An optical tomography method that accounts for a tilted chest-wall in breast imaging

The chest-wall underneath the breast tissue distorts the diffused near infra-red light measured at distant source-detector pairs. Common image reconstruction method consider the media as homogeneous and applying the semi-infinite model. In this paper, we have compared the performance of our two-layer model with semi-infinite model by simulation and a clinical case. The results show that when the chest wall has significant effect on the measurement data, a benign lesion with low absorption can be misled as a malignant case with high absorption by using semi-infinite model. We have also shown the influence of mismatch geometry of breast tissue and chest-wall at lesion and reference sides on the reconstructed image and a correction method has been introduced to reduce these effects. With the assistance of two orthogonal co-registered ultrasounds, the geometry of the breast tissue and chest wall interface can be determined and modeled as a two-layer medium with 3D finite element mesh. Since numerical algorithms based on finite element methods (FEM) are suitable for complex geometry and boundary conditions, this method is adapted to model the chestwall. Four parameters of bulk absorption and reduced scattering coefficients of the first and second layers are estimated and used to characterize the optical properties of the medium. We used a finite element model based on modified born approximation for image reconstruction. A mismatch correction algorithm has been applied to compensate the mismatch geometry of the breast tissue and chest-wall interface at the reference and the lesion side.