64-Slice Pictures From the Heart
New-Generation Diagnostic
Wizardry
By Howie Doyle
Author's Note: During the last two years I have
had occasional, vague feelings of discomfort in the
left side of my chest. A year or so ago I had a
stress test done (the type where you run on a
treadmill until you feel like your lungs are going
to explode) and they reported that my numbers –
heart rate, breathing, blood pressure, and
electrocardiogram – all looked within the normal
range. The symptoms persisted, and although they
were not so bad that I had a need to be treated for
them, I did want to rule out an impending heart
attack... so when we got word that Tomball Regional
Medical Center had acquired a new, state-of-the-art,
and non-invasive method of diagnosis, I jumped at
the chance to get a clearer, surer view of the
state-of-my-heart: the 64-slice coronary CT scan.
--
The classic signs of a heart attack, chest
discomfort and shortness of breath, do not always
indicate that a patient is indeed experiencing heart
problems. Conversely, sometimes the symptoms come on
so gradually that one is tempted to shrug them off
as non-specific 'aches and pains.' But with the
excellent diagnostic procedures now available, rapid
treatment is increasing the survival rate from heart
attack, and physicians are able to diagnose and
treat conditions that lead to heart attack before it
becomes necessary to diagnose and treat the heart
patient in the emergency room.
Tomball Regional Medical Center has acquired a
new tool for evaluating the arteries of the heart
that provides imagery so clear and detailed it
rivals the quality of heart angiograms, or cardiac
catheterization, as a diagnostic tool.
It is called the 64-slice coronary CT scan, and
it is a new twist on old technology – the CAT scan.
Simply stated, the new machine gathers data at a
higher resolution, and more quickly. The detailed
digital imagery is used to create multiple views of
the coronary arteries, and by capturing the images
very quickly, the motion of the heart while beating,
and from breathing, is minimized.
The most important innovations relating to this
new capability are that it is a non-invasive
procedure, and that it costs much less than cardiac
catheterization. About 13 million people in the U.S.
have coronary artery disease, which is known to be
the leading cause of death in our country (about
half a million annually) in both men and women. The
impact of improved diagnostic technology could be
vast, as cardiovascular disease and stroke cost us
$400 billion a year.
Invasive Versus Non-Invasive Diagnosis
Cardiac catheterization is an invasive procedure, as
it involves threading a catheter, or thin tube of
plastic, into an artery (usually the femoral artery
of the leg) where it is then guided via x-ray to the
coronary arteries. The catheter is used to inject
contrast dye into the heart, providing the
cardiologist with moving-picture views of the heart
as the dye flows through the chambers and connecting
vessels of the heart.
A heart angiogram is still often preferred,
because the catheter technique allows the physician
to treat blockages immediately using balloon
angioplasty. This not only removes the need for a
second procedure, but in some cases having immediate
access for intervention can be a life-saver.
The 64-slice coronary CT scan is a simple
procedure. Upon arrival the patient will be given a
dose of beta blockers to slow the heart rate. (This
facilitates better resolution by providing a
fraction of a second between heartbeats to capture
the images.) Then an IV is inserted, and when the
heart rate has slowed to a desirable level, the
patient lays out on the gantry in preparation for
the scan.
A small amount of contrast dye is injected, and
the patient slides into the donut-shaped CT machine
on the gantry. The CT Technologist will then ask the
patient to take slow breaths and regular intervals,
and then to hold the breath for about 10 seconds.
During this time the CT scanner collects a vast
amount of digital data that its specialized software
will reconstruct into a three-dimensional map of the
heart.
After a few minutes on the gantry the patient is
allowed to go on about his or her day, as opposed to
the post-procedural recovery time associated with
any invasive procedure.
A Picture of the Heart
"The pictures of the coronary arteries are captured
in slices as small as six-tenths of one millimeter,"
commented Dr. Ravi Bikkina, staff radiologist. “By
comparison, the head of a pin is three times this
size, or two millimeters.”
The remarkable aspect of this procedure is that
the software builds a three-dimensional view of the
heart and arteries that can be viewed from multiple
angles, and in ways that help doctors really see the
condition of the vessels and plaque deposits.
Plaque is an accumulation of deposits from fluids
that bathe an area of the body. In the circulatory
system, cholesterol, fat, and calcium are the key
components that gather on the inner walls of veins
and arteries. This condition is known as
atherosclerosis – or commonly 'hardening of the
arteries' – and is the chief cause of heart attack
(myocardial infarction) and stroke. Atherosclerosis
in the arteries that supply oxygen to the actual
muscle of the heart is called coronary artery
disease (CAD).
There is more than one type of plaque buildup in
the arteries. Hard plaque is stable – that is, not
subject to suddenly breaking free of the artery wall
– and is often associated with angina, or chest pain
that results when the heart muscle is
oxygen-deprived. Soft plaque is semi-solid,
unstable, and can rupture or break free of the
artery wall and create a blood clot that causes a
serious heart attack.
A narrowing in the arteries is called stenosis,
and that is what radiologists are looking for as
they pore over imagery of the heart. At Tomball
Regional Medical Center, Dr. Bikkina and other
radiologists review these images on a large,
high-definition computer monitor in a quiet room
with muted lighting. Fifty years ago this setting,
and this technology, could only have been envisioned
by science fiction writers.
The views afforded by the 64-slice CT are simply
amazing, and one cannot help but think of the 60s
movie Fantastic Voyage, where a team of scientists
and their submarine are shrunk to miniature size and
injected into the body of Jan Benes, a diplomat who
has escaped from behind the Iron Curtain. The team
has one hour to find and remove a blood clot from
Benes' brain. Notwithstanding the fact that Raquel
Welch was one of the team members, the views of the
body's interior in Fantastic Voyage are becoming
reality in the 21st century as technology marches
forward.
The software even allows the radiologist to take
an artery, with its loops and twists, and straighten
it out on the screen, providing a linear view of the
vessel walls and giving a more objective basis to
identify and measure stenosis.
When radiologists write a report based on the
coronary scan, they refer to stenosis in
percentages, e.g. "30% stenosis near the third
diagonal artery." This percentage is determined by
comparing the full vessel diameter with the
resulting diameter with existing plaque deposits.
They are also able to characterize the deposits,
as calcified plaque looks different than soft plaque
to the CT scanner. The 64-slice technology has
provided a significant improvement over previous
16-slice technology in quantifying calcium-based
plaque, as these deposits previously created a
'bloom' (think lens-flare) on the CT image.
The 64-Slice Question
The question facing radiologists and cardiologists
at this time is, "Where, exactly does 64-slice
technology fit in the diagnostic toolkit?" Although
it is early in the game, the indications for a
64-slice coronary CT scan are solidifying as
insurers get onboard with the technology and doctors
learn more about its capabilities.
"The 64-slice scan is being used for patients who
have unclear results from a stress test, and for
those who have high risk factors in lifestyle and
family history, but no significant symptoms,"
commented Dr. Ravi Bikkina. "It is also being used
for young athletes who experience symptoms during
peak performance times."
Dr. Bikkina said that young athletes who die on
the court or on the field usually have birth defects
in the formation of their coronary arteries, as
opposed to older athletes who may be at risk of
heart attack due to atherosclerosis.
In one such defect, an artery supplying blood to
the heart muscle could be rerouted between two other
large arteries, such that during peak performance
the two arteries swell as they supply increased
blood flow, thus pinching and shutting off the
artery running between them.
Dr. Bikkina said that the 64-slice coronary CT
scan could become a screening tool for any young
athlete who wishes to rule out any such defect, due
to its relatively low cost and its reliability in
affirming a healthy condition of the heart and its
arteries.
"This tool has excellent capabilities in ruling
out significant coronary artery disease," Dr.
Bikkina said. "About one in four catheterizations
show a negative result – no significant stenosis –
so the 64-slice CT scan will definitely have an
increased role in patients where there is no
compelling evidence to show that blockages are
present."
In Closing: The report on the author's 64-slice
coronary CT scan showed that the chest discomfort
was not caused by arterial disease. There was minor
narrowing (from "less than 10%" to "less than 20%")
found in some arteries and none in others, generally
consistent with the normal range for a 46-year old
male, and dietary modifications were recommended...
good advice for everyone to follow.
For information on Tomball Regional Medical
Center's 64-slice coronary CT scan, visit
www.tomballhospital.org or ask your doctor.
Photo caption: (L-R) Ravi Bikkina, M.D., Roxann
Meyer, CT Tech, and David Olifant, M.D. stand in
front of Tomball Regional Medical Center's new
LightSpeed VCT scanner, a technologically-advanced
CT scanner that provides the data for a new
generation of diagnostic wizardry.
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