New Techniques for Imaging the Digestive Tract
A “video pill” and virtual
colonoscopy appear to be more patient friendly than established
diagnostic exams for
viewing the intestines. But are they as good?
imaging and computer techniques, researchers have developed two
new ways for gastroenterologists to view the
small and large intestines. Patients can now swallow a video
pill—a technique called capsule endoscopy—that produces
images of the entire 20 feet of the small intestine. Another
procedure, virtual colonoscopy, uses computed tomography or magnetic
resonance imaging to view the large intestine (colon) noninvasively—that
is, without having to insert a viewing tube through the rectum
and up into the colon.
While at first glance these new techniques
may appear to be improvements over endoscopy and colonoscopy,
both have drawbacks that limit
their widespread use. Nonetheless, capsule endoscopy appears
to be useful for detecting problems that can’t be found
with standard endoscopy. Virtual colonoscopy, however, appears
to offer only limited advantages over standard colonoscopy for
detecting colorectal cancer in most patients.
Capsule endoscopy, approved by the U.S. Food
and Drug Administration in 2001, has three main components. First
is the capsule itself,
which is somewhat larger than a vitamin pill (0.4 x 1 inches)
and contains a video camera, light, battery, and radio transmitter.
The capsule is swallowed, and it takes pictures of the small
intestine as it passes through the gastrointestinal tract. The
images are sent to the second component, an antenna and recording
device about the size of a Walkman that is worn at the waist.
The third component, a personal computer, is needed to download
and view the images.
The Procedure. Capsule endoscopy
requires some preparation beforehand. You may need to perform
purge the night before using
laxatives prescribed by your doctor, followed by a period of
fasting. Alternatively, you may only need to fast for 8 to 12
hours before the procedure. On the day of the procedure, you
will swallow the capsule with a glass of water. The capsule is
then propelled through your gastrointestinal tract by rhythmic
muscle contractions called peristalsis, which normally move food
through the intestines.
The capsule takes pictures of the gastrointestinal
tract, at a rate of two pictures per second. You can continue
daily activities, and you can begin to drink clear liquids two
hours after swallowing the pill and can eat a light meal after
four hours. You may be asked to keep a diary of everything you
eat and drink and any symptoms you experience. The battery in
the capsule wears out after about eight hours, and you will be
asked to go back to your doctor around this time to return the
recording device. The images are then downloaded and analyzed.
capsule is not digested and passes intact through the digestive
system and into your stool, usually within 24 hours. You do not
need to return the capsule, but you should let your doctor know
that it has passed out of your body. In general, no pain or discomfort
is experienced with capsule endoscopy.
Benefits. For selected
patients with symptoms that cannot be explained by the results
of standard diagnostic techniques, capsule
endoscopy appears to be a useful option and may reduce the need
for exploratory surgery. It provides a complete view of the small
intestine, particularly of areas that are usually unreachable
with endoscopy or colonoscopy. Capsule endoscopy can shed light
on bleeding, chronic abdominal pain or diarrhea, or malabsorption
that might originate from the small intestine. For many patients,
the procedure can pinpoint tumors and diagnose conditions like
celiac disease or Crohn’s disease. A November 2002 study
in the American Journal of Gastroenterology reported on
35 patients with unexplained gastrointestinal bleeding that was
to originate in the small intestine. In 63% of the cases, a diagnosis
was made through capsule endoscopy.
Drawbacks. Capsule endoscopy
is not a substitute for conventional endoscopy or any other diagnostic
test of the esophagus, stomach,
and duodenum. It should only be performed after an endoscopy
is unable to provide an adequate explanation for symptoms. In
addition, the capsule moves too fast through the esophagus to
produce good images of this structure, and the stomach and large
intestine are too big to view with the capsule. Also, doctors
are unable to perform biopsies or stop bleeding as they can with
One potential complication is not passing
the capsule: It gets stuck in the intestines of about 1 in every
200 patients. To
prevent this complication, you may need to have a barium swallow
before capsule endoscopy to look for any narrowings or obstructions
in the intestines where the capsule can get stuck. The risk of
having the capsule become stuck is greater in people who have
undergone gastrointestinal surgery or have a history of gastrointestinal
Furthermore, capsule endoscopy may not
be appropriate for people who have an implanted electrical device
(such as a pacemaker),
since it may interfere with the device’s electrical functioning.
Introduced in 1994, virtual colonoscopy has piqued
the interest of lay people and health care professionals alike
as a way to
inspect the colon noninvasively. The technique involves computed
tomography scanning or magnetic resonance imaging of the abdomen
to create two- and three-dimensional images of the inside of
the colon. Because only about 40% of people at risk for colon
cancer undergo regular screening for the disease, some experts
have proposed that a noninvasive virtual colonoscopy might be
more acceptable to many people and would result in more people
However, a great number of drawbacks to
virtual colonoscopy make it an undesirable option for most people.
First, a standard colonoscopy
is still needed for confirmation of the diagnosis and biopsy
if any abnormalities are detected. In one study, about two thirds
of people who underwent virtual colonoscopy needed a subsequent
standard colonoscopy because of abnormal findings. In addition,
polyps cannot be removed during a virtual colonoscopy as they
can during a standard one. Also, virtual colonoscopy cannot distinguish
stool from polyps or malignant growths, leading to a large number
of false-positive results (that is, the test indicates the presence
of polyps or cancer when none really exists).
colonoscopy requires a bowel purge the evening before, just like
in standard colonoscopy. Many patients find
the purge to be the worst part of a colonoscopy. And air is pumped
into the colon just before a virtual colonoscopy, which can cause
cramping. During a standard colonoscopy, patients are usually
sedated and do not feel the cramping.
Last, virtual colonoscopy
doesn’t always visualize the
colon as well as a standard colonoscopy. One study found that
virtual colonoscopy missed about 10% of the polyps found during
standard colonoscopies and indicated trouble in 28% of cases
when the standard colonoscopy was normal. While virtual colonoscopy
can detect large growths almost as well as standard colonoscopy,
it is not as good at detecting small polyps.
No medical organization
recommends virtual colonoscopy as a screening method for colorectal
cancer. However, the procedure may be appropriate
for people who have medical conditions that make a standard colonoscopy
risky or physically difficult.
The Bottom Line
Although capsule endoscopy doesn’t replace
standard diagnostic procedures, it has proven useful in many
cases where symptoms
could not otherwise be explained. In addition, health insurance
companies are beginning to recognize the utility of the procedure.
Recently, six private insurance companies announced they will
pay for it, and in some states, Medicare now reimburses certain
patients who undergo the procedure. If insurance does not cover
it, a capsule endoscopy can cost as much as $1,500. Insurance
companies will likely not pay for a virtual colonoscopy, and
the procedure will be useful only for a small subgroup of patients.