OPQR mosby2

  1. 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
  2. What is Opacification
    the increase in CT density of a structure due to filling with positive contrast material
  3. 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...
  4. What is Orthogonal
    Imaging planes that are perpendicular to each other
  5. What is Orthographic Volume Rendering
    A Technique yielding a 3D model with the perspective of externally viewing the reconstructed objects
  6. What is Osmolaltiy
    the tendency of an iodinated contrast medium to cause fluid from outside the blood vessel to move into the bloodstream
  7. 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)
  8. 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
  9. What is Overlapping Images
    CT images produced with a reconstruction interval that is less than the section width
  10. 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
  11. What is PACS
    • Picture Archival and Communication System
    • Responsible for storing, retrieving, distributing and displaying CT and other digital medical images
  12. What is the Pancreatic Phase
    • the delayed arterial enhancement phase
    • happens about 35-45 seconds after the start of contrast injection
  13. What is the flow rate of injection for Pancreatic phase
    3mL/sec or greater
  14. What is Parallel Processing
    the ability of a computer to perform multiple functions simultaneously
  15. 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
  16. 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
  17. 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
  18. 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
  19. 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
  20. What is a Photon Flux
    the rate at which a quantity of xray photons passes through a unit area over a unit time
  21. What is Pipelining
    a form of parallel processing used by a computer to improve computations speed
  22. What is Pitch
    the relationship b/w collimation and table movement per gantry rotation
  23. What is a Pixel
    • AKA: Picture Element
    • refers to the individual boxes arranges in the matrix used to display the CT image
  24. 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
  25. 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
  26. What is Polyenergetic
    • Consisting of spectrum of differing energies
    • used to describe the beam of xrays
  27. What is the Portal Venous Phase
    Period of peak hepatic parenchymal enhancement when contrast material redistributes from the blood into the extravascular spaces
  28. When does Portal venous phase happen
    60-70 seconds after the start of contrast
  29. 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
  30. What is Prospective Reconstruction
    the initial construction of the acquired raw data into CT image data with selected DFOV, algorithm, image center, ect
  31. 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
  32. What is a Pulse Oximeter
    an electronic device placed on a patients finger, toe or earlobe to measure pulse and blood oxygen levels
  33. What is Quality Assurance
    measurements of scanner performances through quality testing procedures and evaluation of the test results
  34. What is Quality Control
    the implementation of corrective action to improve any identified performance inadequacies of CT system
  35. What is Raw Data
    the transmission measurement obtained by the detector used to mathematically reconstruct the CT image
  36. What is a Ray
    the portion of the xray beam transmitted through the patient and incident upon a single detector
  37. What is a Ray Sum
    the measurement of transmitted radiation made by an individual detector used to determine the attenuation occurring along a ray
  38. What is ROI
    • Region of Interest
    • a user defined graphic outline that calculates the average Ct number of a given anatomic area
  39. What is Rendering
    the 3D algorithm to provide a specific perspective to the construction of a 3D model
  40. What is Response time
    the ability of the CT detector to quickly measure xray and then recover before the next measurement
  41. 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
  42. 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
  43. What is Ring Artifact
    a incorrect ring of density on the reconstructed CT image resulting from detector malfunction
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OPQR mosby2
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