Direct Iterative Reconstruction of Multiple Basis Material Images in Photon-counting Spectral CT

TL;DR

This paper introduces a direct iterative reconstruction method for multiple basis material images in photon-counting spectral CT, accurately estimating material concentrations from spectral data with regularization, paving the way for advanced molecular imaging.

Contribution

It presents a novel model-based iterative reconstruction approach that directly estimates multiple material images from spectral CT data, incorporating a calibration step for material attenuation coefficients.

Findings

Accurate reconstruction of material concentrations in phantom scans.

Effective estimation of attenuation coefficients for multiple materials.

Foundation laid for complex molecular and clinical spectral CT applications.

Abstract

In this work, we perform direct material reconstruction from spectral CT data using a model based iterative reconstruction (MBIR) approach. Material concentrations are measured in volume fractions, whose total is constrained by a maximum of unity. A phantom containing a combination of 4 basis materials (water, iodine, gadolinium, calcium) was scanned using a photon-counting detector. Iodine and gadolinium were chosen because of their common use as contrast agents in CT imaging. Scan data was binned into 5 energy (keV) levels. Each energy bin in a calibration scan was reconstructed, allowing the linear attenuation coefficient of each material for every energy to be estimated by a least-squares fit to ground truth in the image domain. The resulting $5\times 4$ matrix, for $5$ energies and $4$ materials, is incorporated into the forward model in direct reconstruction of the $4$ basis material images with spatial and/or inter-material regularization. In reconstruction from a subsequent low-concentration scan, volume fractions within regions of interest (ROIs) are found to be close to the ground truth. This work is meant to lay the foundation for further work with phantoms including spatially coincident mixtures of contrast materials and/or contrast agents in widely varying concentrations, molecular imaging from animal scans, and eventually clinical applications.