Dual-Energy X-ray Imaging by Simultaneous Integration and Campbelling Readout

Dual-energy imaging is based on the acquisition of two spectrally distinct attenuation measurements. The two most common techniques are the dual-kV technique and the dual-detector layer technique. More recently, another technique was introduced based on the simultaneous acquisition of photon-counting and current integration data (CIX) by means of a dedicated detector readout ASIC. All of the above methods have certain advantages and disadvantages. While depending on the particular realization (e. g., kVp switching, dual-tube systems in computed tomography), the dual-kV technique suffers from a time-lag between the two acquisitions and as a result from susceptibility to motion. The dual-layer technique usually offers less spectral separation and requires a dedicated detection system. The CIX technique suffers from a reduced dynamic range due to the limiting rate performance in the counting channel. In this paper we introduce yet another dual-energy technique, similar to the CIX, however, without the restrictions coming from the limited count rate. We propose dual-energy imaging based on simultaneous acquisition of the mean (DC) and variance (AC) components of the electrical detector signal, i.e., simultaneous integration-mode readout and Campbell-mode readout (fluctuation mode). The method is based on "Campbell's theorem" which states that the variance of the deviations from the mean detector signal is proportional to the second moment of the incoming x-ray energy spectrum. We compare in simulations the dual-energy performance of the proposed new technique with conventional dual-kV and dual-crystal techniques and present first experimental Campbell-mode CT images obtained from a scintillator crystal coupled to a photomultiplier tube. Moreover, we demonstrate the feasibility of separating iodine from calcium with the novel technique and compare it to the separability achieved with a dual-kV technique.