Unsupervised-learning-based method for chest MRI-CT transformation using structure constrained unsupervised generative attention networks

TL;DR

This paper introduces a novel unsupervised generative model that uses structural constraints to accurately transform chest MRI images into CT images, aiding attenuation correction in PET/MRI without requiring manual annotations.

Contribution

The study proposes a structure-constrained unsupervised generative attention network that improves chest CT synthesis from MRI, addressing challenges of motion and complex anatomy.

Findings

Outperforms existing methods in chest MRI to CT translation

Minimizes anatomical structural changes without human annotation

Achieves clinically acceptable CT synthesis from MRI

Abstract

The integrated positron emission tomography/magnetic resonance imaging (PET/MRI) scanner facilitates the simultaneous acquisition of metabolic information via PET and morphological information with high soft-tissue contrast using MRI. Although PET/MRI facilitates the capture of high-accuracy fusion images, its major drawback can be attributed to the difficulty encountered when performing attenuation correction, which is necessary for quantitative PET evaluation. The combined PET/MRI scanning requires the generation of attenuation-correction maps from MRI owing to no direct relationship between the gamma-ray attenuation information and MRIs. While MRI-based bone-tissue segmentation can be readily performed for the head and pelvis regions, the realization of accurate bone segmentation via chest CT generation remains a challenging task. This can be attributed to the respiratory and cardiac motions occurring in the chest as well as its anatomically complicated structure and relatively thin bone cortex. This paper presents a means to minimise the anatomical structural changes without human annotation by adding structural constraints using a modality-independent neighbourhood descriptor (MIND) to a generative adversarial network (GAN) that can transform unpaired images. The results obtained in this study revealed the proposed U-GAT-IT + MIND approach to outperform all other competing approaches. The findings of this study hint towards possibility of synthesising clinically acceptable CT images from chest MRI without human annotation, thereby minimising the changes in the anatomical structure.