source image distance is increased
The primary control of radiographic contrast is by varying kVp
Optical density is primarily controlled by changing mAs
Image forming xray are those which have been transmitted without interaction or absorbed or scattered through compton interaction
The % of Compton interaction increases as kVp increases
Approximately ___ % of incident beam is transmitted through the patient. 0-9
Compton scatter contributes only to image noise
Decreasing kVp will _____ patient dose increase
Photoelectric interaction increases when kVp is decreased
Scatter radiation increase as field size increase
The most common beam restricting device Is the variable collimator
Compression devices will increase contrast
The use of collimation improves contrast and reduces patient dose
Beam restriction with an aperture diaphragm is only accurate at a fixed distance
You can improve image contrast with heavy patients without increasing patient dose by using tight collimation