Dual energy CT material decomposition from inconsistent rays (MDIR)

In dual energy CT (DECT) the object is scanned with two different detected spectra in order to provide material-selective or energy-selective images of the object. Thereby, generally a higher order correction of beam hardening artifacts than it can be applied to usual single energy scans is possible. All known methods to do that need to combine the sinograms in rawdata space before image reconstruction. Therefore, a precondition of those methods is that geometrically identical rays are measured for each sinogram (consistent rays). However, most CT scanners actually acquire inconsistent rays in the sense that geometrically different rays are measured for each spectrum. Then the possibility of higher order beam hardening corrections remains unused and the resulting dual energy specific images show significantly reduced quality. We propose an iterative algorithm for material decomposition from inconsistent rays (MDIR) that allows even in the case of inconsistent rays to reconstruct material-selective or energy-selective images that are almost free of beam hardening artifacts. The algorithm is assessed using simulated data without noise (to enhance the visibility of beam hardening artifacts) and a micro CT scan of a mouse. The simulation studies find that the method is able to completely remove beam hardening caused image quality degradation after few (two to four) iterations. For the mouse scan an improvement in image quality can be noticed. In any case MDIR succeeds in reducing image artifacts that origin from beam hardening considerably while the image noise remains constant.