Phys - Med

Question 2

X-Ray Production

Answer 2

1. Electrons are emitted from a filament by thermionic emission in a vacuum using a low p.d
2. They are accelerated towards the anode using a high p.d
3. Collide with the heavy metal target, which emits x-ray photons by the photoelectric effect

Question 3

X-Ray Beam Intensity Control

Answer 3

1. Changing the p.d of the high voltage circuit will change the beam intensity proportionally, as emitted x-ray photons will have higher energies
2. Changing the current in the low voltage circuit will change the beam intensity, as more electrons, therefore x-ray photons, will be released

Needed to control the ionising effect of radioactivity on the patient

Question 4

X-Ray Image Sharpness Control

Answer 4

1. Placing detection plate close to patient and moving the x-ray source far away
2. Ensuring the patient holds still
3. Using a lead grid between the patient and detection source to stop scattered x-rays

Question 5

Radiation Dose Factors

Answer 5

Exposure time

X-ray beam intensity

Question 6

Attenuation

Answer 6

X-ray photons lose energy as they travel through matter

I = I₀e^(-μx)

Question 7

CT

Answer 7

Computerised Tomography scanners produce high-contract images of cross-sections

Question 8

CT scan

Answer 8

1. An x-ray source rotates around the patient with an array of detectors opposite it, emitting an x-ray beam that the detectors detect the intensity of at different points as the beam travels through different angles
2. The varying intensities are processed to form an image

Question 9

CT Advantages and Disadvantages

Answer 9

Hig quality images of bones and organs
Non-invasive

Ionising radiation
Images may be distorted due to similar densities

Question 10

PET

Answer 10

Positron Emission Tomography scanners produce a cross-section image of the body

Question 11

PET scan

Answer 11

1. The patient is injected with a positron-emitting radionuclide, attached to a substance that is appropriate to the investigated area
2. The patient is left for an hour to allow the radionuclide to move
3. The radionuclide will be absorbed and broken down, emitting positrons which will annihilate electrons in the body, releasing two high-energy photons which share the energy of the positron-electron pair
4. The released photons are detected and their energies are processed to create an image of the radioactivity in the region

Image formed based on metabolic activity in region of radionuclide, as high metabolism cells will break down the radionuclide more, causing more gamma rays to be detected.

Question 12

PET Advantages and Disadvantages