correction of ring artifacts in micro ct wes armstrong medical biophysics 3970z university of...

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

anda

rd D

evia

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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