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IMAGE QUALITY

IMAGE QUALITY . NOISE LINEARITY CROSS-FIELD UNIFORMITY IMAGE ARTIFACTS. NOISE IN CT. FLUCTUATION OF CT# BETWEEN POINTS IN THE IMAGE FOR A SCAN OF UNIFORM MATERIAL SUCH WATER. NOISE IN CT. NOISE LEVEL. PERCENTAGE OF CONTRAST OR IN CT NUMBERS. NOISE LEVEL %= STANDARD DEVIATION /CT # RANGE.

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IMAGE QUALITY

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  1. IMAGE QUALITY • NOISE • LINEARITY • CROSS-FIELD UNIFORMITY • IMAGE ARTIFACTS

  2. NOISE IN CT • FLUCTUATION OF CT# BETWEEN POINTS IN THE IMAGE FOR A SCAN OF UNIFORM MATERIAL SUCH WATER.

  3. NOISE IN CT

  4. NOISE LEVEL • PERCENTAGE OF CONTRAST OR IN CT NUMBERS NOISE LEVEL %= STANDARD DEVIATION /CT # RANGE

  5. NOISE CAN BE MEASURED BY SCANNING A WATER PHANTOMAND COMPUTING THE MEAN AND STANDARD DEVIATION FOR FOR A REGION OF INTEREST. (ROI)

  6. THE NOISE LEVELS FOR CT SCANNERS VARY AND DEPEND ON: • MAS • SCAN TIME • KVP • SLICE THICKNESS • OBJECT SIZE • ALGORITHM

  7. MASKVPSCAN TIMESLICE T.NOISE

  8. OBJECT SIZE NOISE

  9. ALGORITHM vs NOISE DETAIL EDGE-ENHANCEMENT STANDARD SMOOTHING NOISE

  10. NOISE IN CT IS MAINLY RELATED TO • PHOTON FLUX ( # OF DETECTED PHOTONS) • MATRIX SIZE (PIXEL SIZE) • SLICE THICKNESS • ALGORITHM • ELECTRONIC NOISE ( DETECTOR ELECTRONICS) • SCATTER RADIATION

  11. WIDTH OF PIXEL SLICE THICKNESS DOSE NOISE SPATIAL R. NOISE SPATIAL R. NOISE NOISE

  12. LINEARITY • RELATIONSHIP OF CT# TO THE LINEAR ATTENUATION COEFFICIENT

  13. CROSS-FIELD UNIFORMITY • THE UNIFORMITY OF CT # THROUGHOUT THE ENTIRE SCAN FIELD OF VIEW IS ONE INDICATION THAT CT SCANNER IS PERFORMANCE IS ACCEPTABLE. • IT REFERS TO THE VALUES OF THE PIXELS IN THE RECONSTRUCTED IMAGE THEY SHOULD BE CONSTANT AT ANY POINT IN THE IMAGE OF PHANTOM

  14. CROSS-FIELD UNIFORMITY CROSS-FIELD UNIFORMITY

  15. IMAGE ARTIFACTS • A DISTORTION OR ERROR IN AN IMAGE THAT IS UNRELATED TO THE SUBJECT BEING STUDIED

  16. IMAGE ARTIFACTS STREAKS RING CT# DISTORTION

  17. SOURCES OF ARTIFACTS • PATIENT • IMAGING PROCESS • EQUIPMENT

  18. STREAKS IMPROPER SAMPLING OF DATA PARTIAL VOLUME AVERAGING PATIENT MOTION METAL & BEAM HARDENING NOISE SPIRAL SCANNING MECHANICAL FAILURE TYPES AND CAUSES OF ARTIFACTS

  19. SHADING PART. VOLUME AVG. BEAM HARDENING SPIRAL SCANNING SCATTER OFF-FOCUS RADIATION INCOMPLETE PROJECTION TYPES AND CAUSES OF ARTIFACTS

  20. RINGS AND BANDS BAD DETECTOR IN III GENERATION CT TYPES AND CAUSES OF ARTIFACTS

  21. MOTION ARTIFACT- VOLUNTARY & INVOLUNTARY CORRECTION: • IMMOBILIZATION • PROPER EXPLANATION OF PROCEDURE • SHORT SCAN TIME • MOTION REDUCTION SOFTWARE (SHIMADZU –MAC) I

  22. MOTION

  23. METAL ARTIFACTS INCOMPLETE PROJECTION PROFILES STAR SHAPED ARTIFACTS

  24. METAL ARTIFACTS

  25. METAL ARTIFACT

  26. MAR

  27. BEAM HARDENING ARTIFACT-CUPPING ARTIFACT • INCREASE IN THE MEAN ENERGY OF THE X-RAY BEAM AS IT PASSES THROUGH THE PATIENT • IT CAN OCCUR WHEN RADIATION BEAMS HAVE DIFFERENT PATH LENGTHS

  28. BEAM HARDENING

  29. BEAM HARDENING ARTIFACTSTREAKS OR BROAD DARK BANDS

  30. REDUCTION OF BEAM HARDENING • BOW TIE FILTER UTILIZATION • SPECIAL CORRECTION SOFTWARE

  31. CORRECTED

  32. PARTIAL VOLUME ARTIFACT AVERAGE CT NUMBERS IN SLICE

  33. CORRECTING PARTIAL VOLUME ARTIFACT • THIN SLICES

  34. NOISE – PHOTON STARVATION

  35. OUT OF FIELD ARTIFACT

  36. EQUIPMENT INDUCED ARTIFACTSSTREAK ARTIFACTS • MECHANICAL FAILURE • POOR GANTRY RIGIDITY • MECHANICAL ASSIGNMENT • TUBE ROTOR WOBBLE • POOR SAMPLING OF THE DETECTOR • BAD DETECTOR-RING ARTIFACTS ( III GEN.) • TUBE ARCING

  37. RING ARTIFACTS- III GENERATION

  38. CORRECTION OF RING ARTIFACT • DETECTOR RECALIBRATION • BALANCING ALGORITHM UTILIZATION

  39. ALIASING ARTIFACT • NOT ENOUGH SAMPLES

  40. CORRECTION OF ALIASING ARTIFACT • INCREASE NUMBER OF VIEWS OR RAY SAMPLES PER VIEW. • CONVOLUTION FILTER (SOFTWARE METHOD)

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