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kVp rule
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2 kVp/cm is sufficient below 85 kVp; 3 kVp/cm is sufficient above 85 kVp
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kVp rule
2 kVp/cm is sufficient below 85 kVp; 3 kVp/cm is sufficient above 85 kVp
what are some advantages of a fixed rate kVp?
the optimum kVp is selected and set, more exposure of latitude; MORE LEEWAY FOR ERROR
What are some advantages of a variable rate kVp?
you can adjust kVp 2 or 3 cm for differences in technique charts, overall contrast is lower, more anatomy detail, small exposure adjustments
tangential projection
centeral ray "skims" the profile of the subject.
transvers or horizontal plane
divides the body into superior and inferior portions
EAM ( external auditory meatus)
ear canal
coronal
divides body into front and back ( anterior and posterior)
why would a grid be used for the main trunk and not the extremities?
scatter is often increased with larger body structures; decreases fog produced by scatter radiation
sagittal
divides body into right and left ( does not have to be equal)
mid sagittal
EQUAL right and left halves ( aka median plane)
coherent scattering ( aka thompson scatter)
low energy level scatter; no ionization occurs
compton effect
occurs through all energy levels of the diagnostic X-ray ; this scatter goes in ANY direction
photoelectric effect
secondary or characteristic X-ray
higher kVp results in :
more scatter radiation fog
if you increase the mA by two what will happen to the mAs?
it will double.
air gap
found between patient and film
larger OID causes
increaes magnification; decreased detail
decreasing the kVp will increase the contrast in 2 ways:
it narrows the scale of contrast ( to short scale); it also decteases the energy in the x-rays wich decreases the production of scatter radiation...( so you will need to increase the mAs to compensate, 15% rule)
grid cut off occurs when
the grid is not perpendicular to the CR
what is a good reason for selecting a low mA station to obtain a given amount of mAs would be:
to use the small focal spot
if your radiograph comes out with little or no image of interior stuctures you usually have underpenetrated the patient. How would you correct this?
increase kVp
When you increase the kVp you increase the number of X-rays that are produced in the tube...T/F
false
long scale gray would mean you have?
alot of gray and a high kVp
density is the overall darkness on the radiograph, will it affect the length of the scale of gray if the density increases? Yes/ No
NO
a good reason for selecting the highest available mA station to obtain a given amount of mAs would be:
to keep the exposure time as short as possible
when you have alot of subject contrast ( alot of tissue that will show up as gray, cause they are about the same in density) you will need to do what with your kVp?
lower kVp ( which creates black and white, witch is needed since the subject has little contrast. With low kvp, you will either get x-ray through or not. This means black if it gets through and white if it dosen't B/W= high contrast
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