Pencil beam X-ray Luminescence Computed Tomography (XLCT) is a developing hybrid molecular imaging modality combining the merits of both x-ray imaging (high spatial resolution) and optical imaging (high sensitivity). Narrow x-ray beam-based XLCT imaging has shown promise for high spatial resolution imaging and high molecular sensitivity, but so far there is no quantitative study of XLCT imaging for x-ray excitable nanophosphor targets in deep tissue. In this study, we have for the first time performed quantitative study on the reconstructed nanophosphor target concentrations through phantom experiments. We have upgraded our XLCT imaging system by mounting four optical fiber cables to increase the efficiency in collecting x-ray induced optical photons. We also used a piece of scintillator crystal to monitor the x-ray pencil beam’s intensity to sense automatic phantom boundary and to perform parallel beam-based CT imaging simultaneously, which can be used to verify the true locations of the reconstructed XLCT targets. We have scanned a cylindrical agar phantom containing twelve targets filled with three different nanophosphor concentration (2.5 mg/ml, 5 mg/ml, and 10 mg/ml) and reconstructed XLCT images with the Filtered Back-Projection (FBP) algorithm. We have conducted quantitative analysis of the phantom experimental results employing different numbers of optical fiber cables and found the reconstructed signals ratio is calculated to be 1: 2.17: 3.55, which is close to the ground truth target concentrations ratio of 1:2:4.
Oxygenation concentration of tissue is an important factor in culturing stem cells and in studying the therapy response of cancer cells. The hypoxia bone marrow is the site to harbor cancer cells. Thus, direct high-resolution measurements of molecular O2 would provide powerful means of monitoring cultured stem cells and therapied cancer cells. We proposed an imaging approach to measure oxygenation concentration in deep tissues, based on the XLCT, with combined strengths of high chemical sensitivity and high spatial resolution. We have developed different biosensing films for oxygenation measurements and tested these films with X-ray luminescent experiments. We have also performed phantom experiments with multiple targets to validate the XLCT imaging system with measurements at two channels.
X-ray luminescence computed tomography (XLCT) is a hybrid molecular imaging modality combining the merits of both X-ray imaging (high spatial resolution) and optical imaging (high sensitivity to tracer nanophosphors). Narrow X-ray beam based XLCT imaging has been demonstrated to have the capacity of high spatial resolution imaging at the cost of the data acquisition time. We have primarily focused on improving the performance of the narrow X-ray beam based XLCT imaging. In a previous study, we proposed a scanning strategy achieved by reducing the scanning step size for improving the spatial resolution from double the X-ray beam size to close to the X-ray beam size. For the imaging speed, we recently introduced a continuous scanning scheme to replace the selective excitation scheme and used a photon counter to replace the oscilloscope to acquire measurement data, yielding a 16 times faster scanning time compared with what used in traditional XLCT systems. In addition, we developed a deep learning based XLCT reconstruction algorithm to reduce the number of projection views in a previous work. Moreover, we previously synthesized and compared biocompatible nanophosphors of distinct X-ray luminescence spectra to make multi-color XLCT imaging possible. Here, based on the previous work, we designed and built a first-of-its-kind fast and three-dimensional XLCT imaging system with the capacity of multi-wavelength measurements. A lab-made image acquisition software has been developed to control the system. We have performed physical experiments and verified the system performance.
X-ray luminescence computed tomography (XLCT) is a hybrid molecular imaging modality combining the merits of both x-ray imaging (high spatial resolution) and optical imaging (high sensitivity to tracer nanophosphors). Narrow x-ray beam based XLCT imaging has shown promise for high spatial resolution imaging, but the slow acquisition speed limits its applications for in vivo imaging. We introduced a continuous scanning scheme to replace the selective excitation scheme to improve imaging speed in a previous study. Under the continuous scanning scheme, the main factor that limits the scanning speed is the data acquisition time at each interval position. In this work, we have used a gated photon counter (SR400, Stanford Research Systems) to replace the high-speed oscilloscope (MDO3104, Tektronix) to acquire measurement data. The gated photon counter only counts the photon peaks in each measurement interval, while the oscilloscope records the entire waveform including both background noise data and photon peak data. The photon counter records much less data without losing any relevant information, which makes it ideal for super-fast three-dimensional (3D) imaging. We have built prototype XLCT imaging systems of both types and performed both single target and multiple target phantom experiments in 3D. The results have verified the feasibility of our proposed photon counter based system and good 3D imaging capabilities of XLCT within a reasonable time, yielding a 14 times faster scanning time compared with the oscilloscope based XLCT system. Now, the total scan time is reduced to 27 seconds per transverse section.
X-ray fluorescence computed tomography (XFCT) is a molecular imaging technique of x-ray photons, which can be used to sense different elements or nanoparticle (NP) agents inside deep samples or tissues. XFCT has been an active research topic for many years. However, XFCT has not been a popular molecular imaging tool because it has limited molecular sensitivity and spatial resolution. To further investigate XFCT imaging, we present a benchtop XFCT imaging system, in in which a unique pencil beam x-ray source and a ring of x-ray spectrometers were simulated using GATE (Geant4 Application for Tomographic Emission) software. An accelerated majorization minimization (MM) algorithm with an L1 regularization scheme was used to reconstruct the XRF image of Molybdenum (Mo) NP targets from the numerical measurements of GATE simulations. With a low x-ray source output rate, good target localization was achieved with a DICE coefficient of 83.681%. The reconstructed signal intensity of the targets was found to be relatively proportional to the target concentrations if detector number and placement is optimized. The MM algorithm performance was compared with maximum likelihood expectation maximization (ML-EM) and filtered back projection (FBP) algorithms. In the future, the benchtop XFCT imaging system will be tested experimentally.
KEYWORDS: X-ray imaging, Luminescence, Computed tomography, Imaging systems, X-rays, Stereoscopy, 3D image processing, Data acquisition, 3D scanning, 3D acquisition
X-ray luminescence computed tomography (XLCT) imaging is a hybrid molecular imaging modality combining the merits of both conventional x-ray imaging (high spatial resolution) and optical imaging (high measurement sensitivity). The narrow x-ray beam based XLCT imaging has been shown to be promising. However due to the selective excitation scheme, the imaging speed is slow thus limiting its practical applications for in vivo imaging. In this work, we have introduced a continuous scanning scheme to acquire data for each angular projection in one motion, eliminating the previous stepping scheme and reducing the data acquisition time, which makes it feasible for multiple transverse scans for three-dimensional (3D) imaging. We have introduced a high accuracy vertical stage to our focused x-ray beam based XLCT imaging system to perform high-resolution and 3D XLCT imaging. We have also included a scintillator crystal coupled to a PMT to act as a single-pixel detector for boundary detection purposes to replace our previous flat panel x-ray detector. We have verified the feasibility of our proposed scanning scheme and imaging system by performing phantom experimental studies. A phantom was embedded with a set of cylindrical targets with 200 μm edge-to-edge distance and was scanned in our imaging system with the proposed method. To test the feasibility for 3D scanning, we took measurements from 4 transverse slices with a vertical step size of 1 mm. The results of the experiments verified the feasibility of our proposed method to perform 3D XLCT imaging using a narrow x-ray beam in a reasonable time.
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