Xray settings

Question 1

Intensity

Answer 1

• quantity of electrons
• number of photons
• density = darkness of the image

Question 2

Energy

Answer 2

• quality of electrons
• energy of photons
• contrast = diffrence among grey levels

Question 3

Eposure time (s) = seconds

Answer 3

• affects intensity
• too long > too dark, overexposed
• too short > noisy, underexposed
• setting that is most frequently changed
  you increase exposure time for = bigger patients, adult patients
  and you decrease exposure time for smaller patients, edentoulous patients, children

Question 4

Tube current (mA) = millampenes

Answer 4

• affects intenisty
• too much > too dark, overexposed
• too little > noisy, underexposed
• usually cannot adjust

Question 5

Tube potential (kVp) = peak kilovoltage

Answer 5

• affects intensity and energy
• too high > too gray, not enough contrast; mostly compton scattering
• too low - too light, very high contrast; mostly photoelectric absorption

Question 6

Filtration

Answer 6

• involves aluminium
• remove lower energy photons from the beam to reduce patient exposure
• conceptually similar to beam hardening

Question 7

Collimation

Answer 7

• metallic barrier usually made of lead
• reduces beam size (round or rectangular) to reduce patient exposure
  (Round is reduced to 7cm diameter circle and rectangular area just larger than the image receptor)
• rectangular collimation is best method to reduce radiation dose
• ‘PID’ - position-indicating device helps to line up the xray beam properly and it also provides built in collimation

Question 8

What is the best way to reduce raditation?

Answer 8

collimation

Question 9

Distance

Answer 9

• inverse sqaure law = further from source, less photons per unit area
• operator should be at least 6 feet away
  (less photons = lighter the rad image)

Question 10

Geometry

Answer 10

• UMBRA is the shadow behind an image
• PENUMBRA is the side shadow
• focal spot size (FSS) - the smaller this is produces a smaller penumbra and a sharper image
• source to object distace (SOD)
• object to image distance (OID)
• when the SOD increases, the intensity of the xray beam decreases
• the smaller the OID is you get a sharper image as well as less magnification

Question 11

blurriness of an image equation =

Answer 11

SOD