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The amount of the xray beam that is reduced by absorption as it passes through an object
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Quantified beam attenuation is also know as what unit
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CT/MRI test 2
CT image processing & Display
| Question | Answer |
|---|---|
| The amount of the xray beam that is reduced by absorption as it passes through an object | Attenuation |
| Quantified beam attenuation is also know as what unit | Hounsfield Units |
| Hounsfield units are also called... | ct number |
| Beam attenuation occurs when the xrays go through the patient and hit the ______ | detectors |
| Hounsfield units are directly related to.... | Linear attenuation |
| finite set of steps performed to solve a problem | Algorithm |
| The process of using RAW DATA to create an image | Image reconstruction |
| Mathematical method of estimating the value of an unknown by using known values on either side | interpolation |
| Data from detectors that have NOT been assigned a hounsfield unit | Raw data (Scan data) |
| Processed raw data; each pixel within the data has been assigned a hounsfield unit | Image data |
| image data = | Processed data |
| do we store raw data or image data? | image data, raw data takes up too much space but when we store image data we cannot do anything with it when it goes in pacs |
| 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 | Image reconstruction |
| The time from the end of scanning to image display | Reconstruction time |
| image that is produced during scanning | Prospective reconstruction |
| Taking the raw data after scanning is over and at a later time using it to create a new image | Retrospective reconstruction |
| The path the xray beam takes from the tube to the detector | Ray |
| The measurement of how much beam attenuation occurs for EACH RAY | Ray sum |
| A complete set of ray sums, many views are needed to create an image | View |
| Accounting for the attenuation properties of each ray sum and correlation it to a position of the ray | Attenuaation profile |
| A summation technique of the attenuated profiles collected from all projections during scanning and converting it into a matrix; this results in a non-uniform image because the xray attenuation is not uniform over the entire path length | Back projection |
| Similar to back projection, except it applies a correction filter to attenuation information of the raw data; allows for exact representation of the object scanned | Filtered back projection |
| The process of applying a filter function to an attenuation profile | Convolution |
| What are 5 filtering functions | Standard, smoothing, edge enhancement, bone, detail |
| This allows us to use less does, but get granny images but then allows us to reconstruct the image as if we gave the patient 100% of the radiation | Adaptive statistical iterative reconstruction (ASIR) |
| Interpolation occures before/after filtered back projection in spiral image | before |
| interpolation relates to what | pitch |
| What are the 2 different FOVs? | Scan field of view (SFOV) Display field of view (DFOV) |
| what FOV is the area within the gantry that the raw data will be collected; determines the number of detectors collecting data for a particular scan | SFOV |
| What FOV is the region of interest in the resulting images; always equal to or smaller then the SFOV | DFOV |
| True/False SFOV has a max field of view & it is not the entire diameter of the gantry | true |
| DFOV only shows you | the field in which you are interested in |
| Manipulating both the raw AND image data AFTER the scanning has taken place | Post- processing |
| When raw data is manipulated to create pixels that are then used to create an image | Image reconstruction |
| Image that us produced during scanning | Prospective reconstruction |
| Taking the raw data after scanning is over and at a later time using it to create a new image | Retrospective reconstruction |
| uses image data to produce images in different planes or to produce 3D images; uses only image data | image reformation (image rendering) |
| Image reformation = | Image rendering |
| You cannot use image reformation unless you have what?? | identical DFOV, image center, gantry tilt, contiguous, no patient motion |
| Quantitative measurements = | analyzing image data |
| A post- processing technique performed on an image data set to produce new slices in a different orientation | Multi-planar reformation (MPR) |
| This represents the entire scan volume in only one image | 3D |
| Includes only information from the surface of a defined tissue threshold | Surface rendering (shaded surface display) |
| Every voxel is used; the sum of the voxels along a line are assigned an opacity value to form the final image | Volume rendering |
| This is a software program that will create a 2D image from a 3D data set; utilized commonly in angiography imaging, Used to separate superimposed vessels. This picks out the highest values of voxels | Maximum intensity projetion |
| Specialized software can quantitively measure images and obtain information about volume, distance, and diameter | Quantitative measurements |
| The measurement of the linear attenuation coefficient for a given tissue; corresponds to a shade of gray in the image | CT number |
| This is the standard scale of CT numbers. (what are CT numbers also called) | Hounsfield scale or hounsfiled units |
| water= | 0 |
| air= | -1000 |
| bone= | 1000 |
| When air shows up on a CT image it looks... | black |
| when bone shows up on a CT image it looks | White |
| Can we change the attenuation of a specific tissue? | Yes, with contrast |
| Why are HU/CT numbers useful? | We can compare the unknown number with the known number to make it easier to see that there is something wrong. |
| Changing the displayed contrast of an image by manipulation of window width and window level | Windowing |
| This is the range of CT numbers | Window Width (ww) |
| Reducing WW increases/decrease contrast | Increases contrast, short scale, black and white |
| Increasing WW increase/deceases contrast | decreases contrast, long scale, lots of grays |
| The CENTRAL VALUE of the ww; "the center CT number" | Window level |
| Hounsfield measurements are the result of the.... | Region of interest (ROI) |
| Standard deviation is | how accurate you average is of the pixels in the ROI |
| This is a display function that defines an area of an image | Region of interest (ROI) |
| Used to measure distance of structures | Distance Measurements |
| Addition of additional information on an image or within an imaging study. (You always do this on portables) | Image annotation |
| Displays the slice lines in corresponding location to the scout image. (you always see surgeons doing this to make sure they are at the right vertebrae) | Reference image |
| For image magnification you only need what information? | Image data |
| for display field of view you need what information? | Raw data |
| Continuous acquisition scanning WITHOUT TABLE MOVEMENT; important when observing arterial contrast enhancement | Cine imaging |
| Spaital resolution in CT refers to the... | Ability of the ct scanner to discriminate objects of varying density a small distance apart |
| a smaller pixel creates a better.... | Spacial resolution |
| A bigger pixel creates a better____ | contrast resolution |
| When you have good spatial resolution, you have ______ contrast resolution | worse |
| When you have good contrast resolution, you have _____ spatial resolution | Worse |
| When you have a big matrix like 512x512, this will result in better____ | Spatial resolution |
| Contrast resolution in CT refers to the ability of the scanner | to demonstrate small changes in tissue contrast |
| When you have a larger slice thickness and a higher mAs, this improves what | Contrast resolution |
| The fluxuation of CT numbers from point to point in an image for a scan is called | Noise |
| When you have a larger DFOV, increase slice thickness and does increases this decreases what | Noise |
| Contrast resolution, spatial resolution and noise all affect the change of ___ | DFOV |
| Increasing slice thickness and ________ spacial resolution | decreases |
| what 2 things can you increase to compensate for noise? | MA, KVp |
| Display FOV and matrix affects what | pixel size |
| slice thickness determines what | voxel size |
| You want a std of ___ | zero |
| This is a comparison of an image to the actual object | Image quality |
| Imaging parameters that affect quality are... (7). These are things that WE control to make an image look good | Ma, Scan time, slice thickness, FOV, reconstruction algorithum, kvp and pitch |
| This is the quantity of xray photons | MAS |
| This is the current of electrons that flow from the filament to the anode | MA |
| In SDCT it is the time the xray beam is on for each slice, in MDCT it is the time it takes for a 360 degree rotation of the tube | Time |
| When you increase MA, you increase flow of ______ | electrons |
| This is the intensity (penetrating power) of the xray beam | Kvp |
| increasing the kvp increases the speed of the ______ that strike the target | electrons |
| This is how THICK the data is acquired | Slice thickness |
| DFOV is either equal to or less than the _____ | SFOV |
| True/false: Can DFOV be more than the SFOV? | False |
| This aids un reconstructing optimal images by tissue types; filter to enhance certain tissue characteristics and applied to raw data | Reconstruction algorithms |
| This is the relationship between slice thickness and table travel per rotation | pitch |
| What are the 4 influences on parameter selection (4) | Spatial resolution, Contrast resolution, Noise and dose |
| Spatial resolution is also referred to as ______ | Detail resolution |
| This is very close strips of metal close together | Spatial resolution |
| How often an object will fit into a given space | Spatial frequency |
| Large objects have a _____ spatial frequency | low |
| Small objects have a _____ spatial frequency | high |
| CT has ____ spatial frequency | Low |
| What are the 6 factors of spatial resolution | Slice thickness, display FOV, matrix, pixel size, pitch and focal spot size |
| MA will make a difference in | Focal spot size |
| This is able to distinguish between similar tissues | Contrast resolution |
| Noise is when not enough _____ are picked up by _____ | photons, pixels |
| a decrease in photons is a ______ in noise | Increase |
| Larger the slice thickness, the more photons per pixel, the better __________ and less ____ | Contrast resolution, noise |
| When you increase scan time, you increase ____ | dose |
| higher Ma= higher ___ | dose |
| Increase in Kvp, increasaes the number of photons = ______ dose | increased |
| Tube current _______ dose the most | increase |
| This is how rapidly data is acquired | Temporal resolution |
| What three things plays apart if temporal resolution | Gantry speed, number of detector channels, speed that the system can record changing signals |
| This program is ensuring that system is producing the BEST QUALITY IMAGES using the lowest dose to patient | Quality control programs |
| in a CT quality control phantom, what does the first line stand for? | Positioning aligment, CT accuracy/slice thickness |
| in a CT quality control phantom, what does the second line stand for? | Low contrast resolution |
| in a CT quality control phantom, what does the third line stand for? | CT number uniform in plane distance measures |
| in a CT quality control phantom, what does the fourth line stand for? | spatial resolution |
| Who are responsible for QEs (3) | CT tech, service engineer and physicist |
| Is QA necessary? | yes |
| Why are QAs necessary? (4) | Maintains uniformity among scans, maintains accuracy among scans, requirement of regulation agencies and defines CT scanner problems |
| What are 2 quality assurance tests? | Spatial resolution and contrast resolution |
| _______ resolution uses line pair phantoms | spatial |
| _____ resolution uses contrast resolution phantoms with objects varying size; 0.5% of a sum object;performed monthly | Contrast resolution |
| A phantom that has a step-wedge, ramp or spiral; contains objects with known measurements; performed semiannually | Slice thickness accuracy |
| Slice thickness greater of 5mm, +/- ____ mm | 1 |
| Slice thickness less of 5mm, +/- ____ mm | .5 |
| Phantom designed and provided by the manufacturer; the light field should coincide with the radiation field to within 2mm; performed semiannually | laser light accuracy |
| This assesses the relationship between CT numbers and linear attenuation values; measured semiannually | Linearity |
| A water phantom is used; done on a weekly basis | noise and uniformity |
| ROI should not be more than ___ in water feature | 10 |
| The more _____ the less contrast resolution | noise |
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