X Ray Imaging

Question 1

How are x rays produced?

Answer 1

1. Electrons are emitted by thermionic emission
2. They are accelerated by pd towards a tungsten target acting as an anode
3. They collide with the target, decelerating rapidly and emitting X-ray photons
4. Some electrons continue to collide with the target atoms, ionising them and producing the line spectra seen on an X-Ray graph

Question 2

What equation does X-Ray absorption follow?

Answer 2

I=Iₒe⁻ᵘˣ

Question 3

What is the attenuation coefficient?

Answer 3

Different body parts have different thickness and hence can absorb different amounts of X-rays

Question 4

What does a scintillator do?

Answer 4

Intensifies X-rays

1. They convert x ray photons to visible light photons.
2. These are easier to detect since they have less energy
3. This is also safer since it reduces the amount of ionising radiation needed by a factor of 50-1200

Question 5

How does an x-ray cassette/ scintillator sandwich work?

Answer 5

Most x-rays pass through the first scintillator so using a second one behind meaning the intensification can be doubled

Question 6

What is fluroscopy?

Answer 6

Moving X ray images that surgeons can use to carry out operations

Question 7

How does fluoroscopy work?

Answer 7

A tube, simple collimeter and filter are used to keep the beam directed and at a constant wavelength.
The anti-scatter grid is a group of hollow tubes ensuring only the x-rays travelling in the correct direction are detected so the image doesn’t blur
The scintillator intensifies the image.
The CDC camera continually sends images of the scintillator the monitor for the surgeon to see. The scintillator and camera are kept in a dark container as only light from the scintillator needs to be detected.

Question 8

Why are contrast media used?

Answer 8

Similar soft tissues have low contrast. A contrast medium has a high atomic number so the X-Ray absorption increases in certain areas.

Question 9

What is a barium meal?

Answer 9

Barium sulfate mixed with water used to increase absorption particularly for the alimentary canal

Question 10

What is an iodine contrast medium?

Answer 10

Iodine liquids are injected into veins or arteries to provide pictures of blood flow (angiograms)

Question 11

How does a CT scan work?

Answer 11

A CT scan rotates the x-ray beam and the detector around the patient in a helical pattern.
This takes slice like images that can be built up into 3D images.

Question 12

What are the disadvantages of CT scans?

Answer 12

They require larger doses of x rays, are more expensive and can take longer for a detailed scan