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PRINCIPLES OF CT

PRINCIPLES OF CT. TOMOGRAPHY TOMOS ---SECTION. RADIOGRAPHY LIMITATIONS. SUPERIMPOSITION DIFFICULTY IN DISTINGUISHING BETWEEN HOMOGENOUS OBJECTS OF NON-UNIFORM THICKNESS. . SUPERIMPOSITION. RADIOGRAPHY LIMITATIONTISUE DIFFERENCE SENSITIVITY >10%. TOMOGRAPHY (CONVENTIONAL).

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PRINCIPLES OF CT

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  1. PRINCIPLES OF CT

  2. TOMOGRAPHYTOMOS---SECTION

  3. RADIOGRAPHY LIMITATIONS • SUPERIMPOSITION • DIFFICULTY IN DISTINGUISHING BETWEEN HOMOGENOUS OBJECTS OF NON-UNIFORM THICKNESS.

  4. SUPERIMPOSITION

  5. RADIOGRAPHY LIMITATIONTISUE DIFFERENCE SENSITIVITY>10%

  6. TOMOGRAPHY (CONVENTIONAL) • ELIMINATES TISSUE SUPERIMPOSITION • INCREASES CONTRAST OF LOW SUBJECT CONTRAST TISSUES

  7. TOMOGRAPHY

  8. TOMOGRAPHY

  9. TOMOGRAPHY LIMITATIONSMOTION BLURR

  10. CT ADVANTAGES

  11. LIMITATIONS OF CT • UNABLE TO DIFFERENTIATE BETWEEN TISSUES WITH SLIGHT CONTRAST DIFFERENCES < 1%.

  12. GOALS OF CT • MINIMAL SUPERIMPOSITION • IMAGE CONTRAST IMPROVEMENT • SMALL TISSUE DIFFERENCE RECORDING

  13. CT DATA AQUISITION

  14. TRANSMISSION RELATIVE TRANSMISSION=Io/I

  15. HISTORY OF CT

  16. Sir Godfrey Newbold Hounsfield CBE (28 August 1919 – 12 August 2004) was an English electrical engineer who shared the 1979 Nobel Prize for Physiology or Medicine with Allan McLeod Cormack for his part in developing the diagnostic technique of X-ray computed tomography (CT).

  17. HOUNSFIELD’S SKETCH

  18. CONSTRUCTION OF FIRST CT • RADIATION SOURCE – AMERICUM GAMMA SOURCE • SCAN—9 DAYS • COMPUTER PROCESSING—2.5 HOURS • PICTURE PRODUCTION 1 DAY

  19. HOUNSFIELD’S LATHE BED SCANNER

  20. 1972 FIRST CLINICAL PROTOTYPE CT BRAIN SCANNER FIRST SCANS—20 MIN. LATER REDUCED TO 4.5 MIN.

  21. CLINICALLY USEFUL CT SCANNER

  22. 1974 DR. ROBERT LEDLEY DEVELOPED THE FIRST WHOLE BODY CT SCANNER .

  23. SCANNER GENERATIONS • I • II • III • IV

  24. 180 DEG ROTATION

  25. 180 DEG ROTATION

  26. 360 DEG ROTATION

  27. 360 DEG ROTATION

  28. MODERN SCANNER

  29. CT MAIN SYSTEMS • IMAGING SYSTEM • COMPUTER SYSTEM • DISPLAY, RECORDING, STORAGE SYSTEM • DATA ACQUISITION SYSTEM

  30. IMAGING SYSTEM • PRODUCTION OF X-RAYS • SHAPING OF X-RAY BEAM ENERGY • FILTERING X-RAY BEAM

  31. SCANNER GANTRY TABLE/COUCH

  32. GANTRY INSIDE

  33. COMPUTER SYSTEM • RECONSTRUCTION AND POSTPROCESSING • CONTROL OF ALL SCANNER COMPONENTS • CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY. • DATA FLOW DIRECTION

  34. COMPUTER SYSTEM IN CT • MINICOMPUTERS

  35. IMAGE DISPLAY, RECORDING, STORAGE • DISPLAYS IMAGE ( OUTPUT FROM COMPUTER) • PROVIDES HARD COPY OF THE IMAGE • FACILITATES THE STORAGE AND RETRIEVAL OF DIGITAL DATA • COMMUNICATES IMAGES IN THE NETWORK

  36. DATA ACQUISITION SYSTEM (DAS) • SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER.

  37. CT COMPONENTS GANTRY COMPUTER TABLE/COUCH CONSOLE

  38. ORIGINAL CLINICAL CT SCANS COMPOSED OF 80 X 80 MATRIX PIXELS 6400

  39. EARLY DAYS vs TODAY 80 x 80 512 x 512

  40. COORDINATE SYSTEM IN CT X

  41. COORDINATE SYSTEM IN CT Y

  42. COORDINATE SYSTEM IN CT Z

  43. COORDINATE SYSTEM IN CT ISO-CENTER

  44. SCAN FOV SFOV DETECTORS

  45. DFOV – DISPLAYED FIELD OF VIEW • SIZE DISPLAYED ON THE MONITOR

  46. PIXEL SIZE PIXEL SIZE= DFOV (mm)/ MATRIX SIZE

  47. RECONSTRUCTION RECONSTRUCTION

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