Volume-selective fluorescence X-ray Counting - Towards 3-D mapping of naturally occurring trace metals without image reconstruction

Synchrotron-based X-ray fluorescence computed tomography (XFCT) is a relatively new medical imaging platform that can be used for effectively mapping indicative pathologies of metals such as copper or magnesium in Parkinson´s disease and other neurodegenerative disorders [1]. At the present, the sensitivity from these potential in vivo systems is limited due to (a) the intrinsically low interaction probability of the incident X-rays, (b) the limited fluorescence signal from the sample as limited by radiation dose considerations, (c) the relatively inefficient data collection methods currently in use for most of XFCT studies, and (d) the need for high flux such as those from synchrotron X-ray sources. The authors of this work demonstrate a novel method of X-ray fluorescence-based elemental mapping, called volume selective counting, that relies on apertures designed to target a single specifically dimensioned linear segment at a time and X-ray detectors constructed in certain imaging geometries capable of deriving the elemental concentration of these trace metals inside a selected volume without the need for full 3-D image reconstruction. Cross-sectional images and spectra of both a zebra fish and triple glass phantom consisting of copper, bromide, and iron exemplify the viability and practicality of the volume-selective counting method.