AP09 - Imaging the musculoskeletal system

Question 1

Describe how X-rays are produced

Answer 1

1. X-rays are photons - a type of EM radiation - and are generated from a complex X-ray tube (a type of cathode ray tube)
2. X-rays are then collimated to the appropriate area of the body
3. As the X-rays pass through the body, they are attenuated (reduced in energy) by the tissues
4. Those X-rays that pass through the tissues interact with the photographic film

Question 2

What does collimated mean when talking about X-rays?

Answer 2

X-rays are directed through lead-lined shutter to stop them from fanning out

Question 3

Describe the different attenuations of X-rays by air, fat and bone? What different would it make to the final image?

Answer 3

1. Air attenuates a little
2. Fat attenuates more than air but less than water
3. Bone attenuates the most
   - Air appears dark on film because these regions were exposed to the greatest number of X-rays

Question 4

What are the advantages of X-rays?

Answer 4

• Cheap

Question 5

Describe how doppler ultrasound works

Answer 5

• Enabled determination of flow , direction and velocity within a vessel
  1. Uses simple ultrasound technique
  2. Sound waves bouncing off moving structures are returned
  3. The degree of frequency shift determine whether the object is moving away from or toward the probe and the speed at which i is travelling

Question 6

What are the advantages of doppler ultrasound?

Answer 6

• Precise measurements of blood flow and velocity can be obtained –> indicate sites of blockage in BV

Question 7

Describe how CT scans work (computerised tomography)

Answer 7

• Obtains a series of images of the body (tomogram) in the axial plane
  1. Patient lies on a bed
  2. X-ray tube passes around the body and a series of images are obtained
  3. A computer carries out a complex mathematical transformation on the multitude of images to produce the final image

Question 8

Describe how MRI scans work

Answer 8

• The process is dependent on the free protons in the hydrogen nuclei in molecules of water
  1. Patient placed in a strong magnetic field which aligns the protons
  2. When a pulse of radio wave is passed through the patient, the protons are deflected and as they return to their aligned position they emit small radio pulses
  3. The strength and frequency of the emitted pulses and the time it takes for the protons to return to their pre-excited state produces a signal
  4. Signal analysed a powerful pc and an image created