Jae hak Lee

Information theoretic discrepancy based iterative reconstruction for transmission tomography

The monochromatic approximation, which postulates that a source emits monochromatic radiation, has been widely used in the transmission tomography. However, due to the ignorance of energy dependency, image degradations such as beam hardening artifact are often occurred. In this paper, we present novel reconstruction algorithms to reflect the exact polychromatic model. Departing from the conventional algebraic and statistical reconstructions, the generalized information theoretic discrepancy (GID) is employed as the new data fidelity metric. By using the particular features of the GID, the cost function is derived in terms of imaginary variables, which incorporates energy dependency and leads to a tractable optimization problem even without the monochromatic approximation. In preliminary experiments with a simulated dual energy CT and a real experimental tomosyn-thesis, the proposed information theoretic discrepancy based iterative reconstruction (IDIR) algorithm showed superior performances over conventional reconstruction schemes.

Comparative studies on exposure conditions and reconstruction algorithms in limited angle tomography

Digital breast tomosynthesis (DBT) has been investigated as a promising alternative to conventional X-ray mammography for breast cancer screening. By reconstructing 3D volumetric images from multiple 2D projections measured over a limited angular range, it can offer depth-directional information and improve both sensitivity and specificity of cancer detection in dense breasts. The diagnostic performance of DBT can be affected by a number of imaging parameters. The angular range of scan orbit is one of the most crucial factors, since it determines the depth-directional resolution. Recently, we proposed the wide angle tomosynthesis based on voltage modulations of X-ray source. By using X-rays with large penetration power on exterior positions, it can acquire high-SNR projections over a wide angular range. In this paper, we present comparative studies on exposure conditions in DBT, including narrow and wide angle scan using an invariant tube voltage of X-ray source, and wide angle scan with the voltage modulation technique. In addition, we compared the conventional reconstruction methods with recently proposed IDIR algorithms. In preliminary studies, the wide-angle scheme with proposed IDIR algorithm showed superior performances in detecting abnormal lesions over conventional approaches.