Reproducibility and validity of ultrasound for the measurement of visceral and subcutaneous adipose tissues

Abstract

Background

Ultrasound represents a low-cost and widely available field method for assessing visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) but its measurement properties are uncertain. The aim of the current study was to examine the reproducibility and validity of ultrasound to quantify abdominal fat compartments.

Methods

In two study centers, VAT and SAT thicknesses were quantified by ultrasound two times by two observers each among 127 adults aged 20–70 years. In a separate sample of 30 adults, the ultrasound method was validated by comparing VAT and SAT thicknesses with VAT and SAT areas at vertebrae L2/L3 as obtained by a single magnetic resonance imaging (MRI) slice.

Results

For VAT, the intra-rater reproducibility values for observers 1 and 2 were r = 0.996 (95% CI = 0.994–0.997) and r = 0.999 (95% CI = 0.999–0.999), respectively. For SAT, the intra-rater reproducibility values were r = 0.992 (95% CI = 0.989–0.994) and r = 0.993 (95% CI = 0.990–0.995), respectively. The inter-rater reproducibility values for VAT and SAT were r = 0.998 (95% CI = 0.997–0.999) and r = 0.990 (95% CI = 0.986–0.993), respectively. For VAT and SAT, the correlation coefficients between ultrasound and MRI measurements were r = 0.898 (P < 0.001) and r = 0.705 (P < 0.001), respectively.

Conclusion

Ultrasound provides reproducible and valid estimates of VAT and SAT and represents a useful method to assess abdominal fat in large scale epidemiologic studies.

Introduction

Obesity is a major public health problem, the prevalence of which has doubled since 1980 in the developed and many developing parts of the world [1]. Obesity is a strong determinant of type 2 diabetes, hypertension, stroke, and numerous other chronic diseases, including several types of cancers [2], [3], [4]. Emerging research has targeted the distribution of fat in the body. Abdominal weight gain is manifested in the visceral and subcutaneous tissues, with visceral adipose tissue (VAT) considered to be more pro-inflammatory than subcutaneous adipose tissue (SAT) [5]. SAT has an independent anti-atherogenic effect and is associated with a higher level of insulin sensitivity and a lower risk for developing type 2 diabetes and dyslipidemia [6], [7], [8], [9]. Currently, the gold standard for quantifying abdominal adipose tissue is computed tomography (CT) or magnetic resonance imaging (MRI). The use of these techniques in field settings is limited because of the associated costs, accessibility issues, contraindications, and possible adverse effects of radiation. Previous epidemiologic studies have used waist circumference (WC) and waist-to-hip ratio (WHR) to estimate abdominal fat and body fat distribution, respectively. However, those methods do not differentiate between VAT and SAT and therefore, cannot satisfactorily characterize body fat distribution patterns. A precise characterization of VAT and SAT is important for the assessment of risk of a host of major chronic diseases, such as cardiovascular disease, type 2 diabetes, and several types of cancer. Although ultrasound has been proposed as a suitable technique to accurately measure abdominal adipose tissue in research settings [5], [10], [11], [12], previous validation studies of ultrasound have reported inconsistent results [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. The aim of the current study was to evaluate an ultrasound-based quantification of VAT and SAT with regard to its feasibility, reproducibility, and validity.