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CT Physics Terms II
Image Reconstruction and Display
| Question | Answer |
|---|---|
| A precise set of steps to be performed in a specific order to solve a problem; basis for most computer programming | algorithm |
| A method to study waves of many different sorts and also to solve several kinds of linear differential equations. Loosely speaking it separates a function into its frequency components | Fourier transform (FT) |
| A technique for expressing a waveform as a weighted sum of sines and cosines | discrete Fourier transform |
| The simplest type of a math method of estimating the value of an unknown function using the known value on either side of the function. Assumes that an unknown point falls along a straight line between two known points | linear interpolation |
| Portions of the computer that can be physically touched | hardware |
| Instructions that tell the computer what to do and when to do it | software |
| An essential component of all CT systems. It saves the thousands of bits of data acquired with each gantry rotation | hard disk |
| Ancillary pieces of computer hardware designed to feed data into the computer. Examples include keyboard, mouse, touch-sensitive plasma screen, and CT detector mechanisms | input device |
| Saving studies on auxiliary devices for the purpose of future viewing | archiving |
| Component that interprets computer program instructions and sequences tasks. It contains the microprocessor, the control unit, and the primary memory | central processing unit |
| Now outdated, it is a CPU design frequently used for CT image reconstruction; this design was able to run mathematical operations on multiple data elements simultaneously. General increases in performance & processor design have made this design obsolete | array processor; AKA vector processor |
| Process of converting the data from the attenuation profile to a matrix | back projection |
| The section of data selected for display on the image | display field of view (DFOV) |
| Devices that store data. | memory |
| Ancillary pieces of computer hardware designed to accept processed data from the computer. Examples include monitor, laser camera, printer, and archiving equipment such as optical discs or magnetic tape | output device |
| Type of computer memory that includes instructions that are frequently changed, such as the data used to reconstruct images. It is so named because all parts of it can be reached easily at random | random access memory (RAM) |
| Directional coordinate system—an acronym for right-left, anterior-posterior, superior-inferior—used to determine image center | RAS coordinates |
| Inaccuracies in the image caused when parts of the patient are located outside the scan field of view. These artifacts occur because the anatomy outside the SFOV attenuates and hardens the x-ray beam, but is ignored in the image reconstruction process | out-of-field artifacts |
| Specific area within the SFOV that will be displayed on the center of the image | image center |
| The absolute center of gantry | isocenter |
| Applied to the scan data before back projection occurs to minimize artifacts | filter functions |
| All measurements obtained from the detector array and sitting in the computer waiting to be made into an image. Also called scan data | raw data |
| Type of computer memory that is imprinted at the factory and is used to store frequently used instructions such as those required for starting the system | read-only memory (ROM) |
| The area, within the gantry, from which the raw data are acquired. Also called calibration field of view | scan field of view |
| Type of computer memory that stores data that can only be accessed sequentially (like a cassette tape) | serial access memory (SAM) |
| The path that the x-ray beam takes from the tube to the detector | ray |
| The detector senses each arriving ray and senses how much of the beam was attenuated | ray sum |
| Process of using the same raw data to later generate a new image | retrospective reconstruction |
| Image reconstruction that is automatically produced during scanning | prospective reconstruction |
| Type of computer memory in which data can be written to once, but read from many times | Write-once ready-many times memory (WORM) |
| Mechanism that determines the quantity of Hounsfield units represented as shades of gray on a specific image | window width |
| Mechanism that selects the center CT value of the window width. Also called the window center. | window level |
| Reformation that seeks to represent the entire scan volume in a single image. These techniques manipulate or combine CT values to display an image; the original CT value information is not included | three-dimensional reformation |
| Indicates the amount of CT number variance within the ROI | standard deviation |
| An area on the image defined by the operator | region of interest (ROI) |
| Two-dimensional reformation done to show anatomy in various planes | multiplanar reformation (MPR) |
| Function that allows more than one image to be displayed in a single frame | multiple image display |
| When the displayed image is made larger. Uses only image data and does not improve resolution | image magnification |
| Information that appears on images. Can include facility name, patient name, ID number, date, slice number and thickness, pitch, table location, measurement scale, gray scale, and right and left indicators | image annotation |
| A graphical display showing how frequency a range of CT numbers occur within an ROI | histogram |
| Measure of the beam attenuation capability of a specific structure. Also called pixel values, density numbers, or CT numbers | Hounsfield units (HU) |
| The system calculates the distance between two deposited points in either centimeters or millimeters | distance measurement |
| Changes the digital signal from the computer memory back to an analog format so that the image can be displayed on the monitor | digital-to-analog converter |
| Display functions that include multiplanar reformation and three-dimensional reformation | advanced display functions |
| System that assigns a certain number of Hounsfield values to each shade of gray | gray scale |
| CT component that assigns a group of Hounsfield units to each shade of gray | display processor |
Created by:
sspatel
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