Factors controlling the X-ray beam intensity

Question 1

What is the intensity of the beam mean?

Answer 1

Total amount of energy contained in the x-ray beam

Question 2

What does the quantity mean?

Answer 2

Number of photons in the beam. Primarily related to tube current and exposure time

Question 3

What is the equation for intensity?

Answer 3

Intensity: Quantity X Quality

Question 4

What is quantity expressed as?

Answer 4

tube current (mA) X time (sec) → mAs

Question 5

What is quality?

Answer 5

Average energy the x-ray beam

Question 6

What is quality of beam controlled by?

Answer 6

tube voltage (kVp)

Question 7

What is quantity of beam controlled by?

Answer 7

tube current and exposure
time

Question 8

X-ray of beam is heterogeneous or homogeneous?

Answer 8

heterogeneous

Question 9

What are the factors that control x-ray beam intensity?

Answer 9

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

Question 10

As the tube voltage increases what happens to the…

Number of photons
Mean energy
Maximum energy

Answer 10

o Number of photons generated increases
o Mean energy of photons increases
o Maximum energy of photons increases

Question 11

As tube voltage increases the beams become more or less efficient?

Answer 11

more

Question 12

As the exposure time increases what happens to the…

Number of photons
Mean energy
Maximum energy

Answer 12

o Number of photons generated increases
o Mean energy of photons is unchanged
o Maximum energy of photons is unchanged

Question 13

As the tube current (mA) increases what happens to the…

Number of photons
Mean energy
Maximum energy

Answer 13

o Number of photons generated increases
o Mean energy of photons is unchanged
o Maximum energy of photons is unchanged

Question 14

If double the mA you must _____ the time to have the same energy/number of photons

Answer 14

half

Question 15

What does filtration do?

Answer 15

Selectively removes long wavelength (low energy) x-rays

Question 16

What are the inherent filtrations in the x-ray machine?

Answer 16

o Glass envelope
o Immersion oil
o Metal housing
o Tube window

Question 17

What are the added filtrations in the x-ray machine?

Answer 17

aluminum disks

Question 18

As the filtration increases what happens to the…

Number of photons
Mean energy
Maximum energy

Answer 18

o Number of photons decreases
o Mean energy of photons increases
o Maximum energy of photons is unchanged

Question 19

What does collimation do?

Answer 19

Restricts the size and shape of the beam.

Question 20

Adding a collimator does what to the…

Number of photons
Mean energy
Maximum energy

Answer 20

o Number of photons decreases
o Mean energy of photons is unchanged
o Maximum energy of photons is unchanged

Question 21

What is the inverse square law for the source-to-receptor distance?

Answer 21

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

Question 22

What does the inverse square law say if the distance is doubled the intensity will be…

Answer 22

1/4

Question 23

What does the inverse square law say if the distance is tripled the intensity will be…

Answer 23

1/9

Question 24

What does the inverse square law say if the distance is halved the intensity will be…

Answer 24

4x

Question 25

As the source-to-receptor distance increases what happens to the…

Number of photons
Mean energy
Maximum energy

Answer 25

o Number of photons decreases
o Mean energy of photons is unchanged
o Maximum energy of photons is unchanged

Question 26

What is the density altered by?

Answer 26

altered by factors affecting Quantity (number of photons) of the beam
- exposure time and mA

Question 27

What is the contrast altered by?

Answer 27

altered by factors affecting Quality (average energy) of the beam
- kVp and filtration

Question 28

The amount of blackness of an image is related to…

Answer 28

how many x-rays reach the receptor

Question 29

What is density primarily controlled by?

Answer 29

mAs
- less so by kVp

Question 30

Why does increasing mAs and kVp increase the density?

Answer 30

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 31

If mA is increased, exposure time must be _____________ to maintain the same density of the image

Answer 31

decreased

Question 32

If mA is decreased, exposure time must be ___________ to maintain the same density of the image

Answer 32

increased

Question 33

What is contrast?

Answer 33

The difference in densities between light and dark regions of a radiograph

Question 34

What is contrast primarily controlled by?

Answer 34

voltage

Question 35

What is better low or high contrast?

Answer 35

depends on what you are looking for

Question 36

High contrast has what kind of gray scale?

Answer 36

short gray scale
- fewer shades of gray

Question 37

Low contrast has what kind of gray scale?

Answer 37

long gray scale
- more shades of gray

Question 38

High contrast images are caused by what kind of kVp?

Answer 38

Low kVp (long wavelengths, less penetrating)

Question 39

Low contrast images are caused by what kind of kVp?

Answer 39

High kVp (short wavelengths, more
penetrating)

Question 40

If a patient has a big mandible do you need to raise or lower the kVp?

Answer 40

higher kVp

Question 41

High kVp: ____ contrast (large gray scale)

Answer 41

Low

Question 42

Low kVp: ____ contrast (low gray scale)

Answer 42

High