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RADT 411
Unit 2
| Question | Answer |
|---|---|
| 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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