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CT Test 5
weeks 11-12
| Question | Answer |
|---|---|
| Attenuation | the amount of the x-ray beam that is reduced by absorption as it passes through an object (patient) |
| 1 Hounsfield unit is equal to ___ | 10% difference between linear attenuation coefficient of water |
| Algorithm | finite set of steps performed to solve a problem |
| Image reconstruction | the process of using raw data to create an image |
| Interpolation | mathematical method of estimating the value of an unknown by using known values on either side |
| Raw data (scan data) | data from detectors that have not been assigned a HU |
| image data | processed raw data; each pixel within the data has been assigned a HU |
| Image reconstruction | to take all of the multiple data projections collected during scanning, compute and assign a CT number to each pixel in the digital image; process of using raw data to create an image |
| Reconstruction time | the time from the end of scanning to image display |
| Prospective reconstruction | 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 correlation 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 |
| Filtered back projection | similar to back projection except it applies to a correction filter to accentuate the edges of the attenuation information of the raw data; allows for exact representation of the object scanned |
| Convolution | the process of applying a filter function to an attenuation profile |
| What is used to extract additional image clarity and suppress noise? | noise profiles |
| interpolation | the mathematical process of creating an unknown value by utilizing the known values on either side |
| What occurs before the filtered back projection in a spiral image? | interpolation |
| Scan Field of View (SFOV) | the area within the gantry that the raw data will be collected; determines the number of detectors collecting data for a particular scan |
| Display Field of View (DFOV) | the region of interest in the resulting images; always equal to or smaller than the SFOV) |
| When a smaller or narrower DFOV is present, what does this do? | acts like zoom; restricts the area of interest to a select field |
| 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; uses only image data |
| Multi-Planar Reformation (MPR) | a post processing technique performed on an image data set to produce new slices in a different orientation |
| Curved Planar Reformation | images created along center of tubular organs |
| surface rendering | includes only information from the surface of a defined tissue threshold; shaded surface display |
| Volume rendering | every voxel is used; the sum of the voxels along a line are assigned on opacity value to form the final image |
| Maximum Intensity Projection | a software program that will create a 2D image from a 3D data set; utilized commonly in angiography imaging; used to separate superimposed vessels |
| Quantitative Measurements | specialized software can quantitatively measure images and obtain information about volume, distance, and diameter |
| CT number | the measurement of the linear attenuation coefficient for a given tissue; corresponds to a shade of gray in the image |
| What is the standard scale of CT numbers? | Hounsfield Units |
| On the Hounsfield Scale of Hounsfield Units, what is water? | 0 |
| On the Hounsfield Scale of Hounsfield Units, what is air? What is its appearance? | -1000, black |
| On the Hounsfield Scale of Hounsfield Units, what is dense bone? What is its appearance? | 1000, white |
| Can we change the attenuation of a specific tissue? | |
| Why are HU/CT numbers useful? | |
| Windowing | changing the displayed contrast of an image by manipulation of window width and window level |
| Window Width | the range of CT numbers |
| Reducing window width _______ contrast | increases |
| What does the gray scale look like for wide window width bone imaging? | gray /long gray scale/ low contrast |
| What does the gray scale look like for narrow window width soft tissue imaging? | black and white /short gray scale/ high contrast |
| window level | the central value of the window width; "the center CT number" |
| Region of Interest (ROI) | a display function that defines an area of an image |
| Reference Image | displays the slice lines in corresponding location to the scout image |
| Cine Imaging | continuous acquisition scanning without table movement; important when observing arterial contrast enhancement |
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