EFFECTS OF VARIATIONS IN REGIONAL COMPOSITION ON SOFT-TISSUE MEASUREMENTS BY DUAL-ENERGY X-RAY ABSORPTIOMETRY

OBJECTIVE: To assess the effect of Variations in regional composition on the accuracy of dual-energy X- ray absorptiometry (DXA) in humans b y placing packets of lard, water and ground beef, to simulate fat, ver y lean tissue and high density lean material. on the thighs and abdome n. SUBJECTS : 28 healthy males and females (mean age: 25 y; mean % fat : 24.6%). METHODS: Up to six consecutive total body DXA scans (baselin e plus five scans with added packets) at 16 cm/s were performed on eac h subject (Lunar DPX-L, software version 1.3y). Eight conditions were examined: one lard packet (n = 18). two stacked lard packets, one grou nd beef packet and one water packet (all n = 10) alternately placed on the thighs and abdomen. Masses (kg) and percentage fats (% fat) of th e lard, water and ground beef packets were 1.45 and 90%, 2.80 and 4% a nd 1.80 and 24%, respectively. RESULTS: Differences between actual (ba seline plus packet) and measured composition were assessed using paire d t-tests (p < 0.05). Under all conditions except with two abdominal l ard packets, actual and measured total mass were similar (p > 0.05). P ercentage fat of one lard packet was significantly underestimated when placed on the abdomen (90% actual vs 52% measured). The % fat of two lard packets was underestimated when placed on the thighs (90% vs 77%) and abdomen (90% vs 47%) while the % fat of the water packet was over estimated in both locations. CONCLUSION: The Lunar DXA underestimates the % fat of lard placed over the abdomen moreso than when placed over the thighs and overestimates % fat of water in both locations indepen dent of thickness. Ground beef is accurately detected.