Johns Hopkins Medicine has installed for three months
of initial safety and clinical testing a 256-slice computed
tomography scanner, believed to be the world's most
advanced CT imaging software and machinery.
The new 2-metric-ton device — the first of its
kind in North America and only the second outside of Japan,
where its manufacturer is based — has four times the
detector coverage of its immediate predecessor, the 64-CT.
It can measure subtle changes in blood flow or minute
blockages forming in blood vessels no bigger than the
average width of a toothpick (1.5 millimeters) in the heart
and brain.
Made by Toshiba, the Aquilion beta 256 is expected to
win approval for general clinical use within a year, its
makers say. Johns Hopkins is negotiating purchase of the
equipment, whose sticker price is more than $1 million.
Johns Hopkins cardiologist Joao Lima, who will lead
all cardiovascular testing, says the scanner's strength
means it can find the earliest signs of restricted blood
flow, long before symptoms appear or an organ becomes
permanently damaged.
Lima, an associate professor at the School of Medicine
and its
Heart Institute, says that blockages in arteries, veins
or capillaries in any organ can simmer for years, with
signs of chest pain, severe fatigue and headache emerging
only after the disease has become seriously life
threatening.
The key technological advance of the 256-CT, which
looks like a patient table surrounded by a massive
doughnut-shaped metal ring (called a central gantry), is
its greater number of detectors, which cover in a single
scan four times the area of the 64-CT. Hopkins currently
has a 64-slice CT scanner.
According to company descriptions, a single rotation
of the device's X-ray-emitting gantry can image a diameter
of 12.8 centimeters (5 inches), a slice thick enough to
capture most individual organs in one swoop, including the
brain and heart; entire joints; and most of the lungs and
liver. This is an increase in coverage from 3.2 centimeters
per image with the 64-slice, which required several
rotations or scans to fully image an organ.
Interventional neuroradiologist Kieran Murphy, an
associate professor of radiology, says he believes that
whole-head perfusion imaging scans will be able to find
slowed blood flow areas in the brain that are vulnerable to
stroke, and with just one scan.
CT imaging consists of X-rays sent through the body to
produce digitized signals that can be detected and
reconstructed by computers. Each of the 256 detectors on
the new machine picks up a "slice" of an organ or tissue.
The more detectors, the better the resolution of the
picture. A computer puts all the slices together to render
detailed 3-D images of the heart or brain and surrounding
arteries. In some cases, a patient is injected with a
contrast solution to increase the visual detail.
Murphy, who is in charge of neurological testing with
the scanner, says the expanded coverage is a "tremendous
advantage" over older machines, where images had to be
matched and stacked, "like reconstructing layers of a
marble statue on top of each other over time," a
technologically complex procedure.
Cooling systems, he also notes, will no longer be
required to deal with the friction and heat caused by
multiple rotations of the gantry, although a cooling system
still will be required for the computer hardware. Murphy
says the increase in data traffic will range from five
gigabytes to 10 gigabytes per scan with the 256-CT. With
64-CT, the range is one gigabyte to 2.5 gigabytes.
However, he does not expect the higher volume of data
to slow testing, which is expected to speed up imaging the
brain to less than one second for the 256-CT, down from
four or five seconds with the 64-CT. Lima says the overall
time required for testing the heart will similarly decline
to one or two seconds with the 256-CT, from eight to 10
seconds with the 64-CT.
Lima says the new, faster device will also make it
possible to scan patients with arrhythmia, or irregular
heartbeats. The 256-CT can acquire a full image in the time
it takes for just one beat, whereas the 64-CT takes as many
as six or eight heartbeats. Any disturbances between
successive beats, he notes, such as those produced in
arrhythmia, can lead to distortions in the composite
scanned image.
A single scan with the 256-CT device can also perform
a full bank of five key diagnostic tests on hearts, or
single tests in the brain, of the most severely ill
patients, exposing them to far less radiation, as little as
one-eighth to one-third of the dose required in testing
with the 64-slice scanner.
Because single scans with the 256-CT should provide a
patient's calcium score, to detect hardening of the
arteries, along with blood-flow data and strength of the
pulse and heartbeat, it is expected to have value in
determining more precisely the best candidates for more
invasive procedures, such as cardiac catheterization or
catheter angiograms of the brain.
The new scanner and nine technicians are on loan to
Johns Hopkins from Toshiba America Medical Systems.
Installation and renovation costs for the machine's
temporary installation at Johns Hopkins were also paid for
by Toshiba.
GO TO