Ultra Dual-Energy X-ray Absorptiometry (DXA): Accurate and Precise Quantitative Multi-compartment Body Composition

Ultra DXA: Accurate and Precise Quantitative Multi-compartment Body Composition

The central hypothesis is that the combination of measurements from 3D optical scans with standard DXA scans can be used to calculate 4 unique body composition compartments: water, fat, protein, mineral. This is significant because it will allow for accurate assessment of adiposity and functional protein status independent of hydration. The hypothesis is based on preliminary data collected demonstrating the use of thickness and dual energy X-ray measurements to calculate three-compartment breast composition.

This is a cross-sectional comparative technology study using a sample of convenience stratified by age, sex, and BMI. Following consent, each participant will undergo:

• 6 DXA whole body scans. The primary measure is bone mineral mass and body volume. DXA body volume is measured using equations from previous work that relate the fat, lean, and bone masses to individual volumes in an image pixel using the physical densities of the components and the know area of the pixel.
• Total body water measurement using standard deuterium dilution methods. The primary measure is total body water in liters.
• Body volume measurement using air displacement plethsymography. The primary measure is volume in liters.
• Whole body 3D optical surface scans. The primary measures mesh points that make up a point cloud of the surface of the body. Approximately 500,000 mesh points are used and placed on the surface of the participants body image. The variation of the location of these mesh points can be described using Principal Component Analysis (PCA). In addition, the 3D optical scans can be used to measure the thickness of the body along the path of each X-ray that goes through the body resulting in a tissue thickness for each DXA image pixel.
• Bioelectrical impedance analysis (BIA). The primary measure is percent body fat, and total body water.
• Physical anthropometry. The primary measure is waist circumference.

Inclusion Criteria:

• ambulatory
• tolerate lying on their back on a table for 20 minutes
• less than 250 lbs
• tolerate standing and holding still for 1 minute

Exclusion Criteria:

• cannot stand for several minutes
• cannot lie down on a table for 10 minutes
• over 250 lbs