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Absorciometría de rayos X de doble energía en la
medición de la composición corporal:
fundamentación y estudios en Brasil
Flavia Fioruci Bezerra
Instituto de Nutrição
Universidade do Estado do Rio de Janeiro
Julio/ 2013
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Histórico
Dual-energy X-ray absorptiometry (DXA, antes DEXA)
Aparece no mercado - 1987
Substituto das técnicas
SPA (single photon absorptiometry) – 125I
DPA (dual photon absorptiometry) - 153Gd
Raios X - melhor resolução de imagens, maior precisão
e rapidez
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Histórico
Inicialmente desenvolvida para medir densidade
óssea detecção de osteoporose
última década – aumento significativo da
aplicação composição corporal
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DXA - Princípios
Atenuação, pelo corpo do paciente, de um feixe de
radiação gerado por uma fonte de raios X com 2
níveis de energia
Este feixe passa através do indivíduo na direção
antero-posterior e é coletado por um detector
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Pietrobelli et al, 1996
Princípios fundamentais: interação dos raios X com a
matéria
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Atenuação depende:
Energia dos raios
Natureza dos componentes que atravessam
Espessura do material
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Coeficientes de atenuação de materiais
homogêneos
Pietrobelli et al, 1996
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Coeficientes de atenuação
Podem ser utilizados para calcular a massa por
unidade de superfície de materiais homogêneos
irradiados com um nível específico de energia
corpo humano não homogêneo necessita
feixe com raios X de dupla emissão de energía
Pietrobelli et al, 1996
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Absorciometria por dupla emissão de raios X (DXA)
Diferentes coeficientes de atenuação em 2 níveis
de energia permitem a separação em 3
compartimentos:
Conteúdo mineral ósseo,
massa gorda
massa livre de gordura
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DXA - princípios
Massa
Corporal
Total
Massa
Gorda
Água
Proteína
Glicogênio
Mineral não ósseo
Mineral ósseo
Compartimentos
podem ser
agrupados…
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Massa
Gorda
Massa
Livre de
gordura
Massa
Gorda
Água
Proteína
Glicogênio
Mineral não ósseo
Mineral ósseo
DXA - princípios
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Massa
Gorda
Água
Proteína
Glicogênio
Mineral não ósseo
Mineral ósseoMineral
ósseo
Tecidos
moles
DXA - princípios
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Mineral
ósseo
Tecidos
molesMassa
Livre de
gordura
Massa
Gorda
Pixel de tecido mole
(sem osso)
Pixel de tecido ósseo
(tecido + osso)
DXA - princípios
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DXA - princípios
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gordura
tecido magro
osso
Pixel
tecido
mole
Pixel
tecido
ósseo
DXA - princípios
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Leitor 70KeV Leitor 40KeV
70.0 40.0
DXA – princípios
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Leitor 70KeV Leitor 40KeV
0.358 2.281
DXA – princípios
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Leitor 70KeV Leitor 40KeV
0.080 1.960
DXA – princípios
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DXA – a análise
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ROIsRegions Of Interest:
Delimitam área a ser
analisada
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MG+MM = tecido
Tecido+BMC = MCT
MM+BMC = MLG
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DXA – a análise
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BMC / área = BMD
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Kelly et al, 2009
DXA - Curvas de referência
% Massa gorda em homens e mulheres – NHANES (Hologic QDR4500A)
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DXA - Curvas de referência
% Massa gorda em crianças e adolescentes – NHANES (Hologic QDR4500A)
Kelly et al, 2009
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DXA - limitações
Não é portátil
Apesar da radiação – não recomendável para gestantes
Paciente imóvel – dificuldade com crianças
Curvas de referência ainda limitadas
Assume % constante de hidratação da MLG (73%)
Algumas evidências: superestima massa gorda em
indivíduos obesos e subestima em muito magros
Não diferencia MG visceral e subcutânea
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DXA – vantagens e aplicabilidade
exposição a radiação aplicável a diferentes
faixas etárias
Composição corporal total e em regiões
específicas
Rápido – 5 a 10 min
Requer mínimo preparo para o exame
Em comparação com CT e MRI mais barato,
mais disponível e menos invasivo
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Estudos no Brasil
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Estudos no Brasil
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Estudos no Brasil
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Estudos no Brasil
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Estudos no Brasil
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PHYSICAL EXERCISE IS ASSOCIATED WITH BETTER FAT MASS
DISTRIBUTION AND LOWER INSULIN RESISTANCE IN INDIVDUALS
WITH SPINAL CORD INJURY
Giselle Louise C. D’ Oliveira, Flávia A. Figueiredo, Magna Cottini Fonseca
Passos, Amina Chain, Flávia F. Bezerra, Josely Correa Koury
J Spinal Cord Med, 2013 (accepted)
The aim of the study was to compare total and regional body composition
and their relationship with glucose homeostasis in physically active and non-
active c- SCI individuals.
D’Oliveira et al, 2013
Estudos no Brasil
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Fat mass distribution obtained by DXA in non-physically active
and physically active spinal cord injured men
D’Oliveira et al, 2013
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Fat free mass distribution obtained by DXA in non-physically
active and physically active spinal cord injured men
D’Oliveira et al, 2013
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Fasting plasma
insulin
Fasting plasma
glucoseHOMA
r p r p r p
Total FM (%) 0.59 0.004 ns 0.58 0.004
Arms (%) 0.53 0.012 ns 0.51 0.015
Legs (%) ns ns ns
Trunk (%) 0.61 0.003 ns 0.59 0.004
Total FFM(%) -0.59 0.004 ns -0.58 0.004
Arms (%) -0.51 0.016 ns -0.49 0.020
Legs (%) ns ns ns
Trunk (%) -0.62 0.002 ns -0.59 0.003
Correlation between plasma insulin, glucose and HOMA with total and regional FM and FFM
Estudos no Brasil
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PHYSICAL EXERCISE IS ASSOCIATED WITH BETTER FAT MASS DISTRIBUTION AND LOWER
INSULIN RESISTANCE IN INDIVDUALS WITH SPINAL CORD INJURY
Giselle Louise C. D’ Oliveira, Flávia A. Figueiredo, Magna Cottini Fonseca Passos
Amina Chain, Flávia F. Bezerra, Josely Correa Koury
Objectives:The aim of the study was to compare total and regional body composition and their
relationship with glucose homeostasis in physically active and non-active c- SCI individuals.
Methods: Individuals with lesion level between C5-C7 were divided into two groups: physically
active (PA n=14; who practiced physical exercise for at least 3 months, 3 times/week or more,
minimum of 150 minutes/week): and non- physically active (N-PA n=8). Total fat mass (t-FM) and
regional fat mass (r-FM) were assessed by dual energy X-ray absorptiometry (DXA). Fasting
plasma insulin (FPI) was determined by ELISA. Results: PA group present lower (p<0.01) total fat
mass (t- FM), % and Kg, regional fat mass (r-FM), % and Kg, FPI levels and HOMA index, while
they had higher (p<0.001) total free fat mass (t-FFM), %, and regional free fat mass (r- FFM), %,
compared to the N-PA group. In the N-PA group, FPI and HOMA index were negatively (p<0.05)
correlated with FFM% (r=-0.71; r=-0.69, respectively) and positively correlated to trunk-FM (r=0.71,
r=0.69, respectively) and trunk-FM:t-FM (kg) ratio (r=0.83, r=0.79, respectively). Conclusion:
Physical exercise is associated with lower t-FM, r-FM and insulin
resistance, which could contribute to the decrease of the risk of
cardiovascular and metabolic conditions in c-SCI individuals.
J Spinal Cord Med, 2013 (accepted)
Estudos no Brasil
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Composição corporal da mãe
concentração de
leptina no leite materno
composição corporal do bebê
Rezende, et al , a ser apresentado no ICN 2013
INFANT BODY COMPOSITION IS INFLUENCED BY BREAST MILK LEPTIN CONCENTRATIONS
Rezende, EP; Chain, AC; Diogenes, MEL; Taveira, MFSS; Normando, P; Bezerra, FF.
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Características n Média ± DP Minimo - Máximo
Nutriz
Idade (anos)* 55 17,4 ± 1,3 14,0 - 19,3
Ganho de peso gestacional (kg) 43 13,8 ± 6,0 5,7 - 36,5
Peso (kg)* 55 60,6 ± 12,9 42,0 - 109,5
Estatura (cm)* 55 1,59 ± 0,62 1,48 - 1,71
IMC (kg/m²)* 55 23,7 ± 4,3 15,8 - 38,4
Retenção de peso pós-parto (kg) 39 5,2 ± 6,1 -7,4 - 27,8
Bebê
Peso ao nascer (kg) 55 3,241 ± 0,539 2,050 - 4,980
Comprimento ao nascer (cm) 55 48,5 ± 2,7 43,0 - 54,0
Idade (dias)* 55 32,6 ± 10,4 10,0 - 58,0
Peso (kg)* 55 4,150 ± 0,654 2,400 - 5,380
Comprimento (cm)* 55 54,0 ± 2,6 47,3 - 58,5
Características gerais das nutrizes e seus bebês
*Dados obtidos no dia da avaliação pós-parto
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0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
20 30 40 50 60
Lep
tin
a leit
e (n
g/m
L)
Gordura total (%)
r = 0,54
p = 0,001
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Associações entre a composição corporal do bebê e
as concentrações de leptina no leite materno
Variáveis na criança Leptina leite
r p
Peso do bebê no 1º mês de
lactação -- --
% Gordura 0,43 0,022
Massa Gorda (kg) 0,39 0,037
Dados obtidos por correlação parcial após ajustes pelo n° de dias pós-parto
(--) Valores não significativos
Rezende, 2012
composição corporal materna parece influenciar a concentração de leptina secretada no leite materno, que por sua vez pode ter implicações para o crescimento e desenvolvimento do bebe.
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possível influência negativa da massa gorda
sobre massa óssea
Limitação metodológica (equipamento) para a
análise nesses indivíduos
DXA MEASURES OF BONE MASS IN MORBIDLY OBESE YOUNG ADULT WOMEN
Crivelli, M; Chagas, G; da Silva, ITF; Waked, AM; Bezerra FF.
Crivelli et al, a ser apresentado no ICN, 2013
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Ferramenta espelhamento
Estima uma “metade” do paciente a partir da “metade” escaneada
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Mapeamento en colores basada en el % masa
grasa
Pontos de corte ajustáveis
para mapear regiões de
maior % massa gorda
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Resultados preliminares em 20 mulheres jovens:
Coluna lombar
Z score <-2.0 (abaixo do esperado para idade) em 4 muheres
Z score entre -1.0 e -1.9 em 6 mulheres
Necessário considerar possível interferência da gordura na análise de coluna lombar
Ainda assim, os resultados sugerem algum prejuízo da massa óssea nacoluna lombar
Crivelli et al, a ser apresentado no ICN, 2013
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Referências e links interessantes:
Andreolli et al. Radiol. Med. 114:286–300, 2009
Chen et al. J. Nutr. 137: 2775–2780, 2007.
Ellis KJ. Phys. Rev. 80: 650-671, 2000
Kelly et al. PLoS ONE 4(9): e7038, 2009.
Pietrobelli et al, Am. J. Physiol. 271:E941-951, 1996
Wang et al. Phys. Med. Biol. 55: 2619–2635, 2010
Department of Nutrition and Food Science – University of Vermont -
http://nutrition.uvm.edu/bodycomp
Sociedade Brasileira de Densitometria Clínica (SBdens) -
http://www.sbdens.org.br
International Society for Clinical Densitometry - http://www.iscd.org
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Muchas gracias!