Johns 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 Joaoo 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.

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