Chapter 11 Flashcards
define 15% rule
- The 15% rule states that changing the kVp by 15% has the same effect as doubling the mAs or reducing the mAs by 50%
- Maintaining or adjusting exposure to the IR can be accomplished with kVp
define body habitus
the general form or build of the body, including size
what are the 4 different types of body habitus
- sthenic
- hyposthenic
- hypersthenic
- asthenic
define sthenic
define hyposthenic
define hypersthenic
define asthenic
define direct square law
provides a mathematical calculation for adjusting the mAs when changing the SID.
define exposure maintenance formula
provides a mathematical calculation for adjusting the mAs when changing the SID.
define inverse square law
- states that the intensity of the x-ray beam is inversely proportional to the square of the distance from the source
- The relationship between distance and x-ray beam intensity
define magnification factor (MF)
- indicates how much size distortion or magnification is demonstrated on a radiographic image.
- MF = SID / SOD
define object to image receptor distance (OID)
- When distance is created between the object radiographed and the IR
- decreased beam intensity may result
define source to image receptor distance (SID)
- The distance between the source of the radiation and the IR
- affects the amount of radiation reaching the patient
- the intensity of the radiation varies at different distances
define source to object distance (SOD)
- the distance from the x-ray source (focal spot) to the object being imaged
- SOD = SID - OID
what are the 3 primary exposure factors?
- mA
- seconds
- kVp
does mAs control quality or quantity?
- quantity
- controls the number of electrons boiled off the filament
does mAs and exposure value have a direct or indirect relationship?
direct
What happens to the exposure value when mAs is increased?
- exposure increases
what happens when the exposure value when mAs is decreased?
- exposure decreases
true or false: In order to get a certain mAs, the milliamperage or time can be adjusted to get the same byproduct
true
- when we look for a mAs of 20, different methods can be applied:
100 mA x 0.2s = 20 mAs
200 mA x 0.1s = 20 mAs
what type of relationship does milliamperage and exposure time have?
- indirect
- when adjusting mAs and time, they have an indirect relationship in order to get a specific mAs
- 50 mA x 200ms (0.2s) = 10 mAs
- 200 mA x 50ms (0.05s) = 10 mAs
- the variables depend on the type of examination being done and the type of tissue density (pediatrics, elders, etc.)
Can mAs control brightness level when using digital IR?
- no
- need to make sure your exposure is correct in order for the Image to be diagnostic
How is the brightness level affected when thr mAs is too low?
- image is bright, but there’s an increased on quantum noise
How is the brightness level affected when the mAs is too high?
- exposes the patient with too much radiation
