production of subject contrast - chapter 12

contrast

the ratio or percentage different between two adjacent brightness (density) levels

visibility

contrast is essential to the ________ of detail in any radiographic image

subject contrast

difference of intensity between portions of the remnant x-ray beam, determined by the various absorption characteristics of tissues within the patients body. Produced by differential absorption

differential absorption

varying degrees of x-ray attenuation by all interactions with different tissues that produce subject contrast in the remnant x-ray beam

differential absorption

subject contrast is produced by what

attenuation

reduction in the number or intensity of the x-ray beam; all interactions (photoelectric, compton or coherent scattering) represent some degree of attenuation of the overall x-ray beam

absorption and scattering

general attenuation occurs due to what

1.5

When looking at different contrast ratios between soft tissue and bone, which ration will have INCREASED subject contrast

tissue thickness, density, atomic number

what are the three essential aspects of tissues which determine their attenuation properties and the resulting subject contrast

increases

as tissue thickens, attenuation ________ exponentially

doubled

for every 4 cm of additional thickness, the attenuation of the x-ray beam is _______; the penetration of x-rays reaching the receptor is cut in half

increases

as tissue thickness increases, attenuation

physical density

the amount of physical mass that is concentrated into a given volume of space

higher tissue density

more atoms/molecules packed into a given space

lower tissue density

less atoms/molecules packed into a given space

increases

as tissue density increases, the probability of interaction

7.6

average Z# of air

7.4

average Z# of soft tissue

higher

the higher the atomic number, the _______ probability of interaction

exponential

the impact of the atomic # on the attenuation of x-rays is

exponential

small differences in atomic # mean large differences in the absorption of the x-ray beam

increases

as tissue atomic number increases, the probability of interaction

subject contrast

the effect of any scattered radiation reaching the image receptor reduces the ______ _______ carried by the remnant beam

decrease

an increase in scatter with ______ the subject contrast

penetration

the ability of a photon to penetration tissue, x-ray quality

penetration

what is the opposite of attenuation

increases

as kVp increases, the quality (hardness) of the beam increases, what happens to penetration

increased

as penetration is increased, what happens to gray scale

decreased

as penetration is increased, subject contrast is

decreases

as kVp increases, subject contrast

darker

penetrating x-rays produce what areas on image

lighter

photoelectric interactions produce what areas on image

fog

Compton scatter lays down a blanket of ___ at the IR

low kVp and high atomic #

the greatest number of PE interactions occur when