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

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

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

MAS KVP SCAN TIME SLICE T. NOISE

OBJECT SIZE NOISE

ALGORITHM vs NOISE DETAIL EDGE-ENHANCEMENT STANDARD SMOOTHING NOISE

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

NOISE WIDTH OF PIXEL SLICE THICKNESS DOSE NOISE SPATIAL R.

LINEARITY RELATIONSHIP OF CT# TO THE LINEAR ATTENUATION COEFFICIENT

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

CROSS-FIELD UNIFORMITY

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

IMAGE ARTIFACTS STREAKS RING CT# DISTORTION

SOURCES OF ARTIFACTS PATIENT IMAGING PROCESS EQUIPMENT

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

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

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

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

MOTION

INCOMPLETE PROJECTION PROFILES METAL ARTIFACTS INCOMPLETE PROJECTION PROFILES STAR SHAPED ARTIFACTS

METAL ARTIFACTS

METAL ARTIFACT

MAR

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

BEAM HARDENING

BEAM HARDENING ARTIFACT STREAKS OR BROAD DARK BANDS

REDUCTION OF BEAM HARDENING BOW TIE FILTER UTILIZATION SPECIAL CORRECTION SOFTWARE

CORRECTED

PARTIAL VOLUME ARTIFACT AVERAGE CT NUMBERS IN SLICE

CORRECTING PARTIAL VOLUME ARTIFACT THIN SLICES

NOISE – PHOTON STARVATION

OUT OF FIELD ARTIFACT

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

RING ARTIFACTS- III GENERATION

CORRECTION OF RING ARTIFACT DETECTOR RECALIBRATION BALANCING ALGORITHM UTILIZATION

ALIASING ARTIFACT NOT ENOUGH SAMPLES

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

ALIASING ARTIFACT

TUBE ARCING

SPIRAL ARTIFACTS WINDMILL MOTION STAIRCASE SHADING

WINDMILL

MOTION

MOTION

STAIRCASE