Biology Reference
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FIGURE 14.6 DEXA scanning of femur with rice as soft-tissue equivalent.
subtracted the age of the decedent from the scanning date to arrive at a birth date that was
entered into the computer. To standardize the amount of radiation in each scan, the weight of
the individual was set to 90 pounds, thus using the “thin mode” setting of the machine. This
is consistent with a soft-tissue thickness of 12 cm, as suggested by the manufacturer. See
Figure 14.6 . If we reported a higher body weight, the machine would expect more soft-tissue
equivalent material over the bone and would abort the scan. This had no bearing on the
results except for Z-scores because the Z-scores are calculated in comparison to individuals
of the same age, sex, height, and weight. This method, however, maintained a constant level
of radiation to ensure an accurate reading through each scan. This aspect of the research
differs from previous research with living subjects because the DEXA scanner must accom-
modate different tissue thicknesses for obese and emaciated individuals, which may reduce
the accuracy of comparisons in living individuals between these two body mass extremes.
Dual energy X-ray absorptiometry machines are designed to scan living individuals with
both soft and hard tissues. If only bone is present, the machine would abort a scan. To avoid
this, the bone was placed at the bottom of a plastic container that was filled with dry white
rice to a depth of approximately 12 cm over the proximal end of the bone only. The rice serves
as a human soft-tissue density equivalent for the DEXA scans, as per GE, the manufacturer of
the DEXA Lunar scanner . The average density of human soft tissues, both lean and fat
combined, is approximately equivalent to dry rice. A precedent for this method was created
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