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Experimental and Theoretical Margins for Gadolinium-Based Preclinical X-Ray Fluorescence Computed Tomography

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D Vernekohl

D Vernekohl*, L Xing , Stanford Univ School of Medicine, Stanford, CA


TH-AB-708-4 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: 708

Purpose: Gadolinium (Gd) based contrast agents are already used in standard radiology and promise great applications in future use as high atomic number contrast agents for x-ray fluorescence computed tomography (XFCT). The study aims to prospects detectability limits and to discuss advantages of different instrumental approaches for preclinical Gd XFCT.

Methods: The theoretical detection limit for a given dose of x-ray radiation is studied with Monte-Carlo simulations while the experimental validation is provided by comparing measured spectral response of photon counting detectors to simulation predictions. The setup for the simulation study includes mouse and rat sized phantoms with 5 mm diameter target cylinders with different Gd concentrations. The phantoms are scanned with a fine controlled pencil beam and a target dose of 30 cGy at the center of the phantom. For the experimental evaluation, a 4 mm diameter Gd vial is irradiated where the fluorescent x-rays are measured with a Cadmium telluride detector. Spectra are obtained for different Gd concentrations and compared by their signal to background ratio (SBR).

Results: The simulations report a detection threshold for the mouse and rat phantom of 1.6 and 4.2 µg/ml of Gd when excited with 125 keV photons, respectively. For an excitation energy of 51 keV, the detectability drops to 1.9 and 10.6 µg/ml.For the comparison between experiments and simulations, a SBR around 1.4 at the Kα peak at 42 keV was observed for similar conditions.

Conclusion: In summary, it was presented that tiny amounts of contrast agents can be detected by XFCT. To reach high sensitivity, large photo counting detectors and monochromatic x-ray sources are required. In the specific case of Gadolinium a higher energetic excitation is beneficial to reach higher contrast via Compton scatter reduction.

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