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ARTIFACTS IN COMPUTED TOMOGRAPHY

ARTIFACTS IN COMPUTED TOMOGRAPHY. ARTIFACT. Any discrepancy between the CT numbers represented in the image and the expected CT number based on the linear attenuation coefficient. APPEARANCE OF ARTIFACTS. STREAKS SHADING BANDS RINGS. SOURCES OF ARTIFACTS. PATIENT

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ARTIFACTS IN COMPUTED TOMOGRAPHY

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  1. ARTIFACTS IN COMPUTED TOMOGRAPHY

  2. ARTIFACT • Any discrepancy between the CT numbers represented in the image and the expected CT number based on the linear attenuation coefficient

  3. APPEARANCE OF ARTIFACTS STREAKS SHADING BANDS RINGS

  4. SOURCES OF ARTIFACTS • PATIENT • IMAGING PROCESS AND EQUIPMENT

  5. PATIENT INDUCED ARTIFACTS • MOTION • BEAM HARDENING • METAL ARTIFACT • OUT OF FIELD ARTIFACT

  6. MOTION ARTIFACT CAUSED BY: • VOLUNTARY MOTION • INVOLUNTARY MOTION IT PRODUCES “GHOSTING” EFFECT OBJECT CT IMAGE APPEARS– AS IF COMPOSED OF SUPERIMPOSED IMAGES

  7. MOTION

  8. MOTION

  9. MOTION

  10. MOTION

  11. REMEDY: • VOLUNTARY MOTION: EXPLANATION OF THE PROCEDURE AND GOOD COMMUNICATION WITH A PATIENT • INVOLUNTARY MOTION: SHORT SCAN TIME

  12. BEAM HARDENING • IT OCCURS WHEN THE AVERAGE ENERGY OF AN X-RAY BEAM PASSING THROUGH THE PATIENT INCREASES. BEAM IS “HARDENED” HIGH ENERGY PHOTONS ARE ATTENUATED LESS BY THE TISSUE. AS A RESULT, THEY ARE PASS THROUGH THE PATIENT AND REACH THE DETECTORS. THIS ARTIFACT IS ALSO CALLED “CUPPING” ARTIFACT BEACAUSE THE HARDENING IS MOST PRONOUNCED IN THE CENTER AND LESS AT THE PERIPHERY. IT RESAMBLES A CUP.

  13. COMMON AREAS OF MANIFESTATION: • SKULL – PETROUS PYRAMIDS • UPPER CHEST AND SHOULDERS • HIPS

  14. BEAM HARDENING

  15. BEAM HARDENING - CONTRAST

  16. BEAM HARDENING

  17. REMEDY • INCREASE kVp • DECREASE SLICE THICKNESS • INCREASE FILTRATION – BOWTIE FILTER

  18. METAL ARTIFACT • MANIFEST ITSELF AS “STAR STREAKING” ARTIFACT. IT’S CAUSED BY PRESENCE OF METALLIC OBJECTS INSIDE OR OUTSIDE THE PATIENT. METALLIC OBJECT ABSORBS THE PHOTONS CAUSING AN INCOMPLETE PROFILE

  19. METAL ARTIFACT

  20. METAL ARTIFACT

  21. REMEDY • REMOVAL OF EXTERNAL METALLIC OBJECTS • MAR SOFTWARE • GANTRY ANGULATION

  22. OUT OF FIELD ARTIFACT • PATIENT IS NOT ENTIRELY ENCLOSED IN THE SCANNING FIELD OF VIEW. PATIENTS BODY CAN OBSTRUCT DETECTORS. IN ADDITION, PATIENT TISSUE OUTSIDE THE SFOV WILL FURTHER HARDEN THE X-RAY BEAM. ARTIFACT APPEARS AS STREAKS AND SHADING.

  23. OUT OF FIELD ARTIFACT

  24. OUT OF FIELD ARTIFACT

  25. OUT OF FIELD ARTIFACT

  26. REMEDY: • SELECTION OF LARGER SFOV • TAPING PATIENT TISSUE • RAISING PATIENTS ARMS ABOVE THEIR HEAD ON THE SCAN OF CHEST AND ABDOMEN

  27. EQUIPMENT IMAGING PROCESS ARTIFACTS • PARTIAL VOLUME EFFECT • AILIASING • PHOTON STARVATION (NOISE) • AIR-CONTRAST INTERFACE • RING • TUBE ARCING • LINE IN TOPOGRAM • STAIRCASE

  28. PARTIAL VOLUME EFFECT • Mechanism of partial volume artifacts, which occur when a dense object lying off-center protrudes part of the way into the x-ray beam.

  29. REMEDY • THIN SLICE SELECTION • THIN SLICE INREMMENTATION

  30. AILIASING • FINE LINE ON AN IMAGE

  31. REMEDY • INCREASE SCAN TIME • USE COMPLETE ARC SCAN

  32. PHOTON STARVATION - NOISE • FLUCTUATION OF CT# BETWEEN POINTS IN THE IMAGE FOR A SCAN OF UNIFORM MATERIAL SUCH WATER.

  33. NOISE

  34. NOISE

  35. NOISE

  36. REMEDY • kVp INCREASE • mAs INCREASE • SLICE THICKNESS INCREASE

  37. AIR-CONTRAST INTERFACE STREAKING

  38. REMEDY • CHANGE THE PATIENT POSITION

  39. RING • MALFUNCTION OF A DETECTOR IN A THIRD GENERATION SCANNER

  40. RING

  41. RING

  42. REMEDY • DETECTOR CALIBRATION • DETECTOR REPLACEMENT

  43. TUBE ARCING • TUNGSTEN VAPOR FROM ANODE AND CATHODE INTERCEPTS THE PROJECTILE ELECTRONS INTENDED FOR COLLISIONS WITH THE TARGET. CRACKLING SOUND!!!!

  44. TUBE ARCING

  45. REMEDY • GAS BURNOFF • TUBE REPLACEMENT

  46. LINE IN TOPOGRAM • BAD DETECTOR CAUSES CONTINUOUS LINE ON THE TOPOGRAM

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