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Determination Ofoptimal X-Ray Spectra and Concentration of Gold Contrast Agents

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Y Yuan

Y Yuan*, Y Zhang , E Sajo , H Yu , University of Massachusetts-Lowell, Lowell, MA


TU-C1-GePD-IT-4 (Tuesday, August 1, 2017) 9:30 AM - 10:00 AM Room: Imaging ePoster Theater

Purpose: The efficacy of gold as an x-ray contrast agent in vivo has become increasingly recognized in the last decade. X-ray tube potential energy and contrast agent concentration are two main determinants of attenuation. The aim of this study is to optimize voltage below K-edge and investigate the influence of different concentrations of gold contrast agent in a numerical study.

Methods: To determine the optimal x-ray tube potentials, we simulated 2D phantoms containing bone, soft tissue, and four mixtures of gold solution at ratios 4:1, 3:2, 2:3 and 1:4 in pixel fraction. The respective concentrations of gold are 4 mg/ml, 8 mg/ml, 16 mg/ml and 24 mg/ml. In all simulations, a 2D fan-beam CT geometry was considered. The phantom was virtually irradiated to create projection images with 5 kVp decrements starting at 35 kVp and ending at 80 kVp. The reconstruction used a filtered backprojection algorithm. Poisson noise was introduced and the total number of photons was set to 2×10⁴. We implemented an image-domain dual-energy material decomposition algorithm via direct matrix inversion to estimate basis material fraction. The accuracy of decomposition was assessed using the root mean square error (RMSE) computed for all scanning.

Results: The lowest RMSE indicates that the optimal x-ray tube potential pair is between 35kVp and 80kVp, and it varies with the concentration of gold solution. The decomposition accuracy for bone, gold solution is highest when the gold concentration is 4 mg/ml (ANOVA, single factor, p<0.05) with the corresponding potential pair of 35kVp and 75kVp. The decomposition accuracy for soft tissue does not significantly change with the examined gold concentrations.

Conclusion: This study implemented material decomposition to identify the optimal x-ray tube potentials and gold solution concentrations. For this numerical phantom, the optimal concentration is 4mg/ml and the dual-energy scanning spectra are 35kVp and 75kVp.

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