Lecture 5 - 8/31/2010 Objectives Type II Approaches:...

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Unformatted text preview: 8/31/2010 Objectives Type II Approaches: MultiMulti-component Models Present Present 3C and 4C models The The advantage of multi-component over multi2C models Assumptions Assumptions Overview Overview of DXA Session #5 Tuesday September 7th, 2010 Reference Reference Man Models 2C Models vs. Multi-component MultiModels 2C models Have Have the greatest number of assumptions Have Have the most error MultiMulti-component models Reduce Reduce the number of assumptions Reduce Reduce error 2C 4C 3C 3C MultiMulti-component Models: 3C Model with “Water” The The 3 component (3C) model based on reference man Molecular Molecular (Chemical) Level (level 2) Water W ater is measured Protein Protein and Mineral are combined 3C model with “Water” Fat = 2.118 − 0.78 W − 1.354 Db Assumptions: Assumptions: Constant Constant proportions between bone and minerals Proportions Proportions are the same as reference man 1 8/31/2010 MultiMulti-component Models: 3C 3C model with “LST” Mineral Mineral is measured Water W ater and Protein are combined to create “Lean Soft Tissue” Assumptions: Assumptions: Constant Constant proportions of water and protein Proportions Proportions are same as reference man MultiMulti-component Models: 4C 4C model Water W ater and Mineral are measured Assumption: Assumption: Proportion Proportion of protein is constant Fat = 2.559 − 0.734W + 0.983M − 1.841 Db Fat = 6.386 − 3.961M − 6.090 Db 5C model 1 f W P Mo Mc = + + + + Db Df DW DP DMo DMc Db = body density f = proportion of body that is fat proportion Df = density of fat W = proportion of ffm that is water proportion DW = density of water P = proportion of ffm that is protein proportion DP = density of protein Mo Mo = proportion of ffm that is osseous mineral DMo = density of osseous mineral Mc Mc = proportion of ffm that is non-osseous mineral nonDMc = Density of non-osseous mineral non- Dual Energy X-Ray Absorptiometry X(DXA/DEXA) Utilizes Utilizes high/low X-ray Xenergies Energies Energies are attenuated when they pass through tissue Attenuation Attenuation R-values RF = fat; RL = lean soft tissue; RM = mineral Values Values used to calculate % of body that is fat, lean soft tissue, and mineral What multi-component model is DXA based on? DXA Output DXA Output 2 8/31/2010 DXA Output DXA Applications: Total Total bone mineral Total Total body mineral Multicomponent Multicomponent models Regional Regional bone density risks risks for fractures (osteoporosis) Muscle Muscle mass = arms + leg lean soft tissue = appendicular muscle mass • skeletal muscle mass (sarcopenia) (sarcopenia) Regional Regional fat and fat distribution Body Body fat content (obesity) Total Total body mass Limitations of DXA Soft Soft tissue composition is estimated from only ~60% of the body Estimates Estimates vary between different company’s machines (Lunar vs Hologic) Estimates Estimates vary between different technologies (pencil-beam vs fan-beam) (pencilfanfrom same company Review Review What W hat is/are the advantage(s) of using a multimulticomponent model over a 2C model? What W hat is/are the main assumption(s) associated with multi-component models? multiWhat W hat part does reference man play in these assumptions? DXA DXA is based on what model? What W hat does tissue do to X-rays? How is this Ximportant to what DXA does? What W hat are some to the applications and limitations of DXA? From From previous lecture, how does the SEE of DXA compare to other methods? 3 ...
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