Formulas
How do we calculate SID?
OID + SOD
What is the one type of size distortion?
Magnification
What x-rays are those that exit from the patient?
Remnant
Who invented the grid?
Gustave Bucky
What are the two types of AECs?
Ionization chamber or phototimer
mAs x to/from is the formula for what?
Grid conversion
What are the two types of shape distortion?
Foreshortening and elongation
How does a short scale of contrast look on a radiograph?
Black and white with limited shades of gray
What technique could be done in place of a grid to reduce the amount of scatter reaching the IR?
Air Gap Technique
What are 3 out of the 5 things that must be set on your control panel when using AEC?
kVp
mA
back up time
density
detector selection
What is the Inverse Square Law?
I1/I2=D22/D12
What shape distortion that occurs when the image is longer than the true object?
Elongation
Changing the kVp by 15% has the same effect on exposure to the IR as changing the mAs by a factor of what?
2
When are grids used (2 answers)?
When the part is: 10 cm (4 inches) or greater in thickness and when using over 70 kVp
150-200% above the expected exposure
What number is assigned to a 8:1 grid when performing the grid conversion formula?
4
What shape distortion occurs when the image is shorter than the true object?
Foreshortening
What technique chart is preferred because body parts will be penetrated and contrast will be consistent?
Fixed kVp/variable mAs
What grid error occurs when the x-ray beam is not centered side to side with the center of a grid?
Off-center error
What is one cause of overexposure when using AEC?
Wrong bucky selected
Improper cell selected (cell under a thicker part)
Presence of artifacts
Density control left on a "plus" setting
Exposure time needed is less than the minimum response time
How do we calculate the magnification factor?
SID/SOD or Image size/Object size
How will a larger SID affect size distortion?
Less magnified
What is a measure of the imaging system's ability to accurately display small anatomic objects having high spatial frequency?
Modulation transfer function
What is the absorption of the primary beam, reducing the number of photons reaching the IR, mainly occurs with "focused" grids?
Grid cut-off
What is one cause of underexposure when using AEC?
Not enough collimation
Improper photocell selected (cell under a thinner part)
Anatomy is near the edge of the body
Anatomy not centered over the photocell
Back up time is set too short for the time needed
Density control left on a "minus" setting