Factors Effecting X-ray Beam Intensity- Lecture 5 Flashcards
Total amount of energy contained in the x-ray beam:
intensity
Intensity =
quantity x quality
The average energy in the x-ray beam:
quality
Quality is related to:
tube voltage (kVp)
According to quality, the x-ray beam is:
heterogeneous
The number of photons in the x-ray beam:
quantity
Quantity is related to tube ___ and ___
current; exposure time (mAs)
List the factors affecting intensity: (6)
- Kilovoltage
- Milliamperage
- Exposure time
- Filtration
- Collimation
- Source to film distance (inverse square law)
The inverse square law describes:
source to film distance (factor affecting intensity)
As tube voltage increases:
1. The number of photons generated ____ (_____)
2. Mean energy of photon ____ (_____)
3. Maximum energy of photon ____
- increases (increased quantity)
- increases (increased quality)
- increases
As exposure time increases:
1. The number of photons generated ____ (____)
2. The mean energy of photons _____ (_____)
3. Maximum energy of photons _____ (_____)
- increases (increased quantity)
- is unchanged (unchanged quality)
- is unchanged (unchanged quality)
As tube current (mA) increases:
1. The number of photons generated ____ (____)
2. The mean energy of photons _____ (_____)
3. The maximum energy of photons____ (_____)
- increases (increased quantity)
- is unchanged (unchanged quality)
- is unchanged (unchanged quality)
Selectively removes long wavelength (low energy) x-rays:
filtration
- glass envelope
- immersion oil
- metal housing
- tube window
These are all considered:
inherent filtration
The aluminum discs are considered:
added filtration
As filtration increases:
1. Number of photons ____ (____)
2. The mean energy of photons ____ (___)
3. Maximum energy of photons _____.
- decreases (decreased quantity)
- increases (increased quality)
- is unchanged
Restricts the size and shape of the beam:
collimation
With collimation:
1. Number of photons ____
2. mean energy of photons _____
3. maximum energy of photons _____
- decreases
- is unchanged
- is unchanged
The intensity of the beam varies inversely to:
The square of the source-to-receptor distance
A method of calculating the new beam intensity when changing the source-to-receptor distance:
Inverse square law
According to the inverse square law:
If the distance is doubled (8 to 16) = new intensity will be:
If the distance is tripled (4 to 12) = new intensity will be:
If distance is halved (16 to 8) = new intensity will be:
1/4 (inverse of 2^2)
1/9 (inverse of 3^2)
4x (inverse of 1/2^2)
As source-to-receptor distance increases:
- Number of photons ____. (____)
- Mean energy of photons ____. (____)
- Maximum energy of photons _____
- decreases (decreased quantity)
- is unchanged (unchanged quality)
- is unchanged
Increasing the source to film distance by 2 decreases photons by:
1/4 (by 4)
Which of the 6 factors affect the quantity of the x-ray beam?
- Tube voltage (kVp)
- Tube current (mA)
- Exposure time (s)
- mAs
- Distance
- Filtration
All of them affect quantity
Which of the 6 factors affect the quality of the x-ray beam?
- Tube voltage (kVp)
- Tube current (mA)
- Exposure time (s)
- mAs
- Distance
- Filtration
filtration and tube voltage (kVp)
Density is altered by factors affecting the ____ of the beam
quantity
Contrast is altered by factors affecting the ____ of the beam
quality
Amount of blackness in an image:
density
Density is the amount of blackness in an image which is related to:
how many x-rays reach the receptor
Density is primarily controlled by ____ and less so by ___
mAs (mA & exposure time); kVP
Increasing the source-to-film distance will decrease ____ due to decreased number of photons
density
Increasing the source-to-film distance has what affect density? why?
decreases density (due to decreased number of photons)
mA and exposure time are inversely proportional describing:
mAs rule (density)
If mA is increased, what must happen to exposure time to maintain the same density of the image?
exposure time must be decreased
If mA is decreased, what must happen to exposure time to maintain the same density of the image?
exposure time must be increased
The difference in densities between light and dark regions of a radiograph:
contrast
Contrast is primarily controlled by the:
voltage
- air
- bone
- metal
- tongue
- enamel
Put in order from lowest to highest contrast (dark to light on radiograph)
- air (darkest)
- tongue
- bone
- enamel
- metal (lightest)
The short gray scale is involved in:
high contrast
The long gray scale is involved in:
low contrast
High contrast (short gray scale) = ____ kVp
low kVp (long wavelengths; less penetrating)
In the short gray scale (high contrast), density differences between adjacent areas are ___.
____ shades of gray.
greater; fewer
Low contrast (long gray scale) = ____ kVp
high kVp (short wavelengths; more penetrating)
In the long gray scale (low contrast), density differences between adjacent areas are ____.
____ shades of gray
more subtle; more
Effect of kVp on contrast:
Low kVp = ____ contrast
High kVp = _____ contrast
high contrast (short gray scale)
low contrast (long gray scale)
