Effective atomic number and electron density determination using spectral x-ray CT

We present Spectral X-ray Computed Tomography (SCT) estimations of material properties directly from energy-dependent measurements of linear attenuation coefficients (LAC). X-ray Computed Tomography (CT) is commonly utilized to characterize the internal properties of an object of interest. Dual-Energy X-ray CT allows material characterization into energy-independent physical properties such as Z(e) and electron density rho(e). However, it is not robust in presence of dense materials and metal artifacts. We report on the performance of a method for system-independent characterization of materials that introduces a spectroscopic detector into X-ray CT, called spectral rho(e)/Z(e) estimation (SRZE). We benchmark the SRZE method against energy-integrated measurements in material classification tests, finding superior accuracy in the predictions. The advantage of this technique, over other methods for material characterization using x-ray CT, is that it does not require a set of reference materials for calibration. Moreover, the simultaneous detection of spectral features makes it robust to highly attenuating materials, since the energy intervals for which the attenuation is photon limited can easily be detected and excluded from the feature estimation.