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RADT 411

Unit 2

QuestionAnswer
Attenuation The amount of x-ray beam that is reduced by absorption as it passes through the patient/object.
What three things affect beam Attenuation? (1)Density (2)Thickness (3)Atomic Number
Algorithm Finite set of steps performed to solve a problem
Interpolation Mathematical method of estimating the value of an unknown by using known values on either side (see spiral scanning)
Raw Data (Scan Data) Data from the detectors that has not been assigned an HU
Image Data Processed raw data; each pixel within the data has been assigned an HU
Image Reconstruction Process of using Raw Data to create Image Data
Reconstruction Time The time from the end of the scanning to image display
Prospective Reconstruction The image that is produced during scanning
Retrospective Reconstruction Taking the raw data after scanning is over and, at a later time, using it to create a new image
Ray The path the x-ray beam takes from the tube to the detector
Ray Sum The measurement of how much beam attenuation occurs for each ray
View A complete set of ray sums; many views are needed to create an image
Attenuation Profile Accounting for the attenuation properties of each ray sum and correlating it to a position of the ray
Back Projection A summation technique of the attenuated profiles collected from all projections during scanning and converting it into a matrix
What results from Back Projection? A non-uniform image due to the x-ray attenuation not being uniform over the entire path length
Filtered Back Projection Similar to Back Projection except that it applies a correction filter to sharpen the edges of the attenuation information of the RAW DATA; allows for exact representation of the scanned object
Convolution The process of applying a filter function to an attenuation profile
ASIR (Adaptive Statistical Iterative Reconstruction) Noise profiles are used to extract additional image clarity and suppress noise (from low delivery dose)
ASIR has been shown to reduce patient dose by how much? 50%
Does Interpolation occur before or after filtered back projection (in a spiral image)? Before
SFOV (Scan Field of View) The area within the gantry that the raw data will be collected
DFOV (Display Field of View) The region of interest in the resulting images
What does a small or narrow DFOV mimic? Zoom
DFOV is always --(1)-- or --2-- than the SFOV. (1) Equal (2) Smaller
How are the detectors affected by SFOV? SFOV determines the number of detectors collecting data during a scan
How does Field of View affect Spatial Resolution? (1) The greater the Field of View the less the Spatial Resolution (2) The less Field of View the grater the Spacial Resolution
Post-Processing Manipulating both the Raw and Image Data after the scanning has taken place
Image Reformation (Image Rendering) Uses Image Data to produce images in different planes or to produce 3D images
(T/F) Image Reformation uses both Raw and Image Data False: Image Reformation uses Image Data only
MPR (Multi-Planar Reformation) A post-processing technique performed on an image data set to produce new slices in a different orientation (EX. Sagittal, Coronal, Oblique, etc)
CPR (Curved Planar Reformation) Images are created along the center of tubular organs
3D Represents the entire scan volume in only one image
Surface Rendering (Shaded Surface Display) Includes only information from the surface of a Defined Tissue Threshold
Volume Rendering Every voxel is used; the sum of the voxels along a line are assigned an opacity value to form the final image
Maximum Intensity Projection Software program that will create a 2D image from a 3D data set
Where is Maximum Intensity Projection most commonly used? Angiography Imaging
What is Maximum Intensity Projection best able to counteract? Counteracts superimposition of vessels
Quantitative Measurements Specialized software that quantitatively measure images and obtain information about volume, distance, and diameter
CT Number (HU) The measurement of the linear attenuation coefficient for a given tissue
"0" is what on the Hounsfield Scale of Units? Water
"-1000" is what on the Hounsfield Scale of Units? Air
"1000" is what on the Hounsfield Scale of Units? Bone
What is proportional to HU? Pixel Brightness
Windowing Changing the displayed contrast of an image by manipulation of window width and window level
Window Width (WW) The range of CT numbers
How does WW influence contrast? (1) Wide WW creates a long gray scale and low contrast (2) Narrow WW creates a short gray scale and high contrast
Window Level The central value of the WW (the center CT number)
ROI (Region of Interest) A display function that defines an area of an image
A _____ ROI will give a more accurate measurement. Smaller
(T/F) Ideal Standard Deviation should be as close to "0" as possible. True
Distance Measurements Used to measure the distances of structures
Image Annotation Additional study information written on an image
Reference Image Displays the slice lines in the corresponding location on the scout image
Cine Imaging Continuous acquisition scanning without table movement
When is Cine Imaging usually used? When observing arterial contrast enhancement
What is the difference between Raw Data and Image Data? Raw Data has yet to be assigned an HU while Image Data has been assigned an HU
What is the difference between SFOV and DFOV?
What are the alternative names for Convolution Filter? (1) Algorithms (2) Kernels
What are four types of Reconstruction Algorithms used in CT?
What is the difference between Retrospective Reconstruction and Image Reformation?
What are the six different types of image display options?
What is the difference between Filtered Back Projection and ASIR?
How does the pitch of a CT scan affect the interpolation of an image?
What is the difference between Image Reconstruction and Image Reformation?
____ Data is only stored temporarily because of the amount of computer storage space it takes up Raw
Image data only require _____ the computer storage space in comparison to Raw Data One-Fifth
(T/F) Convolution filters can be applied to both Raw and Image data. False: Filters can only be applied to Raw Data.
Created by: rmhale
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