INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT INTRA-RATER RELIABILITY OF DIAGNOSTIC ULTRASOUND IN THE
MEASUREMENT OF SUBCUTANEOUS ADIPOSE TISSUE
Independent Research
Presented to
The Faculty of the College of Health Professions & Social Work
Florida Gulf Coast University
In Partial Fulfillment
Of the Requirement for the Degree of
Doctor of Physical Therapy
By
Matt Juttelstad & Brad Bellingar
2015
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT APPROVAL SHEET
This independent research is submitted in partial fulfillment of the requirements for the
degree of Doctor of Physical Therapy
Matthew Juttelstad, SPT
Approved: April 2015
Ellen Donald, MS, PT
Committee Chair
Dr. Stephen Black, DSc, PT, ATC/L
Committee Member
The final copy of this independent research has been examined by the signatories, and we find that both the
content and the form meet acceptable presentation standards of scholarly work in the above mentioned
discipline.
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT Acknowledgements
The researchers would like to thank and acknowledgement our incredible
committee members: Professor Ellen Donald, our committee chair, and Dr. Stephen
Black, our committee member. They helped us turn a single, small idea into a fully
completed research project. The researchers would also like to thank Dr. Dennis Hunt
and Dr. Arie van Duijn for their assistance with the technical aspects of this research.
Finally, we would like to thank Melinda Coffey and Sonnie Straw for their assistance
with data collection.
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 1 Table of Contents
Abstract
2
Introduction
3
Causes of Obesity
4
Body Fat Measures
6
Body Mass Index
6
Computed Tomography
7
Skinfold Caliper
8
Air displacement Plethysmography
9
Diagnostic Ultrasound
Methods
10
12
Study Design
12
Sampling
12
Procedures
13
Data Analysis
15
Results
16
Discussion
19
Limitations
21
Conclusion
22
References
24
Appendix A: Demographic Data
27
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 2 Abstract
The rise in global obesity rates over the past 30 years is one of the most serious crises in
the world today. Obesity is associated with many serious health risks, and the cost of
medical treatment for obesity is estimated at approximately $150,000,000,000 annually.
Medical professionals need to find methods to not only treat and to help prevent obesity,
but quickly and accurately assess it as well. With dozens of body fat assessment tools of
varying reliability and validity, it is important to investigate all potential measures for use
in combating the obesity epidemic.
PURPOSE: The purpose of this study is to assess the Intra-rater reliability of diagnostic
ultrasound in the measurement of subcutaneous adipose tissue. Previous research has
concluded that diagnostic ultrasound is a valid tool for measurement of total body fat
percentage, but research on the Intra-rater reliability of the tool is limited at this time.
METHODS: 75 participants were recruited to participate in this study. Participants had
their body fat assessed in a Bod Pod prior to ultrasound measurements to further expand
the data analysis. Additionally, age, gender, and ethnicity were collected to better assess
factors that might influence reliability. Participants then had two sites measured for
adipose tissue size based on a previous study (Leahy et al., 2012). Each site was
measured three separate times to evaluate intra-rater reliability of the diagnostic
ultrasound. The collected data were analyzed with intra-class correlation for intra-rater
reliability.
RESULTS: The ICC for diagnostic ultrasound in the measurement of subcutaneous
adipose tissue was found to be .999 for the total sample at all three tested sites. Intra-rater
reliability can vary between 0 and 1.0, where 0 represents no reliability, and 1.0
represents perfect reliability (Weir, 2005). Additionally, ICC was found to be greater than
or equal to .993 at all age groups above 18 at all three tested sites, and above .996 at all
body fat percentages from less than 10% to greater than 30% at all three tested sites.
Finally, ICC was found to be above .967 at all three tested sites in all ethnicities
evaluated, including Asian, Caucasian, Hispanic, and African-American. Overall, the
intra-rater reliability of diagnostic ultrasound in the measure of subcutaneous adipose
tissue was found to be strong in all genders, ethnicities, ages, and body composition types
measured.
CONCLUSION: Diagnostic ultrasound demonstrated excellent intra-rater reliability in
the measurement of subcutaneous adipose tissue. Given the previously demonstrated
validity of diagnostic ultrasound in the measurement of total body fat percentage (Leahy
et al., 2012), this research further supports diagnostic ultrasound as an effective tool for
accurately measuring total body fat percentage.
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 3 Introduction
The global obesity epidemic is one of the most serious health risks in the world
today. Unfortunately, neither children nor adults have been immune from the increased
prevalence of obesity. Childhood obesity rates have risen steadily in recent years, and
have reached levels never seen before. For example, the Center for Disease Control and
Prevention states that childhood obesity in the United States has nearly tripled over the
past 30 years. In children aged 6-11, the percentage has gone from 7% in 1980 to 20% in
2008. Additionally, in adolescents of ages 12-19, the percentage has gone from 5% to
18% over the same time period. (“Childhood obesity facts”, 2012). The United States has
been hit particularly hard, with nearly 35% of the adult population now classified as
obese according to the National Health and Nutrition Examination Survey.
Obesity is a serious public health problem, as it is associated with diabetes
mellitus, cardiovascular disease, stroke, and a number of other conditions. Additionally,
the CDC estimates that the medical cost of treating obesity in the United States is nearly
150 billion dollars a year. This averages out to nearly 1500 dollars more per year that
obese patients have to spend on health care. If current trends continue, this cost will
increase dramatically. The American Heart Association estimates that by 2030, the
healthcare cost associated with obesity could reach as high as 957 billion dollars (Roger
et al., 2012). With large numbers of both obese adults and children suffering from a
variety of health conditions, it is more important than ever to examine the methods in
which obesity is assessed and measured. According to the strategic plan for obesity
research led by the NIH, there is a need for reliable and accurate measures of both total
and regional body fat that are available to both the general and clinical populations
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 4 (Strategic Plan for NIH Obesity Research, 2011). There are a number of viable diagnostic
measures for the evaluation of body fat percentage, including computed tomography
(CT), BMI, Bod Pod™, skinfold measurement, and diagnostic ultrasound (US). One of
the measures that shows the most promise is diagnostic ultrasound. Although CT is
considered the gold standard for measurement of adipose tissue, machines range between
$75,000-$200,000, and the vast majority of people cannot afford regular scans (~$5,000).
Diagnostic US machines can be purchased for between $3,000-$15,000, making it a more
practical option. While BMI and caliper measurements are fast, cheap tools, BMI has a
low sensitivity on women (Farias Junior, Konrad, Rabacow, Grup & Araujo, 2009), and
calipers have poor intra-rater & inter-rater reliability (Mcrae, 2010). Diagnostic US has
been shown to be a valid measure of body fat percentage, can be performed quickly, and
hasn’t been shown to have the sensitivity & reliability issues of BMI & skinfold caliper
measurement (Leahy et al., 2012).
Causes of Obesity
One of the primary influences of body weight is energy consumed daily compared
to energy burned daily. When energy consumed begins to greatly outweigh energy
burned, weight, and more specifically fat, are added to the body. One of the most
important causes of this energy imbalance is insufficient time performing physical
activity and exercise. The CDC recommends that children engage in some kind of
physical activity or moderate exercise for at least sixty minutes per day. However,
research has shown that only 18% of adolescents reach the goal of 60 minutes of activity
per day (Herrick, Thompson, Kinder & Madsen, 2012). Additionally, the CDC
recommends that adults engage in 150 minutes of moderate-intensity aerobic exercise,
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 5 and muscle strengthening activities twice a week. While a decrease in physical activity in
both the populations of adults and children is partly responsible for the increase in
obesity, other causes like diet must be considered.
Diet is the other component of the energy imbalance seen in obese individuals,
and is a major indicator of both adult & childhood obesity. Within the United States,
there has been a shift from more natural, well-balanced diets, to diets filled with calorie
dense food and drink. Again, this is a serious problem; a study by Maffeis & Castellani
(2006) states that high-energy food and drink intake in combination with minimal
physical activity has become a common triggers for the development of excessive fat
deposits in predisposed individuals, which is contributing to the fast spread of the obesity
epidemic (Maffeis & Castellani, 2006). Villareal et al. (2011) investigated the relative
results in weight loss when comparing regimens that consist of dieting, exercise, or a
combination of dieting and exercise in an obese population. The researchers looked at
changes in total body weight, lean body mass, and fat. The diet group showed a 10% loss
in total body weight, 5% loss in lean body mass, and 17% loss in body fat. The exercise
group showed a 1% loss in total body weight, 2% gain in lean body mass, and 5% loss in
body fat. Finally, the diet-exercise group showed a 9% loss in total body weight, 3% loss
in lean body mass, and 16% loss in body fat. The results of the study suggest that a
combination of diet and exercise has the greatest effect on reducing body fat while
preserving lean body mass (Villareal et al., 2011).
In addition to diet and exercise influences, economic and cultural backgrounds
can have an impact on likelihood of obesity. For example, the CDC states that Hispanic
boys are much more likely to be obese than their white male counterparts, and African-
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 6 American girls are more likely to be obese than white girls. In adults, African-American
males are more likely to be obese than their Hispanic or non-Hispanic white counterparts.
Additionally, low-income women are more likely to be obese than women with high
incomes. The opposite is seen in Hispanic and African-American males. Men from those
backgrounds with higher incomes are more likely to be obese than low-income men.
Although diet, exercise, and background are key influences on childhood obesity,
genetics and the home environment cannot be overlooked. Overweight parents are more
likely to end up with overweight children than their healthy counterparts. In weight loss
intervention studies, Fassihi et al. (2012) showed that compliance with the program, and
thus weight loss results, were both worse in cases where the child had obese parents when
compared to healthy parents.
Common Adipose Tissue Diagnostic Measures
Body mass index (BMI) is a common diagnostic tool used in the screening of
childhood and adult obesity. BMI is calculated by comparing height to weight, then
comparing that ratio to empirical data values. The exact formula for calculating BMI is as
follows: weight (lb.) / [height (in)]2 x 703. The calculated value is then compared to the
following classification system:
Table 1. BMI Weight Status Categories
BMI
Weight Status
< 18.5
Underweight
18.5-24.9
Normal
25-29.9
Overweight
> 30
Obese
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 7 Although BMI is a fast, simple-to-use method for classifying obesity levels, it has
flaws. For example, studies have shown low sensitivity in female patients. More
specifically, sensitivity as found to be high in males at 85%, but lower in females at less
than 60% (Farias Junior, Konrad, Rabacow, Grup & Araujo, 2009). Specificity is high for
both populations, but some studies have suggested that sensitivity is the more important
value. The low sensitivity of BMI in female patients may potentially lead to the
misclassification of some obese patients. This is a serious problem, due to the nature of
the health risks associated with obesity. Additionally, BMI is a measurement tool that is
incapable of distinguishing between different body tissue levels. BMI is unable to
distinguish between body fat, skeletal muscle, and skeletal mass, which can lead to large
errors during the estimation of body fat percentage (Freedman & Sherry, 2009).
Computed tomography (CT) is an imaging method that was developed in the
1970’s by Godfrey Hounsfield. CT creates a cross-sectional view of body tissues using
technology that is similar to x-ray technology. CT scans produce attenuated x-rays that
are represented on a computer monitor as varying shades of gray. CT scans then produce
cross-sectional slices from nearly 1,000 different angles. The CT machine is comprised of
the gantry, the operator console, and the computer. The gantry is the component of the
machine that the patient slides into, and also contains the x-ray tubes, a voltage generator,
detector arrays, and the collimator. The collimator is the device through which x-rays
pass. It also functions in data collection, and determination of cross-sectional thickness.
The detector arrays are the devices that detect the attenuated x-rays that are returning
from the patient’s body. The operator console and computer controls the scanning
processes, determines thickness, and other necessary functions. CT scans are considered
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 8 the gold standard when measuring adipose tissue volume in children and adults. CT scans
are widely shown to be the most accurate measure of visceral fat content (MookKanamori et al., 2009). The biggest downside to using this imaging method for
measurement of body fat is cost. Although pricing depends nationwide on insurance
carrier, and location, CT scans can cost as much as $5,000, and machines themselves can
cost between $75,000-$200,000. Additionally, the vast majority of people will not have
access to a CT machine for this purpose.
One of the most commonly used body assessment methods is the Skinfold caliper
test. It is quick, simple to perform, and can be done at virtually no cost. The use of
skinfold calipers involves measuring fat at a group of specific anatomical sites, and then
using a regression formula to predict overall body density. Then, the calculated body
density value is used to predict a body fat percentage (Kispert & Merrifield, 1987). The
areas commonly tested include the triceps, the chest, the suprailiac area, subscapular area,
thigh, calf, biceps, and umbilicus.
Despite the ease with which a skinfold test can be performed, it has flaws that
make its use suboptimal for the purposes of this study. For example, a 2010 study
performed by Mcrae found that there were differences in both inter & intra-rater
reliability of the method when being performed on women vs. men. Additionally, the
same study noted a decreased validity of the test when being performed on women. More
specifically, when comparing skinfold measurement to bioelectrical impedance analysis
(BIA), validity was high in men, but body fat percentage measurements in women were
found to be 3.4% higher on average with calipers than BIA (Mcrae, 2010). A study by
Leahy et al. also found that the limitations of skinfold for measuring site-specific fat
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 9 content can be solved through the use of diagnostic ultrasound. They stated that they
found ultrasound to be both reliable and accurate in the measurement of visceral adipose
tissue at major body regions without the problems associated with skin thickness
measures (Leahy et al., 2012).
Air-displacement plethysmography has been used to assess body fat measurement
for nearly a century. However, its use became much more prevalent in the 1990’s. The
only product that uses air-displacement plethysmography and is available for commercial
use is the Bod Pod™ (Fields et al., 2002). It has a number of benefits, including quick
readings, ease of use, safety, and comfort. While CT scan is considered the gold standard
for measurement of adipose tissue, some consider the Bod Pod™ device to be the
practical gold standard due to the reduced cost and availability. Air displacement
plethysmography measures the volume of an object by measuring the volume of air it
displaces inside an enclosed chamber. The volume of air that the subject displaces is
measured by subtracting the amount of air in the chamber when the subject is present
from the volume of air when the chamber is empty (Fields et al., 2002). The Bod Pod™
has advancements from early air-displacement plethysmography devices. It uses subtle
pressure perturbations that are registered by transducers to assess body volume. The set
up of the modern Bod Pod™ does not require static temperature levels as earlier devices
did. Additionally, the Bod Pod™ must collect body surface area by way of height and
weight measurements that are done prior to entering the chamber. One component that
can impact the results of the Bod Pod™ reading is isothermal air. One of the biggest
sources of isothermal air is air within the lungs of the subject being tested. This volume
of air can either be predicted using mathematical formulas, or estimated based on
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 10 standard volumes. The Bod Pod™ must also be calibrated to establish a baseline of
volume within the chamber (Fields et al., 2002).
In adults, the Bod Pod™ device shows good reliability in measuring percentage
of body fat. In a group of seven different studies, the Bod Pod™ showed a coefficient of
variation between 1.7% and 4.5% from mean body weight. In addition to being a reliable
tool, the Bod Pod™ has been found to be a valid tool for the measurement of body
composition in a number of different populations (Fields et al., 2002).
Diagnostic ultrasound (US) is a cross-sectional medical imaging method that was
developed in the 1940s. It uses reflected sound waves to produce diagnostic images. The
US machine is composed of a pulser, an ultrasound transducer, a scan convertor, and a
monitor. The pulser emits electrical energy waves between a frequency of 2 and 15
megahertz (Szabo, 2004). The pulser delivers thousands of these waves per minute. The
ultrasound transducer converts these electrical signals into sound waves that it then
transmits into the body tissue. The reflected waves then pass back through the ultrasound
transducer. The scan convertor is the component of the US machine that changes the
signal from the transducer into a digital image than can be seen on the monitor (Szabo,
2004). The convertor also amplifies the signal and improves the signal-to-noise ratio. In
US, fat appears hypoechoic, or very dark.
There are many benefits to the use of US for diagnosis and analysis of
musculoskeletal structures. For example, it has an extremely long history of safety in the
medical community. Dating back to the 1950’s, no substantiated claims of harm coming
from diagnostic ultrasound have been found (Szabo, 2004). In addition to the safety of
diagnostic US, it is a low-cost imaging method that can be performed in real time.
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 11 Millions of people have avoided damaging and painful exploratory surgeries because of
diagnostic ultrasound’s low cost, and high efficacy. This makes it one of the most
preferred diagnostic imaging modalities in medicine. (Szabo, 2004).
Most importantly, diagnostic ultrasound is a valid tool for the measurement of
subcutaneous adipose tissue. A study done in 2002 showed that US is a better measure of
intra-abdominal fat than traditional anthropomorphic measures. Their results showed that
intra-abdominal fat measurements were more reliably assessed with diagnostic US than
with waist-to-hip ratios and BMI measures (Stolk et al., 2002). Not only is US more
effective in measuring intra-abdominal fat, it has also been confirmed by a number of
studies as a valid measure for total body fat percentage in both men and women.
“Ultrasound estimates of body fat percentage were correlated closely with those of
DEXA in both females (r=0.97, standard error of the estimate=1.79) and males (r=0.98,
standard error of the estimate=0.96)” (Pineau, Filliard, Bocquet, 2009, p. 147). In
research with small subject numbers, US was shown to be an accurate and non-invasive
measurement tool that was capable of providing site and tissue specific fat measures
without recourse associated with radiation (Leahy et al., 2012). In addition to the study
by Leahy et al., a landmark study in 1984 showed that the prediction equations generated
by diagnostic US were better than those generated by skinfold calipers (Fanelli &
Kuczmarski, 1984). The use of diagnostic ultrasound for body density prediction is now
well studied, with body density research studies in lean men (Fanelli & Kuczmarski,
1984), lean women (Volz & Ostrove, 1984), obese adults (Kuczmarski, Fanelli & Koch,
1987), sumo wrestlers (Saito et al., 2003), and prepubertal children (Midorikawa et al.,
2011), (Wagner, 2013). While there is research confirming the validity and reliability of
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 12 diagnostic US for this purpose, the researchers have not found literature regarding the
intra-rater reliability. The purpose of this study is therefore to answer the research
question: What is the intra-rater reliability of diagnostic ultrasound in the measurement of
subcutaneous adipose tissue? The researchers hypothesize that diagnostic ultrasound will
have strong intra-rater reliability in the measurement of subcutaneous adipose tissue.
Methods
Study Design
This study is a quantitative reliability study for which reliability will be measured
by comparing repeated measurements with the diagnostic ultrasound device. The intrarater reliability of measuring subcutaneous adipose tissue (SAT) to predict total body fat
in adults was assessed. Bod Pod™ measurements of body fat percentages will be used to
classify subjects into groups, in order to enhance data analysis. The purpose of the Bod
Pod™ measurements in this experiment are to improve the data analysis and determine if
body fat percentage has an influence on reliability of the diagnostic ultrasound in the
measurement of subcutaneous adipose tissue.
Sampling
The sample population for this study was healthy adults over the age of 18. The
sampling method was a simple random sample. In order to encourage participation, a free
Bod Pod™ body fat assessment was offered to participants. Each volunteer for the study
was assigned a number in a table. After obtaining IRB approval, seventy-five healthy
adult subjects were recruited from the Florida Gulf Coast University campus and
surrounding community, where the measurements were taken after receiving written,
informed consent. Fliers were created to advertise the study. Volunteers sent contact
information to an e-mail account created specifically for interacting confidentially with
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 13 subjects. Contact information was kept confidential, and destroyed after the completion
of the study. Inclusion criteria required that all participants be male or female subjects
greater than age 18. Subjects were told to refrain from exercise for twelve hours prior to
the measurements, and to drink 500 mL of water an hour before the measurements.
Exclusion criteria for this research were inability to lie on a table for 10 minutes while
ultrasound measurements are taken. Additionally, any participants who were too
claustrophobic to complete a Bod Pod™ assessment were excluded from participation in
this study.
Procedures
Prior to initiation of data collection, both researchers completed 5 credits of
online diagnostic ultrasound education through the Philips Learning Center. Additionally,
the researchers underwent training in the use of the Bod Pod™, including all calibration
procedures. Diagnostic ultrasound measures were piloted for 3 additional hours to ensure
competence and confidence with the necessary technical procedures. Additionally, the
researchers completed 3 practice sessions with the Bod Pod™ to ensure all procedures
were completed correctly. Following the completion of the necessary training procedures,
the research took place under the direct supervision of a faculty member per department
standards of diagnostic ultrasound use. Prior to every data collection, all necessary Bod
Pod calibration procedures were completed. Each participant read and completed the
informed consent form prior to participation. During this time, participants had an
opportunity to ask questions about the project. If the participant wished to participate in
the research, they were assigned an identification number. Prior to entering the Bod Pod,
participants were asked to list their ethnicity, age, and height. Participants were then
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 14 asked to remove their clothing, leaving only tight-fitting clothing. The participants then
put on a swim cap that was pre-sanitized by the researchers. Participants were told that if
they were uncomfortable with a male researcher, the male researcher would leave the
room to allow a female researcher to perform the Bod Pod assessment. Researchers then
informed the participants of the Exit Test button in the machine that allows them to exit
the chamber at any time. The participants then entered the Bod Pod chamber and were
instructed to sit still with their hands in their laps and to breathe normally. The subjects
were again informed that the measurement takes approximately 50 seconds. Following
completion of the measurement, the test data were retrieved from the computer and two
copies were printed. Both copies were labeled with the participant identifier number. One
of the printed copies was stored by the researchers for future data analysis. The
participants were informed that following completion of the diagnostic ultrasound
measurements, they could return to collect their test results. These procedures were
repeated for each participant. The participants were then escorted to another room for
ultrasound measurements. Procedures for testing were adapted from a previous research
study by Leahy et al. in 2012.
Leahy et al. (2012) outlined a method for taking subcutaneous adipose tissue
(SAT) measurements with an ultrasound machine. In that study, the measurements were
then used to calculate a total body fat estimate for each subject. As noted in the study,
the optimal sites of ultrasound measurement for these equations are different in men and
women (Leahy et al., 2012). In men, the optimal sites are the abdomen and anterior thigh,
while the optimal sites for women are the abdomen and medial calf. In order to predict
percent body fat, the examiner took measurements at each of those locations, and used
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 15 prediction equations to calculate body fat percentage. The equations, as outlined by
Leahy et al., are listed in Table 2.
Following calibration, the participants had a testing site marked on the anterior
thigh (if the participant is male), the calf (if the participant is female), and the abdomen
with a black felt marker. The measuring researcher then used the diagnostic ultrasound to
measure fat tissue size at one of the predetermined sites. The researcher was blinded to
the results of the measurement, which was then recorded by another researcher after each
measurement. The researcher then measured the amount of adipose tissue at the testing
site two more times while recording the data after each measure. Next, the researcher
measured the other testing site on the participant three times, with the data being recorded
after each measurement. After completion of measurements, the participant were
informed that his or her participation was completed, and that they were free to return to
the original testing room to collect their body fat measurement results and ask any
questions they may have about their results.
Table 2. Ultrasound Body Composition Equation
% Body Fat in Males = 7.65 + (abdominal SAT * 0.36) + (frontal thigh SAT * 0.59)
% Body Fat in Females = 17.95 1 (abdominal SAT * 0.28) + (medial calf * 0.54)
Data Analysis
Reliability was calculated with Intra-Class Correlation (ICC) at a 95% confidence
interval. ICC is commonly used for assessing Intra-rater reliability for ratio variables. All
measurements performed by an observer have a true score component and an error
component. This is described by the equation seen in Table 3. Where Xi is the
observation for the ith subject, µ is an unobservable overall mean, ri is an unobservable
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 16 random effect of the ith measurement, and ei is an unobservable measurement error of the
ith measurement.
Table 3. Reliability Equation
Xi=µ+ri+ei
From this assumption, the model for a population ICC was calculated, as seen by the
equation in Table 4. In this equation, σ r2 is a measurement of the variance of the random
effect, and σ e2 is the variance of the error. This equation provides an output that consists
of a positive number between -1 and 1. Higher values for the ICC are consistent with
stronger IRR, where an ICC of 1 indicates perfect agreement, and an ICC of 0 is
indicative of only random agreement.
Table 4. Intraclass Correlation Equation
ICC = σ2r / (σ2r + σ2e)
ICC was then calculated at each of the three sites tested during this research.
These sites are the abdomen, anterior thigh, and medial calf. The ICC of each site was
calculated for the total sample, all self-identified ethnicities, all age groups, and all body
fat percentage groups.
Results
In total, the sample size collected in this research study was 75 participants taken
from the community in Southwest Florida. Participants were primarily recruited from the
campus of Florida Gulf Coast University using flyers and email solicitation. Out of the 75
participants, 57 described themselves as Caucasian, 10 as Hispanic, 4 as AfricanAmerican, 3 as Asian, and 1 as Middle Eastern. The sample included participants
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 17 between the ages of 18 and 60 with an average age of 28.1 years and a standard deviation
of 10.45. Body fat percentages tested ranged between 3.1% and 40.4% with an average of
21.39% and a standard deviation of 8.54. During body composition analysis by the Bod
Pod™, all body fat percentages were calculated using the “Siri” composition model
designed for the general population. All participants completed the study and had
complete data collected. Table 5 shows all data collected during this research project. Site
1 represents the abdomen, site 2 represents the anterior thigh for males, and site 3
represents the medial calf for females.
The intraclass correlation was calculated for the total sample at each testing site,
as well as by gender, ethnicity, age, and body far percentage at a 95% confidence
interval. As noted in Table 6, the ICC of diagnostic ultrasound in the measurement of
subcutaneous adipose tissue was .999 for the total sample at the abdomen, anterior thigh,
and medial calf. An ICC value of 1.0 represents perfect reliability (Weir, 2005). Table 7
outlines ICC by self-identified ethnic group. In those participants who self-identified as
Asian, the ICC was .998 at site 1, .999 at site 2, and an insignificant sample size at site 3.
In the African-American group, the ICC was .999 at site 1, .999 at site 2, and .967 at site
3. In the Caucasian group, the ICC was .999 at all three sites. In the Hispanic group, the
ICC was .999 at all three sites. Finally, there was one Middle Eastern participant, not
generating a significant result for ICC at any of the three sites.
Table 8 outlines the calculated ICC results based upon body fat percentage groups
calculated by the Bod Pod™. In participants with a body fat percentage less than 10%,
the ICC was .997 at sites 1 and 2, with an insignificant sample size at site 3. In the 1020% body fat group, the ICC at site 1 was .998, .999 at site 2, and .999 at site 3. In the
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 18 20-30% body fat group, the ICC was .997 at site 1, .996 at site 2, and .998 at site 3.
Finally, in the > 30% body fat group, the ICC was .999 at all three sites.
Table 9 outlines the calculated ICC results based on age group. In the participant
group between 18 and 25 years old, the ICC was .999 at all three sites. In the group of
participants between 26 and 35 years old, the ICC was .994 at site 1, .998 at site 2, and
.993 at site 3. The ICC was .999 at all three sites in the 36 to 45 year age group. Finally,
in participants over the age of 46, the ICC was .999 at all three sites.
Table 5. Total Intraclass Correlation of Tested Sites
ICC Site 1 (Abdomen)
ICC Site 2 (Thigh)
.999*
ICC Site 3 (Calf)
.999*
.999*
Note: *Statistically significant value, confidence interval = 95%
Table 6. Intraclass Correlation by Self-Identified Ethnicity
Ethnicity
Sample Size
ICC Site 1
ICC Site 2
ICC Site 3
(Abdomen)
(Thigh)
(Calf)
4
.998*
.999*
.967*
Caucasian
57
.999*
.999*
.999*
Asian
3
.998*
.999*
NS
Hispanic
10
.999*
.999*
.999*
Middle Eastern
1
NS
NS
NS
AfricanAmerican
Note: *Statistically significant value, confidence interval = 95%
NS: Not Significant
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT Table 7. Intraclass Correlation by Body Fat Percentage
Body Fat
Sample Size
ICC Site 1
Percentage
19 ICC Site 2
ICC Site 3
(Abdomen)
(Thigh)
(Calf)
< 10%
7
.997*
.997*
NS
10-20%
27
.998*
.999*
.999*
20-30%
29
.997*
.996*
.998*
>30%
12
.999*
.999*
.999*
Note: *Statistically significant value, confidence interval = 95%
NS: Not Significant
Table 8. Intraclass Correlation by Age Group
Age Group
Sample Size
ICC Site 1
ICC Site 2
ICC Site 3
(Abdomen)
(Thigh)
(Calf)
18-25
46
.999*
.999*
.999*
26-35
15
.994*
.998*
.993*
36-45
6
.999*
.999*
.999*
46+
8
.999*
.999*
.999*
Note: *Statistically significant value, confidence interval = 95%
Discussion & Limitations
Discussion
The incidence of global obesity has greatly increased over the last three decades
(Center for Disease Control). According to the strategic plan for obesity research led by
the NIH, there is a need for reliable and accurate measures of both total and regional
body fat that are available to both the general and clinical populations (Strategic Plan for
NIH Obesity Research, 2011). Diagnostic ultrasound has previously been found to be a
valid tool for the measurement of total body fat percentage (Leahy et al., 2012). The
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 20 purpose of this study was to answer the research question: “What is the Intra-rater
reliability of diagnostic ultrasound in the measurement of subcutaneous adipose tissue?”
This study found the diagnostic ultrasound to be highly reliable in the measurement of
subcutaneous adipose tissue as the ICC for the total sample was .999 at all tested sites.
With the ability to use site-specific fat tissue size measurements to produce a valid total
body fat percentage, this research directly address the strategic plan for obesity research
outlined by the National Institute of Health. Prior to this study, the research on this topic
was limited to a small number of studies, with no research found by the researchers
measuring intra-rater reliability on human subjects. Although the sample size was both
small and homogenous overall, it lays the groundwork for future research on diagnostic
ultrasound in the measurement of body fat. Further research is needed over a larger
sample to evaluate the impact of ethnicity, gender, age, and body fat percentage on
overall reliability. While no factors were found in this study that impacted reliability
significantly, a larger, more heterogeneous sample is needed to further clarify overall
intra-rater reliability. Specifically, a larger sample of ultra-lean (specifically female
participants) or morbidly obese patients is necessary to clarify impact on reliability by
extremes of fat tissue size. Ultra-lean individuals will have extremely thin layers of fat
tissue, which might have a direct impact on reliability of the measurements being taken.
Additionally, ultra-obese patients may have fat tissue that is thick enough to require
measurement adjustments and negatively impact on reliability. In addition to a need for
more ultra-lean and morbidly obese participants, future research requires a larger sample
of Asian and African-American participants (specifically female participants). Finally,
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 21 future research should include a larger sample of patients over the age of 46 to assess
impact on intra-rater reliability from age-related changes.
Limitations
The primary limitation of this study is the lack of diversity among the collected
sample. Data collection and recruitment came primarily from the campus of a Florida
university, which limited the diversity within the group. The majority of the collected
sample was Caucasian males between the age of 18 and 25. Thus, the ICC values
calculated for the other self-described ethnicities, and age groups come from small
sample sizes. In some cases, the sample sizes were too small to generate significant data.
Although the sample lacks significant heterogeneity in ethnicity, 2010 census data of
southwest Florida indicates that the sample is a representation of the demographics of the
area. Additionally, the collected sample lacks a high volume of significantly obese
participants (Body Fat % >40). It is possible that the large size of site-specific fat
deposits would impact the reliability of the diagnostic ultrasound, and thus needs to be
explored further. Additionally, this group is at the highest risk for obesity related health
concerns, and is the most important to be able to measure reliably. These limitations
indicate that the results cannot be generalized to the average adult population due to
overall sample size and lack of heterogeneity of body composition of the subject pool.
However, this study creates a baseline for future studies to further investigate the impact
of ethnicity, gender, and body composition on Intra-rater reliability of diagnostic
ultrasound in the measurement of subcutaneous adipose tissue.
In addition to the homogeneous nature of the collected sample, the procedures
employed to collect body fat percentage with the Bod Pod™ may have an impact on the
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 22 validity of collected body fat percentages. All participants were assessed using the “Siri”
density equation. This equation is designed for the general population, with other density
equations designed for specific ethnic groups. Specifically, the “Schutte” equation is
designed for African-American males, and the “Ortiz” equation is designed for AfricanAmerican females. The collected sample included four African-American participants
who likely would have had more valid results with more appropriate density equations.
All participants were assessed with the same density equation to standardize research
procedures, but may have an impact on the validity of collected Bod Pod™ body fat
percentages.
Conclusion
Overall, the findings of this research support diagnostic ultrasound as a highly
reliable tool for the measurement of site-specific adipose tissue. The intra-rater reliability
of diagnostic ultrasound was almost entirely unaffected by age, ethnicity, or overall body
fat percentage. This study, in conjunction with previous studies, indicates that for the
purpose of measuring site-specific adipose tissue size, diagnostic ultrasound is both valid
and reliable. However, further research is still needed at this time to be able to better
generalize these results to a diverse, adult population. Specifically, further research needs
a larger sample of ultra-obese and ultra-lean participants, and a larger sample of nonCaucasian participants, and participants over the age of 46. Despite limitations in specific
sampled groups, the diagnostic ultrasound was reliable over an appropriately sized
sample per the calculated power number and directly addresses the need for further
research on valid, reliable body fat assessment tools. Given the previously mentioned
benefits of diagnostic ultrasound, including ease of use, speed of measurements, validity,
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 23 and affordability, our research further supports the use of diagnostic ultrasound for sitespecific and total body fat measurements.
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INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 27 Appendix A: Demographic Data
Table 9. Demographic Data of Participants
Subject Sex
Site Site Site Site
Site
Site
Age
(Years)
M=0, 1-1
1-2
1-3
2-1
2-2
2-3
F=1
(cm)
(cm)
(cm)
(cm)
(cm)
(cm)
Ethnicity
Bod
Pod
Body
Fat%
1
0
.89
.74
.75
1.18
1.18
1.21
35
Caucasian 24.7%
2
0
.60
.62
.61
1.66
1.86
1.65
35
Caucasian 26.2%
3
0
.61
.73
.73
1.84
1.83
1.86
25
Caucasian 24
4
0
.46
.49
.49
1.02
1.04
.94
40
Caucasian 22.1
5
1
.48
.43
.43
1.11
1.12
1.13
27
Caucasian 29.3
6
0
.38
.43
.43
1.14
1.21
1.20
27
African-
21.3
American
7
1
.80
.82
.83
1.78
1.86
2.02
23
Caucasian 27.4
8
0
.50
.53
.51
2.31
2.24
2.17
30
Caucasian 17.3
9
0
.28
.29
.28
.28
.29
.28
33
Caucasian 9.4
10
0
.23
.26
.28
1.48
1.45
1.39
20
Caucasian 14.1
11
1
.47
.48
.52
1.38
1.22
1.29
33
Asian
12
0
.21
.20
.18
.67
.66
.69
31
Caucasian 10.5
13
0
.50
.49
.46
2.33
2.36
2.36
53
Caucasian 26.8
14
0
.44
.46
.50
.95
.87
.86
18
Caucasian 14.4
15
0
.61
.59
.58
1.61
1.62
1.63
20
Hispanic
18.6
16
0
.97
1.01
1.04
1.72
1.74
1.76
23
Hispanic
18
40.4
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 28 Appendix A: Demographic Data Continued
Subject Sex
Site
Site
Site
Site
Site
Site
Age
M=0, 1-1
1-2
1-3
2-1
2-2
2-3
(Years)
F=1
(cm)
(cm)
(cm)
(cm)
(cm)
(cm)
Ethnicity
Bod
Pod
Body
Fat%
17
1
.39
.40
.41
.34
.38
.38
23
Caucasian 17.5
18
1
.71
.66
.68
1.08
1.06
1.10
27
Caucasian 27.9
19
1
.83
.86
.86
1.03
1.06
1.06
24
Hispanic
20
0
.45
.44
.38
1.19
1.18
1.19
25
Caucasian 19.3
21
0
.07
.06
.06
.23
.22
.20
25
Caucasian 8.3
22
1
2.01
2.00
2.07
2.40
2.38
2.37
29
Caucasian 31.6
23
1
1.75
1.74
1.70
.95
.94
.91
25
Caucasian 22.5
24
0
.59
.58
.58
1.73
1.71
1.68
18
Caucasian 22
25
1
1.19
1.24
1.29
.64
.63
.64
24
Caucasian 18.6
26
0
.36
.36
.34
.30
.31
.34
22
Caucasian 8.2
27
0
.34
.33
.30
.70
.70
.72
19
Caucasian 13.1
28
1
1.85
1.85
1.87
2.30
2.30
2.31
52
Caucasian 36.9
29
1
.50
.51
.52
.26
.24
.27
22
Caucasian 19.4
30
0
.22
.23
.22
.39
.46
.48
34
Hispanic
31
0
.08
.10
.09
.67
.71
.67
28
Caucasian 7.8
32
1
.62
.61
.60
.81
.83
.85
21
Caucasian 23.8
33
0
.41
.40
.39
.78
.77
.78
20
Hispanic
34
0
.60
.57
.58
1.58
1.57
1.53
52
Caucasian 23.6
29.4
18.9
17.2
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 29 Appendix A: Demographic Data Continued
Subject Sex
Site
Site
Site
Site
Site
Site
Age
M=0, 1-1
1-2
1-3
2-1
2-2
2-3
(Years)
F=1
(cm)
(cm)
(cm)
(cm)
(cm)
(cm)
Ethnicity
Bod
Pod
Body
Fat%
35
1
.53
.57
.56
1.34
1.31
1.30
47
Caucasian 40.4
36
1
.68
.66
.65
.96
.98
.97
38
Caucasian 31.6
37
0
.99
.95
.93
1.79
1.81
1.82
36
Caucasian 35.3
38
1
.71
.74
.73
.48
.48
.48
25
Caucasian 23
39
0
.25
.26
.29
1.37
1.37
1.37
19
Caucasian 12.5
40
1
.64
.65
.67
.41
.39
.43
48
Caucasian 26.7
41
0
.62
.62
.61
1.90
1.90
1.93
26
Asian
42
0
.35
.36
.36
3.55
3.48
3.51
40
Caucasian 13.1
43
0
.28
.27
.28
.32
.33
.29
22
Caucasian 12.1
44
0
.49
.50
.49
1.62
1.56
1.55
28
Caucasian 25.4
45
1
1.51
1.52
1.53
.48
.46
.48
25
Caucasian 22
46
0
.13
.12
.12
.34
.35
.35
22
Asian
47
1
.74
.72
.72
.36
.35
.34
25
Caucasian 17.8
48
0
.19
.21
.19
.26
.24
.24
26
Caucasian 10
49
0
.67
.65
.64
1.35
1.36
1.37
18
Caucasian 26.6
50
0
.57
.60
.59
1.55
1.49
1.51
25
Caucasian 20
51
1
.85
.91
.98
1.74
1.69
1.67
32
Caucasian 34.8
20.8
6.1
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 30 Appendix A: Demographic Data Continued
Subject Sex
Site
Site
Site
Site
Site
Site
Age
M=0, 1-1
1-2
1-3
2-1
2-2
2-3
(Years)
F=1
(cm)
(cm)
(cm)
(cm)
(cm)
(cm)
Ethnicity
Bod
Pod
Body
Fat%
52
0
.37
.36
.40
2.44
2.43
2.39
25
Caucasian 31.3
53
0
.37
.35
.38
.71
.69
.72
21
Caucasian 11.9
54
1
.70
.72
.70
1.47
1.47
1.53
60
Caucasian 27.1
55
1
.67
.65
.65
2.65
2.61
2.55
53
Caucasian 32.4
56
1
.71
.71
.66
1.98
2.03
1.99
25
Caucasian 34.8
57
0
.22
.24
.21
.26
.27
.30
22
Caucasian 3.1
58
1
.77
.78
.80
.85
.81
.84
21
African-
28.5
American
59
1
.42
.39
.38
.48
.50
.53
18
Hispanic
19.7
60
1
.43
.44
.43
1.01
.98
1.06
18
Caucasian 21.2
61
1
.61
.58
.60
1.20
1.21
1.20
18
Caucasian 25.6
62
1
.34
.30
.30
.53
.49
.49
21
Caucasian 10.4
63
1
.64
.65
.62
1.86
1.84
1.80
42
Caucasian 22
64
1
.88
.90
.91
.70
.73
.74
23
Caucasian 25.5
65
1
.15
.14
.15
1.29
1.31
1.33
22
Middle
19.2
Eastern
66
1
.62
.67
.69
.72
.68
.74
21
Caucasian 20.6
INTRARATER RELIABILITY OF US IN ADIPOSE MEASUREMENT 31 Appendix A: Demographic Data Continued
Subject Sex
Site
Site
Site
Site
Site
Site
Age
M=0, 1-1
1-2
1-3
2-1
2-2
2-3
(Years)
F=1
(cm)
(cm)
(cm)
(cm)
(cm)
(cm)
Ethnicity
Bod
Pod
Body
Fat%
67
1
.75
.76
.76
.90
.90
.90
19
African-
16.4
American
68
1
.34
.31
.31
.11
.13
.14
20
Caucasian 8.5
69
1
1.26
1.26
1.30
1.06
1.09
1.10
20
Caucasian 22.4
70
0
.50
.53
.52
.82
.83
.85
25
Hispanic
15.6
71
0
.99
.99
.99
3.24
3.24
3.23
21
African-
32.4
American
72
0
.21
.19
.24
.88
.87
.87
19
Hispanic
11
73
0
.28
.27
.28
.27
.27
.27
19
Hispanic
12.8
74
1
.99
1.01
.99
1.28
1.27
1.29
21
Hispanic
28.3
75
1
.57
.57
.59
1.09
1.10
1.13
56
Caucasian 34.6