TH-AB-204-09: High-Sensitivity L-Shell X-Ray Fluorescence CT Imaging of Gold

Abstract

Purpose: To experimentally demonstrate the feasibility of L-shell x-ray fluorescence CT (XFCT) imaging of gold contrast. Methods: We have built an experimental L-shell XFCT imaging system consisting of two photon-counting detectors, a silicon drift detector (SDD) and a CdTe detector, a miniature x-ray tube, and a programmable translation/rotation stage. A 2.8-mm diameter water phantom containing 4-mm vials with gold solutions of 0.06%, 0.08%, and 0.1% Au located at 4mm depth was constructed. The phantom was imaged with the L-shell XFCT system in 1st generation CT geometry with a 1-mm 50-kV x-ray beam. XFCT data was acquired with both detectors placed at ±120° with respect to the excitation beam at 30 translation and 36 rotation steps. L-shell XFCT images were reconstructed with maximum-likelihood expectation-maximization using gold Lα and Lβ fluorescence x-rays for both detectors. Results: SDD L- shell x-ray fluorescence (XRF) signal was approximately 13 times higher than CdTe XRF signal due to the higher measured SDD energy resolution of 220eV @ 14keV compared to the CdTe energy resolution of 660eV. While all 0.06–0.1% Au vials were detectable in the SDD L-shell XFCT image, none of the vials were visible in the CdTe L-shell XFCT image. The contrast-to-noise ratio of the 0.1% Au vial was 87.1 and 3.2 in the SDD and CdTe L-shell XFCT images, respectively. SDD L-shell XFCT signal was linear with Au concentration (R2>0.99). The detectability limits of the presented L-shell XFCT imaging setup were 0.007% and 0.126% Au for L-shell XFCT imaging performed with the SDD and CdTe detector, respectively. Conclusion: We have demonstrated the feasibility of L- shell XFCT imaging of gold located at shallow depths inside a small animal sized phantom. The very high sensitivity of L-shell XFCT, permitting detection of Au concentrations as low as 0.06%, has not previously been achieved experimentally using conventional K-shell XFCT.