Scatter and beam hardening degrade image quality for X-ray computed tomography (CT). Applying beam hardening correction before scatter being fully removed may be needed in some scenarios. In this paper, we theoretically analyze the outcome of beam hardening correction with scatter uncorrected. Using the effective spectrum of CT system, beam hardening correction function and its derivatives can be explicitly derived and used, along with a Taylor expansion, to approximate the change of scatter-to-primary ratio (SPR) after beam hardening correction. Two types of SPR compensations are compared using cone- and fan-beam scans of a CatPhan phantom on a tabletop cone-beam CT system, validating our analysis to be accurate in practical applications.
This paper presents a feasibility study of using emission tomography (ET) systems for synchrotron X-ray fluorescence
computer tomography (XFCT). The proposed detection system combines high-resolution semiconductor detectors with
multiple-pinhole apertures. The key advantage of using an ET-based detection system is that 3D distributions of trace
elements can be built up with much reduced scanning motion and potentially without need for tomographic
reconstruction. In comparison to the conventional line-by-line scanning scheme, the ET-based imaging system allows
a great reduction in imaging time, which has been one of the major hurdles for current XFCT studies. In order to
compare different imaging schemes for XFCT studies, we developed an analytical performance index that is based on
the fundamental tradeoffs between image noise and spatial resolution achievable with given detection configurations.
To further demonstrate the feasibility of using SPECT apertures for XFCT, a prototype CCD-based multiple-pinhole
imaging system was set up at the Advanced Photon Source (APS) for imaging phantoms that contain solutions of
several trace metals. Simultaneously acquired 3D distributions of these elements are presented.