Ch11: Secondary Factors Flashcards
What sizes of filaments are there?
Large (1-1.2mm)
Small (0.5-0.6mm)
What is the purpose of the filaments in the cathode?
affects heat of tube (tube loading capacity)
affects spatial resolution/sharpness of anatomy
T/F The smaller the focal spot means better spatial resolution or recorded detail.
True
T/F Larger focal spots create heat on a larger surface which could cause heat damage to the tube.
False
Smaller focal spots disperse heat on a smaller area, creating possible heat damage to the tube
Does focal spot size have any affect on the exposure?
no
How does focal spot size affect spatial resolution?
larger size decreases spatial resolution
larger size increases the area of un-sharpness
beam divergence occurs
T/F Distance is a factor that will either increase or decrease exposure dose to people/objects.
True
As distance (from the beam) increases, the exposure dose decreases
T/F As SID increases, the exposure to the IR increases.
False
As SID increases, the amount of radiation hitting the IR will decrease. (as long as the technique remains the same)
How do you fix a low EI if the distance is too far?
Increase your mAs
SID stands for…
source to image receptor distance
SID affects… (quantity/quality)
quantity
affects amount of radiation reaching the IR/patient
What is another abbreviation for SID?
FFD
Focal Film Distance
T/F Beam intensity will change when distance changes.
True
Amount of radiation (beam intensity) on the IR will change at different distances
(quantity)
T/F Increased SID will increase exposure, intensity, and patient dose.
False
Increasing SID will decrease all those amounts
T/F Decreased SID will increase patient dose.
True
Exposure Index and intensity will also increase
Does SID and exposure index have a inverse or direct relationship?
inverse
Does SID and patient dose have a inverse or direct relationship?
inverse
Does SID and beam intensity have a inverse or direct relationship?
inverse
What is the inverse square law?
Intensity of radiation at a given distance from the source is inversely proportional to square of the distance
(Intensity 1 / Intensity 2) =
(distance2^2 / distance1^2)
If you were to double your distance (SID) from 50in to 100in, how has your intensity changed?
intensity has decreased by 1/4
What situation would you use the inverse square law formula?
finding intensity of radiation when distance changes (as long as technical factors remain unchanged)
When would you use the direct square law formula?
maintaining exposure when SID changes, calculating mAs to compensate for change in distance (as long as other factors remain the same)
T/F As distance increases (SID), the beam becomes more perpendicular to the subject and increases magnification.
False
increasing the distance will decrease magnification
the beam does become more perpendicular
As SID increases, mAs should _____ to keep the exposure the same
increase
Direct Square Law or Exposure Maintenance Formula
mas 1 / mas 2 = (SID1^2 / SID2^2)
If SID decreased, but you did not change your mAs technique, what would happen to the EI?
increase
How do you find what % of SID is OID?
OID / SID