Validation of the iNSiGHT Dual Energy X-ray Absorptiometry (DXA) Scanner

Mice either received a standard diet offered by Purima Lab Diet (#5001 Laboratory Rodent Diet) ad libitum or a high fate diet offered by Diet Induced (DIO) Rodent Diet with 45% energy from fat, dyed red (Scott Pharma #58125), provide ad libitum. On day 56 the animals were euthanized by carbon dioxide asphyxiation or inhaled anesthetic isoflurane overdose in accordance with accepted AVMA guidelines. Animals were then placed in the DXA scanner in the prone position center of the measuring plate (16.5 x 25.5 cm scan area). Spine was straightened and paws were laid out from the body. A 25 second dual energy scan was administered with a 60 kV low energy, 80 kV high energy at 0.8 mA. The X-ray exposure was 5 seconds at each energy level, and there was 15 seconds required for image and data processing. Images include an X-ray image, a bone mineral density (BMD) image, and a colour image (lean mass in green, and fat mass in red) for each animal (Figure 2). These measurements were repeated in triplicates for accuracy. Animals were then weighed on an electronic scale with an accuracy down to 10 mg. Gravimetric and chemical extraction techniques (Soxhlet) were used as criterion methods for the determination of body composition; ash content was determined by burning at 600oC for 8 hours. Then Pearson two-tailed correlation was determined to compare the numbers calculated via gravimetric/chemical extraction/ashing/scale weight versus the DXA measurements.

Results

The iNSiGHT DXA scanner has superior correlation to the actual body composition, highlighting the precision of the dual energy scan and its algorithms. The Pearson two-tailed correlation revealed strong correlation between gravimetric/chemical extraction/ashing/scale weight and DXA measurements for total weight, BMC, fat mass and lean mass (Figure 1). Mean r value for total weight in grams (g) is 0.9996 (P<0.0001). Mean r value for bone mineral content (BMC) in grams (g) is 0.8342 (P<0.0001). Mean r value for total fat mass in grams (g) is 0.9872 (P<0.0001). Mean r value for lean mass in grams (g) is 0.9360 (P<0.0001). Thus, the DXA measurements versus gravimetric/chemical extraction/ashing/scale weight were determined to be highly correlated. This is the only scanner on the market that has this complete set of correlated values with a proper cross reference in ashing, chemical carcass, and weight analysis.