Physical Modeling and Performance of Spatial-Spectral Filters for CT Material Decomposition

TL;DR

This paper investigates a novel spectral CT approach using spatial-spectral filters instead of energy-discriminating detectors, modeling physical effects and analyzing performance with simulated physical parameters.

Contribution

It introduces a new spatial-spectral filtering method for spectral CT and models physical effects like focal spot size and motion blur to evaluate performance.

Findings

Performance is feasible with realistic x-ray tubes.

Higher filter speeds can reduce error despite motion blur.

Focal spot size has less than 15% impact on performance.

Abstract

Material decomposition for imaging multiple contrast agents in a single acquisition has been made possible by spectral CT: a modality which incorporates multiple photon energy spectral sensitivities into a single data collection. This work presents an investigation of a new approach to spectral CT which does not rely on energy-discriminating detectors or multiple x-ray sources. Instead, a tiled pattern of K-edge filters are placed in front of the x-ray to create spatially encoded spectra data. For improved sampling, the spatial-spectral filter is moved continuously with respect to the source. A model-based material decomposition algorithm is adopted to directly reconstruct multiple material densities from projection data that is sparse in each spectral channel. Physical effects associated with the x-ray focal spot size and motion blur for the moving filter are expected to impact overall performance. In this work, those physical effects are modeled and a performance analysis is conducted. Specifically, experiments are presented with simulated focal spot widths between 0.2 mm and 4.0 mm. Additionally, filter motion blur is simulated for a linear translation speeds between 50 mm/s and 450 mm/s. The performance differential between a 0.2 mm and a 1.0 mm focal spot is less than 15% suggesting feasibility of the approach with realistic x-ray tubes. Moreover, for reasonable filter actuation speeds, higher speeds are shown to decrease error (due to improved sampling) despite motion-based spectral blur.