ct ch 11-14 (skipping 13)

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Mshel389
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ct ch 11-14 (skipping 13)
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2013-02-19 18:23:04
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  1. slip ring technology's purpose
    • (found in 3rd gen ct)
    • allows xray tube & detectors to rotate continuously so that a volume of the pt (rather than one slice) can be scanned very quickly in a single breath hold
  2. define Pitch in SSCT
    • distance between turns and fastener
    • distances in mm that the ct table moves during one revolution of xray tube
  3. pitch ratio in SSCT
    distance table travels during 360 deg revolution divided by slice thickness (or beam collimation)
  4. When the distance the table travels in 1 complete revolution of the xray tube = the ___________ then the pitch ratio is 1:1
    slice thickness or beam collimation
  5. Pitch affects what (SSCT)
    image quality & pt dose
  6. (SSCT) volume coverage = _________x slice thickness or
    • pitch x slice thickness
    • (beam cvollimation x scan time)
  7. (SSCT) collimation determines
    the slice thickness & in most cases equals the table increments (pitch of 1)

    smaller structures require smaller/narrower collimation (whereas  larger structures require wider collimation)
  8. Table increments is aka
    table speed
  9. (SSCT) as table increment increases, pitch ____(which results in ____ image quality.
    pitch increases (decrease or loss of image detail)
  10. SSCT-compared to conventional for resolution
    • when using same parameters no change
    • however in some studies showed SSCT better at imaging smaller objects
  11. SSCT-Noise is affected by
    beam intensity, beam quality, slice thickness & matrix size & interpolation algorithms
  12. SSCT compared to conventional CT

    Noise 360 deg LI algorithm produces ____ noise
    less
  13. SSCT compared to conventional CT

    Noise 180 deg LI algorithm produces ____ noise
    more (degrades image quality)
  14. SSCT dose compared to conventional CT
    about equal
  15. helical/spiral CT scan uses a pitch of greater than 1 (which ______ pt dose.)
    reduces
  16. Limitations of SSCT
    volume coverage & speed can be increases by using a higher pitch, but image quality is degraded
  17. Multislice CT scanners aka
    • multisection
    • multidetector
    • multichannel
  18. MSCT 2 major components
    • radiation sensor
    • suitable electronic device
  19. Dual slice CT scanner became available in
    1972
  20. MSCT became available in
    1998
  21. overal goal of MSCT
    improve volume coverage speed performance of both single & dual slice ct scanners
  22. SSCT
    collimation defines the
    slice thickness & affects volume coverage speed performance

    a thin collimation results in better resolution but takes longer to scan
  23. SSCT beam geometry
    fan beam
  24. SSCT-slice thickness is determined by
    pitch and width of precollimator
  25. (MSCT) precollimator widthe divided by the number of rows detector arrays =
    slice thickness
  26. (MSCT) beam geometry-as teh #of rows in a multirow detector array increases, the beam
    becomes wider to cover the 2D detector array
  27. MSCT Beam geometry
    cone beam
  28. MSCT--with a cone beam there is more pt dose, with less radiation how
    more scatter radiation in all directions
  29. MSCT definition of PITCH
    distance the table travels per rotation divided by the total collimation
  30. MSCT

    a pitch of less than 1 is effectively overlaping slices & _____ dose
    increases
  31. MSCT

    a pitch greater than 1 results in ______ pt dose
    reduced

    because could potentionally be missing slices
  32. MSCT

    # of detector rows can vary from __ to ___
    4-320
  33. SSCT z-gap
    distance between 2 points used for interpolation

    smaller the Z-gap, better the image quality
  34. MSCT z-gap
    same as SSCT-distance between 2 points used for interpolation (can increase overlap between helices)

    however determined by pitch & detector row spacing
  35. MSCT
    pitch can be increased with a shorter Zgap =
    better quality images
  36. algorithms based on MSCT 4detector rows
    spiral/helical scanning, longitudinal interpolation & fan beam reconstruction
  37. in MSCT 
    as the # of detector  rows increase the cone beam becomes ____
    larger, artifacts become more pronounced

    -increases dose
  38. MSCT--Cone beam algorithms 
    2 classes
    Exact & Approximate
  39. exact algorithm is
    • a cone beam algorithm (MSCT)
    • not successful
    • computionally complex & difficult to implement
  40. Approximate algorithm is
    • a cone beam algorithm (MSCT)
    • 3D-feldkamp-Davis-Kress (FDK)
    • 2D-advanced single slice rebinning (ASSR)
  41. types of detectors in MSCT
    • 1. uniform
    • 2. nonuniform
    • 3. hybrid
  42. Uniform detectors aka
    (MSCT)

    matrix detector, or fixed-array or linear array detector
  43. Nonuniform detectors aka
    (MSCT)

    variable, adaptive-array detectors
  44. matrix detector
    • (type of MSCT detector)
    • aka uniform, fixed array or linear array detector
  45. Variable detector
    • type of MSCT detector
    • aka non uniform, adaptive-array detector
  46. Detector materials
    • Gas ionization detectors
    • Solid-State detectors
  47. gas ionization for detector material why?
    • have low quantom detection efficiency and they have low xray absorption 
    • used in SSCT, not MSCT
  48. Solid state detectors
    examples are
    • scintilation crystal  or ceramics
    • rare earth crystals, cadmium tungstate

    detectors are doped with dopants (ex europium) to decrease the afterglow below 0.1% at 100ms
  49. The most significant difference between SSCT & MSCT is
    detector technology

    • SSCT=gas ionization detector
    • MSCT=solid state detector
  50. Detector configuration describes what
    a term that describes the number of data collection channels & the effective section of thickness determined by the data acquisition system settings
  51. MSCT computer system consists of
    • preprocessing
    • image reconstruction
    • post processing
  52. Isotropic imaging definition
    • size of voxel used in volume data set 
    • when the slice thickness is equal to pixel size, all dimensions of the voxel are equal-or a perfect cube
  53. spatial resolution in MSCT
    • ability of scanner to improve fine detail
    • measured in lp/cm or lp/mm
  54. MSCT- contrast resolution
    ability of the scanner to differentiate small differences in tissue contrast
  55. Advantages of MSCT
    • increase in speed & volume coverage
    • improved spatial resolution
    • efficient use of xray beam
    • potential to reduce radiation exposure
    • cardiac ct imaging
  56. symptoms of a stroke include
    headache, slurred speech, confusion, facial droop, tremors, vomiting, & tetany
  57. Ischemic stroke appears
    • normal brain tissue appears as shades of gray
    • ventricles appear dark
    • portions that are dark are areas lacking blood supply due to stroke
  58. Hemorrhagic stroke appears
    areas of dense white indicate a hemorrhage (bleed)
  59. Appendicitis symptoms
    • RLQ pain
    • vomiting 
    • cramping
    • fever
    • abdominal pressure
  60. Symptoms of Pulmonary Embolism
    • chest pain
    • back pain
    • arm pain
    • shortness of breath
    • high D-dimer
  61. AAA symptoms
    • abdominal aortic aneurysm
    • back pain
    • flank pain
    • weakness
    • pallor
    • ashen skin tone if ruptured
    • & abdominal pressure
  62. Aortic Disection symptoms
    • same as AAA
    • usually very painful
    • back pain
    • & painful to move in any way
  63. Artifact appearance
    • streaks
    • shading
    • rings & bands
  64. Streak is what?
    • an artifact
    • intense straight lines across an image
  65. streaks can be caused from
    • improper sampling
    • partial volume averaging
    • motion
    • metal
    • beam hardening
    • noise
    • spiral/helical scanning
    • mechanical failure
  66. Rings or Bands are what
    • an artifact
    • produced when the projection readings of a single channel or a group of channels consistently deviate from the truth
  67. Rings or Bands can be caused by
    defective detector cells, deficiencies in system calibration or from suboptimal image-gen scanner
  68. ring & bands are predominately from what type of scanner?
    3rd generation
  69. Shading appears
    • an artifact
    • near an object of high densities
  70. shading can be caused by
    • beam hardening
    • partial volume averaging
    • spiral/helical scanning
    • scatter
    • off-focal radiation
    • incomplete projection
  71. Patient motion can be from
    • voluntary-breathing, swallowing
    • involuntary-head motion with injury, peristalsis, cardiac motion
  72. Rationale means
    purpose of 3D imaging is to use the vast amounts of data collected from the patient by volume ct scaning to provide both qualitative & quantitative info in a wide range of clinical applications
  73. Qualitative-
    • type of rationale
    • used to compare how observers perform on a specific vast to demonstrate the diagnostic value of 3D imaging
  74. Quantitatve-
    • type of rationale
    • used to assess three elements of the technique: precision, accuracy & efficiency of 3D imaging procedure
  75. Most common coordinate system used on 3D scanners
    • xyz
    • aka-Cartesian System
  76. (3D imaging)
    Scene
    multidimensional image; rectangular array of voxels with assigned values
  77. (3D imaging)
    scene domain
    Anatomical region represented by the scene
  78. (3D Imaging)
    scene Intensity
    values assigned to the voxels in a scene
  79. (3D Imaging)
    Pixel size
    length of a side of the square cross-section of a voxel
  80. (3D Imaging)
    scanner coordinate system
    origin & orthogonal axes system affixed to the imaging device
  81. (3D Imaging)
    scene coordinate system
    origin & orthogonal axes system affixed to the scene
  82. (3D Imaging)
    object coordinate system
    origin & orthogonal axes system affixed to the object or object system
  83. (3D Imaging)
    Display Coordinate System Rendition
    2D image depicting the object info captured in a scene or object system
  84. (3D Imaging)
    Image space
    translate, rotate, or scale scenes, objects or surfaces
  85. (3D Imaging)
    Object Space
    extract structural information about the object from the 3Dspace
  86. (3D Imaging)
    Parameter Space
    take measurements from the image's view space on the computer screen
  87. (3D Imaging)
    View space
    view the 2D screen of the computer monitor
  88. (3D Imaging)
    Modeling is what
    • generation of a 3D object using computer software
    • Uses mathematics to describe physical properties of an object
    • used to transform a 2D profile into a 3D object
  89. how are shading & lighting used in 3D imaging
    • several shading algorithms
    • Shading determines the final appearance of surfaces of the 3D object
    • Lighting helps us to see the shape & texture of the object
  90. Rendering is what
    • final step in process of generating a 3D object
    • a computer program that converts the anatomical data collected from the patient into the 3D image seen on the computer screen
  91. types of rendering (3D imaging)
    Surface & Volume
  92. Surface Rendering
    • type of 3D rendering
    • uses only the surface contour data
  93. Volume Rendering
    • type of 3D rendering
    • uses the entire data set
  94. slice imaging is waht (3D)
    • simplest method of 3D imaging
    • Like MPR (sag, coronal, paraaxial)
    • it is a 2D image displayed on a flat screen
  95. Projective imaging (3D)
    • Most popular 3D imaging approaph
    • Techniques for extracting multidimensional info from the given image data & for depicting such info in the 2D view space by a process of projection
    • (surface & volume redering)
  96. Projective imaging is technicall a ____ image
    2D
  97. Volume Imaging is what
    • produces a true 3D visualization mode
    • Must not be confused with volume rendering
  98. A generic 3D imaging systems consists of 4 major elements and they are
    • Input-refers to device that acquired data
    • Workstation-a powerful computer that can hand 3D imaging operations
    • Output-displays the results
    • User
  99. Definition of 3D imaging
    process that starts with a stack of sectional slices collected by some medical imaging device and results in computer synthesized displays that facilitate the visulazation of underlying spatial relationships
  100. 4 steps are needed to create a 3D image
    • 1. data acquisition
    • 2. creation of 3D space or scene space
    • 3. processing for 3D image display
    • 4. 3D image display
  101. Surface Rendering is what
    • aka surface display
    • computer creates an internal representation of surfaces that will be visible in the displayed image...it then lights them according to a standard protocol &  displays the image according to its calculation of how the light rays would be reflected to viewers eye
  102. 2 steps of surface rendering are
    • surface formation
    • depiction on a computer screen
  103. Advantage of surface rendering
    • much less storage space
    • (but not as much info as volume rendering)
  104. Volume Rendering is what
    • 3D images have better image quality & provide more info compared with SR techniques
    • Uses the entire data set
    • & requires more computer power
  105. 2 stages of Volume rendering are
    • Preprocessing 
    • Rendering
  106. Intensity Projection Renderings are what
    • used in 3D imaging
    • extension of MPR techniques
    • consist of generating arbitrary thick slices from thin slices, reducing the noise level and possibly improving the visualization of structures
  107. 3 types of Intensity projection renderings are
    • average intensity projection
    • maximum intensity projection
    • minimum intensity projection
  108. Average intensity projection is what
    • type of Intensity projection rendering used in 3D CT
    • algorithm intended to create a thick MPR image by using the average of the attenuation through the tissues of interest to calculate the pixel viewd on the computer
  109. Maximum Intensity Projection
    • type of Intensity projection rendering used in 3D ct
    • Volume Rendering technique
    • Algorithm where only tissues with greatest attenuation will be displayed for viewing by observer
  110. What is the most popular type of intensity projection used in CTA and why
    • Maximum intensity projection
    • vessels containing contrast are clearly seen
  111. Minimum Intensity Projection is
    • type of Intensity Projection Rendering used in 3D CT
    • ensures only the tissues with the minimum or lowest attenuation will be displayed for viewing by the observer
    • Least used projection
  112. Minimum Intensity Projection is the least used but it is useful in which way
    provides a valuable perspective in defining lesions for surgical planning or detecting subtle small airway diseases

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