Simultaneous visualization of left atrial fibrosis and epicardial adipose tissue using 3D Dixon late gadolinium enhancement cardiovascular magnetic resonance
Authors: Skoda I , Henningsson M , Carlhall CJ 
Published: February 2021

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Swedish Medical Research Council (Grant Number: 2018-02779) Swedish Heart and Lung Foundation (Grant Number: 20170440)

Background
Cardiovascular magnetic resonance (CMR) is a powerful tool to identify structural changes of the left atrium (LA). LA fibrosis can be quantified using late gadolinium enhancement (LGE) and is a major risk factor for progression of atrial fibrillation (AF). Epicardial adipose tissue (EAT) around the LA can also be assessed using CMR and is associated with incidence and severity of AF. The theory that EAT may induce LA wall inflammation and thus promoting LA fibrosis highlights the need for assessment of the interrelation of the spatial distribution of these two AF risk factors. However, previous CMR studies have used separate pulse sequences to visualize LA fibrosis and EAT.

Purpose
To develop and evaluate a novel 3D Dixon water-fat separated LGE (Dixon-LGE) pulse sequence for visualization and quantification of LA fibrosis and EAT.

Methods
19 subjects were prospectively included and scanned on a 1.5T scanner (mean age 54 ± 20 years; 9 female): 10 patients with a history of AF, and 9 patients without any known cardiovascular disease (NCD). The 3D Dixon-LGE scan was performed 20 minutes after Gd contrast injection. Dixon reconstructed water images were used for LGE quantification while the fat images were used to quantify EAT. Segmentations of the LA myocardium and EAT were performed manually. The image intensity ratio (IIR) method was used for fibrosis quantification, by normalizing the intensity of the LA wall by the mean value of the blood pool intensity and classifying fibrosis as pixels with normalized intensity more than 1.2. For comparison with the automated IIR method, fibrosis was manually segmented in the LGE images as ground truth (GT).

Results
Example images from an AF and NCD patient are shown in the figure. Heart rate was higher (84 ± 14 vs. 65 ± 14 bpm, P = 0.007), and BMI was higher (28 ± 3 vs. 24 ± 3 kg/m², P = 0.014) in the AF group compared to NCD. AF had also larger LA end-systolic volume index (83 ± 16 vs. 38 ± 9 mL/m², P &lt; 0.001) and larger LA EAT volume index (7.1 ± 4.1 vs. 3.2 ± 2.2 mL/m², P = 0.022) compared to NCD. Further, fibrosis as percentage of LA surface area was larger 14.9 ± 18.4 vs. 3.2 ± 2.5 %, P = 0.028 in AF compared to NCD. The interclass correlation coefficient (ICC) for inter-observer and intra-observer measurements of LA volume were 0.99 (95% CI, 0.97%–0.99%) and 0.99 (95% CI, 0.99%–0.99%), respectively, of LA EAT volume were 0.95 (95% CI, 0.87%–0.98%) and 0.97 (95% CI, 0.89%–0.99%), respectively, and of LA fibrosis, IIR method, were 0.98 (95% CI, 0.94%–0.99%) and 0.99 (95% CI, 0.98%–0.99%), respectively. The IIR method had a very high level of agreement with the GT segmentation, ICC = 0.96 (95% CI, 0.78%-0.99%).

Conclusions
LA fibrosis and EAT can be visualized simultaneously by using a single 3D LGE-Dixon pulse sequence. This new method has a high level of intra- and inter observer repeatability, can reduce the scan time and allows the analysis of spatial correlation of these AF risk factors.
Abstract Figure. Dixon-LGE acquisition and quantification