Introduction
Worldwide, obesity has reached epidemic proportions.
More than 30% of children in the United States are
overweight or obese, and there is no evidence that the
rise in obesity incidence will plateau or decline in the
coming years [1, 2]. Insulin resistance commonly occurs
in overweight and obese children and is associated with
type 2 diabetes, which accounts for a large number of
the new-onset cases of diabetes in children [3]. The
increasing incidence of type 2 diabetes parallels the
increasing occurrence and severity of pediatric obesity
[4–6].
In overweight adolescents, excess fat in the muscle
cells and hepatocytes interferes with insulin signaling,
leading to insulin resistance [7]. As obesity develops,
insulin secretion increases parallel to insulin resistance in
order to maintain normal glucose homeostasis. Al-
though most people are capable of compensating for
insulin resistance by increasing insulin secretion, thus
maintaining normal glucose levels, patients predisposed
to diabetes fail to compensate adequately for the greater
Arzu Kovanlikaya
Steven D. Mittelman
Andrette Ward
Mitchell E. Geffner
Frederick Dorey
Vicente Gilsanz
Obesity and fat quantification in lean tissues
using three-point Dixon MR imaging
Received: 23 November 2004
Revised: 17 December 2004
Accepted: 27 December 2004
Published online: 23 March 2005

Springer-Verlag 2005
Abstract Background: It has been
suggested that increased hepatic and
intramuscular fat is associated with
insulin resistance, and that increased
pancreatic fat is related to impaired
insulin secretion. Objective: We
postulated that in obese nondiabetic
teenagers insulin levels would be di-
rectly related to increases in intra-
muscular and hepatic fat and
inversely related to increases in
pancreatic fat. Materials and
methods: MRI was used to assess the
percentage of fat in the liver, muscle
and pancreas in 15 healthy Mexican-
American girls, 14–17 years old,
with body mass indexes (BMIs)
ranging from 17.7 kg/m2 to
46 kg/m2. Results: Strong correla-
tions were observed between BMI
and fat content in the liver, muscle,
and pancreas (r2s between 0.50 and
0.89; P<0.003). Serum insulin levels
were closely associated with fat
measures in the muscle and liver
(r2s=0.63 and 0.29, and P=0.001
and P=0.023, respectively). In con-
trast to our hypothesis, fat content
in the pancreas was also directly re-
lated to insulin secretion (r2=0.74;
P=0.001). Summary: We conclude
that in nondiabetic teenagers, obes-
ity is associated with an increased
accumulation of fat in the pancreas
without impairment of insulin
secretion.
Keywords Obesity Æ Adolescence Æ
Fat quantification Æ Pancreas Æ MR
Pediatr Radiol (2005) 35: 601–607
DOI 10.1007/s00247-005-1413-y ORIGINAL ARTICLE
Accepted for presentation at the SPR 2005
Meeting
A. Kovanlikaya Æ V. Gilsanz (&)
Department of Radiology, MS#81,
Children’s Hospital of Los Angeles,
4650 Sunset Blvd., Los Angeles,
CA 90027, USA
E-mail: vgilsanz@chla.usc.edu
Tel.: +1-323-6694571
Fax: +1-323-6667816
S. D. Mittelman Æ A. Ward Æ M. E. Geffner
Division of Endocrinology,
Diabetes and Metabolism,
Children’s Hospital of Los Angeles,
Los Angeles, CA, USA
F. Dorey
Department of Pediatrics,
Children’s Hospital of Los Angeles,
Los Angeles, CA, USA

insulin requirements [8]. It has been suggested that the
eventual impairment of insulin secretion in subjects with
type 2 diabetes is related to an overload of adipose tissue
in the pancreas [9, 10]. Indeed, data from experimental
animals indicate that the ectopic deposition of lipids in
the pancreas is associated with destruction of islet cells
and impaired insulin secretion [11, 12].
Whether variations in pancreatic fat accumulation
also account for differences in insulin secretion in hu-
mans is unknown because of technical difficulties in
measuring fat stores in intra-abdominal organs in vivo.
Magnetic resonance (MR) spectroscopy has been used
to assess lipid content in skeletal muscle and, less fre-
quently, in the liver, but inaccuracies related to motion
have limited its use in the pancreas. The availability of
novel magnetic resonance imaging (MRI) techniques
that can provide noninvasive assessments of pancreatic
composition might allow delineation of the phenotypic
characteristics of subjects at risk for type 2 diabetes.
In this study, we used an MR technique that was
described by Dixon [13] and provides accurate measures
of fat content in any tissue to assess which lean tissues
stockpile the most fat in lean and obese subjects. We
postulated that in nondiabetic teenagers, increasing
body mass would be related to increased fat accumula-
tion in the muscle, liver, and pancreas. We also postu-
lated that even though insulin levels in teenagers would
be correlated with the percentage of fat in the liver and
muscle (because of compensation for insulin resistance),
beyond a threshold, pancreatic fat content would be
inversely related to insulin levels (because of impaired
insulin secretion).
Materials and methods
Experimental subjects
Fifteen nondiabetic, healthy Mexican-American girls,
14–17 years of age, were recruited from a lifestyle
intervention program for overweight youth (Kids N
Fitness) in the Division of Endocrinology, Diabetes and
Metabolism at Children’s Hospital of Los Angeles
(CHLA), as well as schools in the area. All obese sub-
jects enrolled in the study had fasting glucose levels and
hemoglobin A1c (HbA1c) as part of their participation
in the Kids N Fitness program to ensure no presence of
type 2 diabetes. Subjects were excluded if they had been
diagnosed with any major illness, including pancreatitis,
had a condition or had taken medications known to
influence body composition, insulin action, or insulin
secretion, or if they had a family history of tpe 2 diabetes
among first-degree relatives. The investigational proto-
col was approved by the institutional review board for
clinical investigations at CHLA, and informed consent
was obtained from all subjects and their parents.
Physical examination
All participants underwent a physical examination by a
pediatric endocrinologist to determine their general
health and stage of sexual development. Tanner stage of
sexual maturity was assessed based on breast develop-
ment [14]. Only girls in Tanner stage 5 were included in
the study. Measurements of total height were obtained
to the nearest 0.1 cm using the Harpenden stadiometer
(Holtain, Crymmych, Wales), and measurements of
weight were obtained to the nearest 0.1 kg using the
Scale-Tronix (Scale-Tronix,, Wheaton, Ill., USA). Body
mass index (BMI) was calculated as weight in kilograms
divided by the square of height in meters.
Biochemical determinations
Blood was drawn and serum levels of fasting glucose,
serum insulin, HbA1c and lipid profiles, including tri-
glycerides, low-density lipoprotein (LDL), high-density
lipoprotein (HDL), and cholesterol were obtained using
validated methods. Fasting glucose levels were measured
with an YSI 2300 Stat glucose/lactate analyzer (YSI,
Inc., Yellow Springs, Ohio, USA). Serum insulin was
determined by RIA [15]. HbA1c was measured by high-
pressure liquid chromatography [16] using the fully
automated Glycosylated Hemoglobin Analyzer System
(Bio-Rad Laboratories, Inc., Richmond, Calif., USA).
Total cholesterol, HDL- and LDL-cholesterol and tri-
glycerides were measured as previously described [17].
Three-point Dixon MR imaging
Subjects underwent imaging examinations of the liver,
pancreas,and soleus muscle in the supine position with
the use of a 1.5 T GE MR unit (GE Medical Systems,
Milwaukee, Wis., USA). The soleus muscle was selected
because it is prevalently composed of slow-twitch oxi-
dative fibers (fiber type I), which have the greatest
insulin sensitivity [18]. After positioning the abdomen in
a phased array coil, axial images were acquired from the
level of the liver and the pancreas (Fig. 1) using the
three-point Dixon sequence (not widely commercially
available). Thereafter, the subjects were repositioned,
and three-point Dixon images from the right calf
(Fig. 2) at the level of the largest circumference were
acquired using the knee coil. The entire procedure,
including positioning and scanning, was completed
within 30 min.
After completion of the automated reconstruction of
the three-point Dixon images, the images were trans-
ferred to a GE Advantage Workstation for analysis. The
signal intensity in the images was calculated with oper-
ator-defined regions of interest (ROIs) at the same
602