X-ray fluorescence computed tomography (XFCT) imaging has been focused on the detection of K-shell x-rays. The potential utility of L-shell x-ray XFCT is, however, not well studied. Here we report the first Monte Carlo (MC) simulation of preclinical L-shell XFCT imaging of Cisplatin. We built MC models for both L- and K-shell XFCT with different excitation energies (15 and 30 keV for L-shell and 80 keV for K-shell XFCT). Two small-animal sized imaging phantoms of 2 and 4 cm diameter containing a series of objects of 0.6 to 2.7 mm in diameter at 0.7 to 16 mm depths with 10 to 250 µg mL(-1) concentrations of Pt are used in the study. Transmitted and scattered x-rays were collected with photon-integrating transmission detector and photon-counting detector arc, respectively. Collected data were rearranged into XFCT and transmission CT sinograms for image reconstruction. XFCT images were reconstructed with filtered back-projection and with iterative maximum-likelihood expectation maximization without and with attenuation correction. While K-shell XFCT was capable of providing an accurate measurement of Cisplatin concentration, its sensitivity was 4.4 and 3.0 times lower than that of L-shell XFCT with 15 keV excitation beam for the 2 cm and 4 cm diameter phantom, respectively. With the inclusion of excitation and fluorescence beam attenuation correction, we found that L-shell XFCT was capable of providing fairly accurate information of Cisplatin concentration distribution. With a dose of 29 and 58 mGy, clinically relevant Cisplatin Pt concentrations of 10 µg mg(-1) could be imaged with L-shell XFCT inside a 2 cm and 4 cm diameter object, respectively.
[Show abstract][Hide abstract] ABSTRACT: X-ray luminescence and X-ray fluorescence computed tomography (CT) are two emerging technologies in X-ray imaging that provide functional and molecular imaging capability. Both emission-type tomographic imaging modalities use external X-rays to stimulate secondary emissions, either light or secondary X-rays, which are then acquired for tomographic reconstruction. These modalities surpass the limits of sensitivity in current X-ray imaging and have the potential of enabling X-ray imaging to extract molecular imaging information. These new modalities also promise to break through the spatial resolution limits of other in vivo molecular imaging modalities. This paper reviews the development of X-ray luminescence and X-ray fluorescence CT and their relative merits. The discussion includes current problems and future research directions and the role of these modalities in future molecular imaging applications.
[Show abstract][Hide abstract] ABSTRACT: A novel x-ray fluorescence imaging setup for the in vivo detection of high-Z tracer distributions is investigated for its application in molecular imaging. The setup uses an energy resolved detection method based on a Bragg reflecting analyzer array together with a multiple scatter reducing radial collimator. The aim of this work is to investigate the potential application of this imaging method to in vivo imaging in humans. A proof of principle experiment modeling a partial setup for the detection of gold nano-particles was conducted in order to test the feasibility of the proposed imaging method. Furthermore a Monte Carlo simulation of the complete setup was created in order to quantify the dependence of the image quality on the applied radiation dose and on the geometrical collimator parameters as well as on the analyzer crystal parameters. The Monte Carlo simulation quantifies the signal-to-noise ratio per radiation dose and its dependence on the collimator parameters. Thereby the parameters needed for a dose efficient in vivo imaging of gold nano-particle based tracer distributions are quantified. However also a number of problems are found like the fluorescence emission as well as scatter from the collimator material obscuring the tracer fluorescence and the potentially large scan time.
[Show abstract][Hide abstract] ABSTRACT: In this work we demonstrated that an optimized detector angular configuration based on the anisotropic energy distribution of background scattered x-rays improves XFCT detection sensitivity. We built an XFCT imaging system composed of a bench-top fluoroscopy x-ray source, a CdTe x-ray detector, and a phantom motion stage. We imaged a 6.4-cm diameter phantom containing different concentrations of gold solution and investigated the effect of detector angular configuration on XFCT image quality. Based on our previous theoretical study, three detector angles were considered. The xray fluorescence detector was first placed at 145° (approximating back-scatter) to minimize scatter x-rays. XFCT image quality was compared to images acquired with the detector at 60° (forward-scatter) and 90° (side-scatter). The datasets for the three different detector positions were also combined to approximate an isotropically arranged detector. The sensitivity was optimized with detector in the 145° back-scatter configuration counting the 78-keV gold Kβ1 x-rays. The improvement arose from the reduced energy of scattered x-ray at the 145° position and the large energy separation from gold Kβ1 x-rays. The lowest detected concentration in this configuration was 2.5 mgAu/mL (or 0.25% Au with SNR = 4.3). This concentration could not be detected with the 60°, 90°, or isotropic configurations (SNRs = 1.3, 0, 2.3, respectively). XFCT imaging dose of 14 mGy was in the range of typical clinical x-ray CT imaging doses. To our knowledge, the sensitivity achieved in this experiment is the highest in any XFCT experiment using an ordinary bench-top x-ray source in a phantom larger than a mouse (> 3 cm).
IEEE Transactions on Medical Imaging 12/2014; 34(5). DOI:10.1109/TMI.2014.2376813 · 3.39 Impact Factor
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