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- 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
- 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
- Fat
- Dark gray
- Darker than water
- Water (blood, soft tissue)
- Bone/calcium/metal/contrast agents
- 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
- 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
- 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