Projection Radiography Flashcards
What are X-rays?
Form of electro magnetic radiation (EM)
What is the main difference between EM radiation?
Different energy levels of individual photons which is related to wavelength/frequency of photons
What are 4 examples of EM radiation?
light
radiant heat
microwaves
radio-waves
What length do wavelengths become visisble?
10^-6
What is the wavelength of X-ray & gamma ray?
x ray = 10^-10
gamma = 10^-12
When does ionization occur?
If radiation with sufficent energy can remove electrons from their shells
Why happens if ionization occurs in humans cells?
DNA could be directly damaged or indirectly by formation of free radicals/harmful substances
Why is indirect damage to DNA thought to more damaging?
water is more abundant than DNA
Who invented the Crookes tube?
Dr. Wilhelm Conrad Roentgen
What are 5 charcteristics of X-rays?
invisible
electrically neutral
no mass
travel at speed of light in a vacuum
cannot be optically focused
When are x-rays produced?
When rapidly moving electrons that have been accelerated through a potential difference of order 1kV to 1MV strikes a metal target
What are the 3 steps of x-ray production?
- electrons from hot filament are accelerated onto a target anode
- electrons are decelerated on impact & kinetic energy is converted to EM energy
- photons produced will have a range of energies (polychromatic)
How much of the energy is converted into x-radiation during the production of x-rays?
Less than 1% - rest is converted into internal energy
How is radiation attenuated when it passes through matter?
by absorption & scattering
What does attenuation result in?
Reduction in intensity of incident radiation beam
What does absorption result in?
Transfer of energy from x-ray photon to atoms of material
What does scattering involve?
photon deflection from its original course
How do x-rays form the radiographic image?
some tissues attenuate more photons than others & therefore beam exiting patient is more intense in some places
What captures the image?
An image receptor reacts to x-ray photons
areas of receptor that are subject to more radiation gain more signal (darker on image)
What is photoelectric absoprtion?
Incident photon interacts with inner shell electron & is completely absorbed
Atomic No (Z)
What is compton scattering?
interaction between incident photon and outer shell electron & ejects the electron which results in a change in direction
What is beam attenuation?
Beam emitted from patient contains radiologically significant info to make a diagnosis
What are 4 factors that affect amount & type of attenuation?
atomic no. of tissue
density of tissue
tissue thickness
energy of x-ray beam
Does air have a higher atomic no. than fat or muscle?
Yes but it has lower density
What does the fewer absorption of photons by air allow for?
More photons to reach the image receptor creating a greater image receptor exposure
How does fat compare to muscle?
Lower atomic no. and density
Why is muscle easy to distinguish?
Greater attenuator of the beam (increased absorption)
What is the greatest absorber of photons?
Bone
What are 2 examples of high density contrast agents?
Barium
iodine
What 4 ways are contrast agents administered?
orally
rectally
intra-venous
intra-arterial
What does fluroscopy involve?
Taking multiple low-dose x-ray images in succession to create a real-time “video”
What are 3 scenarios that fluoroscopy is used?
Theatre
GI system
specialized application
What happens if radiation exceeds threshold level?
Tissue function will be compromised due to cell death beyond what the tissue can cope with
What are 4 reactions that can occur depending on exposure?
Skin reddening
Opacity of lens of the eye
Permanent sterility
ARS
What is the severity of the effects proportional to?
Dose recieved over the threshold
What are stochastic effects?
Damage to cell’s DNA -> somatic or genetic
Is there a threshold below which no effects occur?
No
What 4 thinsg does legislation include protection for?
patients
staff
unborn
members of public
What are the 3 pillars pf reducing radiation risk?
Justification - benefit outweighs risk
Optimisation - technical & procedural steps can optimize doses
Dose limitation - legal limits exist for staff, public and unborn children
What are 3 ways to optimise staff dose?
Less time spent near sources
Greater distance from source
Behind shielding
What are 3 pros of convential radiography?
Accessible
Fast
Cost effective
What are 4 cons of conventional radiography
Limited detail on soft tissue organs
limited detection of early diagnosis in bones disease
non-specific findings
2D
What are 5 clinical applications?
Chest radiography
Skeletal trauma imaging
imaging for exclusion
follow up
SPA imaging
How can projection radiography assess skeletal trauma?
Presence/absence/complexity of fracture/dislocation
relationship of bony fragments
What are 3 signs of fracture?
Disrupted cortical outlines
Radiolucent lines
misalignment of bony fragments
What are 2 fractures associated with SPA?
bucket handle
classic metaphyseal handle
