This work proposes an attenuation correction method for x-ray fluorescence computed tomography (XFCT). The phantom is irradiated by a polychromatic cone-beam source produced by a conventional x-ray tube. X-ray fluorescence (XRF) photons are stimulated by the incident beam and are then collected by a photon counting detector placed on one side of the beamline. A flat-panel detector is placed along the beamline for detection of attenuation information. For quantitative reconstruction of XFCT images, the attenuation of incident photons as well as XRF photons in the phantom are estimated utilizing the transmission CT images. Simulation results show that the attenuation correction method proposed in this work significantly improves the accuracy of image reconstruction for XFCT, which enables quantitative identification of fluorescence materials in the objects.
KEYWORDS: Sensors, Monte Carlo methods, Gadolinium, Gold, Imaging systems, X-ray fluorescence spectroscopy, Computed tomography, In vivo imaging, Luminescence, Computing systems
We present the design concept and initial simulations for a polychromatic full-field fan-beam x-ray fluorescence computed tomography (XFCT) device with pinhole collimators and linear-array photon counting detectors. The phantom is irradiated by a fan-beam polychromatic x-ray source filtered by copper. Fluorescent photons are stimulated and then collected by two linear-array photon counting detectors with pinhole collimators. The Compton scatter correction and the attenuation correction are applied in the data processing, and the maximum-likelihood expectation maximization algorithm is applied for the image reconstruction of XFCT. The physical modeling of the XFCT imaging system was described, and a set of rapid Monte Carlo simulations was carried out to examine the feasibility and sensitivity of the XFCT system. Different concentrations of gadolinium (Gd) and gold (Au) solutions were used as contrast agents in simulations. Results show that 0.04% of Gd and 0.065% of Au can be well reconstructed with the full scan time set at 6 min. Compared with using the XFCT system with a pencil-beam source or a single-pixel detector, using a full-field fan-beam XFCT device with linear-array detectors results in significant scanning time reduction and may satisfy requirements of rapid imaging, such as in vivo imaging experiments.
KEYWORDS: In situ metrology, Magnetism, LabVIEW, Interference (communication), Signal to noise ratio, Electronic filtering, Digital filtering, Sensors, Data acquisition, Numerical simulations
Compared with the other geophysical approaches, magnetic resonance sounding (MRS) technique is direct and nondestructive in subsurface water exploration. It provides water content distribution and estimates hydrogeological properties. The biggest challenge is that MRS measurement always suffers bad signal-to-noise ratio, and it can be carried out only far from sources of noise. To solve this problem, a series of de-noising methods are developed. However, most of them are post-processing, leading the data quality uncontrolled for in situ measurements. In the present study, a new approach that removal of correlated noise online is found to overcome the restriction. Based on LabVIEW, a method is provided to enable online data quality control by the way of realizing signal acquisition and noise filtering simultaneously. Using one or more reference coils, adaptive noise cancellation based on LabVIEW to eliminate the correlated noise is available for in situ measurements. The approach was examined through numerical simulation and field measurements. The correlated noise is mitigated effectively and the application of MRS measurements is feasible in high-level noise environment. The method shortens the measurement time and improves the measurement efficiency.
The noninvasive method of surface nuclear magnetic resonance (SNMR) is a geophysical technique that is directly sensitive to hydrogen protons, besides it can exploit the NMR phenomenon for a quantitative determination of the subsurface groundwater distribution. Traditionally, SNMR utilizes large surface coils for both transmitting excitation pulses and recording the groundwater response. While, in recent research, a low Tc-SQUIDs is taken as a new sensor to replace the large receiving coil (Rx), which performing the best sensitivity for the shallow depth. Nevertheless, SQUID is with the problems of flux trapping and operational difficulties. In this paper, we introduce a room temperature coil system. A Cu coil with diameter of 1 m and a low noise preamplifier was systematically investigated and reached a sensitivity of 0.2fT/Hz1/2.Four preamplifiers are chosen for optimizing the pickup coils. The resolution studies for the array coil systems were performed, and the optimum distance between the adjacent pickup coils to achieve a better experimental results especially for the shallow depth. Our study enable the further use of the room temperature coil for SNMR shallow depth detections.
Rapid development of the X-ray phonon-counting detection technology brings tremendous research and application
opportunities. In addition to improvements in conventional X-ray imaging performance such as radiation dose utilization
and beam hardening correction, photon-counting detectors allows significantly more efficient X-ray fluorescence (XRF)
and K-edge imaging, and promises a great potential of X-ray functional, cellular and molecular imaging. XRF is the
characteristic emission of secondary X-ray photons from a material excited by initial X-rays. The phenomenon is widely
used for chemical and elemental analysis. K-edge imaging identifies a material based on its chemically-specific
absorption discontinuity over X-ray photon energy. In this paper, we try to combine XRF and K-edge signals from the
contrast agents (e.g., iodine, gadolinium, gold nanoparticles) to simultaneously realize XFCT and K-edge CT imaging
for superior image performance. As a prerequisite for this dual-modality imaging, the accurate energy calibration of
multi-energy-bin photon-counting detectors is critically important. With the measured XRF data of different materials,
we characterize the energy response function of a CZT detector for energy calibration and spectrum reconstruction,
which can effectively improve the energy resolution and decrease the inconsistence of the photon counting detectors.
Then, a simultaneous K-edge and X-ray fluorescence CT imaging (SKYFI) experimental setup is designed which
includes a cone-beam X-ray tube, two separate photon counting detector arrays, a pin-hole collimator and a rotation
stage. With a phantom containing gold nanoparticles the two types of XFCT and K-edge CT datasets are collected
simultaneously. Then, XFCT and K-edge CT images are synergistically reconstructed in a same framework. Simulation
results are presented and quantitative analyzed and compared with the separate XFCT and K-edge CT results.
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