Radiography

• 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