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Correction of Ring Artifacts in Micro CT Wes Armstrong Medical Biophysics 3970Z University of Western Ontario March 23, 2011.

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Presentation on theme: "Correction of Ring Artifacts in Micro CT Wes Armstrong Medical Biophysics 3970Z University of Western Ontario March 23, 2011."— Presentation transcript:

1 Correction of Ring Artifacts in Micro CT Wes Armstrong Medical Biophysics 3970Z University of Western Ontario March 23, 2011

2 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

3 Introduction Ring Artifacts Why do they happen? Why are they a problem?

4 Objective To determine if ring artifacts in micro CT images up to a year old can be corrected using this bright field calibration

5 Approach Correct images using a bright field acquired over 100 minutes.

6 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.

7 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.

8 Results Paired t – test: p = 3.89298 x 10 -7

9 Results Region of InterestAverage % Reduction Average Reduction in SD P Value* Center of Rings39.5779.04 3.89298 x 10 -7 Above Center of Rings 47.0328.050.007266483 In Object65.2813.580.00673873 Outside Object50.7815.510.000117016 *Calculated using a paired, two – tailed t-test

10 Results Before CorrectionAfter Correction

11 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

12 Conclusions Using the 100 minute bright field in reconstructions significantly reduces the ring artifacts.

13 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


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