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20 Cards in this Set
- Front
- Back
What are the five key influences on parameter selection? |
Contrast Resolution
Spatial Resolution Temporal Resolution Image Noise Patient Dose |
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______________ is the ability to differentiate small differences in density on the image.
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contrast resolution
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______________ is a measure of the size of the smallest object that can be visualized in an image.
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Spatial Resolution
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Typically, tissues with differences in density of less than ______________ can be differentiated with CT.
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0.5%
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Name the four geometric factors that can affect spatial resolution.
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focal spot size
detector aperture size focal spot to patient distance patient to detector distance |
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Name the four factors that we can control that affect spatial resolution.
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slice thickness
display FOV image matrix reconstruction filter |
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Spatial resolution is often expressed in terms of ______________.
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line pairs
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A resolution test consists of scanning a water phantom and determining the ______________.
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smallest line pair that can be resolved
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In a resolution test, the formula to find the spatial resolution is ______________.
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10 divided by (number of lines)
or 10 divided by (2 times number of line pairs) |
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______________ refers to the precision of a measurement with respect to time.
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Temporal Resolution
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Technological improvements that have allowed CT scans to be completed more rapidly have ______________ the temporal resolution possible with CT.
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increased
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As temporal resolution increases so can ______________.
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spatial resolution
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Name 3 technological improvements that increased temporal resolution over the years.
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helical scanning
multi-row detector scanners retrospective ECG triggering |
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______________ appears in a CT image as a point-to-point fluctuation in the CT number within a uniform material.
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noise
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An image will appear more noisy, or grainy, when there are ______________ contributing to the pixels.
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fewer photons
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A easy way to increase the number of contributing photons is to increase the ______________.
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tube current or the scan time
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The ______________ is the amount of ionizing radiation absorbed by the patient per unit mass.
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dose
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There is a tradeoff between ______________ and minimizing the patient dose.
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maximizing the image quality
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What 7 things affect patient dose in CT?
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scan rotation time
tube current peak tube voltage slice thickness table increment pitch anatomical coverage desired |
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What 4 things does the amount of attenuation depend on?
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atomic number
density of electrons thickness photon energy |