K-edge photon counting CT imaging using a dual-bin photon counting detector and kV switching

Abstract

Multi-energy CT can be used to decompose CT images into different material bases to allow for the quantification of materials. Three-material decomposition is desirable for clinical applications such as K-edge imaging. However, three-material decomposition requires measurements at 3 or more energies or additional assumptions such as volume conservation. This work concerns the following questions: 1) For photon counting detector (PCD) CT with only two energy bins, can the joint use of the PCD and kV-switching improve the performance of three-material decomposition for K-edge imaging? 2) If the PCD energy threshold must be fixed for both kV levels, how can its optimal value be pre-determined for a given K-edge imaging task? 3) While in conventional kV-switching multi-energy CT the separation of the two kV levels needs to be as wide as achievable, is this still the case when kV-switching is jointly used with a dual-bin PCD? These questions were answered by performing Cram´er-Rao lower bound (CRLB) analysis for dual-bin PCD-CT with kV-switching to optimize the PCD threshold and kV levels for the decomposition of water, iodine, and gadolinium bases using a previously modeled CdTe PCD energy response function. Experimental dual-bin PCD-CT images were acquired with kV-switching, and without kV-switching but with the volume conservation constraint, using the optimal acquisition parameters obtained from the CRLB analysis. Dual-bin PCD-CT with kV-switching allowed separation of all three basis materials with improved quantitative accuracy over dual-bin PCD-CT without kV-switching, which also suffered from poorer material separation and residual or missing signals from other materials.