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

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

MASKVPSCAN TIMESLICE T.

NOISE

OBJECT SIZE

NOISE

ALGORITHM vs NOISE

DETAIL

NOISE

STANDARD

SMOOTHING

EDGE-ENHANCEMENT

NOISE IN CT IS MAINLYMAINLY 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.

NOISE SPATIAL R.

NOISE

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

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 & INVOLUNTARYCORRECTION: IMMOBILIZATION PROPER EXPLANATION OF

PROCEDURE SHORT SCAN TIME MOTION REDUCTION

SOFTWARE (SHIMADZU –MAC)

I

MOTION

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 ARTIFACTSTREAKS 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