Radiography

From greek.doctor
  • Fundamentals of x-ray
    • X-rays (electromagnetic radiation with a wavelength of 0,01 – 10 nm
      • Hard x-rays
        • Higher energy
        • > 90 kV
        • Wavelength < 0,1 nm
        • Penetrate tissues better
        • The type mostly used in medicine
      • Soft x-rays
        • Lower energy
        • < 40 kV
        • Wavelength > 0,1 nm
        • Highlights differences between tissues with similar x-ray absorption
          • Used in mammography
    • Different tissues absorb different amount of radiation depending on the density and componsition
      • The radiation which is not absorbed will hit a detector behind the patient
      • Different tissues range from radiolucent (black on the screen) to radiopaque (white on the screen)
      • There are four basic tissue densities visible on x-ray
        • Air
          • Black/very dark
        • Fat
          • Dark gray
          • Darker than water
        • Water (blood, soft tissue)
          • Light gray
        • Bone/calcium/metal/contrast agents
          • Almost white
    • Regular x-rays account for 75% of imaging examinations
    • Distortion
      • = how anatomical structures are misrepresented on an x-ray
      • Due to
        • Superimposition (stuff over other stuff)
        • Forgetting (some of the information is lost due to x-ray scattering)
        • Magnification (stuff looks bigger than they are)
    • Contrast agents
      • Agents which are radiopaque
        • They fill a hollow or tublar organ
      • Can be given IV, orally, rectally, by catheter…
      • They work by the photoelectric effect
      • Contraindications
        • Pregnancy
        • Use of metformin
        • Previous reaction to contrast
        • Renal disease
        • Hyperthyroidism
      • Permits visuazilation of anatomical structures which are not normally seen
        • Blood vessels
      • Small risk for contrast reaction if given IV or intraarterially
        • Mild
          • Metallic taste
          • Feeling of warmth
        • Moderate
          • Reduced renal function
          • Vomiting
          • Hives
        • Severe
          • Vasovagal syncope
          • Laryngeal oedema
          • Severe hypotension
          • Anaphylaxis
        • Late reactions (after 1 hour)
          • Skin reactions
          • Contrast-induced nephropathy (renal failure)
      • Examples
        • Barium
        • Iodine
  • Components
    • X-ray tube – produces X-rays
      • Anode
        • Made of tungsten disc
          • Tungsten and wolfram are the same!
        • The positive terminal
        • It’s the target of electrons
      • Cathode
        • Made of tungsten filament
        • The negative terminal
        • It’s the source of electrons
    • Generator
      • Gives power to the x-ray tube
      • The energy of the x-ray depends on the tube voltage (accelerating voltage)
      • The amount of x-rays depends on the cathode current
    • Gantry
      • = Radiation source + detector
    • Table
      • Floating table, can be moved
    • Detector
      • Film/screen (old)
      • Computed radiography (modern)
        • Digital
        • X-rays hit a plate that absorbs the x-rays and stores the energy at a specific location
        • The plate is scanned by a laser, which detects the energies at the different locations
        • The location is detected and stored in a computer
      • Digital radiography (modern)
        • X-rays hit a detector and is converted into light or an electrical charge immediately -> stored in the computer
    • Control panel
      • To control the energy, etc
  • Production of x-rays
    • X-rays are produced in two ways
      • Both types occur in the same x-ray
      • Bremsstrahlung (breaking radiation)
        • A fast-moving electron is attracted to the positively charged nucleus
        • This will slow down the electron, causing it to lose some kinetic energy (speed)
        • This kinetic energy will be released as gamma radiation
        • Bremsstrahlung can have have a large range of energies
          • This causes a continous spectrum of energies
      • Characteristic radiation
        • A fast-moving electron collides with an electron in a shell of an atom in the anode, the electron in the shell is ejected
        • Another electron from an upper shell will take its place
        • This releases gamma radiation
        • This radiation only has characteristic amounts of energy, causing a line spectrum of energies
        • In a mammograpy there is more characteristic radiation than in other types of x-ray images
        • The characteristic elements depend on the material of the anode!
  • Types of regular x-rays
    • Chest radiographs
      • 120 kV tube voltage used
      • Posteroanterior (PA)
        • Most common
        • Patient’s chest faces the detector
        • X-rays come from behind the patient (from posterior to anterior)
      • Anteroposterior (AP)
        • Rare
        • Less used because the heart appears larger than it really is
    • Abdominal radiographs
    • Bone radiographs
      • 50 – 100 kV