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

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ROI 1 (Center of the Ring Artifacts)St

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rd D

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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