Design and Construction of a Micro-focus In-line Phase-contrast Cone Beam CT (PC-CBCT) System for Soft Tissue Imaging

In recent years, the in-line phase-contrast (in-line PC) technique has been implemented using synchrotrons and micro-focus x-ray tubes for soft tissue imaging as the in-line PC's image quality enhancement. In this study, a new in-line phase-contrast cone-beam CT (PC-CBCT) system has been designed and tested in our lab to produce higher image quality enhancement. The PC-CBCT system consists of a micro-focus x-ray tube, a high-resolution detector and a rotating phantom holder. The nominal focal spot size is 9 microns, which is expected to produce partially coherent x-rays. The detector system has a phosphor screen, an optical fiber coupling unit and a CMOS chip with an effective pixel pitch of 22.5 microns. Some key system parameters, including tube voltage (or x-ray spectrum), source-to-object distance and object-to-detector distance were balanced and optimized to achieve enough spatial coherence and degree of interference to acquire edge-enhanced phase-contrast images as projection images. The phantom holder was rotated for 360 degrees with a step of 1.2 degrees, and during the rotation in-line PC images were acquired at all angular positions. The FDK algorithm was applied to compute the reconstruction using the edge-enhanced PC images. Small soft tissue samples (breast tissues and animal organs) were scanned and reconstructed. The tomographic images showed enhanced structure edges and details..