Principles of attenuation

Question 1

latent image

Answer 1

unprocessed exposed x-ray film

Question 2

causes of attenuation

Answer 2

• Absorption
• scatter

Question 3

Principles of attenuation

Answer 3

• Coherent scattering
• compton scattering
• Photo-electric effect
• pair production
• photodisintegration

Question 4

coherent scattering

Answer 4

• An incident x-ray photon of low energy interacts with an atom and causes the electrons to vibrate at the same frequency as the incident ray.
• The atom then releases the photon carrying the same energy as the incident ray but travels in a different direction.
• Its ranges are not applicable in diagnostic imaging
• no electron is ejected as it carries very little energy.

Question 5

Compton scattering

Answer 5

an incident x-ray interacts with the outer most electron and ejects it from its orbit, this electron is called compton electron.
* Upon ejecting the electron changes direction with low energy as compared to the incident ray.
* the energy of the incident ray is the difference between the energy of the incident ray and the compton electron.
* occurs through out diagnostic range of medical imaging

Question 6

Photoelectric effect

Answer 6

*Here the incident x-ray beam undergoes ionization reactions with the orbital electron of the k-shell
* All the energy of the incident x-ray photon is totally transfered to the atom and dislodges the electron in the k-shell, known as the photoelectron.
* The photoelectron escapes with kinetic energy equal to the difference in the energy of the x-ray photon and the binding energy of the electron.
* photo electric interactions provide diagnostic information on the image

Question 7

List the components of the photomultiplier tube.

Answer 7

1. X-ray source
2. subject( patient)
3. Input phosphor
4. Photo-cathode
5. Electrostatic lenses/ dinodes
6. Output phosphor
7. video Monitors

Question 8

X-ray source in the photomultiplier tube.

Answer 8

produces and directs x-rays towards the patient.

Question 9

Subject/ patient

Answer 9

Provide an invisible image when x-ray beam passes through them.

Question 10

Input phosphor

Answer 10

made up of cesium iodide and it converts the attenuated x-ray photons to light photons

Question 10

Image intensifier tube

Answer 10

Photo-multiplier tube

Question 11

Photocathode

Answer 11

• Light photons from the input phosphor strike the photocathode and are absorbed by photo-electric interactions, causing it to emit photoelectrons via the photoelectric effect.
• The electrons are then multiplied with the action of the dinodes/ photoelectric lenses and are directed towards the output phosphor by an electric field produced between photocathode and anode.

Question 11

Output phosphor

Answer 11

• The electrons hit the output phosphor and produces large numbers of light photons.
• made of silver activated zinc-cadium sulfide

Question 11

Video monitors

Answer 11

where the image produced is viewed.

Question 11

PLSCs

Answer 11

Photo Stimulated Luminescence complexes.