Hybrid spectral CT reconstruction.

Yuanquan Wang,Darin P Clark,Cristian T Badea

doi:10.1371/journal.pone.0180324

Yuanquan Wang, Darin P Clark + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0180324

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Journal: PloS one	Publication Date: Jul 6, 2017
Citations: 43	License type: CC BY 4.0

Affiliation: Duke Medical Center

Abstract

Current photon counting x-ray detector (PCD) technology faces limitations associated with spectral fidelity and photon starvation. One strategy for addressing these limitations is to supplement PCD data with high-resolution, low-noise data acquired with an energy-integrating detector (EID). In this work, we propose an iterative, hybrid reconstruction technique which combines the spectral properties of PCD data with the resolution and signal-to-noise characteristics of EID data. Our hybrid reconstruction technique is based on an algebraic model of data fidelity which substitutes the EID data into the data fidelity term associated with the PCD reconstruction, resulting in a joint reconstruction problem. Within the split Bregman framework, these data fidelity constraints are minimized subject to additional constraints on spectral rank and on joint intensity-gradient sparsity measured between the reconstructions of the EID and PCD data. Following a derivation of the proposed technique, we apply it to the reconstruction of a digital phantom which contains realistic concentrations of iodine, barium, and calcium encountered in small-animal micro-CT. The results of this experiment suggest reliable separation and detection of iodine at concentrations ≥ 5 mg/ml and barium at concentrations ≥ 10 mg/ml in 2-mm features for EID and PCD data reconstructed with inherent spatial resolutions of 176 μm and 254 μm, respectively (point spread function, FWHM). Furthermore, hybrid reconstruction is demonstrated to enhance spatial resolution within material decomposition results and to improve low-contrast detectability by as much as 2.6 times relative to reconstruction with PCD data only. The parameters of the simulation experiment are based on an in vivo micro-CT experiment conducted in a mouse model of soft-tissue sarcoma. Material decomposition results produced from this in vivo data demonstrate the feasibility of distinguishing two K-edge contrast agents with a spectral separation on the order of the energy resolution of the PCD hardware.

Highlights

Photon counting x-ray detector technology promises to revolutionize both clinical and preclinical x-ray CT imaging applications; current x-ray CT systems, are largely based on energy integrating x-ray detectors (EIDs), which integrate incoming x-rays over a polychromatic source spectrum
We propose and demonstrate a hybrid spectral CT reconstruction technique which combines the spectral contrast of the photon counting x-ray detector (PCD) data with the spatial resolution of the EID data, yielding high-resolution spectral CT reconstructions
The algebraic model we have proposed for hybrid spectral CT reconstruction successfully synergizes the reconstruction of EID and PCD data, yielding improved denoising performance and evidence of resolution enhancement

Summary

Introduction

Photon counting x-ray detector technology promises to revolutionize both clinical and preclinical x-ray CT imaging applications; current x-ray CT systems, are largely based on energy integrating x-ray detectors (EIDs), which integrate incoming x-rays over a polychromatic source spectrum. These funding sources had no direct role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Dectris AG reviewed this manuscript prior to its initial submission to PLOS ONE, but had no direct role in the study design or the analysis methods employed

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