Diagnostic Radiology Flashcards
What determines if an object is visible in an image?
Contrast
Noise
Size
Which interaction provides contrast?
Photoelectric effect
How is the k-edge used?
Optimise X-ray capture in image receptors
What does the contrast of an object depend on?
Thickness of the object
Difference in attenuation coefficient between object and background
At what energy is contrast maximised?
Low energy
How does the probability of photoelectric absorption change with E and Z?
1/E^3
Z^3
How does the probability of Compton scattering change with E and Z?
Constant over diagnostic range
Independent of Z
Define the 3 types of noise
Quantum noise - fluctuation in the number of photons in an area of the beam
Electronic noise
Fixed pattern noise - pixel to pixel variation
What is SNR?
Quantum noise is poisson
SNR = root N
What is spatial resolution effected by?
Pixel size
Spread of signal in detector
Focusing of electrons in image intensifier
Focal spot size
Magnification
What are the components of a fixed radiographic system?
Ceiling mounted tube on rails
Generator cabinet
Operator console behind screen
2 Buckie’s with grid AEC and image receptor
What is AEC?
Automatic exposure control
Ensures image receptor gets right amount of radiation
Ionisation chambers
Monitor air KERMA and terminates exposure when predetermined limit reached
How does a mobile system differ?
Tube on an adjustable arm
No grid or AEC
No screen
How does a mammography system differ?
Digital detector
U-arm
How does a dental system differ?
Low mA
Stationary anode
