# Joint Reconstruction in Low Dose Multi-Energy CT

## TL;DR

This paper introduces a joint regularization approach combined with a low-dose, non-overlapping projection protocol to improve multi-energy CT reconstruction, reducing radiation dose while maintaining image quality.

## Contribution

It proposes a novel joint regularization model based on the structural similarity index and demonstrates its effectiveness with a new low-dose data acquisition protocol.

## Key findings

- Joint regularization outperforms individual reconstructions.
- The combination reduces radiation dose significantly.
- The new model improves multi-energy CT image quality.

## Abstract

Multi-energy CT takes advantage of the non-linearly varying attenuation properties of elemental media with respect to energy, enabling more precise material identification than single-energy CT. The increased precision comes with the cost of a higher radiation dose. A straightforward way to lower the dose is to reduce the number of projections per energy, but this makes tomographic reconstruction more ill-posed. In this paper, we propose how this problem can be overcome with a combination of a regularization method that promotes structural similarity between images at different energies and a suitably selected low-dose data acquisition protocol using non-overlapping projections. The performance of various joint regularization models is assessed with both simulated and experimental data, using the novel low-dose data acquisition protocol. Three of the models are well-established, namely the joint total variation, the linear parallel level sets and the spectral smoothness promoting regularization models. Furthermore, one new joint regularization model is introduced for multi-energy CT: a regularization based on the structure function from the structural similarity index. The findings show that joint regularization outperforms individual channel-by-channel reconstruction. Furthermore, the proposed combination of joint reconstruction and non-overlapping projection geometry enables significant reduction of radiation dose.