Physics of radiography and radiation safety

Question 1

What are the 4 things you can alter to affect the image that is produced?

Answer 1

• Kv
• mA
• Time
• Film Focal Distance

Question 2

What is KVp?

Answer 2

Peak voltage across the cathode and the anode

Question 3

What does increasing KVp do?

Answer 3

• More photons
• Increased energy
• More penetrating

Question 4

What does increasing mA do?

Answer 4

• Increased heat in the cathode filament
• Increased number of electrons
• Increased number of protons

Question 5

What is FFD?

Answer 5

Film Focal Distance
distance between the focal spot on the anode and the detector under the patient

Question 6

What is absorption?

Answer 6

• Removed energy is transferred to the patient
• Increases with increasing atomic number
• Creates contrast between tissues

Question 7

What is Scatter?

Answer 7

• Removed energy is emitted away from the patient
• Gets worse with increasing KV
• Hazard to radiographer
• Causes loss of contrast due to fogging

Question 8

What causes film blackening?

Answer 8

Transmission and interaction with film-screen detector

Question 9

What is the function of the emulsion part of the image?

Answer 9

• Produces image
• Silver bromide questions

Question 10

What is a latent image?

Answer 10

• Not visible to the naked eye
• Must undergo chemical processing

Question 11

What is the advantage of an intensifying screen/ casette?

Answer 11

• Reduced dose
• Shorter exposure time
• Less motion blurring
• Less scatter

Question 12

What is the disadvantage of an intensifying screen/ casette?

Answer 12

Lost resolution

Question 13

How does computed radiography work?

Answer 13

• Casette contains a storage phosphate image plate containing photosimulable crystals
• X-ray energy is absorbed and temporarily stored during an exposure to create a latent image
• Cassette put into the processor where the image plate is removed and scanned by a laser which sets the stored energy as visible light
• Photodiodes capture the light emitted and converts it to a digital signal
• Image plate is exposed to bright white light to delete the latent image and allow re-use

Question 14

What is direct radiography?

Answer 14

• Flat-Panel detectors convert x-rays into electrical charge
• either direct or indirect converting systems
• Detectors either sit underneath the x-ray table or on the tabletop and can be used with grids
• Signal from the detector to the computer can be wired or wireless

Question 15

What are the advantages of digital radiography?

Answer 15

• Greater tolerance to sub-optimal exposure factors
• Images can be manipulated
• Images can be shared
• Quicker
• Easy storage
• No replacement film costs

Question 16

What are the disadvantages of digital radiography?

Answer 16

• High initial set up cost and ongoing maintenance
• Overexpenses can be overlooked
• Interpretation can be limited if the computer monitors are not of adequate quality

Question 17

What does deterministic mean in terms of radiography?

Answer 17

• threshold levels for effects exist
• Severity is proportional to the dose received

Question 18

What does stochastic mean in terms of radiography?

Answer 18

• No threshold level of radiation exists
• Probability is proportional to the dose received

Question 19

What does hereditary mean in terms of radiography?

Answer 19

Stochastic effects which occur in the offspring of the exposed

Question 20

What are the three principles of radiation protection?

Answer 20

• Radiation should only be undertaken if there is a definite clinical justification
• Any exposure to personnel should be kept to a minimum
• No legal dose limit should be exceeded

Question 21

How would you limit occupational exposure?

Answer 21

• Rotate staff
• Record any exposure involving staff
• Exposure chart
• Electronic charge

Question 22

How would you use a personel dosimeter?

Answer 22

• One badge per employee
• Worn on trunk underneath the protective clothing
• Stored outside the controlled area
• Store away from heat and sunlight
• Retain records for two years

Question 23

What is the function of emulsion in x-ray film?

Answer 23

• Produces an image
• made from silver bromide crystals

Question 24

What do the photon + Silver Bromide crystal produce together?

Answer 24

Silver atom is deposited

Question 25

What are the three different X-ray interactions with tissue?

Answer 25

• Deterministic
• Stochastic
• Hereditary

Question 26

How do you create a controlled area for radiation?

Answer 26

• Defined by a physical boundary
• Walls must be shielded
• Warning light and sign