PULMONOLOGY • CONTINUED FROM PREVIOUS PAGE
You solve for the unknowns using equations
derived from Maxwell’s laws, a set of
mathematical models that describe electrical
fields — the same ones that power technologies
like generators, radar, electric motors and wireless
communications.
Iterative algorithms then solve the governing
equations to produce what’s called a candidate
distribution, essentially a guess at how
conductivity is distributed within the field, with
the goal of matching the inputs to the outputs. The
algorithm will then adjust the variables and run
the equations again and again until it gets within a
margin of error.
The system plots the conductivity distribution as
pixels, and those pixels form an image. Areas of
high conductivity — like the heart — are rendered
in red. Low conductivity — like the lungs — in
blue. Run continuously, the image becomes an
animation.
“You can see where air and blood are going,” says
Dr. DeBoer. “Breath to breath, beat to beat.”
“You’re going from hundreds of measurements
on the outside to thousands of pixels inside,” says
Michelle Mellenthin, PhD, a post-doctoral fellow
in biomedical engineering at the University of
Colorado School of Medicine who, as a graduate
student of Dr. Mueller’s, built a prototype EIT
device. “The math is incredibly complex.”
Dr. Mueller has been working on the math,
specifically inverse problems for medical imaging,
for 20 years. Until recently, that work was
confined to the lab. She was giving a talk on EIT’s
potential in cardiac imaging when she met Robin
Deterding, MD, Chief of Pediatric Pulmonology at
Children’s Colorado.
“I immediately thought of air trapping in cystic
fibrosis,” says Dr. Deterding.
“That was my first clinical project,” says Dr.
Mueller. “Before that I was only looking at healthy
subjects, looking at ventilation and perfusion and
refining the algorithms. I wasn’t satisfied doing
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that. I wanted to make a clinical difference. I was
looking for a partner.”
Validating a new view
Dr. Mueller found that partner in Dr. DeBoer, who
had a research interest in pulmonary imaging.
When she saw Dr. Mueller’s animations — the
lungs in cross section, filling and emptying of blue,
the heart pulsing red — she knew she was looking
at potential.
“It’s very exciting,” Dr. DeBoer says. “There’s no
radiation, no sedation. It’s very safe. You can put it
on a baby, you can put it on an adult. We’re doing
studies in the ICU and the OR. You could even do
studies at home.”
Indeed, Children’s Colorado is already testing
the device with several patient populations. It
could help treat regional pneumonia, a common
comorbidity of neuromuscular disease. In the
NICU, it could help manage bronchopulmonary
dysplasia. It could help treat patients on
mechanical ventilation and young children with
asthma. It can reveal aspects of heart function,
blood flow, fluid accumulation in the lungs. It
can show the boundary between living and dead
tissue. It can show regions of lung collapse and of
hyperinflation.
Compared to CT, it reliably reproduces
anatomy and abnormality. Compared to
spirometry, it measures very accurate lung
volumes. Dr. DeBoer’s team published those
results in Physiologic Measurement last year.
“Our goal is to use it all the time, routinely, over a
period of three years,” says Dr. DeBoer. “If it works,
it can go everywhere.”
But there will be challenges.
For one thing, EIT in its current iteration is not
particularly user-friendly. Dr. Mueller travels with
the device and helps set it up and gather the data.
She processes it afterward, in her lab. Then she
sends the images to Dr. DeBoer for analysis.
That’s not ideal.
Direct algorithms, first used clinically by
Dr. Mueller’s team, solve several complicated
equations in one step to produce an image
in real time. In a new collaboration with GE
Global Research, Dr. Mueller is developing
that group’s prototype into a highly-portable,
hospital-friendly system that can do just that,
in a configuration easy enough for a nurse to
set up.
Then there are the inherent challenges of
testing a novel medical device.
“It’s definitely learning on both sides,” says
Dr. DeBoer. “Dr. Mueller could say, ‘This signal
is abnormal, what do you think it means?’ And
then we have to go back and try to figure that
out. There aren’t many studies — maybe any
studies. We’re certainly the biggest group in
cystic fibrosis.”
And in some ways, it’s the sheer number of
people involved — and their expertise —
that makes the difference. It’s engineers
and pulmonologists, cooperation between
institutions, partnerships with industry.
That’s what it takes.
“It’s difficult to validate,” says Dr. Mueller,
“when you’re seeing things that haven’t been
seen before.” ●
Biomedical engineer Michelle Mellenthin, PhD,
solders a circuit-board, part of the continual
process of refining a new technology for the clinic
(top). EIT is so safe its test subjects have been
entirely human, but Dr. Mellenthin hopes a mouse
model can help her develop the technology from a
mechanical engineering angle. She’s still working
out the kinks of miniaturization (bottom).
To see more on EIT for
cystic fibrosis, visit
childrenscolorado.org/EIT.
NEW CONSTELLATIONS
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