Mustafa Cem Altunbas PhD, Presenter: Nothing to Disclose

Chris Chorng-Gang Shaw PhD, Abstract Co-Author: Nothing to Disclose

Lingyun Chen, Abstract Co-Author: Nothing to Disclose

We are developing and investigating cone beam breast CT(CBCT) imaging techniques for diagnosis and management of breast cancers. In order to obtain uniform CT image data for image segmentation, we have investigated a technique to correct for the cupping effect from x-ray scattering and beam hardening in the post-reconstruction phase.

The artifacts due to x-ray scattering and beam hardening appear as circularly symmetric cupping artifact with no detectable shading streaks in reconstructed axial images. The magnitude of cupping nonuniformity was estimated from the CT numbers of the adipose tissue. To achieve this, voxels that are equidistant from the central axis were grouped and the minimum value in each group was picked to construct a radial profile of CT numbers representing the adipose tissue. Each profile was fitted with a parabolic curve. To reduce the slice-to-slice variation of curves, a smoothing operation was performed along the central axis. The smoothed curves for each axial slice were then used to calculate the CT number correction factors as a function of the radial distance from the central axis. The same correction map was used for the glandular tissue due to the relatively small density difference.

Our preliminary results showed that the cupping artifact in reconstructed images could be reduced to an insignificant level with the above described technique. Before cupping correction, the difference in HU values for the adipose tissue could be as much as 100 units between the central and peripheral region of the axial image.

A method for correcting scattering and beam hardening artifacts was implemented in the post image reconstruction phase to obtain more uniform HU values for the adipose or glandular tissue in the CBCT breast images. This method allowed us to improve the visualization of axial slices and segment the image volume using threshold based region growing techniques for 3D visualization or quantitative analysis. This work was supported in part by a research grant EB000117 from the NIBIB and a research grant CA104759 from the NCI .

Altunbas, M, Shaw, C, Chen, L, A Post-reconstruction Technique to Correct for the Cupping Effects in Cone Beam Breast CT Imaging.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4419690.html