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Unit 3

Image Acquisition and Evaluation

What is recorded detail? The clarity, or resolution, in which anatomic structures are represented; sharpness of borders; measured by test pattern pg.298
What is distortion? The misrepresentation of the actual size or shape of the structure pg.299
How is resolution expressed? Line pairs per millimeter; one line pair refers to one line and the one space adjacent to it pg. 299
What is visibility of detail? How well the recorded detail can be seen; excessive density, brightness, or scattered radiation fog impairs detail visibility pg.299
What is contrast resolution? Anything that effects density/brightness or visibility of detail pg. 300
How does the use of high kV affect the production of scattered radiation fog? Scattered radiation fog increases
As the thickness and density of tissues increase, does scatter increase or decrease? Increase
What happens as grid ratio increases? The cleanup of scatter increases and contrast improves, contrast scale decreases, patient dose increases
What is a grid factor? The ratio of the total amount of radiation incident on the surface of the grid to the amount of radiation transmitted through the grid pg. 347
What are two types of AECs? Phototimer and ionization chamber pg. 349
What is signal to noise ratio used to describe? Contrast resolution; the higher the SNR, the better contrast resolution
What is The Detective Quantum Efficiency? DQE; The ability of receptor material to perceive and interact with x-ray photons
What is the most common result of incorrect film storage? Fog
What temp. should film be stored? 70 degrees F pg. 381
What humidity should film be stored? 40% to 60% pg. 381
What causes CR graininess? Underexposure, Incorrect processing algorithm/LUT, excess scattered radiation, inadequate collimation, grid misalignment or cutoff pg. 405
What causes CR resolution to increase? PSP phosphor size decreasing, laser beam size decreasing, monitor matrix size increasing pg. 406
What causes excessive density on film? Elevated developer temperature, insufficient dilution of developer pg. 389
What causes inadequate density on film? Too low developer temp., excessive dilution of developer pg. 389
What causes subject/object unsharpness? Object shape does not match the shape of x-ray beam, object plane is not parallet with x-ray tube and/or IR, anatomic objects of interest are not in path of CR, anatomic objects are a distance from the IR
What terms describe distortion? Magnification, elongation, and foreshortening pg. 300
How does focal spot size affect detail? It influences the degree of blur or unsharpness pg. 308
What is involuntary motion? Peristaltic activity, muscle spasms, and heart action; motion that cannot be controlled pg. 309
What is the active ingredient in intensifying screens? Fluorescent phosphor pg. 311
When is quantum mottle more likely to occur? When using fast screens with low mAs and high kV factors pg. 313
What is the definition of the reciprocity law? Any combination of mA and exposure time that produces a particular mAs, will produce identical image density pg. 317
Doubling the mAs will do what to the density? Double pg. 318
What percentage of change must occur to mAs in order for a recognizable change in density? 30% change pg. 318
What is the inverse square law formula? I1/I2=D squared 2/D squared 1 pg. 319
What is the density maintenance formula? mAs1/mAs2=D squared 1/D squared 2 pg. 319
Created by: cfdishon