Quantitative study of x-ray luminescence computed tomography

Abstract

Pencil beam X-ray luminescence computed tomography (XLCT) is a developing hybrid molecular imaging modality combining the merits of both x-ray imaging (high spatial resolution) and optical imaging (high sensitivity). Narrow x-ray beam based XLCT imaging has shown promise for high spatial resolution imaging and high molecular sensitivity, but so far there is no quantitative study of XLCT imaging for x-ray excitable nanophosphor targets in deep tissue. In this study, we have for the first time performed quantitative study on the reconstructed nanophosphor target concentrations through phantom experiments. We have upgraded our XLCT imaging system by mounting four optical fiber cables to increase the efficiency in collecting x-ray induced optical photons. We also used a piece of scintillator crystal to monitor the x-ray pencil beam's intensity to sense automatic phantom boundary and to perform parallel beam based CT imaging simultaneously, which can be used to verify the true locations of the reconstructed XLCT targets. We have scanned a cylindrical agar phantom containing twelve targets filled with three different nanophosphor concentration (2.5 mg/ml, 5 mg/ml, and 10 mg/ml) and reconstructed XLCT images with the filtered back-projection (FBP) algorithm. We have conducted quantitative analysis of the phantom experimental results employing different numbers of optical fiber cables and found the reconstructed signals ratio is calculated to be 1: 2.17: 3.55, which is close to the ground truth target concentrations ratio of 1:2:4.