Radiology 3. X-Ray With Matter

Question 1

what happens when an xray photon interacts with some matter?

Answer 1

3 Things;
Transmission - mass through unaltered
Absorption - stopped by the matter
Scatter - changes direction

Question 2

what happens during attenuation?

Answer 2

Attenuation is the reduction in intensity of the x-ray beam which means less is reached to the radiographic film.

This can be because of Absorption and scattering of the photon - a result of this means different shading on the radiograph.

Absorption & scattering = lighter colours on xray film since it doesn’t make it through to the film

Transmission = darker colours since the photons hit the film

Question 3

what is the attenuation of the following things?
Lead, paper, enamel, cheek (tissue).

Answer 3

Thick lead = All attenuation = white on the xray
piece of paper = almost all transmission = black on xray
enamel = mainly attenuation = white/light grey on xray
Cheek = mostly transmission = black/dark grey on xray

Question 4

what is the photoelectric effect?

Answer 4

when a photon in an x-ray beam interacts with an INNER SHELL electron in a piece of matter. Creating a photoelectron which ionises and is emitted from the object.

= tissue damage since electrons are lost

Question 5

what is the compton effect?

Answer 5

Photon in x-ray beam interacts with outer shell electron

Question 6

what is the compton effect?

Answer 6

Photon in x-ray beam interacts with OUTER SHELL electron, the photon is scattered in a different direction, the electron is recoiled and displaced out of the atom making it unstable (ionised)

Question 7

whats the effect of scatter on radiographs?

Answer 7

photons scattered backwards, sideways or obliquely forwards WONT reach receptor - dont affect image. Stays lighter in colour

Photons scattered forwards reaching the receptor may cause darkening of the image in the wrong place

Question 8

how do you reduce scatter?

Answer 8

The collimator on an xray machine helps by:

reducing;
- surface area irradiated
- volume of irradiated tissue
- number of scattered photons produced in the tissue
- scattered photons interacting with receptor
- loss of contrast on radiographic image

Question 9

what effect does photoelectric effect have on radiation dose?

Answer 9

Xray photon energy deposited into the tissue (electron). To compensate you need a higher patient dose but it is necessary for producing a clear image.

Question 10

what effect does compton effect have on radiation dose?

Answer 10

xray photon energy is deposited into the tissue however because of scattering, increasing the dose wont help have a clear image

Question 11

what is the unit of xray dosage?

Answer 11

Sv = Sieverts

xrays are measured in x10^-6 µ

µSv

Question 12

what are the effective doses for
Periapical/Bitewing
Maxillary occlusal
panoramic

radiographs?

Answer 12

Periapical/Bitewing - 4 µSv
Maxillary occlusal - 8 µSv
panoramic - 20 µSv

Question 13

what is the effect of lowering kilo volts on x-ray unit?

Answer 13

lower x-ray potential different -> lower energy photons produced -> increased photoelectric effect interactions -> more contrast between different tissues HOWEVER/BUT patient ABSORBS MORE photons which can result in tissue damage

Question 14

what is the effect of raising kilo volts on x-ray unit?

Answer 14

higher x-ray potential difference -> higher energy photons produced -> reduced photoelectric effect interactions -> less absorption by patient. HOWEVER/BUT the contrast between different tissues is LESS