Description and evaluation of a method based on magnetic resonance imaging to estimate adipose tissue volume and total body fat in infants

The mysterious values of adipose tissue density and fat content in infants: MRI-measured body composition studies

Adipose tissue is a type of connective tissue composed of closely packed adipocytes with collagenous and elastic fibers. These adipocytes store triglycerides at a high percentage and the estimate of this amount is important for the calculation of body fat mass. For example, magnetic resonance imaging (MRI) measures adipose tissue volume, but adipose tissue density (fat content percentage and density) is required to calculate fat mass. However, in previously published studies, the conversion factor for white adipose tissue density varies from study to study. This paper aimed to investigate the different adipose tissue densities used as conversion factors to clarify differences between studies. Furthermore, we include a new proposal for adipose tissue density and fat content of infants based on the results of recent water-fat MRI studies. IMPACT: Magnetic resonance imaging (MRI) is one of the methods used to measure body composition in infants and the inherent density of tissue/organs is needed in order to calculate the mass of target organs and tissues. The conversion factor used for white adipose tissue density currently varies from study to study. This article includes a new recommendation for the adipose tissue density and fat content of infants based on the results of recent water-fat MRI studies.

Nutrition for the Extremely Preterm Infant

With advancements in the care of preterm infants, the goals in nutritional care have expanded from survival and mimicking fetal growth to optimizing neurodevelopmental outcomes. Inadequate nutritional support may be a risk factor for major complications of prematurity; conversely, higher disease burden is a risk for growth restriction. Early complete parenteral nutrition support, including intravenous lipid emulsion, should be adopted, and the next challenge that should be addressed is parenteral nutrition customized to fit the specific needs and metabolism of the extremely preterm infant. Standardized feeding protocols should be adopted.

Body fat differences by self-reported race/ethnicity in healthy term newborns

BACKGROUND

Ethnic differences in total body fat (fat mass [FM]) have been reported in adults and children, but the timing of when these differences manifest and whether they are present at birth are unknown.

OBJECTIVES

This study aimed to assess whether ethnic differences in body fat are present at birth in healthy infants born at term, where body fat is measured using air displacement plethysmography and fat distribution by skin-fold thickness.

METHODS

Data were from a multiracial cross-sectional convenience sample of 332 term infants from four racial or ethnic groups based on maternal self-report (A, Asian; AA, non-Hispanic Black [African-American]; C, non-Hispanic White; and H, Hispanic). The main outcome measure was infant body fat at 1-3 days after birth, with age, birth weight, gestational age and maternal pre-pregnancy weight as covariates.

RESULTS

Significant effects for race (P = 0.0011), sex (P = 0.0051) and a race by sex interaction (P = 0.0236) were found. C females had higher FM than C males (P = 0.0001), and AA females had higher FM than AA males (P = 0.0205). C males had less FM than A males (P = 0.0353) and H males (P = 0.0001).

CONCLUSION

Race/ethnic and sex differences in FM are present in healthy term newborns. Although the implications of these differences are unclear, studies beginning in utero and birth set the stage for a life course approach to understanding disease later in life.

Evaluation of DXA vs. MRI for body composition measures in 1-month olds

BACKGROUND

Detailed measures of infant body composition are needed for understanding the impact of genes and environment on growth early in life.

OBJECTIVE

The purpose of this study was to compare the accuracy and bias of body composition in infants.

METHODS

Dual energy X-ray absorptiometry (DXA) and magnetic resonance imaging (MRI) were used to determine body composition and the trunk depot. The depots measured were total fat mass (FM), total fat-free mass (FFM) and trunk FM and FFM using DXA and MRI in 14 infants.

RESULTS

None of the regression lines between DXA and MRI significantly deviate from the line of identity for any of the depots studied. However, Bland-Altman analyses revealed bias for trunk FM and trunk FFM.

CONCLUSION

Our data showed DXA to be accurate (regression not significantly deviating from the line of identity), with high agreement (indicated by high R(2) ) and without bias (non-significant Bland-Altman) when estimating total FM and FFM. This could not be said for trunk estimates.

Sonographic assessment of abdominal fat distribution during the first year of infancy

BACKGROUND

Longitudinal data regarding the fat distribution in the early postnatal period is sparse.

METHODS

We performed ultrasonography (US) as a noninvasive approach to investigate the development of abdominal subcutaneous (SC) and preperitoneal (PP) fat depots in infants ≤1 y and compared longitudinal US data with skinfold thickness (SFT) measurements and anthropometry in 162 healthy children at 6 wk, 4 mo, and 1 y postpartum.

RESULTS

US was found to be a reproducible method for the quantification of abdominal SC and PP adipose tissue (AT) in this age group. Thickness of SC fat layers significantly increased from 6 wk to 4 mo and decreased at 1 y postpartum, whereas PP fat layers continuously increased. Girls had a significantly higher SC fat mass compared to boys, while there was no sex-specific difference in PP fat thickness. SC fat layer was strongly correlated with SFT measurements, while PP fat tissue was only weakly correlated with anthropometric measures.

CONCLUSION

US is a feasible and reproducible method for the quantification of abdominal fat mass in infants ≤1 y of age. PP and SC fat depots develop differentially during the first year of life.

Neonatal Body Composition: Measuring Lean Mass as a Tool to Guide Nutrition Management in the Neonate

Neonatal nutrition adequacy is often determined by infant weight gain. The aim of this review is to summarize what is currently known about neonatal body composition and the use of body composition as a measure for adequate neonatal nutrition. Unlike traditional anthropometric measures of height and weight, body composition measurements account for fat vs nonfat mass gains. This provides a more accurate picture of neonatal composition of weight gain. Providing adequate neonatal nutrition in the form of quantity and composition can be a challenge, especially when considering the delicate balance of providing adequate nutrition to preterm infants for catch-up growth. Monitoring weight gain as fat mass and nonfat mass while documenting dietary intake of fat, protein, and carbohydrate in formulas may help provide the medical community the tools to provide optimal nutrition for catch-up growth and for improved neurodevelopmental outcomes. Tracking body composition in term and preterm infants may also provide critical future information concerning the nutritional state of infants who go on to develop future disease such as obesity, hypertension, and hyperlipidemia as adolescents or adults.

Accuracy and reproducibility of adipose tissue measurements in young infants by whole body magnetic resonance imaging

PURPOSE

MR might be well suited to obtain reproducible and accurate measures of fat tissues in infants. This study evaluates MR-measurements of adipose tissue in young infants in vitro and in vivo.

MATERIAL AND METHODS

MR images of ten phantoms simulating subcutaneous fat of an infant's torso were obtained using a 1.5T MR scanner with and without simulated breathing. Scans consisted of a cartesian water-suppression turbo spin echo (wsTSE) sequence, and a PROPELLER wsTSE sequence. Fat volume was quantified directly and by MR imaging using k-means clustering and threshold-based segmentation procedures to calculate accuracy in vitro. Whole body MR was obtained in sleeping young infants (average age 67±30 days). This study was approved by the local review board. All parents gave written informed consent. To obtain reproducibility in vivo, cartesian and PROPELLER wsTSE sequences were repeated in seven and four young infants, respectively. Overall, 21 repetitions were performed for the cartesian sequence and 13 repetitions for the PROPELLER sequence.

RESULTS

In vitro accuracy errors depended on the chosen segmentation procedure, ranging from 5.4% to 76%, while the sequence showed no significant influence. Artificial breathing increased the minimal accuracy error to 9.1%. In vivo reproducibility errors for total fat volume of the sleeping infants ranged from 2.6% to 3.4%. Neither segmentation nor sequence significantly influenced reproducibility.

CONCLUSION

With both cartesian and PROPELLER sequences an accurate and reproducible measure of body fat was achieved. Adequate segmentation was mandatory for high accuracy.

Preterm birth and body composition at term equivalent age: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

Infants born preterm are significantly lighter and shorter on reaching term equivalent age (TEA) than are those born at term, but the relation with body composition is less clear. We conducted a systematic review to assess the body composition at TEA of infants born preterm.

METHODS

The databases MEDLINE, Embase, CINAHL, HMIC, "Web of Science," and "CSA Conference Papers Index" were searched between 1947 and June 2011, with selective citation and reference searching. Included studies had to have directly compared measures of body composition at TEA in preterm infants and infants born full-term. Data on body composition, anthropometry, and birth details were extracted from each article.

RESULTS

Eight studies (733 infants) fulfilled the inclusion criteria. Mean gestational age and weight at birth were 30.0 weeks and 1.18 kg in the preterm group and 39.6 weeks and 3.41 kg in the term group, respectively. Meta-analysis showed that the preterm infants had a greater percentage total body fat at TEA than those born full-term (mean difference, 3%; P = .03), less fat mass (mean difference, 50 g; P = .03), and much less fat-free mass (mean difference, 460 g; P < .0001).

CONCLUSIONS

The body composition at TEA of infants born preterm is different than that of infants born at term. Preterm infants have less lean tissue but more similar fat mass. There is a need to determine whether improved nutritional management can enhance lean tissue acquisition, which indicates a need for measures of body composition in addition to routine anthropometry.

Ethnic and sex differences in body fat and visceral and subcutaneous adiposity in children and adolescents

Body fat and the specific depot where adipose tissue (AT) is stored can contribute to cardiometabolic health risks in children and adolescents. Imaging procedures including magnetic resonance imaging and computed tomography allow for the exploration of individual and group differences in pediatric adiposity. This review examines the variation in pediatric total body fat (TBF), visceral AT (VAT) and subcutaneous AT (SAT) due to age, sex, maturational status and ethnicity. TBF, VAT and SAT typically increase as a child ages, though different trends emerge. Girls tend to accumulate more TBF and SAT during and after puberty, depositing fat preferentially in the gynoid and extremity regions. In contrast, pubertal and postpubertal boys tend to deposit more fat in the abdominal region, particularly in the VAT depot. Sexual maturation significantly influences TBF, VAT and SAT. Ethnic differences in TBF are mixed. VAT tends to be higher in white and Hispanic youth, whereas SAT is typically higher in African American youth. Asian youth typically have less gynoid fat but more VAT than whites. Obesity per se may attenuate sex and ethnic differences. Particular health risks are associated with high amounts of TBF, VAT and SAT, including insulin resistance, hepatic steatosis, metabolic syndrome and hypertension. These risks are affected by genetic, biological and lifestyle factors including physical activity, nutrition and stress. Synthesizing evidence is difficult as there is no consistent methodology or definition to estimate and define depot-specific adiposity, and many analyses compare SAT and VAT without controlling for TBF. Future research should include longitudinal examinations of adiposity changes over time in representative samples of youth to make generalizations to the entire pediatric population and examine variation in organ-specific body fat.

Body-composition assessment in infancy: air-displacement plethysmography compared with a reference 4-compartment model

BACKGROUND

A better understanding of the associations of early infant nutrition and growth with adult health requires accurate assessment of body composition in infancy.

OBJECTIVE

This study evaluated the performance of an infant-sized air-displacement plethysmograph (PEA POD Infant Body Composition System) for the measurement of body composition in infants.

DESIGN

Healthy infants (n = 49; age: 1.7-23.0 wk; weight: 2.7-7.1 kg) were examined with the PEA POD system. Reference values for percentage body fat (%BF) were obtained from a 4-compartment (4-C) body-composition model, which was based on measurements of total body water, bone mineral content, and total body potassium.

RESULTS

Mean (+/- SD) reproducibility of %BF values obtained with the PEA POD system was 0.4 +/- 1.3%. Mean %BF obtained with the PEA POD system (16.9 +/- 6.5%) did not differ significantly from that obtained with the 4-C model (16.3 +/- 7.2%), and the regression between %BF for the 4-C model and that for the PEA POD system (R2 = 0.73, SEE = 3.7%BF) did not deviate significantly from the line of identity (y = x).

CONCLUSIONS

The PEA POD system provided a reliable, accurate, and immediate assessment of %BF in infants. Because of its ease of use, good precision, minimum safety concerns, and bedside accessibility, the PEA POD system is highly suitable for monitoring changes in body composition during infant growth in both the research and clinical settings.

Maternal body composition in relation to infant birth weight and subcutaneous adipose tissue

Infant birth weight has increased recently, representing an obstetric and potentially a public health problem since high birth weight involves a risk of obesity later in life. Maternal nutritional status is important for fetal growth and therefore relationships between maternal body weight and composition v. birth weight and infant subcutaneous adipose tissue were investigated in twenty-three healthy women and their newborn infants using multiple and simple linear regression analysis. Furthermore, using previously published data for nineteen infants, it was demonstrated that an anthropometric method could provide useful estimates of the amount of subcutaneous adipose tissue. Birth weight was correlated with the maternal content of total body fat (TBF) both before pregnancy and in gestational week 32 and, together with gestational age at birth, TBF (%) before pregnancy explained 45% of the variation in birth weight. This figure was not increased when gestational gains in weight or TBF were added to the model. Furthermore, in infants, birth weight correlated with the amount of their subcutaneous adipose tissue. Together maternal TBF (%) and amount of subcutaneous adipose tissue in infants explained 61-63% of the variation in birth weight while the amount of infant subcutaneous adipose tissue alone explained only 55%. The maternal TBF content is likely to be important for the recent increase in birth weight. This factor probably causes a general augmentation in fetal growth rather than a specific stimulation of adipose tissue growth.

Assessment of total body fat using the skinfold technique in full-term and preterm infants

BACKGROUND

Assessment of body composition may be of interest when the nutritional status of infants is evaluated but is often difficult since simple and valid methods are lacking. With appropriate validation, measurements based on skinfold thickness (SFT) may be useful for this purpose.

AIMS

To evaluate the potential of a published method, based on measurements of SFT, to assess total body fat (TBF) of infants; and to calculate the fat content of adipose tissue (AT) in infants using previously published information regarding AT volume and total body water.

SUBJECTS AND METHODS

Forty-five full-term infants and eight infants born in gestational weeks 31-33 were studied at a postnatal age of 4-131 and 44-75 d, respectively. The body water dilution method was used to obtain reference estimates of TBF (TBF-BWD).

RESULTS

In full-term infants, TBF assessed using the skinfold method (TBF-SFT) minus TBF-BWD was 1.5+/-10.8% (mean+/-2 SD). Furthermore, TBF-SFT minus TBF-BWD (%, y) was correlated (p<0.0001) with the average of TBF-SFT and TBF-BWD (%, x), showing that TBF-SFT was too high in lean infants and too low in infants with more TBF. In the full-term infants, AT contained 0.68+/-0.14 g fat/ml. In the premature infants, TBF-SFT (%), TBF-BWD (%) and the AT fat content were similar to the corresponding figures in nine full-term newborns.

CONCLUSION

The results indicate that the SFT method produced inaccurate and biased estimates of TBF in infants. A considerable variation between infants regarding their AT fat content may be an important reason for these findings.

Distribution of adipose tissue in the newborn

Regional differences in adipose tissue distribution are associated with differences in adipocyte metabolism and obesity-related morbidities. Intrauterine growth restriction appears to place individuals at greater risk of obesity associated morbidities in later life. Despite this, little is known regarding the quantity and distribution of adipose tissue in infants during early development. The aim of this study was to compare total and regional adipose tissue content in appropriate-for-gestational-age (AGA) and growth-restricted (GR) newborn infants born at or near term. Whole body adipose tissue magnetic resonance imaging (MRI) was performed as soon as possible after birth. Total and regional adipose tissue depots were quantified. A total of 35 infants (10 GR; 25 AGA) were studied. Mean (SD) total percentage adipose tissue was lower in GR infants than AGA infants [GR: 17.70% (2.17); AGA: 23.40% (3.85); p = 0.003]. This difference arose from differences in subcutaneous adipose tissue mass [mean (SD) percentage subcutaneous adipose tissue mass, GR: 16.13% (2.20); AGA: 21.44% (3.81); p = 0.004], but not intra-abdominal adipose tissue mass [mean (SD) percentage intra-abdominal adipose tissue, GR: 0.42% (0.22); AGA: 0.61% (0.31); p = 0.45]. In contrast to subcutaneous adipose tissue, intra-abdominal adipose tissue is not reduced in infants with intrauterine growth restriction. This suggests that subcutaneous and intra-abdominal adipose tissue compartments may be under different regulatory control during intrauterine life.

Studies on human body composition during the first 4 months of life using magnetic resonance imaging and isotope dilution

Assessing body composition during infancy requires data for the so-called reference infant. Currently available data for this purpose need to be updated and extended using methods based on principles different from those used previously to define the reference infant. Thus, magnetic resonance imaging was applied to full-term healthy boys (n = 25) and girls (n = 21), 4-131 d old, to estimate adipose tissue volume (ATV) and the amounts of s.c. and non-s.c. adipose tissue (AT). Total body water was estimated using isotope dilution. Total body fat (TBF), fat free weight (FFW) and the degree of hydration in FFW were calculated. Increases in weight, TBF, and FFW with age agreed with current reference data, although when compared with the reference, a slightly more rapid increase in % TBF was observed for boys. The degree of hydration in FFW was 78.9 +/- 4.5% (n = 45). Both sexes showed significant increases with age in s.c. ATV (14.7 and 13.0 mL/d for boys and girls, respectively) and in non-s.c. ATV (1.58 and 1.26 mL/d, respectively). Subcutaneous ATV was 90.5 +/- 1.8% (boys) and 91.1 +/- 1.9% (girls) of total ATV. In conclusion, a pronounced increase with age in the amount of AT was demonstrated involving a considerable gain in s.c. fat during early life. Except for % TBF in boys, changes in body composition with age agreed with current reference data.

Anatomy and physiology of subcutaneous adipose tissue by in vivo magnetic resonance imaging and spectroscopy: relationships with sex and presence of cellulite

BACKGROUND

Little is still known concerning subcutaneous adipose tissue and cellulite, and controversial questions are still under discussion.

AIMS

Magnetic resonance imaging and spectroscopy were used to address two unresolved questions relating to the anatomy and physiology of subcutaneous adipose tissue.

METHODS

Using high spatial resolution magnetic resonance imaging we characterized the topography of the dermo- hypodermal junction, and the three-dimensional architecture of the subcutaneous fibrous septae. Using proton spectroscopy, we measured water and lipid fractions within a fat lobule, and T1 and T2 values of the detected compounds. All these data were analysed according to sex and presence of cellulite.

RESULTS

MR imaging quantified deeper indentations of adipose tissue into the dermis, and evidenced for the first time a great increase in the thickness of the inner fat layer in women with cellulite. Moreover, 3D reconstruction of the fibrous septae network showed a higher percentage of septae in a direction perpendicular to the skin surface in women with cellulite; but our study also depicted the tortuous aspect of this network. MR proton spectroscopy could not show any differences related to sex or presence of cellulite concerning T1 and T2 relaxation times of the detected compounds within a fat lobule, neither the unsaturated lipid fraction, the saturated lipid fraction, nor the water fraction.

CONCLUSIONS

Magnetic resonance imaging showed that the 3D architecture of fibrous septae couldn't be modelled simply as perpendicular planes for women and tilted planes at 45 degrees for men. MR spectroscopy did not confirm the hypothesis of increased water content in the adipose tissue of women with cellulite as suggested by others, except if such water would be located in the connective septae.

Fast and reproducible method for the direct quantitation of adipose tissue in newborn infants

The role of body fat content and distribution in infants is becoming an area of increasing interest, especially as perception of its function appears to be rapidly evolving. Although a number of methods are available to estimate body fat content in adults, many are of limited use in infants, especially in the context of regional distribution and internal depots. In this study we developed and implemented a whole-body magnetic resonance imaging (MRI)-based protocol that allows fast and reproducible measurements of adipose tissue content in newborn infants, with an intra-observer variability of <2.4% and an inter-observed variability of <7%. The percentage total body fat for this cohort of infants ranged from 13.3-22.6% (mean and standard deviation: 16.6 +/- 2.9%), which agrees closely with published data. Subcutaneous fat accounted for just over 89% of the total body fat, whereas internal fat corresponded to almost 11%, most of which was nonabdominal fat. There were no gender differences in total or regional body fat content. These results show that whole-body MRI can be readily applied to the study of adipose tissue content and distribution in newborn infants. Furthermore, its noninvasive nature makes it an ideal method for longitudinal and interventional studies in newborn infants.

Body composition measurements during infancy

Infancy is the period of most rapid postnatal growth and is accompanied by major changes in body composition (BC). There are many challenges to successfully measuring BC of infants in vivo, which include the inherent limitations in the underlying assumptions for each technique. The small body mass and rapid nonuniform changes in body parts, that is, the components of BC during infancy, can strain the technical limits of all methods. Many techniques for in vivo BC measurement used in older people have been applied to infants. However, the vast majority of them either are difficult to adapt for widespread use in infants, or the roles and limitations for using them during infancy are ill-defined because of limited or no critical validation and cross-calibration studies. Based on validation data from animals, well-defined methodological issues in data acquisition and analyses, availability of normative data, and pertinent accuracy and precision of the technique to allow us to determinate clinically relevant changes in BC within a reasonable time interval, three techniques appear to be most suitable for in vivo BC measurement in infants. Anthropometric measurements can be used in field studies or for group comparisons, and total body electrical conductivity (TOBEC) and selected dual-energy X-ray absorptiometry (DXA) measurements can be used to compare BC in individual infants. DXA has the advantages of being able to measure bone mass and the potential to be adaptable to the widely available existing instruments. However, regardless of the techniques used in measuring BC in infants, meticulous attention to details in data acquisition and data analysis, and a knowledge of the limitations of the particular technique are the prerequisites for generating valid data.

Neonatal body composition: dual-energy X-ray absorptiometry, magnetic resonance imaging, and three-dimensional chemical shift imaging versus chemical analysis in piglets

An animal study to evaluate dual-energy x-ray absorptiometry (DXA) and magnetic resonance (MR) imaging and spectroscopy for measurement of neonatal body composition was performed. Twenty-three piglets with body weights ranging from 848 to 7550 g were used. After measuring total body water, animals were killed and body composition was assessed using DXA and MR (1.5 T; MR imaging, T1-weighted sagittal spin-echo sequence; MR spectroscopy, three-dimensional chemical shift imaging) as well as chemical carcass analysis (standard methods) after homogenization. Body composition by chemical analysis (percent of body weight, mean +/- SD) was as follows: body water, 75.3 +/- 3.9%; total protein, 13.9 +/- 8.8%; and total fat, 6.5 +/- 3.7%. Absolute content of fat and total ash was 7-674 and 35-237 g, respectively. Mean hydration of fat-free mass was 0.804 +/- 0.011 g/kg and decreased with increasing body weight (r2 = 0.419) independent of age. Using DXA, bone mineral content was highly correlated with calcium content (r2 = 0.992), and calcium per bone mineral content was 44.1 +/- 4.2%. DXA fat mass correlated with total fat (r2 = 0.961). Using MR, spectroscopy and chemical analysis were highly correlated with fat-to-water ratio (r2 = 0.984) and absolute fat content (r2 = 0.988). Total fat by MR imaging volumetry showed a lower correlation (r2 = 0.913) and overestimated total fat by a factor of 2.46. Conversion equations for DXA were developed (total fat = 1.31 x fat mass measured by DXA--68.8; calcium = 0.402 x bone mineral content + 1.7), which improved precision and accuracy of DXA measurements. In conclusion, both DXA and MR spectroscopy give accurate and precise estimates of neonatal body composition and may become valuable tools for the noninvasive assessment of neonatal growth and nutritional status.