During routine measurements of body composition using a 153Gd
based dual photon densitometer, it was observed that negative
values were being obtained for the body fat fraction in some
adults, in children and in small animals. In these three groups,
there appears to be a body size dependent error whereby the
measured fat fraction becomes increasingly negative as subject size
becomes smaller.
The fat fraction is derived from relating the measured mass
attenuation coefficient of soft tissue to an internal calibration
based on the use of water and lard as substitutes for muscle and
fat. To investigate whether this procedure for instrument
calibration is the cause of the fat fraction errors, soft tissue
phantoms which contained known amounts of fat, water and protein
were prepared. Over the range of fat fractions used, accurate
results were obtained.
By using prepared soft tissue and water phantoms it was
established that the measured fat fraction incorrectly became
progressively smaller as object thickness decreased and incorrectly
increased with object thickness. However, accurate measurements
were obtained if the equivalent tissue thickness is greater than
9 em and less tnan 16 em of water. Equally reproducible
measurements are obtained at all thicknesses investigated.
When dual photon measurements of body composition in 13 adolescent females were compared with measurements obtained from
skinfold thicknesses or bioimpedance, there was good agreement
between techniques but dual photon results demonstrated a broader
range of variation with body size. Comparisons between dual photon
absorptiometry derived body composition measurements of 52 male
athletes with results obtained from under water weighing allowed
for derivation of a simple correction factor for the accuracy
errors due to body size. / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22640 |
| Date | 04 1900 |
| Creators | Gordon, Christopher L. |
| Contributors | Webber, C.E, Physics |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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