CARDIOLOGY & HEART SURGERY • CONTINUED FROM PREVIOUS PAGE
the irregular flows of the shunt breaking up into
sprays of blue. Each line represents a direction
of flow. Each color represents a velocity. From
this dashboard, he and Dr. Truong can get a read
on most of the information a cath provides. But
they’re seeing much more than that.
Dr. Schafer rotates the view and points to where
the shunt empties into the aorta. “You can see
all these spirals and vortices here. The shunt is
helping the heart pump less against pressure,
but the system is not designed to convey flow
in this fashion. Dr. Truong said, ‘Let’s check the
descending aorta.’ Well voilà, we find there is
some stiffening there.”
“We’ve never been able to see that before,” adds
Dr. Truong. “We’re putting together the first case
report on this. When I presented it, people were
blown away.” tool that surgeons can use to seal them off. “You can’t do this with any other imaging
technique,” he says. Voxel: the 3D
What they’ve seen is so novel, so groundbreaking,
in fact, that Dr. Truong’s group has published 15
papers in the last two years alone. Their National
Institutes of Health-funded comparison study
of catheterization and 4D MRI in patients with
pulmonary arterial hypertension, like the one on
their screen, just finished its first of five years. “We’re using it in a number of studies,” says
pediatric endocrinologist Kristen Nadeau, MD,
MS. “We want to detect early disease in youth
with diabetes, but we’re not going to cath or do
something invasive. We’ve already used this
to uncover some signs of vascular disease that
weren’t detectible by less sensitive methods.” a pixel
So far, signs are promising that MRI data
correlate with conventional cath data. It’s faster,
cheaper and safer, all with no radiation, no risk
and no downtime. One such study looked at markers of stiffness
and compliance in the aorta of 50 kids with
type 1 diabetes and found that metformin could
improve vascular stiffness over time. Given that
metformin doesn’t improve blood sugar control
in type 1 diabetes — and thus isn’t currently
included in the typical treatment regimen — that
finding stands to change the standard of care.
“This technology lets us understand the physics
of pulmonary hypertension better than we ever
have,” says D. Dunbar Ivy, MD, Chief of Pediatric
Cardiology. “We’re not there yet, but it’s possible
it will help us pick treatment options to improve
flow characteristics in these patients lifelong.”
The next frontiers
“It’s a concise way to process a ton of information
in a way that makes a lot of sense,” says
bioengineer Alex Barker, PhD, Director of the
Advanced Imaging Lab.
A key player in the development of 4D flow
MRI, Dr. Barker is using the technology to study
complex hemodynamics in vascular disease,
specifically in neurovascular malformations
where blood short circuits from the arterial to
the venous system without traveling through
capillary beds. Those can have devastating
consequences for the patient, but they’re also
difficult to localize, impossible with conventional
MRI. Dr. Barker’s sequences can help map those
connections — a potentially lifesaving planning
Bioengineer Michal Schafer, PhD, looks over 4D
flow animations in the radiology lab.
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Dr. Nadeau and her group recently published that
in Circulation, and they’re starting to apply the
technology in type 2 diabetes populations (see “In
Reverse,” p. 20).
Meanwhile, Dr. Truong’s team of cardiologists,
radiologists, bioengineers and computer scientists
is working to apply 4D MRI on a smaller scale.
Because neonates are at even higher risk for
cath, the main disease tracking tool tends to
be echocardiogram — the limitations of which
can render its information imprecise. Reliable
4D images could change the care landscape
for newborns with PH and related conditions
like bronchopulmonary dysplasia. But the
implications of that capability extend far beyond
the heart.
“One day,” says Dr. Ivy, “this is going to be
ubiquitous.” ●
equivalent of
Building a
better sequence
One advantage of 3D scanning is that a
volume contains more signal than a plane,
which maximizes the signal-to-noise ratio —
meaning cleaner, higher-resolution images.
The challenge is that more signals mean
more data, and that means more time in the
machine. A lot more time.
“We’re going under the hood of the scanner
and redesigning how it obtains this data,” says
Dr. Barker.
To do that, he and Dr. Naresh, who cut her
teeth programming Seimans machines,
are applying techniques similar in concept
to file compression in computing. Building
algorithms that account for known sparcity,
they are training the machine not only to
minimize the time of data acquisition, but also
to enable scanning in patients of minimal size.
Essentially a 3D pixel, a voxel is a scanner’s
most basic unit of meaning. A neonate’s aorta
might measure 10mm across. The sequence
needs at least five voxels in that volume
to extract meaningful information — and
currently, there’s no way to measure with
that kind of precision. But Dr. Naresh is
working on it.
“We’re pushing the limits of the sequence,”
says Dr. Truong.
To see 4D MRI technology
at Children’s Colorado, visit
childrenscolorado.org/4D.
NEW CONSTELLATIONS
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