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| This British physicist/engineer first demonstrated the technique for CT in 1970: |
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| Before Hounsfield first demonstrated the technique for CT in 1970, ____ ______, a Tufts University medical physicist, had previously developed the mathematical algorithms now used to reconstruct CT images. |
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| _____ generation CT systems were characterized by a finely collimated pencil beam and single detector assembly translating across the patient and rotating between successive translations. |
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| _____ generation CT systems took up to five minutes to complete one image. |
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| In _________ tomography, the plane of the image is parallel to the long axis of the body. |
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| Conventional tomography uses ____ tomography. |
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| In _________ tomography, the image is perpendicular to the long axis of the body. |
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| Computed tomography uses _______ tomography. |
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Definition
| transaxial (transverse image) |
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| What was the first modality to use transaxial tomography imaging methods? |
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| When the source-detector assembly makes one sweep across the patient, this is known as a __________. |
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| The intensity of the radiation detected varies according to the attenuation pattern and forms an intensity profile aka a: |
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| ______ generation CT systems used the translate-rotate methodology to acquire images and incorporated multi-detector linear arrays and fan-beam technology. |
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Definition
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Term
| What were the disadvantages of 2nd gen CT? |
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Definition
- slow
- the fan beam increased scatter radiation which degraded image contrast, and it increased radiation intensity toward the edges of the beam |
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Term
| The fan beam caused an increase in radiation intensity toward the edges of the beam. What was done to compensate for this? |
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Definition
| implementation of the bow-tie filter |
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Term
| What was the principle advantage of 2nd gen CT over 1st gen? |
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Definition
| Increased speed - using a fan beam and a detector array of 5 to 30 detectors, rotation increments of five degrees or more could be used, greatly reducing the number of translations required for a given procedure |
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Term
| Was speed a principle advantage or disadvantage of 2nd gen CT? |
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Definition
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| _____ generation CT imaging systems were the first designed so that the source and detector arrays rotated around the patient. No translation was required. |
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Definition
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| _____ generation CT scanners used a curvilinear detector array and a fan beam. This results in a constant source-to-detector path length, which is an advantage for good image reconstruction. |
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Definition
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| 3rd gen CT scanners were much faster than 2nd gen because the # of detectors and the width of the fan beam (30-60 degrees) were substantially larger. 3rd gen CT systems could produce images in less than _____ second/s. |
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| What was the principle disadvantage of third gen CT scanners? |
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Definition
| The appearance of ring artifacts |
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Term
| This artifact was typically caused by malfunction of any one detector or bank of detectors in a CT imaging system. This lack of signal caused a ring to appear on reconstruction known as a: |
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Term
| It took a ______ gen CT scanner 20s per slice. |
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Term
| The linear detector array is characteristic of ______ and ______ generation computed tomography imaging systems. |
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Definition
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| The curvilinear detector array is used in ______ and ______ generation computed tomography imaging systems. |
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Definition
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| ___ gen CT system completes a 360 degree rotation around the pt in .5 seconds. |
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Definition
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| The ______ generation of CT scanners use a rotate-stationary configuration. The x-ray source rotates around the patient, but the detectors remain stationary. This is accomplished through a fixed array of detectors containing as many as 4000 elements. |
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Definition
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| This generation of scanners were first capable of subsecond imaging times and can accommodate variable image slice thickness through the use of automatic prepatient collimation: |
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| (True/False): 4th gen CT systems experience fewer ring artifacts than 3rd gen systems. |
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Definition
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| What is the greatest drawbacks of the 4th gen CT imaging system? |
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Definition
- increased pt dose
- high cost |
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Term
| What are the 3 major subsystems of the CT system? |
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Definition
- gantry
- computer
- operating console |
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Term
| What are the components within the gantry? |
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Definition
- x-ray tube
- detector array
- high voltage generator
- pt support couch
- mechanical support for each of these components |
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Term
| It is essential that CT x-ray tubes have these 3 properties: |
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Definition
- high heat capacity (at least several million HU)
- high speed rotors (to help dissipate heat)
- small focal spot (increased spatial resolution) |
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Term
| What type of detector is used by modern CT systems: |
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Definition
- scintillation (used almost solely now-a-days)
(gas detectors used to be used but were too inefficient in comparison) |
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Term
| What type of crystal is most commonly used in today's CT scintillation detectors? |
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Definition
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| The overall efficiency of scintillation detectors is about __%. |
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Definition
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| Modern detectors are extremely efficient because they can be packed tightly together, and because they absorb up to __% of the x-rays that interact with them. |
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Definition
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Term
| What are the two collimators used in CT to reduce pt dose and scatter radiation? |
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Definition
- prepatient collimation
- predetector collimation |
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Term
| The _________ collimator is mounted on or adjacent to the x-ray tube housing. It limits the area of the patient that is exposed to the useful beam, and thereby determines patient dose. |
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Definition
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| The _________ collimator restricts the x-ray beam seen by the detector array, thus reducing scatter radiation and improving image contrast. |
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Definition
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Term
| What is another term to describe slice thickness? |
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Definition
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Term
| Most CT systems operate in excess of ___ kVp. |
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Definition
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| Slice thicknesses can range from __ mm - _ cm. |
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Definition
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Term
| CT images are stored in _____ format and displayed on monitors as a matrix of intensities. |
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Definition
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Term
| The CT image format consists of many cells of information, each assigned a _______ and displayed as an optical density or brightness level on a monitor. |
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Definition
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| Each cell of information is a _____, and the numeric information contained in each _____ is a CT Number, also known as a Hounsfield Unit (HU). |
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Definition
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Term
| The diameter of image reconstruction is called the: |
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Definition
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| A (large/small) matrix is better for fine detail images. |
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Definition
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| When FOV is increased for a fixed matrix size, the size of each pixel increases proportionately. By the same token, when the matrix size is increased for a fixed FOV, the pixel size _______ proportionately. |
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Definition
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Term
| What is the actual dynamic range of the CT image? |
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Definition
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| A process called ________ _____ projection is used to reconstruct CT images from the projections stored in memory. |
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Definition
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| The term ______ refers to a mathematical function used to perform the reconstruction. |
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Definition
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Term
| What are the five image characteristics that are regularly assessed to measure CT image quality? |
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Definition
- spatial resolution
- contrast resolution
- noise
- linearity
- uniformity |
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Term
| Spatial Resolution on the CT image can be affected by: |
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Definition
- pixel size
- slice thickness
- voxel size
- collimation |
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Term
| The smaller the pixel, the (higher/lower) the spatial resolution. |
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Definition
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Term
| The thinner the slice, the (higher/lower) the spatial resolution. |
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Definition
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Term
| _________ _______ _______ and its graphic representation are most often cited to express the spatial resolution of a CT imaging system. |
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Definition
| Modulation Transfer Function (MTF) |
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Term
| ___ is the ratio of the size of the object on the image to the actual size of the object being imaged. |
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Definition
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Term
| If the size of the object in comparison to the object on the image were equal, the MTF value would be (_). If the object did not appear on the image at all, the MTF value would be (_). |
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Definition
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Term
| Spatial _________ represents the line pairs per unit length on a CT image. |
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Definition
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Term
| The loss in faithful reproduction of objects on a CT system occurs because of limitations of the: |
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Definition
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Term
| An MTF curve that extends farther to the right indicates (higher/lower) spatial resolution, which means the imaging system is better able to reproduce very small objects. |
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Definition
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Term
| An MTF curve that is higher at low spatial frequencies indicates better ________ resolution. |
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Definition
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Term
| Most systems are judged by the spatial frequency at an MTF equal to 0.1, also called the ________ resolution. |
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Definition
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Term
| The best possible spatial resolution for any CT imaging system is the size of the: |
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Definition
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Term
| The CT Imaging system is able to amplify the subtle differences in _______ contrast so that image contrast is high. |
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Definition
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Term
| _____ is the percentage standard deviation of a large number of pixels obtained from a water bath image. |
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Definition
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| A large variation of pixel values (CT Numbers) for the same type of tissue imaged represents high: |
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Definition
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Term
| Image noise depends on what factors? |
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Definition
- kVp & filtration
- pixel size
- slice thickness
- detector efficiency
- pt dose |
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Term
| With _____ CT, the x-ray tube rotates continuously during the procedure. While the tube rotates, the couch moves the pt through the imaging plate. |
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Definition
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| With _____ CT, the x-ray tube is continuously energized, and data are collected continuously. An image can be constructed along any desired z-axis position along the pt. |
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Definition
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Term
| The ability to reconstruct an image at any z-axis position is possible because of a mathematical process called: |
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Definition
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Term
| Interpolation is performed by a special computer program called an: |
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Definition
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Term
| Interpolation algorithms use ___ or ___ degree rotations of the x-ray tube. |
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Definition
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Term
| 180 degree interpolations improve z-axis resolution and result in better reformatted sagittal and coronal views; however they increase: |
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Definition
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Term
| _____ ____ ____ is the relationship between the patient couch movement and the x-ray beam collimation. |
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Definition
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Term
| The relationship of the speed of the couch to the thickness of the slice: |
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Definition
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Term
| Determines thickness of the slice and is expressed as a ratio (i.e., 0.5:1, 1:1, 1.5:1): |
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Definition
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Term
| A pitch above _:_ increases the volume of tissue that can be imaged at a given time. |
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Definition
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Term
| What is the principle advantage of spiral CT? |
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Definition
| The ability to image a large volume of tissue in a single breath hold |
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Term
| The volume of tissue imaged = |
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Definition
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Term
| Spiral CT was made possible by the advent of ____ ____ technology. |
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Definition
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Term
| ____ ____ are electromechanical devices that conduct electricity and electric signals through rings and brushes from a rotating surface onto a fixed surface. |
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Definition
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Term
| There are usually __ slip rings on a gantry. |
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Definition
3
- one provides high-voltage power to the x-ray tube and high-voltage generator
- a second provides low-voltage power to control systems on the rotating gantry
- the third transfers digital data from the rotating detector array |
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Term
| For spiral CT, the x-ray tubes must have high heat capacity (_ MHU or more) and high cooling rates (_ MHU per minute). |
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Definition
heat capacity 8 MHU or more
cooling rate 1 MHU per minute |
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Term
| In spiral CT, the volume of tissue that can be imaged is determined by: |
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Definition
- examination time
- couch travel
- pitch
- collimation |
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Term
| In multislice CT, there are two designations for pitch: |
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Definition
- beam pitch
- slice pitch |
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Term
| ____ pitch relates patient translation per 360 degree tube rotation to the width of the x-ray cone beam. |
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Definition
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Term
| ____ pitch relates to the patient translation in relation to the slice thickness selected for the scan. |
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Definition
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Term
| The ability to overlap transverse images improves: |
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Definition
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Term
| In multislice scanning, the signal from each detector is connected to a computer-controlled electronic amplifier and switching device called a: |
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Definition
| Data Acquisition System (DAS) |
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Term
| The ____ ________ System selects combinations of detector arrays for various slice thicknesses. |
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Definition
| Data Acquisition System (DAS) |
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