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A Field Guide to Body Scans
Routine X-rays usually are used
to show broken bones or general
anatomical structures such as
the chest or abdomen. But sometimes
doctors need other ways to see what's
happening inside your body. "Your
doctor may want to look at different
tissues, blood vessels, or organs," says
Dan Flynn, M.D., chief of Radiology at
Jersey Shore University Medical Center.
"We may want to see different views or
obtain more detailed information about
how your body is functioning in order
to diagnose an illness or determine the
best course of treatment."
There are several technologies that
can give your doctor this information.
Here's a guide to four scans you're
likely to hear about.
1. CT scan
For a computed tomography (CT)
scan, you lie on a table that slides
into the CT scanner. A device rotates
around you, emitting X-rays. Your different
body tissue absorbs the X-rays,
and the scanner detects the radiation
that passes through your body. With
the use of a high-powered computer,
this information becomes crosssectional
pictures, or "slices." These
slices can be stacked to form a threedimensional
image.
"Doctors use CT scans to examine
blood vessels and organs, look for
tumors, diagnose injuries, and locate
the right site for a biopsy," says Dr.
Flynn. "CT scans provide clearer pictures
of more types of tissue than traditional
X-rays do. We work closely with
cardiologists with the most advanced
technologies to screen for and diagnose
risks for cardiovascular disease."
2. MRI scan
For magnetic resonance imaging
(MRI), you also slide into a scanner
while you lie on a table. "Magnets in the machine make hydrogen atoms
in your body align in a certain way.
Then the machine emits radio waves,
which bounce off different tissues
differently. "The machine creates twoand
three-dimensional images from
the returning signals," says Dr. Flynn.
Doctors often use MRIs for the
same reasons as CT scans — for
example, to detect tumors. However,
MRIs are better at creating detailed
images of soft tissue, such as at knee
or shoulder joints.
3. PET scan
A positron emission tomography
(PET) scan begins with a small
amount of radioactive tracer that is
injected into your vein. Then you lie
on a table that slides into the scanner.
The scanner detects positrons,
tiny particles emitted by the tracer. A
computer converts these signals into a
three-dimensional image.
"A PET scan shows the size, shape,
and position of tissues," says Dr. Flynn.
"It also tells doctors how they're functioning.
It's used to look for activity
that indicates disease, such as growth
of a tumor or impaired blood flow to
the heart. We also combine PET/CT in
cases to leverage both technologies to
precisely diagnose disease."
4. Bone density scan
Also called dual-energy X-ray absorptiometry
(DEXA), this scan measures
how much energy your bones absorb
from low-dose X-rays. From this information,
your doctor can tell how dense
your bones are.
Adds Dr. Flynn, "This scan helps
monitor bone loss, detect osteoporosis,
and assess fracture risk."
In the most common type, you
lie on a table and the machine scans
your low back and hips. A small,
portable scanner can also check your
wrist, fingers, or heel.
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