CT- Basic Principles of CT
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what does CT accomplish that conventional radiographs cant?
- scans thin sections of the body with a narrow x-ray beam that roatates around the body, producing images of each cross section
- allows for the differentiation between tissues of similar densities
what are the main advantages of ct over regular xray?
main advantages of ct over regular xray are in the elimination of superimposed structures, the ability to differentiate small differences in density of anatomic structures and abnormalities and the superior quality of the images.
what does the z-axis, x-axis, and y-axis refer to in CT imaging?
- z-axis: the thickness of the cross-sectional slice
- x-axis: width
- y-axis: height
what does an x-axis and y-axis form?
2 dimensional squares or a pixel (picture element)
what does an x-axis, y-axis and z-axis form?
a cube or voxel (volume element)
what is a matrix?
the grid formed from the rows and columns of pixels.
what is the most common matrix size?
the total number of pixels in a matrix is calculated how?
multiply number of rows and the number of columns: i.e 512x512= 262,144
what happens to pixel size when matrix size increases?
pixel size decreases because the outside perimeter of the square is held constant.
what is attentuation?
the degree to which an xray beam is reduced by an object
what does Hounsfield units quantify?
the degree that a structure attenuates an x-ray beam
what are the hounsfield units for water, air, and bone?
- distilled water = 0
- air = -1000
- bone = 1000
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