Vol. 3 No. 1 - Mar 2017

Tomography is a scientific journal for publication of articles in imaging research

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Intrathoracic Fat Measurements Using Multidetector Computed Tomography (MDCT): Feasibility and Reproducibility Jadranka Stojanovska, El-Sayed H. Ibrahim, Aamer R. Chughtai, Elizabeth A. Jackson, Barry H. Gross, Jon A. Jacobson, Alexander Tsodikov, Brian Daneshvar, Benjamin D. Long, Thomas L. Chenevert, and Ella A. Kazerooni Department of Radiology, University of Michigan, Ann Arbor, Michigan Corresponding Author: El-Sayed H. Ibrahim, PhD Department of Radiology, University of Michigan, UH-B1-209, 1500 East Medical Center Drive, Ann Arbor, MI 48109; E-mail: Key Words: epicardial fat volume, intrathoracic fat, MDCT, feasibility, reproducibility Abbreviations: Cardiovascular disease (CVD), body mass index (BMI), coronary artery disease (CAD), multidetector computed tomography (MDCT), computed tomography (CT), coronary CT angiography (CCTA), epicardial fat volume (EFV), region of interest (ROI), Advantage Workstation (AW), Hounsfield Unit (HU) Intrathoracic fat volume, more specifically, epicardial fat volume, is an emerging imaging biomarker of ad- verse cardiovascular events. The purpose of this work is to show the feasibility and reproducibility of intratho- racic fat volume measurement applied to contrast-enhanced multidetector computed tomography images. A retrospective cohort study of 62 subjects free of cardiovascular disease (55% females, age 5 49 6 11 years) conducted from 2008 to 2011 formed the study group. Intrathoracic fat volume was defined as all fat voxels measuring 250 to 2250 Hounsfield Unit within the intrathoracic cavity from the level of the pulmo- nary artery bifurcation to the heart apex. The intrathoracic fat was separated into epicardial and extraperi- cardial fat by tracing the pericardium. The measurements were obtained by 2 readers and compared for interrater reproducibility. The fat volume measurements for the study group were 141 6 72 cm 3 for intratho- racic fat, 58 6 27 cm 3 for epicardial fat, and 84 6 50 cm 3 for extrapericardial fat. There was no statisti- cally significant difference in intrathoracic fat volume measurements between the 2 readers, with correlation coefficients of 0.88 (P 5 .55) for intrathoracic fat volume and 20.12 (P 5 .33) for epicardial fat volume. Voxel-based measurement of intrathoracic fat, including the separation into epicardial and extrapericardial fat, is feasible and highly reproducible from multidetector computed tomography scans. INTRODUCTION Cardiovascular disease (CVD) remains the number one cause of mortality among adult men and women in the USA despite recent decrease in the mortality rate (1). A major contributor to increased CVD events is central obesity, which has been impli- cated as a cardiovascular risk factor and a public health problem (2). Several studies have shown that increased abdominal vis- ceral fat is a strong predictor of metabolic syndrome and CVD (3-5). Waist circumference and body mass index (BMI) are com- monly used anthropometric measures for quantifying general and regional adiposity (3-8). However, both measures have been criticized for providing general measurements that do not di- rectly correlate well with the underlying visceral fat component (6-8), such as abdominal and intrathoracic fat that are more highly correlated with cardiovascular risk compared with waist circumference and BMI alone (9, 10). An independent associa- tion between increased intrathoracic fat volume (ie, intraperi- cardial fat) and abdominal fat volume with atrial fibrillation and coronary artery disease (CAD) was shown (11-13). However, most of these studies do not explicitly describe the methodology used to quantify thoracic fat or define intrathoracic fat compart- ments. Multidetector computed tomography (MDCT) scans are often used in research protocols for the measurement of visceral or intrathoracic adiposity (14), but these have been limited in the clinical setting owing to cost and radiation exposure. Some centers have developed and validated in-house semi- and full- automated software as part of research tools to calculate the epicardial fat volume from noncontrast-enhanced computed tomography (CT) (15). Although the epicardial fat may be an important measurement for identifying individuals at increased CVD risk (11, 12), the feasibility of intrathoracic fat compart- ment measurements obtained from clinically acquired contrast- enhanced chest MDCT scans using commercially available software has not been assessed. In this paper, we discuss the definitions of intrathoracic fat, its clinical significance, and the methodology of quantifying intrathoracic fat volume. RESEARCH ARTICLE ABSTRACT © 2017 The Authors. Published by Grapho Publications, LLC This is an open access article under the CC BY-NC-ND license ( ISSN 2379-1381 TOMOGRAPHY.ORG | VOLUME 3 NUMBER 1 | MARCH 2017 33

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