Practical multi-material decomposition method for variable threshold micro-focus photon-counting cone-beam CT

Abstract

Micro-focus photon-counting cone-beam computed tomography (MF-PCCBCT) utilizes a micro-focus X-ray source and a flat-panel photon-counting detector (PCD) to simultaneously acquire high-resolution multi-energy projections of the measured object by setting different energy thresholds on the PCD. This technique has significant applications in medical imaging, including microcalcification detection, bone microstructure analysis, and small animal imaging. However, due to hardware cost and anti-noise performance considerations, some commercial PCDs currently include only a single high-energy threshold, meaning that only projections from two energy bins of the measured object can be collected at a time, restricting their multi-material decomposition (MMD) capabilities. To address this limitation, we propose a practical variable-threshold circular scanning mode, taking advantage of the long scanning period of a micro-focus X-ray source. In this mode, the object is scanned two laps consecutively, and the sampling views of the second lap are staggered with those of the first scan while changing the energy threshold. Consequently, the sample views and projections are doubled without additional hardware and scanning duration. In this scanning mode, the dual-energy projections obtained from the same lap are geometrically consistent, whereas the dual-energy projections from different laps exhibit geometric inconsistency. Thereby, we propose a nonlinear MMD mathematical model based on this scanning mode and a high-precision two-step Levenberg-Marquardt filtered back-projection (TSLM-FBP) algorithm to solve this novel mathematical problem. Finally, numerical simulation and real data experiments demonstrate that the proposed method outperforms existing state-of-the-art model-based approaches and achieves high-precision multi-material decomposition.