Material decomposition with inconsistent rays (MDIR) for cone-beam dual energy CT

Abstract

Dual energy CT (DECT) provides material-selective CT images by acquiring the object of interest with two different x-ray spectra, a low and a high energy spectrum. Today, two techniques to process the rawdata are in use: Image-based DECT reconstructs the low and the high energy data separately and then performs a linear combination of the images to yield the desired material-selective images. This method can only provide a first order approximation of the true material decomposition and it will not be able to remove higher order beam hardening artifacts from the images. By contrast, rawdata-based DECT naturally deals with higher order effects and is therefore the better way to go. However, rawdata-based DECT requires the same line integrals to be available for both scans (consistent scans). This requirement may not be met for CT scanners that are available today. To handle the material decomposition of DECT from inconsistent scans (i.e. non-overlapping rays for each measured spectrum) a material decomposition algorithm (MDIR) that allows for different scan trajectories and scan geometries for the low and the high energy scan was developed and evaluated. The results of our iterative algorithm are comparable to those obtained by a rawdata-based approach. However, conventional rawdata-based approaches are often not applicable since inconsistent rays are acquired. It should be noted that MDIR can be extended to scans with more than two different spectra and to decompositions into more than two basis functions in a straightforward way.