The Wall Street Journal | SHIRLEY
S. WANG
Scientists are developing ever
more sophisticated versions of "virtual patients" with the aim of
testing medical devices and procedures that can't readily be assessed in real
people.
Medical innovations typically
undergo extensive trials before they are approved for use in people. But
sometimes such analysis isn't practical because of the risks to patients.
Medical testing, for example, is rarely done in children and pregnant women due
to worries about what a procedure could do to a growing body.
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Virtual patients can help
estimate how much radiation a fetus gets during a mother's CT scan.
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Virtual patients are
realistic-looking computerized models. They use medical data and computer
software and graphics to mimic real people, with skin, bones, fat and organs of
realistic size, shape and composition. Scientists are currently testing virtual
patients to answer such questions as: How much radiation are various organs in
the body exposed to as a result of a CT scan? How risky is it for a pregnant woman
to get a scan? Should a heart device like a defibrillator be implanted in a
child differently than in an adult?
Virtual patients could allow
medical-device companies to test new products earlier, helping the devices get
to market more quickly and cheaply, according to the Food and Drug
Administration.
Virtual technology also
someday could provide opportunities for doctors and medical students to train
for certain surgical procedures by seeing and feeling organs virtually while
using real tools. Doctors could be able to calculate the probability of a
pregnant woman having a high-risk delivery, based on synthesized,
three-dimensional images of the pelvic region and fetus, researchers say.
X. George Xu leads a team of
nuclear engineers at Rensselaer Polytechnic Institute in Troy, N.Y., studying
how radiation interacts with the human body. Computerized tomography, or CT,
scans are frequently used in medicine to image tissues and bones in the body.
But repeated exposure to radiation from the scans is believed to raise the risk
for cell damage that may cause cancer and other health problems. Such risks
also can exist for patients receiving radiation to treat tumors, for example.
Virtual
Benefits
Defibrillators may help people
with irregular heartbeats who don't respond to drugs. Little is known about the
best way to implant the device in a child.
- Children's heart anatomy is different from adults
- Defibrillators have been primarily studied for adult use
- Studying defibrillator use in children is risky and expensive
- Using a virtual child patient to determine best practices for defibrillating children…
- Can show where to connect the electrodes on child's heart to best detect abnormal beats that trigger the defibrillator
- Can help calculate how much electrical impulse is needed to regulate a child's heart rhythm while minimizing side effects
In Dr. Xu's lab, virtual
patients are exposed to virtual radiation in doses similar to that of a CT scan
or cancer-radiation treatment. Simulating a dose of radiation is a complicated
process. It involves mapping out the physics of how radiation waves travel
through the body and interact with different biological substances. Bones tend
to absorb radiation; fat scatters it.
The researchers recently
created an obese virtual patient to demonstrate what happens to radiation in
this body type. Because fat can disperse the waves, overweight people usually
need a higher dose of radiation in medical procedures. The aim is to administer
sufficient radiation to achieve an image scan of adequate quality, but not too
much to cause harm to the patient. Currently, some doctors may use existing
computer software to estimate how much additional radiation is required based
on factors such as weight, height and age of the patient.
Dr. Xu's team showed that the
virtual patient, using more sophisticated modeling such as how fat is
distributed in the body, can provide more accurate calculations of how much
additional radiation an overweight person requires. The work was presented
early this year at a conference of the American Nuclear Society and has been
submitted for publication at a peer-reviewed journal, according to Dr. Xu.
In related work, supported by
a $1.2 million government grant, researchers developed computer software that
provides readings about how much radiation each organ of the body receives
after radiation exposure from a medical procedure, says Aiping Ding, a
Rensselaer Polytechnic research associate who is spearheading the project. The researchers recently
tested the new software, called VirtualDose, in a simulation of an abdominal CT
scan of a woman in her sixth month of pregnancy. They found that although the
fetus did absorb radiation, the dose was 40% less than that calculated by a
more rudimentary software tool that is currently in use. The team hopes that
calculations from virtual patients will help guide doctors in targeting tumors
or making clinical decisions, like figuring out if the benefits to the mother
in getting a CT scan outweigh the risks to the fetus.
Dr. Xu began decades ago
creating models of human patients to understand how radiation affects the body.
His first-generation designs were models that could be touched and felt. They
were built of substances meant to mimic biological materials and had radiation
sensors embedded throughout the torso. Karl, a faceless,
putty-colored model Dr. Xu created 20 years ago, still sits on a desk in his
lab. It contrasts sharply with the strikingly vivid and anatomically correct
virtual patients on the computer screen nearby.
Additional work is being done
at the Center for Devices and Radiological Health, part of the FDA. Researchers
there have created a "virtual family" of adults and children in order
to study how best to implant medical devices in children, such as heart defibrillators.
Defibrillators have been mainly studied for adult use, although children's
heart anatomy is different from that of adults.
The FDA also is exploring
improved diagnostic techniques using virtual patients. In a virtual
catheterization lab, scientists are inserting virtual blockages in blood flow
into the heart. They then run a series of scans aimed at determining which
images best detect the locations and size of the blockages. The research mimics
a clinical trial, but can be performed more quickly and without risk to real
patients, says Kyle Myers, director of the Division of Imaging and Applied
Mathematics at the FDA division. She says researchers hope in the future to use
the techniques to investigate potential treatments.
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