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Cards In This Set
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What are the 5 key influences on CT parameter selection?
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*Contrast Resolution
*Spatial Resolution
*Temporal Resolution
*Image Noise
*Patient Dose
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What is contrast resolution?
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The ability to differentiate small differences in density on the image.
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What is spatial resolution?
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A measure of the size of the smallest object that can be visualized in an image.
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What is temporal resolution?
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Refers to the precision of a measurement with respect to time.
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When helical scanning became available, the exam times ___________.
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Decreased
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What is image noise?
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Noise appears in a CT image as a point-to-point fluctuation in the CT number within a uniform material, it makes the image look grainy or speckled.
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What is the easiest way of increasing the # of photons that contribute to the pixels in the image?
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Increase the tube current or the scan time.
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What happens to patient dose when tube current or scan time is increased.
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Patient dose increases.
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What is patient dose?
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The dose is the amount of ionizing radiation absorbed by the patient per unit mass.
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What parameters in CT affects patient dose?
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*scan rotation time *slice thickness
*tube current *table increment
*the peak tube voltage *pitch
*anatomical coverage desired
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What is attenuation?
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The progressive reduction of the intensity of the x-ray beam as it passes through the patient's tissue.
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The x-ray photons are attenuated via what 2 processes?
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Absorption and scattering
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The amount of attenuation is dependent upon what factors?
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*atomic number
*density of electrons
*thickness
*photon energy
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The attenuation of an x-ray beam is highly dependent upon what?
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The energy of the x-ray photons.
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What is mA?
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The tube current.
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