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Correction of Ring Artifacts in Micro CT
Wes ArmstrongMedical Biophysics 3970Z
University of Western OntarioMarch 23, 2011
Introduction
Computed Axial Tomography• Compiles a series of 2D X –
rays into a 3D volume of data.
• Our Protocol: 1200 X – rays.
GE eXplore speCZT
Introduction
Ring Artifacts• Why do they happen?• Why are they a
problem?
Objective
To determine if ring artifacts in micro CT images up to a year old can be corrected using this bright field calibration
Approach
Correct images using a bright field acquired over 100 minutes.
Hypothesis
Null – There will be no difference in the standard deviation (SD) of the grey scale values in the images before and after the bright field correction.
Alternate – There will be a difference in the standard deviation (SD) of the grey scale values in the images before and after the bright field correction.
Methods
• Reconstruct the images using the 100 minute bright field.
• Once corrected compare the standard deviations in various regions of interest (ROI) using Microview.
• Measure standard deviation due to photon counting noise
• Use quadature equation to determine the standard deviation due to the rings.
Results
April July November December January January0
20
40
60
80
100
120
140
160
180
ROI 1 (Center of the Ring Artifacts)St
anda
rd D
evia
tion
Paired t – test: p = 3.89298 x 10-7
ResultsRegion of Interest Average
% ReductionAverage Reduction
in SDP Value*
Center of Rings 39.57 79.04 3.89298 x 10-7
Above Center of Rings
47.03 28.05 0.007266483
In Object 65.28 13.58 0.00673873
Outside Object 50.78 15.51 0.000117016
*Calculated using a paired, two – tailed t-test
Results
Before Correction After Correction
Discussion
• Accept the alternate hypothesis for ring artifact correction.
- Amount of correction decreases as distance from the center of the rings increases.
- GE Healthcare - Fine tuning
Conclusions
• Using the 100 minute bright field in reconstructions significantly reduces the ring artifacts.
Acknowledgements
Dr. David Holdsworth, PhD- Professor, Departments of Medical Biophysics and Surgery,
Shulich School of Medicine and Dentistry, UWO.- Scientist, Robarts Research Institute.- Dr. Sandy Kirkley Chair in Musculoskeletal Research.
Matt Teeter, BSc - PhD candidate