factors controlling x ray beam intensity

Question 1

intensity

Answer 1

total amount of energy in the beam
intensity: quantity x quality

Question 2

Quantity:

Answer 2

Number of photons in the beam. Primarily related to tube current and exposure time and less so by tube voltage (kVp)
Expressed as: tube current (mA) X time (sec) → mAs
increased mA=more e released

Question 3

Quality:

Answer 3

Quality: Average energy the x-ray beam.
▪ Controlled primarily by the tube voltage (kVp)
X-ray of beam is heterogeneous (bremmsstrhaghlung)

Question 4

factors controlling beam intensity

Answer 4

1. Tube voltage
2. Exposure time
   3.Tube current
3. Filtration
   5.Collimation
4. Source-receptor distance

Question 5

tube voltage effect on intensity (increased)

Answer 5

As tube voltage increases:
oNumber of photons generated increases (increased quantity)
oMean energy of photons increases (increased quality)
oMaximum energy of photons increases

Question 6

Exposure time effect on intesity

Answer 6

As exposure time increases:
oNumber of photons generated increases(increased quantity)
oMean energy of photons is unchanged (quality unchanged)
oMaximum energy of photons is unchanged(quality unchanged)

Question 7

tube current effect on intensity

Answer 7

As mA increases:
oNumber of photons generated increases(increased quantity)
oMean energy of photons is unchanged (quality unchanged)
oMaximum energy of photons is unchanged(quality unchanged)

Question 8

filtration effect on intensity, types of filtration

Answer 8

Selectively removes long wavelength (low energy) x-rays.
Inherent Filtration: Glass envelope, Immersion oil, Metal housing, Tube window
Added Filtration: Aluminum disks
As filtration increases:
oNumber of photons decreases (reduced quantity)
oMean energy of photons increases (increased quality)
oMaximum energy of photons is unchanged

Question 9

why would low energy rays be filtered

Answer 9

not useful, only increase dosage

Question 10

Collimation effect on intensity

Answer 10

Restricts the size and shape of the beam.
oNumber of photons decreases
oMean energy of photons is unchanged
oMaximum energy of photons is unchanged

Question 11

Source-to-receptor distance follows what law

Answer 11

Inverse Square Law
Intensity of the beam varies inversely to the square of the source-to-receptor distance.

Question 12

inverse square law examples
doubled
tripled
halved

Answer 12

If distance is doubled (8” to 16”) = new intensity will be ¼ (inverse of 22)
If distance is tripled (4” to 12”) = new intensity will be 1/9 (inverse of 32)
If distance is halved (16” to 8”) = new intensity will be 4x (inverse of 1/22)

Question 13

As source-to-receptor distance increases:

Answer 13

oNumber of photons decreases (decreased quantity) divergence
oMean energy of photons is unchanged (unchanged quality)
oMaximum energy of photons is unchanged

Question 14

DENSITY – altered by factors
affecting?

Answer 14

quantity

Question 15

CONTRAST – altered by factors
affecting?

Answer 15

CONTRAST – altered by factors
affecting Quality of the beam

Question 16

Density
primarily controlled by?
Why?

Answer 16

oAmount of blackness of an image → Related to how many x-rays reach the receptor
oPrimarily controlled by mAs, and less so by kVp

Why? Because increasing mAs and kVp will increase the quantity. Increasing quantity more x-rays will reach the receptor → the darker the image will be (higher density)

Question 17

density mAs/exposure time rule

Answer 17

mA and exposure time are inversely proportional.
o If mA is increased, exposure time must be decreased to maintain the same density of the image.
o If mA is decreased, exposure time must be increased to maintain the same density of the image.

Question 18

Contrast
primarily controlled by?

Answer 18

o The difference in densities between light and dark regions of a radiograph
o Primarily controlled by the voltage

Question 19

high and low contrast diagram

Answer 19

Question 20

High Contrast (Short Gray Scale)
kVp/wave?
density differences?

Answer 20

▪ Low kVp (long wavelengths, less penetrating)
▪ Density differences between adjacent areas are greater; fewer shades of gray.

Question 21

Low Contrast (Long Gray Scale)
kVp/ waves?
densities?

Answer 21

▪ High kVp (short wavelengths, more penetrating)
▪ Density differences between adjacent areas are more subtle; more shades of gray.

Question 22

Effect of kVpon contrast

Answer 22

Low kVp: High contrast (low gray scale)
High kVp: Low contrast (large gray scale)

Question 23

which is low/high contrast?

Answer 23

left: low
right: high