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Basic principles of CT scanning

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This presentation gives an information about Basic principles of CT scanning covering the syllabus of Non Destructive testing

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Basic principles of CT scanning

  1. 1. 6/3/2014 1Hareesha N G, Dept of Aero Engg, DSCE
  2. 2. The basics of CT • CT imaging chain • System components • Acquisition methods • Image quality • Applications 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 2
  3. 3. X-ray: The beginning • X-Rays founded in 1895 by Wilhelm Conrad Roentgen 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 3
  4. 4. CT: The beginning • CT founded in 1970 by Sir Godfrey Hounsfield – Engineer with EMI, LTD. – first applications were in neuroradiology 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 4
  5. 5. CT Scanner • X-Ray modality used to the body in cross section • Used to determine – extent of trauma – location and type of tumors – status of blood vessels – pre surgical planning 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 5
  6. 6. CT System 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 6
  7. 7. CT System 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 7
  8. 8. Basic CT scanner components • Gantry • X-Ray Tube • Detector • Control Console 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 8
  9. 9. Gantry • CT X-ray tube • High voltage generator • Detector array • Data acquistion system • Slip ring 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 9
  10. 10. The CT X-ray Tube • Anode heat capacity – 3.5 MHU up to 6.5 MHU • Determines maximum mAs • Determines volume length • Dictates generator size 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 10
  11. 11. Detector Elements • Capture energy that has not been attenuated by the patient 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 11
  12. 12. Control console • Set scan parameters – kVp, mA, scan time, reconstruction filter, etc. • Set scan mode – Digital radiograph, axial or volume • Houses reconstructor • Review and archive images • Post-processing 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 12
  13. 13. CT • CT - Computed Tomography • CAT Scan - Computerized Axial Tomography 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 13
  14. 14. Scanning methods • Digital projection – AP, PA, Lat or Oblique projection – Surview, Scanogram • Conventional CT – Axial • Start/stop • Volumetric CT – Helical or spiral CT • Continuous acquisition 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 14
  15. 15. Digital Projection • X-ray tube and detector remain stationary • Patient table moves continuously – With X-rays “on” • Produces an image covering a range of anatomy – Similar to a conventional X-ray image, e.g. flat plate of the abdomen • Image used to determine scan location 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 15
  16. 16. Axial CT • X-ray tube and detector rotate 360° • Patient table is stationary – With X-ray’s “on” • Produces one cross-sectional image • Once this is complete patient is moved to next position – Process starts again at the beginning 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 16
  17. 17. Volume CT • X-ray tube and detector rotate 360° • Patient table moves continuously – With X-ray’s “on” • Produces a helix of image information – This is reconstructed into 30 to 1000 images 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 17
  18. 18. Volume Scanning: Pitch 1:1 2:1 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 18
  19. 19. Advantages of Volume CT • More coverage in a breath-hold – Chest, Vascular studies, trauma • Reduced misregistration of slices – Improved MPR, 3D and MIP images • Potentially less IV contrast required • Gapless coverage • Arbitrary slice positioning 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 19
  20. 20. Fundamentals of Multislice CT 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 20
  21. 21. Multislice Fundamentals • Everything is better • (R)esolution – Z-axis, spatial, low contrast • (S)peed – Temporal - bolus capture, stopped motion • (V)olume – Thin slice - – organ-specific coverage • (P)ower – Enough photons - uncompromising image quality 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 21
  22. 22. Single Slice = One 10mm slice per rotation Dual Slice = Two 5mm slices per rotation Quad Slice = Four 2.5mm slices per rotation Multislice Effectiveness • Everything is better – Resolution 2x 4x-8x – Speed same same – Volume same same – Power same same Dual Quad 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 22
  23. 23. . . single detector arc dual detector arc pre-patient collimation post-patient collimation x-ray tube focal spot ___ Mx8000 Dual Slice Dual Slice Detector Optimized for 2 Slice Acquisition 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 23
  24. 24. Approximately 10% more efficient than matrix detectors Variable Wide Area Detector Asymmetrix™ Variable detector length Fixed detector length Quad Detector Technology • Philips patented variable wide area detector • Variable slice thickness – 4 x 1mm – 4 x 5mm – 4 x 2.5mm – 2 x 0.5mm – 2 x 8mm – 2 x 10mm 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 24
  25. 25. 8 Element 2-D array 4 Slices Quad Technology How it works 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 25
  26. 26. 2x0.5mm 4x1mm 4x2.5mm 4x5mm 2x10mm p-plane fused fused to FEE Asymmetrix™ Technology Variable slice thickness 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 26
  27. 27. CT • CT attenuation information • CT image quality 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 27
  28. 28. Attenuation • X-ray beam passes through patient • Each structure attenuates X-ray beam differently – According to individual densities • Radiation received by detector varies according to these densities 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 28
  29. 29. Density information • Transferred from detector to CT computer (A to D converter) • Reconstructed by computer into a cross-sectional image – Displayed on screen – Each pixel displayed on monitor has varying brightness • The greater the attenuation, the brighter the pixel • The less attenuation, the darker the pixel 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 29
  30. 30. Density information • Density values correspond to a range of numbers – Hounsfield scale 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 30
  31. 31. Window settings • Window width – Determines range of CT numbers displayed on an image • Values above this range = white • Values below this range = black – Window level • Sets the center CT number displayed on the monitor • Determines the location on the Hounsfield scale about which the window width will be centered 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 31
  32. 32. CT image quality • Spatial resolution – Ability to resolve small objects in an image – Measured in lp/cm 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 32
  33. 33. Isotropic Imaging • True 0.5mm Isotropic imaging 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 33
  34. 34. CT image quality • Contrast resolution – Ability to differentiate small density differences in an image 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 34
  35. 35. Post Processing Options • Visualization of vasculature in relation to pathology – Show course of vessels – Show stent placement – Define vascular stricture 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 35
  36. 36. Cervical Spine Spiral Acquisition Rotation – 0.75 sec Coverage – 160 mm Pitch – 0.875 Acq. Time – 36 sec FOV – 250 mm ST – 1.0 mm Rec. Incr. – 0.6 mm Std Res. – 8 lp/cm 120 kV, 200 mAs CTDI100w – 39 mGy CTDIFDAw – 17 mGy Thin-Slice Spiral Neck 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 36
  37. 37. Neuro-Angiography Circle of Willis 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 37
  38. 38. Thin-SliceSpiralLungs 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 38
  39. 39. MIP 4D-Angio MasterCut Panoramic View RenalArteries 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 39
  40. 40. Ext. Spiral Acq. Spiral Acquisition UltraFast – 0.5 sec Coverage – 1400mm Pitch – 1.75 Acq. Time – 41.5 sec FOV – 420 mm ST –2.5 mm Rec. Incr. – 1.6 mm Std Res. – 8 lp/cm 120 kV, 96 mAs CTDI100w – 7.3 mGy CTDIFDAw – 4.9 mGy Extended Spiral Acquisition 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 40
  41. 41. CT Scanners • Provide a window into the body • Customer considerations – How many patients – Referring physicians – Budget – Upgrade expectations • Philips has ALL the answers 6/3/2014 Hareesha N G, Dept of Aero Engg, DSCE 41

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