1 / 77

PHYSICAL PRINCIPLES OF COMPUTED TOMOGRAPHY

PHYSICAL PRINCIPLES OF COMPUTED TOMOGRAPHY. RADIOGRAPHY LIMITATIONS. SUPERIMPOSITION DIFFICULTY IN DISTINGUISHING BETWEEN HOMOGENOUS OBJECTS OF NON-UNIFORM THICKNESS. SUPERIMPOSITION. TISUE DIFFERENCE SENSITIVITY 5%-10%. TOMOGRAPHY ( CONVENTIONAL).

kelly-hoover
Download Presentation

PHYSICAL PRINCIPLES OF COMPUTED TOMOGRAPHY

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PHYSICAL PRINCIPLES OF COMPUTED TOMOGRAPHY

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

  3. SUPERIMPOSITION

  4. TISUE DIFFERENCE SENSITIVITY 5%-10%

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

  6. TOMOGRAPHY

  7. TOMOGRAPHY

  8. TOMOGRAPHY

  9. CT ADVANTAGES

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

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

  12. CT DATA AQUISITION

  13. SLIP RINGS

  14. SEQUENTIAL-SLICE BY SLICE SCANNING

  15. SCANNING

  16. TRANSMISSION RELATIVE TRANSMISSION=Io/I

  17. Total # of trans. measurements=# of views X # of rays in each view

  18. ATTENUATION

  19. DATA AQUSITION GEOMETRIES • CONTINUOUS • STATIONARY

  20. CONTINUOUS

  21. STATIONARY

  22. CT 120-140 KVP • REDUCED DEPENDENCY ON ATTENUATION COEFFICIENT • REDUCED CONTRAST • INCREASED PHOTON FLUX

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

  24. X

  25. Y

  26. Z

  27. ISOCENTER

  28. SCAN FOV SFOV DETECTORS

  29. SCAN FOV-SMALL SFOV DETECTORS

  30. SFOV - HEAD

  31. TOO SMALL OF SFOV – OUT OF FIELD ARTIFACT

  32. SCAN FOV-RESOLUTION SFOV

  33. RECONSTRUCTION RECONSTRUCTION

  34. SCAN FOV-RESOLUTION SFOV

  35. DISPLAY FOV vs SCANNING FOV • DFOV CAN BE EQUAL OR LESS OF SFOV • SFOV – AREA OF MEASUREMENT DURING SCAN • DFOV - DISPLAYED IMAGE

  36. PIXEL SIZE PIXEL SIZE= FOV (mm)/ MATRIX SIZE

  37. MOST SCANNERS PIXEL SIZE 1 TO 10mm

  38. EXAMPLE: • FOV= 40 CM= 40 X 10 MM=400 mm • MATRIX= 512 X 512 = 5122 400/512 = 0.78 mm 0.8 mm

  39. EACH PIXEL IN CT HAS RANGE OF GRAY SHADES • 2 8 = 256 SHADES • 2 12 = 4096 SHADES = -100 TO 3095 SHADES OF GRAY

  40. PIXEL vs VOXEL PIXEL VOXEL

  41. PIXEL SIZE DEPENDS ON: • MATRIX SIZE • FOV

More Related