Radiology Flashcards
- Formation and characteristics of x-rays, biological effects of x-rays
Characteristics:
Wilhelm Rontgen, 1895
Nobel prize
photon-radiation, EM-specter
0,01-10nm
100eV –> 100keV
shorter wavelength = higher penetration
speed of light, divergent beam
higher material density = higher absorption
techniques: radiography, CT, angiography, mammography
Formation:
vacuum tube - thermionic cathode (tungsten filaments in coil) + rotating anode + protective housing
high-voltage electric current in vacuum tube
thermionic emission: electrons from cathode –> anode
anode: tungsten material
electrons from cathode collide with anode = electrons decelerate and produce X-rays (1%) and heat (99%)
high electric field: accelerate passing of electrons from cathode to anode
vacuum chamber: remove obstruction to electrons
air molecules block path of electrons (scatter them away from target)
protective tube housing: lead shielding for patient/operator protection
filter: thin aluminium shield absorbs low-energy photons
no useful contribution
Attenuation:
decreased x-rays according depth of target
less dense –> blacker film
lungs - very low density –> black
bones - very high density –> white
Air: lungs, trachea, outside the body
Fat: perirenal fat, fascial plane
Water: muscle, organs
Bone: bone, atherosclerotic plaque
Metal: fillings, markers, ortho devices.
conventional vs digital x ray:
conventional - less than 40% of original signals
digital x ray - more than 80% of original signals
Biological effects:
excitation and ionization of atoms, especially dividing cells
effects:
direct - radiation to DNA
indirect: free radicals –> bond to DNA
types of damage:
1. undamaged cells - alteration but no neg. eff.
2. sublethal injury - damaged but repaired
3. mutation - incorrectly repaired, somatic/genetic
4. cell death -
severity:
stochastic (no threshold) - increased dose = increased risk, not severity
non-stochastic (threshold) - increased dose = increased severity
- Fetal abnormality (0.1-0.5Gy)
- Sterility (2-3Gy)
- Skin erythema (2-5Gy)
- Hair loss (2-5Gy)
- Lethality - whole body (3-5Gy)
- Cataracts (5gy)
- Irreversible skin damage (20-40Gy)
- Principles of radiation protection
ICRP:
1. Occupational protection: >20mSV/year
2. Medical radiation protection >1mSv/year
- Justification of practice:
- Optimization of protection:
- Individual dose limits: ALARA
- Time:
- Distance: Inverse square law
- Shielding: lead sheets
- Surveillance: dosimeters, detectors, external dose rates, air conc.
International system of units: Gray (Gy) + Sv (Sievert)
Absorbed dose: Gy, 1J/1Kg
Equivalent dose: Sv, Absorbed dose x Q (quality factor)
- X/Gamma/Beta/positrons = 1
- Alpha/neutrons/protons = 20
Weighting factor (tissue): testes/ovaries vs bone/skin
Dose rate:
Dose fractionation:
- Imaging techniques - fluoroscopy, radiography, tomography, tomosynthesis
Fluoroscopy: dynamic x-ray
- Barium swallow:
- barium meal:
- barium follow through:
- barium enema:
Angiography:
Guide in procedures: ERCP, lumbar puncture, biopsy
Hystero-salpingography:
Arthrography, cystography:
Advantages: dynamic, inexpensive, real-time
Disadvantages: high radiation, overlapping anatomy, patient-mobility
Radiography: plain x-ray
density, attenuation
scatter
contrast: barium, iodinated compounds
advantages: inexpensive, fast
disadvantages: exposure, overlapping anatomy, no dynamic imaging
X-ray devices: chest-wall stand, Bucky table
Tomography: slices, deep organs
1. Linear: simplest, tube in one direction + film in other, only pivot point is focused
2. Multi-directional: tube + film in circular pattern, sharper imaging
3. Computerized tomography: CT
Tomosynthesis: high-res tomography at radiographic dose
1. Digital TS: simple detector motion (as in CT). Limited rotation angle 15-60*. Fewer projections = exposure/cost reduced
- Breast: Digital breast TS (higher accuracy than conventional mammography)
- Musculoskeletal: healing fractures, evaluation of erosions in RA (rheumatoid arthritis)
- Vascular + dental imaging
