Experimental feasibility of multi-energy photon-counting K-edge imaging in pre-clinical computed tomography

TLDR

K‑edge computed tomography using multi‑energy photon‑counting detectors has been theoretically shown to enable material‑specific imaging with high‑Z contrast agents, promising new medical applications. This study experimentally demonstrates the feasibility of quantitative K‑edge CT imaging with a photon‑counting system. The authors constructed a CT system that acquired energy‑resolved projections of a phantom containing PMMA, calcium‑hydroxyapatite, water, iodine, and gadolinium, reconstructed photoelectric and Compton attenuation maps via maximum‑likelihood basis‑component decomposition, and calibrated the detector response using synchrotron‑derived energy‑bin sensitivities. The reconstructed images revealed individual contrast agents and their concentrations, which matched the known iodine and gadolinium levels.

Abstract

Theoretical considerations predicted the feasibility of K-edge x-ray computed tomography (CT) imaging using energy discriminating detectors with more than two energy bins. This technique enables material-specific imaging in CT, which in combination with high-Z element based contrast agents, opens up possibilities for new medical applications. In this paper, we present a CT system with energy detection capabilities, which was used to demonstrate the feasibility of quantitative K-edge CT imaging experimentally. A phantom was imaged containing PMMA, calcium-hydroxyapatite, water and two contrast agents based on iodine and gadolinium, respectively. Separate images of the attenuation by photoelectric absorption and Compton scattering were reconstructed from energy-resolved projection data using maximum-likelihood basis-component decomposition. The data analysis further enabled the display of images of the individual contrast agents and their concentrations, separated from the anatomical background. Measured concentrations of iodine and gadolinium were in good agreement with the actual concentrations. Prior to the tomographic measurements, the detector response functions for monochromatic illumination using synchrotron radiation were determined in the energy range 25 keV-60 keV. These data were used to calibrate the detector and derive a phenomenological model for the detector response and the energy bin sensitivities.