title:new ct scanner - 256-slice - being tested
in north americajohns hopkins medicine has
installed for three months
of initial safety and clinical testing a 256-slice computed tomography (ct)
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. hopkins is negotiating
purchase of the equipment, whose sticker price is more than $1 million.
johns hopkins cardiologist jo?o lima, m.d., 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 johns hopkins
university school of medicine and its heart institute, says 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 (or 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, m.d., an associate professor of radiology at hopkins, 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 is 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
will still be required for the computer hardware. murphy says the increase in data
traffic will range from 5 gigabytes to 10 gigabytes per scan with the 256-ct.
with 64-ct, the range is 1gigabyte 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 1 second for the 256-ct, down from 4 or 5
seconds with the 64-ct. |
发表于 2007-5-18 08:38
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