8/27: Factors Controlling X-Ray Beam Intensity Flashcards
- The total amount of energy contained in the x-ray beam
Intensity
- Intensity =
a. Quantity x Quality
- The number of photons in the beam
a. Quantity
- “Quantity” is primarily related to ____ and ____ and less so by tube voltage (kVp)
a. Tube current
b. Exposure time
- This is the average energy in the x-ray beam
a. quality
- Quantity is expressed as
a. Current (mA) x Time (sec) → mAs
- This is controlled primarily by the tube voltage (kVp)
a. Quality
- X-ray of the beam is
a. Heterogenous
- What are the 6 factors that control the x-ray beam intensity?
a. Tube voltage
b. Exposure time
c. Tube current
d. Filtration
e. Collimation
f. Source-receptor distance
- As the tube voltage increases, what happens to the number of photons generated?
a. Increases (quantity)
- As the tube voltage increases, what happens to the mean energy of photons?
a. Increases (quality)
- As the tube voltage increases, what happens to the maximum energy of photons?
a. increases
- As the tube voltage increases, what 3 things occur?
a. Increase # of photons
b. Increase mean energy of photons
c. Increases maximum energy of photons
- As exposure time increases, what happens to the number of photons generated?
a. Increase (quantity)
- As exposure time increases, what happens to the mean energy of photons?
a. Quality unchanged
- As exposure time increases, what happens to the maximum energy of photons?
a. Quality unchanged
- The tube current is represented as
mA
- As mA increases, what happens to the number of photons?
a. Increases (increased quantity)
- As mA increases, what happens to the mean energy of photons?
a. Remains unchanged
- As mA increases, what happens to the maximum energy of photons?
a. Remain unchanged
- This selectively removes long wavelength (low energy) x-rays
a. Filtration
- Kind of x-rays does filtration remove?
a. Long wavelength (low energy)
- Total filtration =
a. Inherent filtration + added filtration
- What factor that affects x-ray intensity decreases the quantity of photons?
a. filtration
- What are examples of inherent filtration?
a. Glass envelope
b. Immersion oil
c. Metal housing
d. Tube window
- What are examples of added filtration?
a. Aluminum disk
- As filtration increases, what happens to the number of photons?
a. Decreases (decrease quantity)
- As filtration increases, what happens to the mean energy of photons?
a. Increases (increases quality)
- As filtration increases, what happens to the maximum energy of photons?
a. Remains unchanged
- This restricts the size and shape of the beam
a. Collimation
- What 3 things happen with collimation?
a. # of photons decreases
b. Mean energy of photons is unchanged
c. Maximum energy of photons is unchanged
- The intensity of the beam varies to what law?
a. Inverse square law
- The intensity of the beam varies inversely to the square of the
a. Source-to-receptor distance
- If the distance is doubled (8-16), the new intensity will be
a. 1⁄4
- If the distance is tripled (4-12), the new intensity will be
a. 1/9
- If the distance is halved (16-8), the new intensity will be
a. 4x
- As source-to-receptor increases, what 3 things happen?
a. # of photons decreases (decreased quantity)
b. Mean energy of photons is unchanged
c. Maximum energy of photons is unchanged
- This is altered by factors affecting Quantity of the beam
a. Density
- The amount of blackness of an energy is related to what?
a. How many x-rays reach the receptor
- This is altered by factors affecting the Quality of the beam
a. Contrast
- Density is primarily controlled by mA or kVp?
a. mA
- Decreasing mA does what to density?
a. decreases
- Increasing the quantity will increase what?
a. Density of an image (making it darker)
- if you increase density, what happens to the radiograph image?
a. Becomes darker
- If you decrease density, what happens to the radiograph image?
a. Becomes lighter
- Density controls what?
a. blackness
- What is the mA rule of density?
a. mA and exposure time are inversely proportional
- Are mA and exposure time directly or inversely proportional?
a. Inversely
- This is the difference in densities between light and dark regions of a radiograph
a. Contrast
- Lower contrast means what?
a. More shades of gray
- Higher contrasts means what?
a. Less shades of gray
- Contrast is primarily controlled by what?
a. Voltage (kVp)
- What affects contrast?
kV
- Does high contrast have low or high kVp?
a. Low kVp
- Does low contrast have low or high kVp?
a. High kVp
- High contrasts produce what?
a. Short gray scale, low kV
- Low contrast produces what?
a. Long gray scale, high kV