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CT...
CTomography
| Question | Answer |
|---|---|
| Define computed tomography | CT is the process of creating cross-sectional tomographic plane nof any part of the body |
| The x-ray tube _____________ around the pt or part | rotates |
| A ___________________ measures the radiation exiting the pt and feeds the data to a computer. | detector assembly |
| The computer compiles and calculates the data according to a preselected___ and assembles it inot a ____. | algorithm, matrix |
| The image is then displayed on a _____. | liquid crystal display LCD or cathode ray tube CRT |
| List the 3 major components of a CT scanner | Gantry, Computer and operator console, Pt table |
| Electronic component of scanner that measures remnant radiation exiting the pt and converts it to a proportional analog signal | detector assembly |
| the array of numbers arranged in a grid; comprises the digital image | matrix |
| number used to describe average density of tissue | Hounsfield unit |
| Part of detector assembly that converts analog signals to digital signals | Data acquisition system (DAS) |
| area of anatomy displayed by the cathode ray tube (CRT) | Field of view (FOV) |
| volume element; determined by slice thickness | Voxel |
| determines the midpoint of the range of gray levels displayed | window level |
| part of scanner that houses the x-ray tube, cooling system, detector assembly, and DAS | Gantry |
| the range of CT numbers used to map signals into shades of gray | window width |
| one individual cell surface w/in an image matrix used for CRT image display; picture element | pixel |
| What is multiplanar reconstruction? | a digital postprocessing technique that has the ability to reconstruct CT axial images inot other planes w/out additional radiation to the pt |
| What are the most commony used filming devices | matrix camera, laser printer |
| what are the 3 most commonly requested CT procedures | head,chest and abdomen |
| by what 3 routes is contrast introduced for CT procedures? | IV, orally, or rectally |
| 4 main factors that affect CT image quality are: | 1. Spatial resolution 2.contrast resolution 3. noise 4. artifacts |
| the amount of blurring in a CT image is described as _______ | spatial resolution |
| the ability to differentiate btwn small differeences in density w/in the image is termed _________ | contrast resolution |
| the most common cause of noise in a CT image arises frm the random variation in photon detection, or _______ | quantum noise |
| why would it be best to schedule a CT abdomen on a pt several days after the pt's gastrointestinal (GI) fluoroscopy procedure? | to reduce the chance of residual barium in the GI tract causing artifacts on the CT |
| FOV | Spatial resolution |
| matrix size | Noise, spatial resolution |
| slice thickness | spatial, contrast resolution, noise |
| dental fillings | artifacts |
| x-ray beam energy | noise, contrast resolution |
| focal spot size | spatial resolution |
| residual barium | artifacts |
| reconstruction algorithm | spatial, contrast resolution, noise |
| pt size | contrast resolution, noise |
| 4 image quality factors that are under the technologist's control | slice thickness, 2.scan time, 3. scan diameter 4. pt instructions |
| which new CT data acquisition method involves teh continuous rotation of the gantry as the table moves thru the gantry | spiral CT |
| which new CT data acquisition technology has detectors arrays containing multiple rows of elements along the z-axis, instead of a singel row of detectors? | multi-slice spiral/helical CT (MSHCT) |
| 3 advantages of CT angiography (CTA) over conventional angiography | 1.less invasive-no arterial puncture2.postprocessing capable of eliminating overlying structures so only the vascular anatomy is reconstructed 3.any image made w/CT can be reconstructed w/out additional radiation exposure or IV contrast administration |
| 3 common techniques used for creating 3D images from CT data are: | maximum intensity projection (MIP), shaded surface display (SSD), and volume rendering (VR) |
| Which 3D-imaging technique is commonly used for CTA? | MIP (maximum intensity projection) |
| 3D reconsstructions are particularly useful in _____ | surgical procedures or presurgical planning |
| bony structures | CT |
| less scan time | CT |
| soft tissue | MRI |
| Claustrophobic pt | CT |
| better low-contrast resolution | MRI. |
| less costly | CT |
| Most CT systems require _______ or _______ preventative maintenance to ensure proper operation | weekly; biweekly |
| what method was 1st used to describe CT dose as a result of multiple scan locations> | multiple scan average dose (MSAD) |
| 8 factors that directly influence the CT radiation dose to the pt | 1.Beam energy (kVp) 2. tube current (mA) 3.roation or exposure time (seconds) 4.section or slice thickness (collimation) 5.object thickness and attenuation (size of pt) 6.pitch and/or section spacing (table distance traveled in one rotation) |
| last 2 of 8 factors directly influence the CT radiation dose to the pt | 7.dose reduction techniques (mA modulation) 8.distance frm the tube to teh isocenter |
| What term is applied to a single square, or picture element, int eh image display matrix? | Pixel |
| what determines the amt of data displayed on the monitor | FOV |
| a volume element is called a: | Voxel |
| a relative comparison of x-ray attenuation of a voxel of tissue to an equal volume of water is | CT number |
| What is the CT number of water | 0 |
| which of the following ar ethe major system components of a CT scanner? | Gantry, computer & operator's console, and pt table |
| a cirular device that houses the x-ray tube, DAS, and detector array is called the: | Gantry |
| x-ray tubes used in advanced CT scanners can tolerate: | 4 to 5 MHU |
| which of the following can be selected at the operator's console? 1.slice thickness 2.table index 3.radiographic technique factors | 1,2,3 |
| the range of CT numbers that are used to map signals into shades of gray is called the : | window width |
| midpoint of the range of gray levels to be displayed on the monitor is the: | window level |
| a narrow window width would display: | high contrast |
| the window level should be set to: | the CT number of the tissue of interest |
| the preferred device for producing hard copies of CT images is the: | laser printer |
| CT is the examination of choice for | head trauma |
| the amount of blurring in a CT image is termed: | spatial resolution |
| the ability to differentiate btwn small differences in density w/in the CT image is called: | contrast resolution |
| which of the following is the most significant geometric factor that contributes to spatial resolution? | detector aperture width |
| random variation in photon detection results in: | quantum noise |
| which of the following contribute to image noise in CT? 1.detector aperture width 2.matrix size 3.pt size | 1,,2,3 |
| metallic objects, such as dental filling, can cause: | artifacts |
| high-resoluiton CT scans are made using: | thinner sections or slices |
| which of the following quality factors is affected by x-ray beam energy? 1.contrast resolution 2.spatial resolution 3 noise | 1,3 only |
| which image quality factor is affected by focal spot size? | spatial resolution |
| tissue density differences of less than ___ can be distinguished by CT. | .5% |
| reconstruction algorithm affects all of the image quality factors except for: | artifacts |
| the image that appears on the CRT depends on the: | scan diametere |
| what is based on the principle that different structures enhance at different rates after contrast administration? | dynamic scanning |
| what new CT data acquisition method involves continuous gantry rotations combined with constant table movement thru the aperture? | spiral or helical CT |
| which 3D-imaging technique is commonly used for CTA? | maximum intensity projection |
Created by:
rose99