Technical Validation of Lunar iDXA (GE Healthcare) Visceral Fat Tool
Condition: Obesity
Study type: Observational

Summary: 
      The goal of this project is to compare visceral fat measurements derived from Lunar iDXA
      total body scans and from Computed Tomography (CT) scans of the abdominal region.
    

Detailed description: 
      Obesity is one of the greatest public health challenges of the 21st century. The World Health
      Organization (WHO) estimates for 2005 indicate approximately 1.6 billion adults are
      overweight (body mass index (BMI) > 25 kg/m2), with 400 million being characterized as obese
      (BMI > 30 kg/m2). By 2015, the WHO projections predict that the populations of overweight and
      obese adults will increase to 2.3 billion and 700 million respectively. The major determinant
      of obesity is the energy imbalance between calorie intakes and expenditures, which can be
      ascribed to a global dietary shift in favor of energy-dense foods particularly rich in fat
      and carbohydrates, and a global trend towards sedentary behaviors.

      Body fat distribution and abdominal fat in particular is correlated with increased risk of
      cardiovascular disease, diabetes, hypertension, nonalcoholic fatty liver disease, cancer, and
      total mortality. It is therefore important to develop minimally invasive clinical tools to
      assess visceral fat. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) represent
      the gold standards for the quantification of visceral and abdominal fat. However, the
      analytical cost and the limited availability of these instruments for large-scale screenings
      have encouraged the development of alternative methods based on cost effective and widely
      distributed technologies. Dual-energy x-ray absorptiometry (DXA) is a promising technology to
      fill this gap. DXA is being used increasingly as a rapid, precise, and accurate method for
      measurement of regional and total body composition in both clinical and research settings.
      Total body assessment using DXA provides a unique capability of non-invasive measurement of
      skeletal bone status, as well as lean and fat tissue components including percent fat, lean
      tissue mass, and the android (waist)/gynoid (hip) fat ratio. The DXA technology is well
      suited to large-scale screening for assessing body composition and fat distribution as a part
      of a global assessment of metabolic status.

      A recent study of a cross-sectional sample of 5440 US adults participating in the NHANES
      surveys 1999-2004 showed that 29.2% of obese men and 35.4% of obese women (a total of
      approximately 19.5 million US adults) are metabolically healthy, (sometimes referred to as
      "uncomplicated" obesity), whereas 30.1% of normal-weight men and 21.1% of normal-weight women
      (a total of approximately 16.3 million US adults) exhibit clustering of two or more
      cardiometabolic abnormalities. This study concluded that additional research is required to
      understand the physiological mechanisms underlying these differences. Another recent study of
      more than 3000 participants drawn from the Framingham Heart Study showed that both
      subcutaneous fat and visceral fat were correlated with metabolic risk factors. However, only
      the effects of visceral fat remain significant after adjusting for common anthropometric
      indices such as waist circumference and BMI. The issues surrounding cardiometabolic risk
      among different phenotypes along with the increased risks associated with visceral fat
      suggests the need to measure visceral adipose tissue in a diverse population.The gold
      standard, CT, is not a practical solution due to the cost and radiation exposure associated
      with the measurement. Therefore, it is important to develop a low-cost, low-radiation
      screening method for measuring visceral adipose tissue.

      The present study aims at measuring abdominal fat distribution (CT scan and Lunar iDXA) in
      120 adults. These data provide the possibility to validate a new method for measuring
      abdominal fat distribution (visceral versus subcutaneous fat) against the gold standard, CT.
      If validated, such a protocol based on Lunar iDXA could offer a rapid and cost effective
      diagnostic tool for fat distribution assessment of individuals as a basis for future
      personalized and health care programs.
    

Intervention name(s): Visceral fat mass measurement
Intervention type(s): Device
Intervention description(s): Total body DXA measurement, Abdominal CT scan
Other intervention name(s): Lunar iDXA (GE Healthcare)
Observational model: Cohort
Time perspective: Cross-Sectional
Sampling method: Probability Sample
Study population: 
        Age between 18 and 90 BMI between 18.5 and 40
      
Keywords: Abdominal Fat; Visceral Fat; Subcutaneous Fat; Dual-energy x-ray absorptiometry; DXA; Computed Tomography; CT; Body Mass Index; Body composition; Percent fat; Waist circumference; Hip circumference