IP
on which side of the x-ray beam is penumbra (geometric un-sharpness) greater?
on the cathode side of the beam
increases
what is the general rule in regard to imaging extremities that are casted?
increase kVP to penetrate the cast.
what determines which photo-timing cell (AEC detector) is selected?
the part under examination.
why is proper positioning important when using AEC?
radiation exposure depends on the selected cell, requiring accurate positioning and CR alignment.
what is the formula for magnification in radiography?
image size/object size=SID/SOD
as SID increases, magnification_______?
decreases
how much should you adjust kVp for a wet plaster cast?
increase kVp by 8-10
when should the center cell be selected?
when the CR is directed at the part (example: AP hip)
the receptor exposure of a radiograph produced using AEC techniques may be influenced by ________?
adjusting receptor exposure control ( +/- 1 density)
How do you find SOD for the previous formula?
SID-OID=SOD
what are the two types of distortion?
1. size distortion (magnification)
2. shape distortion (elongation and foreshortening)
how much do you adjust your kVp to penetrate a dry plaster cast?
increase kVp by 5-7
When should we not choose the center cell?
for a PA chest exam
for very thing patients or pediatrics, a _______ receptor exposure control may be selected to help prevent overexposure?
A negative receptor exposure control (-1 density)
EXAMPLE QUESTION:
a radiograph image of an object measures 5 cm in diameter. If the SID is 40 inches and the OID is 5 inches, what is the actual size of the object?
1. 5/x=40-(40-5)
2. 5/x=40/35
3. 40x=175
4. x=4.375 cm
what factors affect shape distortion?
angulation of tube/part/IR
how much do you adjust your kVp when penetrating a fiberglass cast?
increase kVp by 3-4
why should the center cell NOT be used for a PA chest exam?
selecting center cell will place it over the heart and may result in over-penetration of the lung fields
for a very large patient, a _______ receptor exposure control may be selected to help prevent under exposure?
positive receptor exposure control
what does SID effect?
recorded detail (spatial resolution) and magnification (size distortion).
what factors affect size distortion?
OID and SID
When is a grid required for an examination?
when part thickness is greater than 10-13 cm
what cells should be selected for a PA chest exam?
outside cells
how does a technologist adjust the rate of exposure when using an AEC device?
adjust density control