Cone-beam reconstruction using retrieved phase projections of in-line holography for breast imaging

This work is a feasibility study of a phase-contrast cone-beam CT (CBCT) system for ROI (region of interest) reconstruction in breast imaging that incorporates the in-line holography technique into a cone-beam CT system. A conventional CBCT scan is done first to find any suspicious lesion, followed by a phase-contrast CBCT scan of the ROI for detailed characterization. The phase-contrast in-line holographic images are generated using Fresnel theory through computer simulation, and the projected phase maps, as line integrals of the phase coefficient of the scanned breast, are retrieved using phase-attenuation duality theory. In this way the object's phase coefficient, as the object function, can be reconstructed using these projected phase maps through FDK algorithm. The reconstruction error is calculated to evaluate the accuracy of this approach. The noise property of this approach is investigated as well by adding Poisson noise to the holographic images. The projected phase maps are retrieved and the object function is reconstructed in the presence of noise. The results show that the object's phase coefficient can be reconstructed with very small reconstruction error, and the noise level can be greatly reduced compared to the conventional CBCT system. In conclusion, the phase-contrast CBCT breast imaging approach is very promising to provide better image quality and to lower x-ray dose level for tumor characterization.