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What is an O-Arm
- portable CT fluoroscopy unit with a telescoping gantry
- used to acquire 3D Ct images and standard fluoroscopy during invasive or surgical procedures
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What is Opacification
the increase in CT density of a structure due to filling with positive contrast material
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What is OS
- Operating System
- the main software of the CT computer, controlling the utilization of the hardware resources including the available memory, CPU time disk space and ect...
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What is Orthogonal
Imaging planes that are perpendicular to each other
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What is Orthographic Volume Rendering
A Technique yielding a 3D model with the perspective of externally viewing the reconstructed objects
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What is Osmolaltiy
the tendency of an iodinated contrast medium to cause fluid from outside the blood vessel to move into the bloodstream
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What is Out-of-Field Artifact
- Hyperdense streaking
- occurs when a portion of the patient has been positioned outside the scan field of view (SFOV)
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What is Overbeaming
Expansion of the primary beam in an MSCT system to ensure that all detectors of the array are exposed to xrays of equal intensity
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What is Overlapping Images
CT images produced with a reconstruction interval that is less than the section width
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What is Overranging
The process of applying radiation dose before and after the acquisition volume to ensure sufficient data collection for the interpolation algorithms of the helical CT reconstruction
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What is PACS
- Picture Archival and Communication System
- Responsible for storing, retrieving, distributing and displaying CT and other digital medical images
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What is the Pancreatic Phase
- the delayed arterial enhancement phase
- happens about 35-45 seconds after the start of contrast injection
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What is the flow rate of injection for Pancreatic phase
3mL/sec or greater
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What is Parallel Processing
the ability of a computer to perform multiple functions simultaneously
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What is Partial Volume Artifact
an error that occurs when a structure is only partly positioned w/in a voxel and the attenuation for the object is not accurately represented by a pixel value
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What is Partial Volume Averaging
- Inaccuracy in pixel values
- occurs when the associated voxels contain attenuation coefficients for multiple tissue types
- the values are averaged together to yield a single pixel value that attempts to represent an assortment of different materials
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What is Perspective Volume Rendering
- AKA: immersive rendering
- a technique yielding a 3D model with the perspective of being w/in the lumen of the object, similar to an endoscopic view
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What is a Phantom
a quality control device typically composed of a radiolucent plastic material containing specialized inserts that is used to measure specific image quality criteria
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What is Photodiode
a device used by a solid state CT detector to convert the light emittted by scintillation crystal into a proportional electronic signal
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What is a Photon Flux
the rate at which a quantity of xray photons passes through a unit area over a unit time
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What is Pipelining
a form of parallel processing used by a computer to improve computations speed
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What is Pitch
the relationship b/w collimation and table movement per gantry rotation
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What is a Pixel
- AKA: Picture Element
- refers to the individual boxes arranges in the matrix used to display the CT image
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What is Pixel Value
- AKA: CT Number
- relative value assigned to each pixel to quantify the attenuation occurring in each voxel comparison with the attenuation of water
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What is PSF
- Point Spread Function
- a measure of Ct systems in plane spatial resolution that evaluates the amount of spread inherent in an orthogonal (right angles) image of a thin wire
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What is Polyenergetic
- Consisting of spectrum of differing energies
- used to describe the beam of xrays
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What is the Portal Venous Phase
Period of peak hepatic parenchymal enhancement when contrast material redistributes from the blood into the extravascular spaces
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When does Portal venous phase happen
60-70 seconds after the start of contrast
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What is Prospective ECG Gating
- a method of improving the temporal resolution of the MSCT system during examination of the heart and mediastinum
- Data are acquired in an axial "step and shoot" mode and only during the diastolic portion of the R-R interval
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What is Prospective Reconstruction
the initial construction of the acquired raw data into CT image data with selected DFOV, algorithm, image center, ect
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What is Pseudoenhancment
- minimal increase in attenuation demonstrated by a structure that typically does not enhance following intravenous contrast administration
- most common used to eval cysts
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What is a Pulse Oximeter
an electronic device placed on a patients finger, toe or earlobe to measure pulse and blood oxygen levels
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What is Quality Assurance
measurements of scanner performances through quality testing procedures and evaluation of the test results
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What is Quality Control
the implementation of corrective action to improve any identified performance inadequacies of CT system
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What is Raw Data
the transmission measurement obtained by the detector used to mathematically reconstruct the CT image
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What is a Ray
the portion of the xray beam transmitted through the patient and incident upon a single detector
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What is a Ray Sum
the measurement of transmitted radiation made by an individual detector used to determine the attenuation occurring along a ray
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What is ROI
- Region of Interest
- a user defined graphic outline that calculates the average Ct number of a given anatomic area
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What is Rendering
the 3D algorithm to provide a specific perspective to the construction of a 3D model
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What is Response time
the ability of the CT detector to quickly measure xray and then recover before the next measurement
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What is Retrospective ECG Gating
- a method of improving the temporal resolution of a MSCT during exams for the hear and mediastinum
- the data acquired during the diastole are used for image reconstruction allowing for reduction of motion artifact in the CT image
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What is Retrospective Reconstruction
- is performed after the initial prospective reconstruction
- multiple retrospective reconstruction from raw data are possible with changes to DFOV, algorithms, image center
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What is Ring Artifact
a incorrect ring of density on the reconstructed CT image resulting from detector malfunction
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