First demonstration of Compton camera used for X-ray fluorescence imaging.

X-ray fluorescence computed tomography (XFCT) is a promising approach used for obtaining the distribution of high-Z elements in the target object. The characteristic energy of X-ray fluorescence (XRF) photons makes XFCT have higher sensitivity and contrast ratio. Conventional XFCT systems usually require mechanical collimators, which leads to a huge loss of incident photons and reduce photon collection efficiency. The Compton camera is an imaging modality that uses electronic collimation to obtain the incident direction of the photons, which brings advantages in the detection area and X-ray photon collection efficiency. Compton cameras can also achieve three-dimensional (3D) imaging with one or several views of scanning without rotation. Therefore, it is a good idea to realize XRF imaging by using Compton cameras, which may provide more potential applications and imaging possibilities, such as handheld XRF imaging or image-guided interventional operation. In this work, we demonstrate the first Compton camera platform which is used for XRF imaging. The proposed X-ray fluorescence Compton camera (XFCC) mainly consists of a conventional X-ray tube (150kVp) and a Timepix3 photon-counting detector (PCD). A PMMA phantom with insertions containing different concentrations of 4%, 6%, 8%, and 10% (weight/volume) Gd solution is scanned by a fan-beam X-ray. Besides, a Compton camera-based X-ray fluorescence imaging reconstruction method (CCFIRM) is developed to solve specific problems in XFCC reconstruction. The reconstruction images and the quantitative analyses of the contrast-to-noise ratio (CNR) are presented. The results indicate that the detectability limit of the proposed XFCC platform is 3.5139 wt.% (CNR=4).