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Electronic Systems and Signals Research Laboratory

CT Imaging in the Presence of Foreign Metal Bodies

CT Imaging in the Presence of Foreign Metal Bodies

Picture X-ray computerized tomography (CT) systems are frequently used in medical imaging because they produce reliable images of the patient anatomy quickly and at a relatively low cost. The limitations of the current image reconstruction method become apparent when metallic objects are present inside the patient's body (e.g. hip implants, surgical clips, etc.). In those cases, the resulting images are plagued with streak-like artifacts, and as such are typically useless to the physician during the treatment planning.

An example of a medical procedure where this problem arises is brachytherapy which is used for treatment of a cancer tumor by placing one or more radioactive sources near the tumor. A variety of typically metallic devices, called applicators, are used to contain these sources. Our group focuses on the use of brachytherapy in treatment of cervical cancer which involves placement of a stainless steel applicator next to the cervix. Unfortunately, it is difficult for the radiation oncologist to discern the precise location of the applicator in relation to the tumor because current CT images contain strong streaking artifacts due to the metal presence. The five-year survival rate for women who suffer from this disease is approximately 50%, which motivates seeking ways for improvement.

picture Our group aims to exploit the available information about the applicator (such as its geometry and composition) in the image reconstruction process in order to eliminate the artifacts. The problem of image formation is formulated as a statistical inverse problem. Modeling data as random enables us to account for photon-fluctuation noise, beam hardening, scatter, and other phenomena occurring in X-ray tomography. We assume data to be Poisson-distributed and seek the maximum likelihood estimate of the attenuation function. Using convex optimization methods, maximizing the log-likelihood functional is equivalent to a double minimization of I-divergence, one of the minimizations being over the attenuation function.

We have shown that our method successfully reduces image artifacts in several experiments on simulated data when compared to the standard technique of filtered backprojection (FBP). Our present research focus is on efficient and fast implementation, processing of real data collected by clinical scanners, as well as extending our method to volume (3-D) reconstruction.

Related Talks

Related Publications

Joseph A. O'Sullivan, Jasenka Benac, Jeffrey F. Williamson, "Alternating Minimization Algorithm for Dual Energy X-Ray CT," 2004. (pdf version)

Joseph A. O'Sullivan, Jasenka Benac, "Alternating Minimization Multigrid Algorithms for Transmission Tomography," 2003. (pdf version)

J. F. Williamson, B. R. Whiting, J. Benac, R. J. Murphy, G. J. Blaine, J. A. O'Sullivan, D. G. Politte, and D. L. Snyder, ``Prospects for Quantitative Computed Tomography Imaging in the Presence of Foreign Metal Bodies Using Statistical Image Reconstruction,'' Med. Phys. Vol. 29, No. 10, pp. 2404-2418, October 2002. (pdf version)

J. F. Williamson, B. R. Whiting, J. Benac, R. J. Murphy, G. J. Blaine, J. A. O'Sullivan, D. G. Politte, D. L. Snyder, ``Prospects for quantitative CT imaging in the presence of foreign metal bodies using statistical image reconstruction,'' Proceedings 2002 IEEE International Symposium on Biomedical Imaging,, pp. 649-652, 2002.

R. J. Murphy, J. A. O'Sullivan, J. Benac, D. L. Snyder, B. R. Whiting, D. G. Politte, J. F. Williamson, ``Incorporating known information into image reconstruction algorithms for transmission tomography,'' Proceedings of the SPIE Medical Imaging 2002: Image Processing, M. Sonka and J. M. Fitzpatrick, Editors, SPIE 4684, pp. 29-37, 2002. (pdf version)

J. Benac, J. A. O'Sullivan, D. L. Snyder, D. G. Politte, B. R. Whiting, J. F. Williamson, and R. J. Murphy, ``A Simulation Study of Alternating Minimization Algorithms for CT Image Formation,'' 39th Annual Allerton Conference on Communication, Control, and Computing, Monticello, IL, Oct. 2001.

D. L. Snyder, J. A. O'Sullivan, B. R. Whiting, R. J. Murphy, J. Benac, J. A. Cataldo, D. G. Politte, and J. F. Williamson, ``Deblurring subject to Nonnegativity Constraints When Known Functions are Present, with Application to Object-Constrained Computerized Tomography,'' IEEE Transactions on Medical Imaging, Vol. 20, No. 10, PP. 1009-1017, October 2001. (pdf version)

Main Project Site

J. A. O'Sullivan Home Page

Edited June 11, 2004

Washington University in St. Louis     School of Engineering     Deptartment of Electrical and Systems Engineering