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Flashcards in Medical Physics Deck (14)
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1
Q

Describe the use of contrast media

A
  1. Iodine/Barium used as contrast media
  2. Injected or ingested into body
  3. High Z number, absorbs more X-Rays
  4. Used to give greater contrast
2
Q

Describe the operation of a CAT scanner

A
  1. Fan shaped X-Rays rotate around the patient
  2. Detected by a ring of detectors
  3. Relative attenuation detected are processed and turned into a 3D image via computer
3
Q

Describe the advantages of CAT scan compared to X-ray

A

Differences: x-ray is one directional/produces single image
CAT produces image from slices
Advantages: - CAT produces 3D images which can be rotated
- greater detail/contrast + soft tissues can be seen

4
Q

Describe the use of medical tracers to diagnose the function of organs

A
  1. Ingested or injected
  2. Technitium99m used as a radioactive source
  3. Path can be followed by gamma detectors and image of organs can be observed
5
Q

Describe the main components of a gamma camera

A

Collimator: allowed parallel gamma photons travel to the scintillator (narrow lead tubes makes image less blurred)
Scintillator: gamma ray photon produces many visible light photons
Photomultiplier: an electrical pulse produced from light photons
Computer: signals user to produce an image

6
Q

Describe the principles of PET scanning

A
  1. Radioactive substance used (fluorine-18)
  2. Positron-electron annihilation
  3. Picked up by diametrically opposite detectors
  4. Computer produces 3D image
  5. Can reveal function of the brain
7
Q

Describe the main components of an MRI scanner

A
Strong electromagnet
Radio transmitting coils
Radio receiving coils
Gradient coils
Computer
8
Q

Outline the principle of MRI

A
  1. Protons have spin/act like tiny magnetic
  2. Protons precesses about the magnetic field provided by the strong electromagnet
  3. Transmitting coil provides pulses of radio waves of equal frequency to the Larmor frequency
  4. Protons absorb radio waves, resonate and flip to higher energy level
  5. When protons flip back to lower energy level they emit radio waves
  6. The relaxation time depends on the tissues
  7. Radio waves picked up by the receiving coils
  8. Gradient coils alter the magnetic flux density throughout the body
  9. Larmor frequency variety throughout the body
  10. Computer processes image
9
Q

Describe advantages and disadvantages of MRI

A

Adv: not ionising and better soft tissue contrast
Disadv: heating effect on metal objects so people with metal or pacemakers can’t use it
Long time to do, have to sit still

10
Q

Describe the need for non-invasive techniques

A

No cutting. Less risk of infection and less trauma

11
Q

Describe the properties of ultrasound

A

Longitudinal vibration with frequency > 20kHz

12
Q

Describe the piezoelectric effect

A

The application of a p.d across a material causes expansion/contraction and vice versa

13
Q

Describe the principles of ultrasound scanning

A
  1. Pulses of ultrasound sent into body
  2. Use of gel for acoustic impedance matching
  3. Pulse reflected at boundaries of tissue
  4. Time delay used to determine depth/thickness
  5. Fraction reflected used to identify tissue
  6. Greater resolution if smaller wavelength used
14
Q

Describe the use of X-Rays in imaging internal body structures including the use of image intensifiers and photomultipliers

A
  1. X-Rays would normally pass through film
    Intensifier converts X-Ray photon to many visible light photons (which can be absorbed by film)
  2. Photon releases electron that is accelerated onto fluorescent screen
    Number of electrons increased/multiplied
  3. Lower exposure/fewer X-Rays needed