Imaging techniques

Imaging techniques

X-rays
1. High frequency, high energy radio waves
  1. They pass through most soft tissues of the body but are absorbed by bone
    1. The x-ray source is placed as close to the patients injury as possible
      1. A piece of unexposed film is placed underneath the injury
        A short burst of x-rays are fired onto the injured area
        The film is developed. This turns the x-ray black
        Dark grey shows fat
        Black shows gas/ air
        Light grey shows muscle/ soft tissue
        White shows bone
        Bright white shows metal
2. Safety precautions
  1. 1. Protective screens made of lead
    1. 2. Lead shield used to cover and protect organs
      1. 3. Limit on the amount of x-rays per person
        4. Only x-ray the injured area
3. Advantages
  1. 1. Clear pictures
    1. 2. Relatively cheap
      1. 3. Quick and simple
4. Disadvantages
  1. 1. High dosages of radiation may lead to radiation poisoning/ cancer
    1. 2. Can't identify soft tissue injuries
      1. 3. There is a limit on the amount you can have
CT or CAT scans
1. Computed tomography or computed axial tomography
  1. Uses x-ray protons to produce an image
    1. Difference: detectors and florescent screen rotate around patient
      1. The rotate around the gantry and scan the patient in a helical pattern
        The image and information is interpreted by a computer software
        This provides the radiographer with a detailed 3D image
2. Advantages
  1. provides a large amount of detailed data
  2. Can be used to look inside the body
    1. Internal organs, blood vessels, bones and brain
  3. Presents images in "slices" through the body
3. Disadvantages
  1. More expensive than x-rays
  2. Higher effective dose than x-rays
  3. Requires a cooperative/ sedated patient
Ultra sound scan
1. Frequency of 2-20MHz
  1. Transmitted and received via a probe
    1. The probe contains a transducer
      1. This acts as a "loud speaker" and "microphone"
      2. Waves are reflected by tissues depending on their density
        Gel is used to prevent reflection at the surface
        The reflected wave signals are converted to an image
2. Advantages
  1. 1. cheaper than other imaging techniques
  2. 2. Non-ionising radiation
  3. 3. Non invasive
  4. 4. Good soft tissue resolution
3. Disadvantages
  1. 1. Nothing can be seen behind bone
MRI
1. Magnetic resonance imaging
  1. A non-ionising radiation imaging technique
    1. The MRI scanner applies magnetic field which causes H atoms to align with it
      1. A radio frequency (RF) pulse is applied at right angles to the magnetic field
        This causes the H atoms to gain energy and spin in the same direction
        (Synchronously)
        The H atoms are described as being "in phase"
        When the RF pulse finishes two things happen:
        First they give out energy to the surroundings
        Secondly they go "out of phase" and spin asynchronously
        Energy given out is detected and interpreted by computer software
        Producing in a highly detailed image
2. Advantages
  1. 1. Non-ionising
  2. 2. Highly detailed images
  3. 3. Useful for soft tissue imaging
    1. Brain, spinal cord, bones, joints, breasts, blood vessels, internal organs such as the liver, womb or prostate gland
3. Disadvantages
  1. 1. Very expensive
    1. 2. Cant be used on patients with metal implants
      1. 3. Cant be performed on claustrophobic or obese patients

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