High-Sensitivity L-Shell X-Ray Fluorescence CT Imaging of Cisplatin
M Bazalova*, G Pratx, L Xing, Stanford Univ School of Medicine, Stanford, CATH-A-141-3 Thursday 8:00AM - 9:55AM Room: 141
Purpose: To increase the sensitivity of x-ray fluorescence computed tomography (XFCT) imaging by excitation of low-energy L-shell x-rays with higher interaction cross-section compared to K-shell x-rays.
Methods: XFCT images of a 2-cm diameter acrylic phantom with 0.1-0.4% (or 1-4 mg/mL) Cisplatin solutions were simulated in a modified version of the EGSnrc/DOSXYZnrc Monte Carlo code. XFCT images were reconstructed based on platinum fluorescence x-rays excited by 15, 30, and 80 keV x-rays. Based on L-edge and K-edge energies of platinum, 15 and 30 keV XFCT images were reconstructed using L-shell x-rays (~10 keV) and 80 keV images were reconstructed with K-shell x-rays (~67 keV). XFCT images were reconstructed with simple filtered back-projection (FBP), maximum-likelihood expectation maximization (ML-EM) without and with attenuation correction to account for the low energy 15 and 30 keV excitation x-rays and L-shell fluorescence x-rays.
Results: For a 2.5 mGy imaging dose, K-shell XFCT images reconstructed with simple FBP resulted in Cisplatin imaging sensitivity limit of 740 μg/mL, which was defined by contrast-to-noise ratio (CNR) value of 4. For the same dose, 15 keV L-shell XFCT imaging sensitivity increased by a factor of 3.8 for objects at the periphery of the phantom. However, contrast in L-shell images decreased drastically towards the center of the phantom due to attenuation of the excitation and fluorescence x-rays. Our ML-EM reconstruction algorithm with attenuation correction applied on the 15 keV L-shell XFCT image 1) significantly increased CNR and resulted in 2) a uniform signal across the phantom, and 3) accurate quantification of Cisplatin concentration.
Conclusion: We have shown that L-shell XFCT imaging in connection with ML-EM and attenuation correction reconstruction algorithm resulted high imaging sensitivity and accurate quantification of imaging contrast. A clinically relevant concentration of 6 μg/mL of Cisplatin can be accurately detected with a low imaging dose of 18 mGy.