![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
Departments of Pediatrics, Obstetrics and Gynecology, and * Computing and Information Technology, Wayne State University, Detroit, MI
1To whom correspondence should be addressed. E-mail: wkoo{at}wayne.edu
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
0.99 for all comparisons. The SD of residuals for DXA prediction of scale weights (with and without covering) were 168 and 157 g, respectively, and were 27, 8.8, 122 and 72 g for the prediction of carcass ash, calcium, lean and fat tissue content, respectively. We conclude that rapid scan acquisition, accurate and precise prediction of scale weight and components of body composition would support the use of fan beam-DXA for body composition studies in growing humans or animals.
KEY WORDS: • pigs • ash • calcium • fat • lean tissue
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
). Extensive validation data for the measurement of bone (2
–4
) and soft tissue (3
,4
) mass have been reported with the use of pencil beam-DXA technique using the piglet model. A newer generation of DXA employing the fan beam technique offers potential improvement for body composition measurements because of the 5- to 10-fold faster scan acquisition and superior spatial resolution compared with the pencil beam technique. The potential error from the magnification inherent in the fan beam geometry for body composition measurement has been substantially resolved by alterations in the analytic algorithm for scans of adults. Equivalency of bone mineral density, lean and fat mass measurements with fan beam-DXA technique has been confirmed by cross-calibration with other criterion methods including pencil beam-DXA, the four-compartment model and multislice tomography scans (5
,6
). However, no data exist concerning whether fan beam-DXA scans can be adapted for body composition assessment in young children and infants because their body composition differs substantially from that of adults. In addition, the currently available software for the fan beam-DXA measurement of infants and young children is based on the algorithm employed for the pencil beam technique (2
,7
) and has not been validated for use with the fan beam instrument. We therefore used a piglet model to validate the measurement of body composition of small subjects using the fan beam-DXA technique. |
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
All measurements were performed using a whole-body densitometer (Hologic QDR 4500A, Hologic Waltham, MA) operated in the fan-beam mode. Each piglet was placed on a cotton blanket in the prone position with front and hind limbs extended. The long axis of the piglet was positioned at the midline of the platform and the snout 
5 cm from the cranial end of the platform (2
). Each piglet was covered with a cotton blanket and a disposable diaper was used in larger piglets to prevent soiling. Each piglet was sedated with sodium pentobarbital (24 mg/kg) and sodium thiopental (6 mg/kg) and duplicate scans obtained with a commercially available experimental software from the instrument manufacturer. Scan acquisition required 2–3 min depending on the size of the piglet. Additional manipulation of the algorithm was performed post-hoc to improve the relation between DXA measurements and the body composition based on chemical analysis of the carcass. Each scan was reviewed by the same operator (M.H.) to ensure that no movement artifact was evident (8
) before scan analysis.
With our densitometer, the typical entry radiation exposure measured with a Victoreen model 450p radiation monitor (Inovision radiation measurements, Cleveland, OH) during an infant whole-body scan showed a maximum dose of 7 µSv (1 µSv = 0.1 mrem). The radiation scatter at 66 cm from the scanner was not significantly different from background after 10 min of measurement.
Animal study.
Domestic swine piglets (n = 14) were obtained commercially (J&M Farms, Lansing, MI) and housed in the institutional animal facility for a minimum of 2 d to allow acclimation before the study. Each piglet was weighed using an electronic scale (Seca, Toledo Scale Company, Toledo, OH) immediately before DXA scanning and killed immediately upon completion of the in vivo study procedures. The study protocol was approved by the Animal Investigation Committee at Wayne State University.
Ashing.
Piglets were stored frozen at -20°C immediately after killing until processing for tissue analysis. The whole carcass of each piglet was placed in a clean aluminum pan of known weight and dried overnight in a convection oven (Precision Scientific, Chicago, IL) at 60°C. The abdomen, thorax, and skin of the limbs were cut open to facilitate drying. The temperature was then raised to 105°C until a constant weight was reached over a 24-h interval. If the carcass was larger than the drying pan, the frozen carcass was sawed into 2 or 3 portions and all fragments from the sawing were recovered, added to one of the portions and processed as above.
Before ashing, the dried piglet was broken into small pieces with heavy-duty stainless steel cutters (Fisher Scientific, Pittsburgh, PA) and homogenized at low speed in a stainless steel blender (Waring Products, New Hartford, CT) with small amounts of type I water with 18 M
-cm resistivity until a smooth paste was reached. All residual fragments from the pan were rinsed with type I water into the blender to ensure homogenization of the complete carcass. The blender was rinsed with type I water to ensure complete recovery of the paste. The stepwise drying procedure was repeated with intermittent mixing of the paste with a teflon-coated spatula until constant weight for 24 h was reached. For large piglets, the dried portions were homogenized as above then combined and mixed in one pan using a Teflon-coated spatula. Additionally, dried homogenate from each piglet was placed in individual polypropylene bag and then vigorously shaken before storage at -70°C until further analyses.
To obtain the ash weight, the homogenate in the polypropylene bags was vigorously shaken; three aliquots were then taken from separate depths of each bag and placed in separate acid-soaked, prewashed, dried and preweighed quartz crucibles for ashing. The stepwise drying procedure was repeated until constant weight was achieved. The crucibles were then placed in a computer-controlled temperature-regulated muffle furnace (Isotemp muffle furnace, 650 series, Fisher Scientific, Pittsburgh, PA) with the temperature raised stepwise to 500°C and maintained for 72 h. After a period of controlled cooling to 105°C, each crucible was reweighed. This procedure was repeated until two consecutive weight measurements (Mettler Instruments, Hightstown, NJ) were within 1 mg at 12 h apart. The average CV of triplicate samples from each piglet for ash measurement was 2.7%.
Chemical analysis.
All chemical analyses were performed on three aliquots of dried homogenate from each piglet obtained as described above. The drying procedure also was repeated before chemical analysis.
Nitrogen was measured by the micro-Kjeldahl method (9
) from 0.5 g of dry tissue homogenate. In our laboratory, the recovery of nitrogen using the National Institute of Standards and Technology (NIST, U.S. Department of Commerce, Gaithersburg, MD) certified standard reference material was 101.7 ± 2.06%. The average CV of nitrogen measured from triplicate samples from each piglet was 2.4%. Total body content of crude protein was determined as total carcass nitrogen x 6.25, and the lean mass was calculated as the crude protein content plus total body water. The latter was taken as the difference between wet and dry weight.
Fat was measured as total lipid extracted from 5 g of dry tissue homogenate using various proportions of chloroform, methanol and water (10
). The extraction procedure was aided with sonication. The extracted fat was quantified after evaporation and drying until two constant weights to the nearest mg were reached. In our laboratory, the recovery of lipid was 98.5 ± 1.46% from commercial vegetable oil. The average CV of total lipid measured from triplicate samples for each piglet was 2.1%.
Calcium was determined from three aliquots of the ash for each piglet. Each aliquot of ash was dissolved in nitric acid. Calcium was measured by atomic absorption spectrophotometry (11
) using NIST-certified standard reference calcium solutions. In our laboratory, the CV for calcium measurements was <1%. The measured calcium content of the NIST-certified bone ash was 38.98 ± 0.71% by weight, compared with the expected values of 38.18 ± 0.13%. The average CV of calcium measured from triplicate samples for each piglet was 1.1%.
Statistical analyses.
Repeated-measures ANOVA was used to determine the equivalence of the duplicate DXA measurements and the relationship among specific measurement from each DXA scan (total body weight, bone mineral content, lean mass and fat mass) with the corresponding validation parameters (scale weight of piglets with and without covering, carcass ash or calcium content, chemically derived lean and fat mass).
Regression analysis was used to determine the relationship between average measurements of various parameters from duplicate DXA scans with the scale weight of the piglets and various components of body composition based on chemical analysis of the piglet carcass. The intraclass reliability coefficient was calculated to determine the level of agreement between specific DXA measurements and the corresponding validation measurements stated above. The precision was calculated as the SD of the residuals.
All statistical tests were performed using SPSS 10.0 for Windows (SPSS, Chicago, IL), and a P-value of <0.05 indicated significant difference.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
. Of the 28 scans performed for this study, one scan was inadvertently deleted during scan analysis, but the data from 27 scans were available. Repeated-measures analyses showed no significant differences in any parameter measured between duplicate DXA scans. All measurements derived from duplicated DXA scans were significantly correlated (P < 0.001) with adjusted r2 values for DXA total body weight and lean mass at 1.000, for bone mineral content at 0.998, bone area at 0.999, bone mineral density at 0.992 and for fat mass at 0.955.
|
A–F. There was a significant systematic effect of covering (i.e., intercept becomes significantly different from zero) on the relationship between DXA total body weight and scale weights. The relationship of bone mineral density with carcass ash and calcium showed an adjusted r2 of 0.937 and 0.950, respectively; the intercepts were significantly different from zero (P < 0.01). Intraclass reliability coefficient among the values obtained from each of the duplicate DXA scans with the dependent variables scale weights, ash weight, calcium, lean and fat mass were 0.9997, 0.9938, 0.9996, 0.9941 and 0.9941, respectively. The SD of the residuals for the prediction of scale weight (with or without covering), ash weight, calcium, lean and fat mass were 167.7, 157.4, 27.1, 8.8, 122.3 and 71.6 g, respectively.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
This is the first report demonstrating that the fan beam-DXA technique can be adapted for the measurement of body composition in small subjects. The scan acquisition time for the fan beam technique is 75–80% less than the 12–15 min required for scanning the larger infant using the pencil beam technique, thus lowering the risk for movement artifacts (8
). Manufacturer specifications of the fan beam compared with the pencil beam instrument show that smaller point resolution (1.95 mm vs. 2.04 mm) and greater sampling per line (327 vs. 246) would support the improved resolution for the fan beam system, the potential for better edge definition among tissue interface and better overall performance in DXA measurements. In this study, the range of the size of piglets studied was about three fold greater than that reported previously for validation of pencil beam-DXA (2
–4
) and covers the greater weight ranges expected during infancy and early childhood.
We demonstrated that fan beam-DXA measurements predict the scale weight of the animals and chemical body composition with high degree of accuracy and precision. The excellent accuracy of the fan beam-DXA technique was supported by the extremely high adjusted r2 in the relation between DXA measurements with the respective scale weights and chemical component weights from carcass analysis. The excellent precision was supported by extremely high intraclass reliability coefficient and low residuals. DXA measures the total mass of the subject including any clothing and covering. For an adult, the mass of light street clothing is a small fraction of the body weight and is of small consequence in the measurement of body composition. However, the amount of clothing is proportionally a much greater fraction of the infant’s weight; thus, consistency in the amount of clothing or covering used for infant studies is critical to interpretation of DXA measurements, i.e., the less clothing/covering used during the DXA scan, the less potential interference with body composition measurements. This information is critical for all clinical studies especially those involving small subjects.
DXA bone mass measurement as bone mineral content was validated against both carcass ash and calcium contents. In contrast to the underestimation of ash content reported for the pencil beam-DXA (2
–4
), we have altered the algorithm in fan beam-DXA to reflect higher ash content in the bones (12
). We did not measure true density of the carcass or its components and did not perform validation studies directly for bone mineral density for the following reasons: 1) DXA provides a projected areal bone mineral density, which is not a true density measurement (13
); and 2) it is generally agreed that bone mineral content is a better representation of bone mass in growing subjects (14
). The fact that the intercept of the DXA bone mineral density prediction equations for carcass ash and calcium is significantly different from zero is consistent with the presence of threshold detection limit in the DXA determination of bone mineral density. Nevertheless, our data show that DXA bone mineral density is also predictive of carcass ash and calcium content, albeit with relatively lower accuracy and precision than the predictions based on DXA bone mineral content.
Our data show that fan beam-DXA can be used to predict soft tissue content, specifically chemical lean and fat mass. The accuracy and precision of DXA lean mass to predict chemically derived lean tissue mass are equal to that for DXA prediction of scale weight. The predictive ability of fan beam-DXA for fat mass is much improved compared with that reported for pencil beam-DXA, but its ability to measure a very low quantity of fat mass (100 g) remains questionable. However, this is of little clinical concern because all infants have much greater amounts of body fat except for the very-low-birth-weight infants during the immediate newborn period. The precision for the prediction of chemical fat mass remains the lowest compared with all other measurements of body composition, and is consistent with that reported for pencil beam-DXA (3
,4
). In any case, the accuracy and precision of fan beam-DXA measurement of body composition are more than adequate for studies of rapidly growing organisms including infants and young children because the reported increase during infancy for body weight and lean mass is three- to fourfold, and for bone and fat mass is four- to sixfold (7
,15
).
We conclude that fan beam-DXA measurements can be adapted to predict scale weight, body contents of ash, calcium, lean and fat tissues, with similar or better accuracy and precision than that reported for the pencil beam technique. Our validation measurements also were performed over a greater range of body sizes and body composition values compared with the pencil beam technique. Thus, coupled with the faster scan acquisition, the fan beam-DXA appears to be well suited for body composition studies in growing humans and animals.
|
ACKNOWLEDGMENTS |
|---|
Manuscript received 31 October 2001. Initial review completed 3 January 2002. Revision accepted 23 February 2002.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
1. Koo, W.W.K. (2000) Body composition measurements during infancy. Ann. N.Y. Acad. Sci. 904:383-392.[Medline]
2. Koo, W.W.K., Massom, L. R. & Walters, J. (1995) Validation of accuracy and precision of dual energy X-ray absorptiometry for infants. J. Bone Miner. Res. 10:1111-1115.[Medline]
3.
Picaud, J. C., Rigo, J., Nyamugabo, K., Milet, J. & Senterre, J. (1996) Evaluation of dual energy X ray absorptiometry for body composition assessment in piglets and term human neonates. Am. J. Clin. Nutr. 63:157-163.
4. Fusch, C., Slotboom, J., Fuehrer, U., Schumacher, R., Keisker, A., Zimmermann, W. & Moessinger, A. (1999) Neonatal body composition: dual energy X ray absorptiometry, magnetic resonance imaging, and three dimensional chemical shift imaging versus chemical analysis in piglets. Pediatr. Res. 46:465-473.[Medline]
5. Bouyoucef, S. E., Cullum, I. D. & Ell, P. J. (1996) Cross-calibration of a fan-beam X-ray densitometer with a pencil-beam system. Br. J. Radiol. 69:522-531.[Abstract]
6.
Salamone, L. M., Fuerst, T., Visser, M., Kern, M., Lang, T., Dockrell, M., Cauley, J. A., Nevitt, M., Tylavsky, F. & Lohman, T. G. (2000) Measurement of fat mass using DEXA: a validation study in elderly adults. J. Appl. Physiol. 89:345-352.
7.
Koo, W.W.K., Walters, J. C. & Hockman, E. M. (2000) Body composition in human infants at birth and postnatally. J. Nutr. 130:2188-2194.
8. Koo, W.W.K., Walters, J. & Bush, A. J. (1995) Technical considerations of dual energy x-ray absorptiometry-based bone mineral measurements for pediatric studies. J. Bone Miner. Res. 10:1998-2004.[Medline]
9. Association of Official Analytical Chemists (1995) AOAC official method 960.52. Microchemical determination of nitrogen. Micro-Kjeldahl method. Cunniff, P. eds. Official Methods of Analysis 16th ed. 1995:7 AOAC Washington, DC. Ch 12.
10.
Folch, J., Lees, M. & Sloane-Stanley, G.H.S. (1957) A simple method for the isolation and purification of total lipids from animal tissues. J. Biol. Chem. 226:497-509.
11. Association of Official Analytical Chemists (1995) AOAC official method 968.08. Minerals in animal feeds. Atomic absorption spectrophotometric method. Cunniff, P. eds. Official Methods of Analysis 16th ed. 1995:7-23 AOAC Washington, DC. Ch 4.
12. Brozek, J., Grande, F., Anderson, J. T. & Keys, A. (1963) Densitometric analysis of body composition: revision of some quantitative assumptions. Ann. N.Y. Acad. Sci. 110:113-140.
13. Tabensky, A. D., Williams, J., DeLuca, V., Briganti, E. & Seeman, E. (1996) Bone mass, areal, and volumetric bone density are equally accurate, sensitive, and specific surrogates of the breaking strength of the vertebral body: an in vitro study. J Bone Miner. Res. 11:1981-1988.[Medline]
14. Nelson, D. A. & Koo, W.W.K. (1999) Interpretation of absorptiometric bone mass measurements in the growing skeleton: issues and limitations. Calcif. Tissue Int. 65:1-3.[Medline]
15.
Koo, W.W.K., Bush, A. J., Walters, J. & Carlson, S. E. (1998) Postnatal development of bone mineral status during infancy. J. Am. Coll. Nutr. 17:65-70.
This article has been cited by other articles:
|
|
 |
|
  B. E Saelens, R. J Seeley, K. van Schaick, L. F Donnelly, and K. J O'Brien Visceral abdominal fat is correlated with whole-body fat and physical activity among 8-y-old children at risk of obesity Am. J. Clinical Nutrition, January 1, 2007; 85(1): 46 - 53. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. Koo Maternal calcium supplementation and bone accretion in infants. Am. J. Clinical Nutrition, October 1, 2006; 84(4): 943 - 943. [Full Text] [PDF]
|
|
|
|
 |
|
 W. W. K. Koo, M. Hammami, R. J. Shypailo, and K. J. Ellis Bone and Body Composition Measurements of Small Subjects: Discrepancies from Software for Fan-Beam Dual Energy X-Ray Absorptiometry J. Am. Coll. Nutr., December 1, 2004; 23(6): 647 - 650. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. T. Clandinin, B. Larsen, J. V. Aerde, and W. W. K. Koo Reduced Bone Mineralization in Infants Fed Palm Olein-Containing Formula: A Randomized, Double-Blinded, Prospective Trial Pediatrics, September 1, 2004; 114(3): 899 - 900. [Full Text] [PDF]
|
|
|
|
|
|
W. W. Koo Reply to LM Klevay Am. J. Clinical Nutrition, May 1, 2004; 79(5): 887 - 888. [Full Text] [PDF]
|
|
|
|
|
|
W. W. K. Koo, M. Hammami, and E. M. Hockman Validation of Bone Mass and Body Composition Measurements in Small Subjects with Pencil Beam Dual Energy X-Ray Absorptiometry J. Am. Coll. Nutr., February 1, 2004; 23(1): 79 - 84. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Chauhan, W. W. K. Koo, M. Hammami, and E. M. Hockman Fan Beam Dual Energy X-Ray Absorptiometry Body Composition Measurements in Piglets J. Am. Coll. Nutr., October 1, 2003; 22(5): 408 - 414. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. W. Koo, M. Hammami, and E. M Hockman Interchangeability of pencil-beam and fan-beam dual-energy X-ray absorptiometry measurements in piglets and infants Am. J. Clinical Nutrition, August 1, 2003; 78(2): 236 - 240. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. W. K. Koo, M. Hammami, D. P. Margeson, C. Nwaesei, M. B. Montalto, and J. B. Lasekan Reduced Bone Mineralization in Infants Fed Palm Olein-Containing Formula: A Randomized, Double-Blinded, Prospective Trial Pediatrics, May 1, 2003; 111(5): 1017 - 1023. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
