Novel imaging biomarkers: epicardial adipose tissue evaluation

Abstract

Epicardial adipose tissue (EAT) is a metabolically activated beige adipose tissue, non-homogeneously surrounding the myocardium. Physiologically, EAT regulates toxic fatty acids, protects the coronary arteries against mechanical strain, regulates proinflammatory cytokines, stimulates the production of nitric oxide, reduces oxidative stress, and works as a thermogenic source against hypothermia. Conversely, EAT has pathologic paracrine interactions with the surrounded vessels, and might favour the onset of atrial fibrillation. In addition, initial atherosclerotic lesions can promote inflammation and trigger the EAT production of cytokines increasing vascular inflammation, which, in turn, may help the development of collateral vessels but also of self-stimulating, dysregulated inflammatory process, increasing coronary artery disease severity. Variations in EAT were also linked to metabolic syndrome. Echocardiography first estimated EAT measuring its thickness on the free wall of the right ventricle but does not allow accurate volumetric EAT estimates. Cardiac CT (CCT) and cardiac MR (CMR) allow for three-dimensional EAT estimates, the former showing higher spatial resolution and reproducibility but being limited by radiation exposure and long segmentation times, the latter being radiation-free but limited by lower spatial resolution and reproducibility, higher cost, and difficulties for obese patients. EAT radiodensity at CCT could to be related to underlying metabolic processes. The correlation between EAT and response to certain pharmacological therapies has also been investigated, showing promising results. In the future, semi-automatic or fully automatic techniques, machine/deep-learning methods, if validated, will facilitate research for various EAT measures and may find a place in CCT/CMR reporting.

Figure 1.

Segmentation of EAT in light blue, and PAT in dark blue on a contrast-enhanced cardiac CT scan in a 64-year-old female patient. EAT, epicardial adipose tissue; PAT, paracardial adipose tissue.

Figure 2.

Contrast-enhanced cardiac CT scan of a 64-year-old female patient depicting the thin pericardium (white arrowheads). The epicardial adipose tissue is immediately internal to the pericardium.

Figure 3.

Unenhanced (A) and arterial phase contrast-enhanced (B) cardiac computed tomography scans of a 52-year-old male patient showing the pericardium(white arrowheads), visible in both images as a thin, hyperdense line. This caseis an example of the difficulties in segmenting the epicardial adipose tissue.

Figure 4.

Cardiac magnetic resonance true fast imaging with steady-state free precession sequence in a 64-year-old female patient, showing the pericardium (white arrowhead) as a thin, just visible, hypointense line surrounded by hyperintense adipose tissue on both sides.