RQF
when should grids be used?
1. to reduce scatter
2. to improve contrast
3. when body part is 10-12 cm or larger
4. using kVp over 70
what tissue type attenuates the least amount of radiation?
the lungs. (lowest atomic number)
what factors influence scatter?
1. kVp
2. patient thickness
3. field size
what are the four primary exposure factors?
1. kVp
2. time
3. mA
4. SID
what part of the body has the highest subject contrast?
the chest
what is the grid interspace material made out of?
plastic and aluminum.
how does SID affect magnification?
SID increases, magnification decreases.
why would a compression device be used during a radiographic exam?
to reduce scatter
How does increased filtration affect beam quality?
1. increased filtration hardens the beam
2. increases energy and quality of the beam
what is the minimum change in mAs, that gives visible difference and what is an equivalent technique change?
1. 30% chance in mAs
2. 5% increase in kVp
how does an increase in scatter produced by the patient affect the image?
decreases contrast due to noise and more shades of gray.
how does SID affect spatial resolution?
increased SID, increased spatial resolution.
what does an increase in focal spot size do?
decreases spatial resolution.
how does increased filtration affect patient dose?
decreases patient dose
what change in kVp is the same as doubling the mAs?
15% increase in kVp
what are the 3 geometric factors that affect image quality?
1. magnification
2. distortion
3. focal spot size
How does OID affect magnification?
increased OID, increased magnification
does an increased focal spot size have any effect on receptor exposure?
no
what are 2 major factors that determine spatial resolution in computed radiography?
1. sampling size/frequency
2. pixel pitch
what happens to receptor exposure and scatter absorption when grid factors are change from a 5:1 grid, to a 16:1 grid?
1. more scatter is absorbed
2. receptor exposure decreases
what field size will result in the shortest scale of contrast?
smallest field size
how does OID affect spatial resolution?
increased OID, decreased spatial resolution
what factors contribute to image blur?
1. large focal spot size
2. large OID
3. patient movement
how can a radiographer reduce the change of distortion?
1. short OID
2. large SID
3. ensure anatomy is parallel to the receptor
what causes the anode heel effect?
1. x-ray absorption in the heel of the anode.
2. reduces x-ray intensity on anode side