Experimental investigation of a HOPG crystal fan for x-ray fluorescence molecular imaging

Abstract

Imaging x-ray fluorescence generally generates a conflict between the best image quality or highest sensitivity and lowest possible radiation dose. Consequently many experimental studies investigating the feasibility of this molecular imaging method, deal with either monochromatic x-ray sources that are not practical in clinical environment or accept high x-ray doses in order to maintain the advantage of high sensitivity and producing high quality images. In this work we present a x-ray fluorescence imaging setup using a HOPG crystal fan construction consisting of a Bragg reflecting analyzer array together with a scatter reducing radial collimator. This method allows for the use of polychromatic x-ray tubes that are in general easily accessible in contrast to monochromatic x-ray sources such as synchrotron facilities. Moreover this energy-selecting device minimizes the amount of Compton scattered photons while simultaneously increasing the fluorescence signal yield, thus significantly reducing the signal to noise ratio. The aim is to show the feasibility of this approach by measuring the Bragg reflected K α fluorescence signal of an object containing an iodine solution using a large area detector with moderate energy resolution. Contemplating the anisotropic energy distribution of background scattered x-rays we compare the detection sensitivity, applying two different detector angular configurations. Our results show that even for large area detectors with limited energy resolution, iodine concentrations of 0.12 % can be detected. However, the potentially large scan times and therefore high radiation dose need to be decreased in further investigations.

High-Spatial-Resolution Benchtop X-ray Fluorescence Imaging through Bragg-Diffraction-Based Focusing with Bent Mosaic Graphite Crystals: A Simulation Study

“…), while all other hkl diffractions result in homogeneous Debye-Scherrer rings [40,87]. In our simulations, the first-order reflection in the (002)-lattice plane, which exhibits the highest intrinsic diffraction intensity compared to other planes, is assumed as the predominant reflection mode considering the focusing configuration described in Section 3.1.3 and central energy corresponding to the tungsten K α characteristic X-rays [39][40][41]43,44,88,89]. X-ray photons with energies central to the tungsten K α emission (E peak ≈ 59 keV) are more likely to be reflected at the Bragg angle, θ B ≈ 1.79 • , on the (002)-lattice.…”

“…This is due to the Bragg diffraction becoming increasingly diffuse from multiple reflexes as the Bragg condition is fulfilled, along with mosaic effects [34,87]. The (002)-lattice planes in these crystals inherently exhibit the strongest diffraction (highest reflection intensity) compared to the other planes, and crystallites tend to preferentially orient parallelly along the film deposition layers with a small spread, particularly under low mosaicity conditions [40,41,43,44,[87][88][89]. However, the impact of deviating effects, such as deviations from the assumed focusing conditions or imperfections in the produced crystal quality, will need evaluation through future experiments, including quality characterization tests.…”