Radiation Characteristics

Question 1

What are 5 things that affect x-ray beam quality?

Answer 1

• Voltage and kilovoltage
• Kilovoltage peak (kVp)
• Density and kVp
• Contrast and kVp
• Exposure time and kVp

Question 2

What determines the energy and penetrating power of radiation?

Answer 2

Wavelength (x-rays with shorter wavelengths have more penetrating power)

Question 3

What is the term x-ray beam quality in reference to? What is the quality controlled by?

Answer 3

Describes the mean energy or penetrating ability of the x-ray beam. Controlled by the kilovoltage peak

Question 4

What is voltage? What is it a measurement of?

Answer 4

The potential difference between two electrical charges. Measurement of force (speed). This force is the electrical force that causes electrons to move from the cathode to the anode.

Question 5

What happens to the speed of electrons when voltage is increased?

Answer 5

The speed of the electrons is increased and the electrons strike the target with greater force and energy. End result is a penetrating x-ray beam with a short wavelength

Question 6

What range of voltage should be used in dental radiography?

Answer 6

Between 65 kilovolts to 100 kilovolts (kV = 1000 volts). 65 kV is inadequate penetration and 100 kV is overpenetration

Question 7

What is the kilovoltage peak?

Answer 7

The maximum or peak voltage, usually referring to the peak voltage of an alternating current

Question 8

What is density in an image?

Answer 8

Overall darkness or blackness of an image

Question 9

How will the image appear if the kilovoltage is increased? How will this affect the contrast?

Answer 9

Image will appear lighter (low-contrast - many shades of gray)

Question 10

How will the image appear if the kilovoltage is decreased? How will this affect the contrast?

Answer 10

Image will appear lighter (high-contrast - black and white)

Question 11

What is the exposure time?

Answer 11

Interval of time during which x-rays are produced and is measured in impulses

Question 12

What should we do if we increase the kilovoltage?

Answer 12

Decrease the exposure time

Question 13

What is x-ray beam quantity?

Answer 13

Number of x-rays produced in a dental x-ray unit

Question 14

What is amperage?

Answer 14

Determines the amount of electrons passing through the cathode filament

Question 15

What does increasing amperage do?

Answer 15

Increases the number of electrons travelling from cathode to anode and produces more x-rays

Question 16

The QUANTITY of the x-rays produced are controlled by what?

Answer 16

Milliamperage

Question 17

What is ampere?

Answer 17

Unit of measure used to describe the number of electrons of current flowing through the cathode filament (milliampere = 1/1000 amperes)

Question 18

What does milliamperage range from in dental radiography?

Answer 18

7-15 mA, any more will produce excessive heat

Question 19

Milliamperage also regulates what?

Answer 19

The temperature of the cathode filament

Question 20

What does increasing milliamperage do to the image?

Answer 20

Makes the image darker (higher density)

Question 21

What are milliampere-seconds?

Answer 21

mAs, the product of milliamperes and exposure time

Question 22

When milliamperage is increased, exposure time must be ____

Answer 22

Decreased

Question 23

What is x-ray beam intensity determined by? (equation)

Answer 23

The product of the quantity and quality per unit of area per unit of exposure time - intensity = (quantity)(quality)/(area)(exposure time)

Question 24

In summary, how does a higher kilovoltage peak affect the x-ray image?

Answer 24

• Produce an x-ray beam with more energy + shorter wavelengths
• Increase the intensity of the x-ray beam
• Controls the amount of contrast (high kVp = low contrast)

Question 25

In summary, how does a higher milliamperage affect the x-ray image?

Answer 25

Produces an x-ray beam with more energy, increasing the intensity of the x-ray beam which increases the density

Question 26

What are the three distances to consider in x-ray imaging?

Answer 26

• Target-surface (source to patient’s skin)
• Target-object (source to patient’s tooth)
• Target-receptor (source to image receptor)

Question 27

How does a higher distance affect the intensity of the beam?

Answer 27

Lower intensity

Question 28

What is the inverse square law?

Answer 28

When the distance increases, the beam intensity is the inverse square of the distance (ie. distance is doubled, beam is 1/4 as intense)

Question 29

What is the half-value layer?

Answer 29

The thickness of a specified material that reduces the intensity by half is termed the half-value layer