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Details emerge from use of 256-slice CT at Johns Hopkins Medicine


Several weeks of clinical tests at Johns Hopkins Medicine have confirmed expectations for Toshiba’s 256-slice CT, establishing the prototype’s ability to measure subtle changes in blood flow and minute blockages in the heart and brain.

Several weeks of clinical tests at Johns Hopkins Medicine have confirmed expectations for Toshiba's 256-slice CT, establishing the prototype's ability to measure subtle changes in blood flow and minute blockages in the heart and brain.

Final results are still pending, but cardiologist Dr. João Lima, who has been directing cardiovascular testing of the CT prototype since its arrival in February at Johns Hopkins, believes the Aquilion beta can detect signs of restricted blood flow long before symptoms appear and well before organs are permanently damaged.

In cardiac tests, the 256-slice CT can acquire a full image in a single beat, eliminating the chance of artifacts creeping into reconstructed data from irregular heart beats, according to Lima, an associate professor of medicine, radiology, and epidemiology. Lima and colleagues at Johns Hopkins are now working out the details for a cardiac perfusion application designed to allow viability testing of the myocardium.

The wide-area single rotation can also capture slow blood flow in areas of the brain vulnerable to stroke, according to interventional neuroradiologist Dr. Kieran Murphy, an associate professor of radiology at Hopkins.

A single rotation of the gantry cuts a 12.8-cm swath, enough to visualize the brain, heart, any of the joints, or most of the lungs and liver. Heart scans are completed in one to two seconds. Brain scans take less than a second. By comparison, 64-slice CT detectors average about a quarter of that area per rotation, requiring several turns to cover the area handled by Toshiba's wide-area detector.

The two-metric-ton device still has a few more weeks on its scheduled three-month safety and clinical test run at Johns Hopkins. Nine technicians from Toshiba America Medical Systems are assisting the Hopkins staff in its testing of the Aquilion beta. The company has also picked up costs associated with site renovations, installation, and deinstallation of the scanner.

Before traveling to Maryland, the Aquilion beta completed three-month stints in Japan at Fujita Hospital and the country's National Cancer Center. The prototype will complete its tour of duty at Johns Hopkins in about a month, returning the end of April or early May to Toshiba's factory in Japan, where it will be tweaked for commercial release in summer 2008.

Operational details are emerging, as testing of the device continues at Johns Hopkins. Staff there note reduced need for cooling in the CT room, as the Aquilion beta's single rotation encounters less friction than the multiple rotations of a 64-slice scanner. Also contributing to lower heat production are the direct drive motors that power the gantry, according to Doug Ryan, senior director of the CT business unit at Toshiba America Medical Systems.

The single rotation of this gantry reduces a patient's radiation exposure to as little as one-eighth to one-third of the dose accompanying scans done on a 64-slice CT, according to the Johns Hopkins staff. This is because the overlap of slices required with helical scanning of the heart is not needed when using the wide-area detector onboard the Aquilion beta.

The amount of data acquired during a typical cardiac scan on the 256-slice system is about equivalent to that acquired during such scans with a 64-slice scanner, Ryan said. But data volume can quadruple to 10 gigabytes in advanced applications like myocardial viability testing.

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