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.