S2 L6 Flashcards
Factors affecting radiographic image contrast
Type
Processing
Exposure
Display
Subject contrast
Photon energy
Kvp
Filter
Differential absorption
Object contrast
Density
Thickness
Z
What is differential absorption
Background vs aoi
C =Ib - Ia / Ib
Monochromatic beam attenuation equation
N =Noe^-yx
Linear attenuation coefficient
Sum of linear attenuation coefficients for each interaction
= photo electric absorption + Compton scattering
Linear attenuation coefficient increase or decrease with increasing energy
Decrease except at k edges
Uses of linear attenuation coefficient
Provide information on attenuation properties of a medium
Measure effectiveness of medium as attenuator
How do Z, density and photon energy affect attenuation
Increase, increase attenuation - Z and density
Increase, increase except decrease at k edge
What is mass attenuation coefficient mean
Dependency on density removed by dividing LAC by density of material
How does iodine affect interactions
Increase photoelectric absorption and decrease Compton scattering
Polychromatic xray attenuation
N(E) = No(E)e^-y(E)x
(E) means as a function of energy
High kv low dose techniques
Decrease dose
Increase scattering
More penetrative so don’t need as many photons
