X-ray Fluorescence Imaging System Research Articles

Dual imaging modality of fluorescence and transmission X-rays for gold nanoparticle-injected living mice.

X-ray fluorescence (XRF) imaging for metal nanoparticles (MNPs) is a promising molecular imaging modality that can determine dynamic biodistributions of MNPs. However, it has the limitation that it only provides functional information. In this study, we aim to show the feasibility of acquiring functional and anatomic information on the same platform by demonstrating a dual imaging modality of pinhole XRF and computed tomography (CT) for gold nanoparticle (GNP)-injected living mice. By installing a transmission CT detector in an existing pinhole XRF imaging system using a two-dimensional (2D) cadmium zinc telluride (CZT) gamma camera, XRF and CT images were acquired on the same platform. Due to the optimal X-ray spectra for XRF and CT image acquisition being different, XRF and CT imaging were performed by 140 and 50kV X-rays, respectively. An amount of 40mg GNPs (1.9nm in diameter) suspended in 0.20ml of phosphate-buffered saline were injected into the three BALB/c mice via a tail vein. Then, the kidney and tumor slices of mice were scanned at specific time points within 60min to acquire time-lapse in vivo biodistributions of GNPs. XRF images were directly acquired without image reconstruction using a pinhole collimator and a 2D CZT gamma camera. Subsequently, CT images were acquired by performing CT scans. In order to confirm the validity of the functional information provided by the XRF image, the CT image was fused with the XRF image. After the XRF and CT scan, the mice were euthanized, and major organs (kidneys, tumor, liver, and spleen) were extracted. The ex vivo GNP concentrations of the extracted organs were measured by inductively coupled plasma mass spectrometry (ICP-MS) and L-shell XRF detection system using a silicon drift detector, then compared with the in vivo GNP concentrations measured by the pinhole XRF imaging system. Time-lapse XRF images were directly acquired without rotation and translation of imaging objects within an acquisition time of 2min per slice. Due to the short image acquisition time, the time-lapse in vivo biodistribution of GNPs was acquired in the organs of the mice. CT images were fused with the XRF images and successfully confirmed the validity of the XRF images. The difference in ex vivo GNP concentrations measured by the L-shell XRF detection system and ICP-MS was 0.0005-0.02% by the weight of gold (wt%). Notably, the in vivo and ex vivo GNP concentrations in the kidneys of three mice were comparable with a difference of 0.01-0.08wt%. A dual imaging modality of pinhole XRF and CT imaging system and L-shell XRF detection system were successfully developed. The developed systems are a promising modality for in vivo imaging and ex vivo quantification for preclinical studies using MNPs. In addition, we discussed further improvements for the routine preclinical applications of the systems.

Monte Carlo modeling of gold nanoparticles detection limits of benchtop three‐dimensional L‐ and K‐shell X‐ray fluorescence mapping systems

AbstractThis study aims to investigate the detection limits of gold nanoparticle (GNP) concentrations by Monte Carlo (MC) modeling of benchtop polychromatic K‐ and L‐shell X‐ray fluorescence mapping system. In Monte Carlo N‐Particle (MCNP version 6.1) simulations, a 0.25‐cm‐diameter cylinder containing GNPs of various concentrations (i.e., 0.005%–1.0% gold by weight, wt%) was assumed to be located at the center of a cylindrical water phantom of various diameters (1.0–10 cm). Two different sets of incident pencil beam X‐rays and detectors were modeled to stimulate X‐ray fluorescence (XRF) of GNPs: (1) 62 kVp and silicon drift detector for L‐XRF, (2) 105 kVp and cadmium telluride detector for K‐XRF. The detection limits were calculated for given radiation doses to the center of phantom (375–1500 mGy). When the diameter of the phantom was 1 cm, the detection limits for L‐XRF and K‐XRF were an order of 0.001 wt% and of 0.01 wt%, respectively. The detectability of K‐XRF turned out to be superior to that of L‐XRF for the phantoms greater than or equal to 3 cm in diameter. The MC results will provide a guide for developing an optimal benchtop XRF imaging system for in vivo preclinical imaging, depending on the sizes of GNP‐loaded objects, GNP concentrations, and radiation doses.

Quantitative x-ray fluorescence imaging system for non-destructive 3D tumor histology.

An in-house dual-modality x-ray fluorescence tomography (XFT) and x-ray computed tomography (XCT) system was developed to quantify iodine contrast distribution through the whole tumor volume ex vivo. The quantitative XFT was calibrated with water phantoms containing iodine solutions of various concentrations (0.0175-1.4 wt.%). The vasculature distribution was reflected by the iodine perfusion, which was validated with histology. This technique may open a new, to the best of our knowledge, route to the non-destructive three-dimensional-imaging-based histological analysis of tumor samples.

Sensitivity enhancement of an experimental benchtop X-ray fluorescence imaging system by deploying a single crystal cadmium telluride detector system optimized for high flux X-ray operations

In this work, an energy-resolving thermoelectrically cooled single crystal cadmium telluride (CdTe) detector system upgraded with the latest firmware was optimized for high X-ray flux operations using high bias voltage and fast peaking time. This detector system was deployed into an experimental benchtop X-ray fluorescence (XRF) imaging/computed tomography (XFCT) system developed for quantitative imaging of metal nanoprobes such as gold nanoparticles (GNPs). Using the firmware-upgraded and existing/old CdTe detector systems, the Compton/XRF spectra from small (8 mm diameter) GNP-containing phantoms were acquired. The phantoms were irradiated with 1.8 mm Sn-filtered 125 kVp cone beam X-rays at 24 mA. The firmware-upgraded detector system produced relatively lower dead time under high X-ray flux, compared with the old detector system, and performed well with the spectral resolution of ∼0.7 keV (in full width at half maximum) at 69 keV photon energy. Given the same 2 mm aperture detector collimator and irradiation time of 10 s, this detector system managed to score nearly 50% more gold XRF signals than the existing one at all GNP concentrations tested. This improvement resulted in the GNP detection limit of 0.02 wt. % which was lower than that (0.03 wt. %) achievable with the existing detector system. When combined with the detector collimator containing a larger (3 mm) aperture, the firmware-upgraded detector system produced drastically more gold XRF signal at a given GNP concentration (e.g., 9 times more for 1 wt. % GNP solution and irradiation time of 10 s), leading to further reduction in the GNP detection limit (i.e., 0.01 wt. %). The present investigation showed that the firmware upgraded CdTe detector system optimized for high X-ray flux operations allowed for better photon counting efficiency, thus leading to sensitivity enhancement of an experimental benchtop XRF/XFCT imaging system.

Characterization of a large-area full-field X-ray fluorescence imaging system based on a commercial full-frame CMOS camera

A new large-area and low-cost full-field X-ray fluorescence imaging system was developed for simultaneous mapping of several chemical elements. It consists of a commercially available full-frame visible-light CMOS digital camera coupled to a tungsten pinhole-collimator. The X-ray fluorescence is produced by irradiating the sample with an external X-ray tube. The system magnification can be continuously adjusted from 0.55 to 1.43 by changing the position of the pinhole in the collimator. To allow X-ray sensitivity, the glass window of the CMOS sensor was removed and the front glass cover of the camera was replaced by an X-ray window. The x-ray spectra and 2D X-ray fluorescence images of different elements are obtained by processing a series of images acquired in a spectroscopy mode using the CMOS camera. The camera is able to resolve fluorescence lines up to 22 keV, with an energy resolution of 213 eV at 6.4 keV. The experimental spatial resolution is 105 μm when using a 90 μm pinhole at 1.43× magnification. The capabilities of the system in performing the 2D resolved X-ray fluorescence imaging were investigated by testing samples of different materials and geometries. The obtained X-ray fluorescence spectra and images show that the system is able to accurately identify the presence of several different elements and visualize their spatial distributions.

Prostate Cancer Targeted X-Ray Fluorescence Imaging via Gold Nanoparticles Functionalized With Prostate-Specific Membrane Antigen (PSMA).

The gold nanoparticle (GNP) as a promising theranostic probe has been increasingly studied. The tumor-targeting efficiency of GNPs is crucial to increase the therapeutic ratio. In this study, we developed PSMA-targeted GNPs to enhance GNP uptake in prostate cancer and developed an x-ray fluorescence imaging system to noninvasively monitor and assess GNP delivery. For targeted therapy of prostate cancer, anti-prostate-specific membrane antigen (PSMA) antibodies were conjugated onto PEGylated GNPs through 1-ethyl-3-(-3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) (EDC/NHS) chemistry. In vivo imaging was implemented using an in-house-developed dual-modality computed tomography (CT) and x-ray fluorescence CT (XFCT) system on mice bearing subcutaneous LNCaP prostate tumors. After intravenous administration of GNPs (15 mg/mL, 200 μL), the x-ray fluorescence signals from the tumor were collected at various time points (5 minutes to approximately 30 hours) for GNP pharmacokinetics analysis. At 24 hours after administration, x-ray fluorescence projection (XRFproj) and XFCT imaging were conducted to evaluate the prostate tumor uptake of active- and passive-targeting GNPs. Inductively coupled plasma mass spectrometry analysis was adopted as a benchmark to verify the quantification accuracy of XRFproj/XFCT imaging. Fluorescence microscopic imaging confirmed the enhanced (approximately 4 times) targeting efficiency of PSMA-targeted GNPs in vitro. The pharmacokinetics analysis showed enhanced tumor uptake/retention of PSMA-targeted GNPs and revealed that the peak tumor accumulation appeared at approximately 24 hours after intravenous administration. Both XRFproj and XFCT imaging presented their accuracy in quantifying GNPs within tumors noninvasively. Moreover, XFCT imaging verified its unique capabilities to simultaneously determine the heterogeneous spatial distribution and the concentration of GNPs within tumors in vivo. In conjunction with PSMA-targeted GNPs, XRFproj/XFCT would be a highly sensitive tool for targeted imaging of prostate cancer, benefiting the elucidation of mechanisms of GNP-assisted prostate-cancer therapy.

X-Ray Fluorescence Imaging Based on CdTe Detector Array for Analysis of Various Materials

An X-ray fluorescence (XRF) imaging system was developed to analyze various materials based on characteristic X-rays emitted from objects exposed to X-ray flux. The XRF system can be used in various industrial fields, such as nuclear fuel analysis, to guarantee combustion stability in the nuclear reactor, glazed material analysis to preserve and restore ceramic cultural assets, impurity measurements in electronic circuits, and so on. In this study, we built an XRF imaging system and performed several material analyses using a lookup table, which contained energy and channel information of the characteristic X-ray peaks of each element. Ceramic specimens coated in various glazes were analyzed and imaged for oriental pottery research. Pigments of various colors were also analyzed and imaged for picture assessment, as were electronic circuits and gold plates. Ceramic, pigment, and metal components in the samples were discriminated by comparing characteristic X-ray peak data on the lookup table. Two-dimensional material images, which showed the material distribution of each sample, were successfully obtained.

Compton Background Elimination for in Vivo X-Ray Fluorescence Imaging of Gold Nanoparticles Using Convolutional Neural Network

This article reports the first application of a convolutional neural network (CNN) to in vivo X-ray fluorescence (XRF) images of gold nanoparticles (GNPs) obtained by a benchtop X-ray system to eliminate Compton-scattered photons. The XRF imaging system comprises a 2-D cadmium zinc telluride (CZT) gamma camera, a pinhole collimator, and fan-beam polychromatic X-rays. An architecture of the 2-D CNN model for Compton background elimination was optimally designed and trained with data sets obtained by the measurements of water only and GNP-embedded imaging phantoms. The XRF images generated by the trained 2-D CNN were compared with those generated by the direct subtraction method. The developed 2-D CNN was also applied to generate in vivo XRF images of gold in living mice exposed to GNPs. The in vivo XRF images generated by the two methods were then compared in terms of the difference in GNP concentrations. The results demonstrate that the 2-D CNN model was successfully applied to in vivo XRF images for detecting the concentration and location of GNPs in living mice. This also implies that in vivo XRF images can be acquired using the 2-D CNN without preinjection scanning; thus, the image acquisition time and imaging dose can be reduced by half. Furthermore, in vivo XRF images of GNPs can be acquired at any time after the injection, as the 2-D CNN eliminates the need to restrict a living object during the interscans.

Modelling of vignetting effects in full-field X-ray fluorescence imaging system based on pinhole optics

The full field X-ray fluorescence (FF-XRF) imaging is a technique capable of analysing the spatial distribution of elements in a sample. An alternative technique is the scanning macro-XRF method. Both techniques are powerful tools for non-destructive analysis of artworks mainly historical paintings. Technically, FF-XRF imaging is usually realised by coupling of a pinhole camera and a position sensitive and energy dispersive X-ray detector. The main advantages of the pinhole camera are its simplicity and infinite depth of field, however it introduces vignetting. For a visible light pinhole camera one distinguishes natural vignetting following the cos4 law and mechanical vignetting due to finite thickness of the camera. For an X-ray pinhole camera one has to take into account an additional component of vignetting due to absorption of X-rays in the air or other gas unless the setup is kept in vacuum. The goal of this study is to work out an analytical model of vignetting effects for a FF-XRF apparatus using an X-ray pinhole camera. Complete quantitative characterisation of the vignetting effects is a key step towards proper correction of the vignetting artefacts in recorded images. The elaborated analytical model has been applied to the images acquired with the FF-XRF apparatus being developed and an example of vignetting correction is presented.

High-sensitivity imaging and quantification of intratumoral distributions of gold nanoparticles using a benchtop x-ray fluorescence imaging system.

A high-sensitivity benchtop x-ray fluorescence (XRF) imaging system, based on a high-power x-ray source and silicon drift detector, has been developed. This system allows gold L-shell XRF-based quantitative imaging of gold nanoparticles (GNPs) at concentrations as low as 0.007 mg/cm3 (7ppm) in biological tissues/water. Its capability for biomedical applications was demonstrated by imaging the GNP distribution within a small (∼12×11×2 mm3) ex vivo sample (extracted from a murine tumor after intravenous GNP administration). The results suggest direct translatability for routine preclinical ex vivo imaging tasks involving GNPs, as well as the possibility for in vivo imaging of small/superficial animal tumors.

Dynamic In Vivo X-ray Fluorescence Imaging of Gold in Living Mice Exposed to Gold Nanoparticles

Dynamic in vivo biodistribution of gold nanoparticles (GNPs) in living mice was first successfully acquired by a pinhole X-ray fluorescence (XRF) imaging system using polychromatic X-rays. The system consisted of fan-beam X-rays to stimulate GNPs and a 2D cadmium zinc telluride (CZT) gamma camera to collect K-shell XRF photons emitted from the GNPs. 2D XRF images of kidney slices of three Balb/C mice were obtained within 2 minutes of irradiation per slice. 40 mg of GNPs suspended in a 0.2 mL phosphate-buffered saline was injected into the mice via a tail vein. The mice were scanned over a 60 min period after the injection of GNPs in order to acquire a dynamic biodistribution of GNPs. The concentrations of GNPs measured by the CZT gamma camera were then validated by inductively coupled plasma atomic emission spectroscopy and ex vivo L-shell XRF measurements using a silicon drift detector. The GNP concentrations in the right-side kidneys were 1.58% by weight (wt%) at T =0 min and 0.77 wt% at T=60 min after the injection. This investigation showed a dramatically reduced scan time and imaging dose. Hence, we conclude that dynamic in vivo XRF imaging of GNPs is technically feasible in a benchtop system. The developed pinhole XRF imaging system can be a potential molecular imaging modality for metal nanoparticles to emerge as a radiosensitizer and a drug-delivery agent.

XRF element localization with a triple GEM detector using resistive charge division

In this work we show the operation and results of an X-ray fluorescence imaging system using a cascade of three gas electron multipliers (GEM) and a pinhole assembly. The detector operates in Ar/CO$_2$ (90/10) at atmospheric pressure, with resistive chains applied to the strip readout, which allow to use only five electronic channels: two for each dimension and a fifth for energy and trigger. The corrections applied to the energy spectra to compensate for small changes in the signal amplitude and also differences in gain throughout the sensitive area are described and the clear improvement of the energy resolution is shown. To take advantage of the simultaneous sensitivity to the energy and to the position of interaction, a color scale matching the energy spectrum to the RGB range was applied, resulting in images where the color has a direct correspondence to the energy in each pixel and the intensity is reflected by the brightness of the image. The results obtained with four different color pigments are shown.

Pinhole X-ray fluorescence imaging of gadolinium and gold nanoparticles using polychromatic X-rays: a Monte Carlo study.

This work aims to develop a Monte Carlo (MC) model for pinhole K-shell X-ray fluorescence (XRF) imaging of metal nanoparticles using polychromatic X-rays. The MC model consisted of two-dimensional (2D) position-sensitive detectors and fan-beam X-rays used to stimulate the emission of XRF photons from gadolinium (Gd) or gold (Au) nanoparticles. Four cylindrical columns containing different concentrations of nanoparticles ranging from 0.01% to 0.09% by weight (wt%) were placed in a 5 cm diameter cylindrical water phantom. The images of the columns had detectable contrast-to-noise ratios (CNRs) of 5.7 and 4.3 for 0.01 wt% Gd and for 0.03 wt% Au, respectively. Higher concentrations of nanoparticles yielded higher CNR. For 1×1011 incident particles, the radiation dose to the phantom was 19.9 mGy for 110 kVp X-rays (Gd imaging) and 26.1 mGy for 140 kVp X-rays (Au imaging). The MC model of a pinhole XRF can acquire direct 2D slice images of the object without image reconstruction. The MC model demonstrated that the pinhole XRF imaging system could be a potential bioimaging modality for nanomedicine.

SU‐G‐IeP3‐07: High‐Resolution, High‐Sensitivity Imaging and Quantification of Intratumoral Distributions of Gold Nanoparticles Using a Benchtop L‐Shell XRF Imaging System

Purpose:To demonstrate the ability to perform high‐resolution imaging and quantification of sparse distributions of gold nanoparticles (GNPs) within ex vivo tumor samples using a highly‐sensitive benchtop L‐shell x‐ray fluorescence (XRF) imaging system.Methods:An optimized L‐shell XRF imaging system was assembled using a tungsten‐target x‐ray source (operated at 62 kVp and 45 mA). The x‐rays were filtered (copper: 0.08 mm & aluminum: 0.04 mm) and collimated (lead: 5 cm thickness, 3 cm aperture diameter) into a cone‐beam in order to irradiate small samples or objects. A collimated (stainless steel: 4 cm thickness, 2 mm aperture diameter) silicon drift detector, capable of 2D translation, was placed at 90° with respect to the beam to acquire XRF/scatter spectra from regions of interest. Spectral processing involved extracting XRF signal from background, followed by attenuation correction using a Compton scatter‐based normalization algorithm. Calibration phantoms with water/GNPs (0 and 0.00001–10 mg/cm3) were used to determine the detection limit of the system at a 10‐second acquisition time. The system was then used to map the distribution of GNPs within a 12×11×2 mm3 slice excised from the center of a GNP‐loaded ex vivo murine tumor sample; a total of 110 voxels (2.65×10−3 cm3) were imaged with 1.3‐mm spatial resolution.Results:The detection limit of the current cone‐beam benchtop L‐shell XRF system was 0.003 mg/cm3 (3 ppm). Intratumoral GNP concentrations ranging from 0.003 mg/cm3 (3 ppm) to a maximum of 0.055 mg/cm3 (55 ppm) and average of 0.0093 mg/cm3 (9.3 ppm) were imaged successfully within the ex vivo tumor slice.Conclusion:The developed cone‐beam benchtop L‐shell XRF imaging system can immediately be used for imaging of ex vivo tumor samples containing low concentrations of GNPs. With minor finetuning/optimization, the system can be directly adapted for performing routine preclinical in vivo imaging tasks. Supported by NIH/NCI grant R01CA155446This investigation was supported by NIH/NCI grant R01CA155446.

Optimisation of the X-ray Fluorescence Imaging System for Mapping of Pigments in Historical Paintings

Optimisation of the X-ray Fluorescence Imaging System for Mapping of Pigments in Historical Paintings

TH-AB-204-12: Practical/ultrasensitive Benchtop Gold L-Shell XRF Imaging System with a Kilowatt-Range X-Ray Source and Silicon Drift Detector

Purpose: To improve the sensitivity and throughput of a benchtop x-ray fluorescence (XRF) imaging system capable of locating and quantifying distributions of gold nanoparticles (GNPs) by detecting gold L-shell XRF photons from subcentimeter-sized ex vivo samples or superficial tumors for preclinical small animal studies. Methods: A proof-of-principle L-shell XRF imaging system has been developed previously. Originally, the system was configured with a low-power (∼50 W) x-ray source (62 kVp, 0.8 mA) and a silicon PIN diode detector. The detection limit of the system was approximately 0.02 mg/cm3 (20 ppm) for an acquisition time of 10 min. Currently, the system has been retrofitted with a high-power (∼3 kW) x-ray source. The detector was replaced with a silicon drift detector (SDD) to handle the increased photon flux at the new settings (62 kVp, 45 mA). Calibration was performed using phantoms containing water/GNPs at a wide range of concentrations (0 and 0.0001–10 mg/cm3). The acquisition time was set to 10 s (60 times shorter than that used with the former configuration, to maintain the same overall x-ray fluence and dose). The XRF/scatter spectrum at 90° was acquired from each phantom. The data were processed to extract XRF signal from background, which was then corrected for attenuation using a Compton-scatter-based normalization algorithm. The corrected XRF signals were plotted vs. GNP concentration and analyzed to determine the detection limit. Results: The detection limit with the current configuration was found to be 0.007 mg/cm3 (7 ppm), a three-fold improvement compared to the former configuration for the same dose. Conclusion: By adopting a high-power x-ray source and SDD, the material detection limit has been improved to a level comparable to that of a synchrotron-based system. Concurrently, much shorter acquisition time afforded by the higher photon flux makes the current setup practical for routine preclinical imaging tasks.

A 3D in vitro cancer model as a platform for nanoparticle uptake and imaging investigations.

In order to maximize the potential of nanoparticles (NPs) in cancer imaging and therapy, their mechanisms of interaction with host tissue need to be fully understood. NP uptake is known to be dramatically influenced by the tumor microenvironment, and an imaging platform that could replicate in vivo cellular conditions would make big strides in NP uptake studies. Here, a novel NP uptake platform consisting of a tissue-engineered 3D in vitro cancer model (tumoroid), which mimics the microarchitecture of a solid cancer mass and stroma, is presented. As the tumoroid exhibits fundamental characteristics of solid cancer tissue and its cellular and biochemical parameters are controllable, it provides a real alternative to animal models. Furthermore, an X-ray fluorescence imaging system is developed to demonstrate 3D imaging of GNPs and to determine uptake efficiency within the tumoroid. This platform has implications for optimizing the targeted delivery of NPs to cells to benefit cancer diagnostics and therapy.

Characteristics of a robust and portable large area X-ray fluorescence imaging system

A low-cost and portable Energy Disperse X-Ray Fluorescence imaging system is presented. It is capable of scanning large areas (up to 10 × 10 cm2) in steps as small as 0.2 mm. It consists of a small X-ray tube and a Silicon Drift Detector, both controlled by a homemade software. The spatial resolution is evaluated as a function of the step width and of the X-ray collimator diameter. The time of acquisition per unit of scanned surface is studied as a function of the step width and of the time of acquisition per point. X-ray fluorescence images showing the 2D distributions of some elements in biological samples are presented. Copyright © 2013 John Wiley & Sons, Ltd.

An x-ray fluorescence imaging system for gold nanoparticle detection

Gold nanoparticles (GNPs) may be used as a contrast agent to identify tumour location and can be modified to target and image specific tumour biological parameters. There are currently no imaging systems in the literature that have sufficient sensitivity to GNP concentration and distribution measurement at sufficient tissue depth for use in in vivo and in vitro studies. We have demonstrated that high detecting sensitivity of GNPs can be achieved using x-ray fluorescence; furthermore this technique enables greater depth imaging in comparison to optical modalities. Two x-ray fluorescence systems were developed and used to image a range of GNP imaging phantoms. The first system consisted of a 10 mm2 silicon drift detector coupled to a slightly focusing polycapillary optic which allowed 2D energy resolved imaging in step and scan mode. The system has sensitivity to GNP concentrations as low as 1 ppm. GNP concentrations different by a factor of 5 could be resolved, offering potential to distinguish tumour from non-tumour. The second system was designed to avoid slow step and scan image acquisition; the feasibility of excitation of the whole specimen with a wide beam and detection of the fluorescent x-rays with a pixellated controlled drift energy resolving detector without scanning was investigated. A parallel polycapillary optic coupled to the detector was successfully used to ascertain the position where fluorescence was emitted. The tissue penetration of the technique was demonstrated to be sufficient for near-surface small-animal studies, and for imaging 3D in vitro cellular constructs. Previous work demonstrates strong potential for both imaging systems to form quantitative images of GNP concentration.

X-ray fluorescence imaging system for fast mapping of pigment distributions in cultural heritage paintings

Conventional X-ray fluorescence imaging technique uses a focused X-ray beam to scan through the sample and an X-ray detector with high energy resolution but no spatial resolution.The spatial resolution of the image is then determined by the size of the exciting beam, which can be obtained either from a synchrotron source or from an X-ray tube with a micro-capillary lens.Such a technique based on a pixel-by-pixel measurement is very slow and not suitable for imaging large area samples.The goal of this work is to develop a system capable of simultaneous imaging of large area samples by using a wide field uniform excitation X-ray beam and a position sensitive and energy dispersive detector. The development is driven by possible application of such a system to imaging of distributions of hidden pigments containing specific elements in cultural heritage paintings, which is of great interest for the cultural heritage research.The fluorescence radiation from the area of 10 × 10 cm2 is projected through a pinhole camera on the Gas Electron Multiplier detector of the same area.The detector is equipped with two sets of orthogonal readout strips.The strips are read out by the GEMROC Application Specific Integrated Circuits (ASIC)s, which deliver time and amplitude information for each hit.This ASIC architecture combined with a Field Programmable Gate Array (FPGA) based readout system allows us to reconstruct the position and the total energy of each detected photon for high count rates up to 5 × 106 cps.Energy resolution better than 20% FWHM for the 5.9 keV line and spatial resolution of 1 mm FWHM have been achieved for the prototype system.Although the energy resolution of the Gas Electron Multiplier (GEM) detector is, by principle, not competitive with that of specialised high energy resolution semiconductor detectors, it is sufficient for a number of applications.Compared to conventional micro-XRF techniques the developed system allows shortening of the measurement time by 2-3 orders of magnitude.