Data acquisition with interleaved/gapped spectral channelization for spectral imaging in photon-counting CT

Abstract

Compared to energy-integration, photon-counting detection of x-ray facilitates spectral channelization (energy binning) in spectral CT and thus offers the opportunity of implementing sophisticated data acquisition schemes, e.g., gapping or interleaving in spectral channels. In this work, we investigate the feasibility and performance of material decomposition based spectral imaging in photon-counting CT via such data acquisition schemes. Using a deliberately designed anthropomorphic head phantom, a simulation study is carried out with the focus on two-material decomposition-based spectral imaging, under both ideal and realistic detector spectral responses. The projection data are acquired in four spectral channels and are sorted to implement the schemes of gapping ((ch₁, ch₃); (ch₂, ch₄); (ch₁, ch₄)) and interleaving ((ch₁, ch₃)+(ch₂, ch₄); (ch₁, ch₄)+(ch₂, ch₃); ((ch₁+ch₃), (ch₂+ch₄)); ((ch₁+ch₄), (ch₂+ch₃))) in spectral channels, in addition to the benchmark scheme ((ch₁+ch₂), (ch₃+ch₄)) and other conventional schemes (ch₁, ch₂), (ch₂, ch₃) and (ch₃, ch₄), where ‘ch’ denotes channel, ‘+’ denote addition, and (·,·) the operation of material decomposition and image reconstruction. The contrast-to-noise ratio between targeted regions of interest as the figure of merit in the study. It is observed that under ideal detector spectral response, the scheme (ch₁, ch₄) outperforms the benchmark scheme ((ch₁+ch₂), (ch₃+ch₄)) and others in gapped and/or interleaved spectral channelization in material specific imaging, while the interleaved scheme (ch₁, ch₄)+(ch₂, ch₃) performs the best in virtual monochromatic imaging. Under realistic detector spectral response, the difference in imaging performance over all spectral channelization schemes diminishes, along with degradation in each scheme’s individual performance. The spectral channelization schemes and associated imaging performance reported herein are novel and informative to the community, which may further the understanding of fundamental physics and design principles for spectral imaging in photon-counting CT and other x-ray related imaging modalities.