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ARTIFACTS IN COMPUTED TOMOGRAPHY. ARTIFACT Any discrepancy between the CT numbers represented in the image and the expected CT number based on the linear.

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Presentation on theme: "ARTIFACTS IN COMPUTED TOMOGRAPHY. ARTIFACT Any discrepancy between the CT numbers represented in the image and the expected CT number based on the linear."— Presentation transcript:

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

9

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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. ITS CAUSED BY PRESENCE OF METALLIC OBJECTS INSIDE OR OUTSIDE THE PATIENT. METALLIC OBJECT ABSORBS THE PHOTONS CAUSING AN INCOMPLETE PROFILE

19 METAL ARTIFACT

20

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

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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

30 REMEDY THIN SLICE SELECTION THIN SLICE INREMMENTATION

31 AILIASING FINE LINE ON AN IMAGE

32

33 REMEDY INCREASE SCAN TIME USE COMPLETE ARC SCAN

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

35 NOISE

36

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38 REMEDY kVp INCREASE mAs INCREASE SLICE THICKNESS INCREASE

39 AIR-CONTRAST INTERFACE STREAKING

40

41 REMEDY CHANGE THE PATIENT POSITION

42 RING MALFUNCTION OF A DETECTOR IN A THIRD GENERATION SCANNER

43 RING

44

45 REMEDY DETECTOR CALIBRATION DETECTOR REPLACEMENT

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

47 TUBE ARCING

48 REMEDY GAS BURNOFF TUBE REPLACEMENT

49 LINE IN TOPOGRAM BAD DETECTOR CAUSES CONTINUOUS LINE ON THE TOPOGRAM

50

51 REMEDY DETECTOR REPLACEMENT

52 STAIRCASE IMPROPER SELECTION OF SLICE THICKNESS AND SLICE INCREMENTATION WHEN GENERATION MPR AND 3-D IMAGES

53 STAIRCASE

54

55 REMEDY THIN SLICE USE 50% OVERLAP ON RECON SLICE INCREMENTATION


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