Factors controlling intensity Flashcards
What is intensity?
total amount of energy in x-ray beam
How do you determine x-ray intensity?
quantity x quality
What is the quantity & what is it related to?
number of photons in a beam
- tube current & exposure time (mAs)
What is the quality & what is it related to?
average energy of the x-ray beam
- tube voltage (kvp)
T/F the x-ray beam is heterogenous?
true: most x-rays are not the maximum energy
As tube voltage increases:
- # photons increases (quantity)
- mean energy increases (quality)
- max energy increases
As exposure time increases:
- # photons increases (quantity)
- mean energy unchanged
- max energy unchanged
As tube current increases:
- # photons increases (quantity)
- mean energy unchanged
- max energy unchanged
What is the purpose of filtration?
selectively removes long wavelength/low energy x-rays
As filtration increases:
- # photons decreases (quantity)
- mean energy increases (quality)
- max energy unchanged
How does collimation affect intensity?
- # photons decreases (quantity)
- mean energy unchanged
- max energy unchanged
How to calculate total filtration?
inherent (glass envelope, immersion oil, metal housing, tube window) + added (aluminum disks)
As the source to receptor distance increases:
- # photons decreases (quantity)
- mean energy unchanged
- max energy unchanged
If the distance to receptor is doubled what will the new intensity be?
1/4
What factors affect density ?
time, mA, distance (quantity)
– things that affect the # of x-rays reaching receptor
What factors affect contrast?
kVp, filtration (quality)
– things that affect the energy of the x-rays reaching the receptor
Higher density images will be lighter or darker & why?
darker because more x-rays reach receptor
If exposure time has been doubled and you want to maintain the same density, what can you do?
half the current (mA)
What primarily controls the contrast?
voltage
Low contrast has short or long gray scale? Why?
long gray scale
– high penetration, high kvp (short-wavelengths)
High contrast has short or long gray scale? Why?
short gray scale
– less penetrating (long-wavelengths)
Which type of scale/contrast has greater density differences between adjacent areas?
high contrast / short gray scale
Which type of scale/contrast has more subtle differences between adjacent areas?
low contrast / long gray scale
How does kVp affect contrast?
- high kvp = high contrast
- low kvp = low contrast
