Three-D Image Reconstruction

The concept of central obesity, or visceral adiposity, was first suggested as an adverse health factor for coronary artery disease as early as 1950, but has only been validated as an important marker for the development of the array of obesity-related medical conditions collectively known as the metabolic syndrome in the last decade. With the advent of computerized tomography (CT) and magnetic resonance imaging (MRI), the significance of visceral “intraabdominal” obesity (rather than subcutaneous fat storage) has been documented in an increasing number of body composition studies.

This apple-shape pattern of intraabdominal obesity, although correlated with the amount of total body fat, body mass index (BMI), and subcutaneous fat in an individual, is unique in that it alone is the source of body fat that has been shown to influence the comorbidities associated with obesity and the metabolic syndrome. In fact, previous studies have shown that even among men of healthy BMI, the amount of visceral fat is correlated with increased prevalence of insulin resistance, hypertriglyceridemia, hypertension, and coronary artery disease—all hallmark markers of the metabolic syndrome. While it is generally thought that women tend to carry the majority of their excess adipose tissue in their thighs and hips, rather than centrally, women do indeed show similar patterns of developing symptoms of the syndrome in direct correlation to the amount of intraabdominal fat that they possess.

Thus, the emergence of research techniques that can accurately access total body composition, measure body fat distribution, and quantify the amount of visceral fat can be profoundly appreciated. The technological advancements of the past decade—particularly in the improvements of CT and MRI scanners—has allowed for greater accessibility of CT and MRI outside the realm of clinical medicine, and a grand impact on body composition research.

Both CT and MRI technology have allowed for the production of three-dimensional (three-D) images. Until their development, body composition analysis by way of radiogrametry and conventional X-rays have been limited to fuzzy two-dimensional images. The three-D image reconstruction offered by CT and MRI scanning allows for three-D tissue volume measurements and the production of sharp contrast images with clearer tissue boundaries. To date, none of the other competitive technologies being explored, such as ultrasound, has been able to assess tissue composition three dimensionally as accurately as in CT and MRI.

CT and MRI technology is founded in a two-stage image reconstruction strategy. The first task at hand is to accurately gauge the amount of specific tissue that is expressed in an individual image (in cm²). Second, this flat image's area is superimposed on various slices of itself to calculate a total volume (in cm³). This is one of the great advantages in using three-D image reconstruction, as it allows for [Page 743]the cross-sectional imaging that can compute areas and volumes of tissue structures inside of body cavities. As in brain and heart volume calculations quantified by MRI and CT for clinical purposes, visceral adipose tissue has also been accurately quantified using this technique. Another important advantage to this technology is that it can easily calculate whole-body estimates of tissue-level composition, whereas competing technologies are currently limited to making only regional measurements. It is worth noting that today, three-D image reconstruction technologies are becoming greatly accessible globally; virtually all major medical research centers in the United States have both a CT and MRI scanner capable of full-body composition analysis, and many developing nations have increasing access to one, if not both, of these tools at major hospitals.

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