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CT Review 4

Technical Factors that influence CT image formation

TermDefinition
List the 9 commonly adjusted CT imaging parameters: Kv, mA, pitch, recon interval, table increment, slice thickness, FOV, matrix, recon filter
A quality image is determined be what 4 factors? density, contrast, resolution, distortion
What is spatial resolution? a measure of the size of the smallest object that can be visualized, or resolved, in an image.
There are 4 geometric factors that affect spatial resolution, what are they? focal spot size, detector aperture size, focal spot to pt distance, pr to detector distance
pre and post collimation reduces what? scatter radiation and pt dose
what is another name for pre collimation? dose collimation / source
detector collimation significantly ___?___ image resolution and __?__ image artifacts. increases, minimizes
What formal is used to determine pixel size? pixel size = DFOV/matrix
What is contrast resolution? the ability to differentiate small differences with CT in density on the image
Tissues with differences in density of less than ___% can be differentiated on a CT. 5%
What is quantum noise? electronic interference that comes from the pt and components of the CT scanner
What is dose? the amount of ionizing radiation absorbed by the pt per unit mass
what factors affect dose? mAs, Kvp, collimation, scan time
What is standard deviation? amount of noise, or spread, can be calculated and expressed by the statistical parameter
spatial resolution is often expressed in terms of what? line pairs
What factors affect spatial resolution? slice thickness, DFOV, image matrix, recon filters
Noise can be controlled by what parameters? mAs, Kvp, kernel, slice thickness, pt size, collimation, image display
Noise has a tendency to make a CT image __?__ and this can obscure fine anatomical detail. grainy
Beam collimation if equal to _?_ _?_ on a single slice helical ct. slice thickness
Some ct scanners allow adjustments of two types of FOV's, what are they? DFOV, SFOV
A cross section of a pt's anatomy should be __?__ contained within the SFOV. completely
Reducing voxel size __?__ noise because __?__ protons are absorbed in voxel. increases, fewer
When we select the shade of gray assigned to the ct number of the pixels in the image it is known as what? wl and ww
What are the parameters that control the contrast in a ct image? focal spot size, pixel size, kernel, recon filter
What is attenuation? the degree to which an xray beam is reduced by an object
What is CTDI? CT dose index-an approx measure of the radiation dose received in a single CT section or slice.
The effects of increasing image matrix: 1.contrast: unchanged 2.resolution: increase 3.noise: increase 4.dose: unchanged
the effects of using sharper recon filters: 1.contrast: decrease 2.resolution: increase 3.noise: increase 4.dose: unchanged
the effects of increasing mAs: 1.contrast: unchanged 2.resolution: decrease 3.noise: increase 4.dose: increase
the effects of increasing Kvp: 1.contrast: up or down 2.resolution: unchanged 3.noise: decrease 4.dose: increase
the effects of increasing slice thickness: 1.contrast: unchanged 2.resolution: decrease 3.noise: decrease 4.dose: decrease
the effects of increasing table increments: 1.contrast: unchanged 2.resolution: decrease 3.noise: unchanged 4.dose: decrease
the effects of increasing pitch 1.contrast: unchanged 2.resolution: increase 3.noise: unchanged 4.dose: decrease
the effects of increasing recon interval 1.contrast: unchanged 2.resolution: decrease 3.noise: unchanged 4.dose: unchanged
the effects of increasing recon FOV 1.contrast: unchanged 2.resolution: decrease 3.noise: decrease 4.dose: unchanged
what is a pixel? the individual boxes arranged in the matrix used to display the ct image
what is a ray? the portion of the xray beam transmitted thru the pt and incident upon a single detector
what is a kernel? mathematical filter applied to raw data during CT image recon to remove the blurring artifact inherent to back projection
what is a matrix? two dimensional grid of numbers arranged in rows and columns.
Created by: Chrslarsen