kVp

Question 1

kVp

Answer 1

The higher the amount of kinetic energy the electron has, the higher the amount of photon energy. kVp determines the amount of KE an electron has. kVp is produced in the form of a wave over time.
Increase kVp - decrease wavelength.
Increase kVp - increase intensity

Question 2

Increase kVp

Answer 2

As kVp is increased the penetrability of the x-ray beam is increased and relatively fewer photons are absorbed in the patient. More x-rays go through the patient and interact with the IR.

Question 3

Explain the 15% rule

Answer 3

A reduction of one half of mAs should be accompanied by an increase of 15% in kVp to maintain a constant exposure of the IR. This will reduce dose to the patient significantly.

Question 4

kVp relationship to intensity
Primary intensity (leaving the tube)
Intensity at image receptor

Answer 4

Primary Intensity leaving the tube proportional to kVp^2

To IR kVp^4

Question 5

HIgh energy photons Vs Low energy photons

Answer 5

Low E: easily absorbed, differential absorption increases, higher subject contrast, short scale (film screen)
High E: more penetration therefore more shades of gray, lower subject contrast, longer scale (film screen)

Question 6

Patient Dose effect if increase:
SID
mAs
kVp
Grids

Answer 6

SID - decreased, but irrelevant since have to increase technique to compensate
mAs - increases
kVp - inverse relationship. Decreases pt dose when we increase kVp and LOWER mAs at the same time.
Grids - when we use grids we have to increase mAs so pt dose increases

Question 7

Increase kVp what affect on scatter

Answer 7

Increase scatter. Decrease image quality as scatter decreases subject and radiographic contrast. Scattered photons have less energy so no differential absorption or penetration is occuring

Question 8

Characteristic of body part that must be assessed prior to selecting an appropriate kVp

Answer 8

thickness of body part must be assessed. In order to determine how much kVp is needed to penetrate to IR.

Question 9

Grids

Answer 9

Grids are made of radiopaque strips alternating with sections of radiographic materials. Photons that don’t change direction will go through to the IR (travel parallel to the grid strips) photons that change direction (scatter) get absorbed by the lead strip. Downside of grids: absorbs some good primary radiation as well so we have to increase mAs. Don’t have to adjust kVp.