Magnetic resonance techniques for fat quantification in obesity

As the prevalence of obesity and its comorbidities continue to rise in the United States and worldwide, robust imaging techniques and accurate post-processing strategies are critically needed to accurately quantify the distribution of fat in the human body. Magnetic resonance imaging and spectroscopy provide a wide array of sensitive methods to assess and characterize fat in storage locations such as white adipose tissue depots and “high-health-risk” ectopic sites such as organs and muscles. Quantitative fat measurements provide useful information to investigators in preventive medicine who monitor the efficacy of dietary, exercise, and surgical interventions to combat weight gain and obesity in longitudinal studies. They are also useful to clinicians who study the implications of steatosis and the pathophysiology of fat. The primary aim of this paper is to provide a technical review of state-of-the-art proton magnetic resonance methods in human body fat quantification. The paper will emphasize the fundamental principles with which several magnetic resonance techniques differentiate lean (water-dominant) and fatty (fat-dominant) tissues and illustrate with examples how each method can be appropriately used for fat quantification. The paper will also briefly summarize post-processing procedures that are currently in practice for extracting quantitative fat endpoints, such as adipose tissue depot volume and percent fat content in organs. Lastly, given its increased attention in recent literature, the paper will discuss progress in the imaging of human brown adipose tissue.