CARDIOLOGY & HEART SURGERY
IN LIVING
COLOR
Kids with pulmonary
hypertension face a real risk of
a cardiac event every time they
undergo catheterization. And
yet cath is currently the reference
standard to monitor the progress
of their disease. At Children’s
Colorado, a cadre of researchers is
working to adapt MRI to that task
— and they’re seeing the heart in
a way it’s never been seen.
Pediatric cardiac interventionist Jenny Zablah,
MD, straps on a lead vest. Her patient, 2-month-
old Marcus *, lies anesthetized in the Cath Lab.
An access sheath is placed in his femoral artery
and vein. The catheters are fed through. Soon
they appear in the monitor above him, one in the
aorta, one in the pulmonary artery.
hypertension and see if Dr. Zablah can safely
close the PDA. can map the location of those signals, that’s how
you get the overall image.”
“This is a low-complexity case,” Dr. Zablah
remarks, “but many of our PH patients are very
sick. Anesthesia makes the systemic blood
pressure drop, so they’re at high risk to go under
sedation. Sometimes they go into cardiac arrest.” “Typically you’re exciting a slice,” adds Nivedita
Naresh, PhD, a bioengineer in the Advanced
Imaging Lab specializing in MRI pulse sequence
programming. “The difference here is that we’re
exciting a volume.”
“For every cath procedure these kids get, the
chance of a catastrophic event is 3.3 percent,”
says pediatric cardiologist Uyen Truong, MD. “But
a lot of kids need it serially, over a lifetime. So you
can imagine the risk.” That’s trickier than it sounds. It changes the
pulse sequence programming, which tells the
scanner how to gather data, and the processing,
which sorts it into a meaningful image. It’s even
trickier when the sequences run continuously to
produce a moving image of blood-flow in an organ
constantly in motion.
The image comes to life
Dr. Truong and bioengineer Michal Schafer,
PhD, talk cases. On their agenda: a patient with
idiopathic pulmonary arterial hypertension, a
rare subset of PH, who had pressures so dire
surgeons shunted his pulmonary artery to the
descending aorta to give his lungs a way to offload
pressure. The need to know his status is urgent
and constant. He’s had several cath procedures.
A day after his last one, he also got an MRI. For the
patient, and for most of the people in the room, it
wasn’t much different from any other scan.
“MRI excites hydrogen,” says Dr. Schafer.
“Anywhere there’s hydrogen, such as in water, you
can excite that atom and get a signal. Then you
The sequences Dr. Naresh is working on
compensate for that by gating to ECG, essentially
syncing to the heart’s natural rhythm. But even
then, there’s no commercial software that can
process the data they generate. For that, Dr.
Schafer uses code he helped develop.
The result is 4D MRI: images of the heart in three
dimensions, over time.
“Here’s where the magic happens,” he says.
On his screen he pulls up the rough shape of his
patient’s heart. Rendered in sinews of color, it
comes alive with a click: A rush of green pours
into the pulmonary artery and then the aorta,
Six weeks premature, Marcus was born with a
large patent ductus arteriosus that failed to close.
In a healthy baby, pulmonary blood pressure
should be about a third of systemic pressure.
Marcus’s open PDA lets the pressures in the
pulmonary artery and the aorta equalize. Today’s
mission: Get a read on Marcus’s pulmonary
* Patient information changed to protect privacy.
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Exercise physiology can uncover early indicators of Blood moves through the heart in these stills taken from a healthy subject’s 4D scan. Lines represent the
disease in conditions like pulmonary hypertension, direction of flow. Color represents velocity.
but you can’t get it from cath. In 4D MRI, patients
can pedal an exercise bike right in the machine.
NEW CONSTELLATIONS
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