You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
body composition is one of the most important long - term indicator of nutritional status and it is directly related with the health status . in the two compartments model of body composition , body weight ( body weight , bw ) is considered as the sum of body fat mass ( bf ) and fat - free or lean mass ( fat free mass , ffm ) .
consequently , change in body weight does not give us information on body composition and often generates diagnoses of obesity without considering the relationship between fat mass and lean body mass .
furthermore , body weight alone does not consider adipose tissue distribution while it is well known that the finding of an excessive increase of fat mass , especially in the abdominal - visceral district , may be associated with an increase in cardiovascular risk .
this instrument allows a fast and accurate measurement of the body composition with an exposure to a minimum dose of x - ray radiation . the high cost , the lack of portability , and the relative invasiveness of the technique are limits to the diffusion of this method .
it is known that by ultrasound technique it is also possible to measure subcutaneous fat thickness and to estimate total fat percentage [ 2 , 3 ] . until now
, the ultrasound technique has often been used for local measurements , in particular to quantify subcutaneous abdominal fat in study of android obesity [ 49 ] , while dxa has rapidly become the reference method for measuring body composition .
we have shown that it is possible to estimate total fat mass using a portable device based on an ultrasound technique .
in particular , we have previously tested and validated this new instrument versus dxa ( hologic qdr-4500w ) as reference technique in a sample of 89 sedentary subjects of both genders .  
in the course of time , new dxa devices have been developed with new software and shorter data acquisition time . because of statistically significant differences between measurements obtained with different machines [ 1013 ] , users had to carry out new cross - validation studies , with a view to longitudinal followup studies [ 1416 ] .
all these reasons lead us to question about the performance of the portable ultrasound - based device , in which measurement of total body fat mass had been estimated in 2002 by comparison with data from a hologic qdr-4500w dxa instrument .   according to the fact that total body fat obtained by two different dxa has a significant individual difference
for all these reasons , we were led to envisage a new calibration of our portable ultrasound device using data collected with a more contemporary dxa instrument .
data was collected on a sample consisted of 83 sedentary women and 41 sedentary men aged respectively 40.1  15.1 and 48  15.3 years at nancy university hospital .
only patients who gave written consent after receiving a letter of information on the measurement protocol were included .
all patients in good health were recruited according to a wide range of body mass index ( bmi ) and consequently of total fat mass . in each subject , body composition was measured by dxa radiological examination and by our ultrasound - based device on the same day .
the reference measures of total body fat mass ( bf in kg ) were obtained by a hologic discovery a ( version 12.7.2 ) .
this technique , which scans the whole body with an x - ray beam at two energy levels ( 40 and 100  kev ) , is a reference method for measurement of fat mass , lean mass , and mineral content .
the subject lies in a supine position for 7 minutes and radiation exposure is very low .
ultrasound measurements were made with a sonographic us box in a - mode from lecoeur electronique company ( chuelles , france ) .
absorption of ultrasound depends on probe depth as well as on the square of the frequency of the waves transmitted .
the us can be used to measure the thickness of subcutaneous fat between the skin and the muscle .
we selected two preferred anatomical areas : the abdominal areas which are often associated with metabolic risk factors [ 1719 ] and the midthigh area .
subcutaneous fat was located in a horizontal plane with approximately 45 axis vertebral at umbilical level and also at the middle of the knee and the top thigh on the anterior side with a 2.25  mhz linear probe ( figure 1 ) .
we used a probe with a 0.75 inches diameter that is the most appropriate in terms of positioning , location , orientation , and contact pressure .
interobserver reproducibility of fat thickness measurements with the ultrasound technique was good , and intraclass correlation obtained by two examiners in the same subjects was greater than 0.98 .
anthropometric measurements , weight , height , and , umbilical waist circumference , were recorded by the same operator using standard anthropometric techniques .
fat mass estimation by ultrasound uses a linear regression equation developed from dxa reference value .
this regression equation includes the anthropometric characteristics and subcutaneous fat thickness at the midthigh and the back of the umbilical level .
statistical analysis was carried out to compare the fat mass obtained by the ultrasound technique and by dxa absorptiometry using student 's paired t - test .
the accuracy of the fat mass estimations calculated through the preceding models was evaluated from the determination coefficient r between true and estimated values of fat mass and the standard error of the estimate ( see ) as described by lohman .
agreement between body composition estimates was examined by calculating the 95% limits of agreement as described by bland and altman .
additionally , potential bias between bf estimates by dxa and the us technique was obtained using residual plots . for all analysis p
statistical tests were performed using statistica software ( version 6 ; statsoft , tulsa , okla .
the descriptive characteristics of the anthropometric measurements , fat thicknesses measured by ultrasound and the total fat mass ( bf in kg ) and bf% by dxa of sedentary women and men separately are given in table 1 .
the regression equations used to estimate total fat mass according to hologic discovery a are as follows . for females ( n = 83 ) 
 ( 1 ) 
  for males ( n = 41 ) 
 ( 2 ) 
 bw is the body weight ( kg ) ; uvw is the umbilical waist - circumference ( in mm ) ; us  omb   = ( ultrasound thickness of fat at umbilical level ( left + right side))/2 ;  us  mid - thigh  =  ( ultrasound thickness of fat at midthigh ( left + right side))/2 .
bf% determined by us ( 31.4  7.0 for women and 20.7  6.4 for men ) were no significantly different ( p > 0.05 ) than bf% dxa for women ( 31.5  7.5 ) and men ( 21.1  7.2 ) ( table 1 ) .
total bf(kg ) estimated by us correlated strongly with bf ( kg ) dxa for females ( r = 0.952 , see = 2.42 ) and for the males ( r = 0918 , see = 2.29 ) .
moreover , bf% obtained by us also correlated with bf% dxa for women ( r = 0.84 , se  = 3.0 ) and men ( r = .80 , see = 3.2 ) .  
the bland et altman evaluation showed no significant bias between the bf% estimates by us and by dxa with respectively r = 0.18 , p = 0.12 and r = 0.25 , p = 0.20 ( figure 2 ) . the limits of agreement for individual bf% difference between us and dxa were [ 5.0% to 5.8% ] in females and [ 7.3% to 5.8% ] in males with a good symmetrically distributed deviations .
the use of a portable device based on ultrasound associated with anthropometry allowed us to measure bf ( in kg ) and bf% with a high level of accuracy in accordance with the reference method dxa .
the us technique that we currently use was first developed in 2002 and based on a dxa reference technique using an hologic qdr-4500w ( version 8.26 ) .
technical advances between 2002 and 2010 have led to changes in the software and in the devices , as the hologic qdr-4500 w ( version 8.26 ) has been repaved by the discovery a ( version 12.6 ) .
these modifications in software and in technique result in a statistically significant difference in individual values between the two apparatus .
most studies comparing body composition measurements between different dxa devices have established that new equation obtained by cross calibration are needed because the apparatus differ in calibration , software , and scan speed [ 23 , 24 ] .
similar studies have shown that fat mass was significantly higher with the hologic qdr-4500w than with the lunar co madison , wi .
standardization of dxa machines is becoming indispensable because of the highly significant differences observed between their results .
generally , machines from the same manufacturers are not interchangeable and cross calibration studies are necessary in order to convent the results of one reference system to the other .
comparison of fat mass in 41 adult women between the hologic qdr-4500w ( version 9.10 ) and the discovery a ( version 12.6 ) by cross validation   revealed overestimation of means values by the discovery a compared with the hologic qdr 4500w .
the authors emphasized the need to perform cross calibration for subjects with high fat mass values .  
for all these reason , we have recalibrated the ultrasound device to determine total bf ( in kg ) and total bf% compared to dual - energy x - ray absorpiometry ( dxa ) , the reference technique .
ultrasound - based device combining us measurements and anthropometric variables proved reliable and accurate for estimating bf and bf% in a sample of dysentery females and males .
the results obtained in 83 females and 41 males based on calibration data from physically inactive adults showed a good accuracy compared to the reference dxa measurements . see for bf estimates were excellent in females ( 2.1 ) and in males ( 2.2 ) and good for bf% in females ( 3.0 ) and in males ( 3.2 ) according to the lohman 's classification .
moreover , the methods described by bland and altman   were used to examine the level of individual agreement between dxa and us bf% .
the 95% limits of agreement found with us ranging from [ 6% ] for females and [ 6.2% ] for males denote a good accuracy for the us technique with a good symmetrical dispersion around the mean difference ( 0.06 for females and 0.4 for males ) .
figure 2 also illustrates that there was not a significant us bias for females ( r = 0.18 , p = .12 ) and for males ( r = 0.25 , p = 0.20 ) .
the ultrasound technique is an accurate method of estimating total body fat mass whatever the reference dxa device used .
dxa absorptiometry techniques are not interchangeable as they lead to under- or overestimation of mean fat mass .
for this reason , it was necessary to established a cross - validation studies to recalibrate the ultrasound device .
major disadvantages of dxa include limited availability and high costs , as well as exposure to ionizing radiation , although radiation exposure is low .   in conclusion ,
our ultrasound - based device is an indirect technique for measuring bf in adult females and males with good accuracy .
objective . to examine measurement of body composition by ultrasound compared with a reference technique : dual energy x - ray absorptiometry ( dxa ) . 
 we evaluated the accuracy of a portable ultrasound - based device in estimating total body fat mass with those assessed by dxa in adult . 
 methods . 
 body fat mass has been estimated using a portable ultrasound - based device in comparison with a contemporary reference dxa apparatus : the hologic discovery a. anthropometric data has been assessed in order to maximize the output of the software associated with the ultrasound - based device . a cross - validation between ultrasound technique ( us ) and dxa was developed in this study . 
 total body fat mass estimated by ultrasound was compared with this dxa model in a sample of 83 women and 41 men 
 . results . 
 ultrasound technique ( us ) of body fat ( bf ) was better correlated with dxa in both women ( r2 = 0.97 , p < 0.01 ) and men ( r2 = 0.92 , p < 0.01 ) with standard errors of estimates ( see ) being 2.1  kg and 2.2  kg , respectively . 
 conclusion . 
 the use of a portable device based on a us produced a very accurate bf estimate in relation to dxa reference technique . 
 as dxa absorptiometry techniques are not interchangeable , the use of our ultrasound - based device needs to be recalibrated on a more contemporary dxa .