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CT Review 3

Image Formation/Processing/Display

What is each small region in the grid? pixel
What is a grid of pixels called? matrix
how do you determine the number of pixels in a matrix? rows x columns (matrix size)
What is used to assign values to the pixels? gray scale
What is the range of the gray scale? -1000 to +1000
What coordinates does a pixel use? X and Y
What coordinates does a voxel use? X,Y, and Z
How is a voxel different than a pixel? it is 3D and has volume
What is scan FOV? the entire area used to collect data for a given body part
What is display FOV? the size of the reconstructed image in the matrix
Which can be changed: scan FOV or display FOV? display FOV
Attenuation coefficient depends on what? 1.photon energy 2.atomic # of tissue 3.thickness of tissue 4.electron density
What is one photon sampling? ray
What is one sample location from the pt body? projection/view
What is the hounsfield units of Air? -1000
What is the hounsfield units of Lung -500 to -200
What is the hounsfield units of fat? -200 to -50
What is the hounsfield units of water? 0
What is the hounsfield units of blood? 25
What is the hounsfield units of muscle? 25 to 40
What is the hounsfield units of bone? 200 to 1000
What is window width? range of CT #s to be displayed in a image, contrast of the image
What is window level? brightness of image/tissue
What is interpolation process? used to divide data into slices at any arbitrary position
What is the thickness at pitch of 1? collimation is equal to slice thickness
What is the thickness at pitch of 2? slice thickness is 30% greater
A pitch of 1.5 is a: 1.faster scan 2.less samples 3.less available mAs
A pitch of .75 is a: 1.slower scan 2.more samples 3.more available mAs (more radiation)
What is Cine? viewing in rapid sequence
What is MIP (maximum intensity) commonly used for? CTA
What is convolution? process of applying filtration
What are the filters used in image recon? 1.sharp 2.smooth
What are sharp filters used for? musculoskeletal
What are smooth filters used for? abdomen
What views do scout images use? AP, PA, Lateral
What are some characteristics of scout images? large FOV, single projection, tissue superimposed
What are the different scanning methods? 1.scout 2.conventional/serial scan 3.helical/spiral/volumetric scan
What is the process of conventional/serial scanning? scan-stop-move
What is the process MPRs (multi planer recon) use? image-raw data-image
What are the 2 steps of image recon? 1.apply filter to raw data (convolution) 2.apply back projection or cone beam to raw data
What are commonly used matrix? 128x128,256x256,512x512,1024x1024
Created by: Chrslarsen