1. The fundamentals of X-ray imaging. X-ray equipments. Radiation protection.

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

Radiation
- Absorbed radiation is measured by Gray (Gy)
  - It does not take into account the biological effect of radiation
- Health effects of radiation is measured by Sievert (Sv)
  - It does take into account the biological effect of radiation
- Types of radiation used for therapy
  - Gamma rays (?)
    - Used in stereotactic radiosurgery with gamma knife
  - Alpha radiation
    - Radium-223
    - For example for bone metastases or prostate cancer
  - Beta radiation
    - Iodine-131
    - For example for thyroid cancer
- Types of radiation used in diagnostics
  - Positron
    - PET scan
  - Gamma
    - X-ray
    - CT
    - Many nuclear imaging studies
- X-ray interactions with matter
  - Compton scattering
    - Makes x-rays scatter off the patient -> the patient becomes the source of scattered radiation
      - This scattered radiation can hit personell or equipment
      - Personell and equipment should be protected
    - Reduces image contrast
  - Photoelectric effect
    - It’s what makes contrast agents work
  - Coherent/Rayleigh scattering
  - Pair production does NOT occur
    - Only at energy levels much higher than medical x-ray
- Biological effects of radiation
  - Deterministic effects (nonrandom)
    - Examples
      - Skin erythema
      - Hair loss (3 Gy)
      - Sterility
      - Death (3 – 5 Gy)
    - Occur when the radiation-induced cell damage exceeds the cell’s ability to repair the damage
  - Stochastic effects (random)
    - May occur at any level of exposure
    - Probability for occuring increases with increasing dose
    - Severity is independent of the dose
    - Due to DNA and free radical damage
    - May occur years after exposure
    - Examples
      - Cancer
        10 mSv increases risk for cancer (0,04 mSv per x-ray)
  - Most radiosensitive organs
    - Organs with rapidly dividing cells
    - Bone marrow
    - Colon
    - Lung
    - Breast
    - Stomach
- Protection from radiation
  - Radiation protection involves 3 parts
    - ALARA
    - Justifiable exposure
    - Dose limits
  - ALARA principle – as low as reasonably achievable
    - High quality images should be obtained by using the lowest possible dose
    - Factors contributing to reducing radiation
      - Beam collimators
        Decrease scattering
      - Lead apron
      - Careful indications
        Asking yourself whether the benefits outweigh the risk, and whether a non-radiating modality could be used instead
      - Standing far away from the patient as possible
      - Accurately setting the field of examination
  - Three major safety practices
    - Time – limiting exposure duration
    - Distance
      - According to the inverse square law one can reduce their exposure to 25% by standing twice as far away from the source
    - Shielding
      - Using lead to limit the amount of radiation exposure
  - Yearly occupational limit – < 20 mSv
  - Personal monitoring = dosimetry
    - Every person can carry a dosimeter which measures the radiation dose received

Fluoroscopy = Real-time x-ray imaging
30 frames/second generally
120 frames/second for heart imaging
Often used with contrast
- Fluoroscopy allows you to see with high temporal solution (many fps) the movement of contrast
Can be recorded as a movie, and single frames can be examined
Indications
- Interventional cardiology
- Peripheral angiography
- GI
- Barium swallow