Siemens packs two 64-slice CTs in one gantry

Siemens hopes to redefine CT with the introduction of a scanner that combines two 64-slice imaging chains in a single unit.

The Somatom Definition, unveiled this morning in a media event in New York City, features two detectors mounted at a 90° angle to one another. Each detector contains 32 elements and is aligned with its own Straton x-ray tube, which fires two beams of x-rays at slightly different angles a moment apart.

This z-Sharp technology is the backbone of Siemens' erstwhile flagship Sensation 64, now deposed by the new scanner.

An evaluation site for Siemens' new unveiling is currently operating at the University of Erlangen in Germany. Ten more such sites are scheduled for installation by spring 2006. Bernd Ohnesorge, Siemens' vice president of CT, predicts as many as 100 Somatom Definitions will be installed by the end of next year on 200 sales.

These customers will be the financial elite of diagnostic imaging. Siemens plans to charge between $2.3 million and $2.5 million per scanner, an astronomical price for a CT scanner but one Ohnesorge considers justified.

"The Somatom Definition delivers a level of performance and technology that has never been addressed before," he said.

With the development of this scanner, Siemens has diverged technologically from the pack. Whereas competitors have locked horns in a battle over slices, seeking to prevail with sheer numbers, Siemens engineers have focused on clinical effect. The integration of two high-power imaging chains in a single scanner and the speed that affords will have an immediate and powerful effect on cardiovascular imaging.

"We believe it can freeze every beating heart," Ohnesorge said. "There is no need anymore for beta blockers to prepare patients."

Siemens expects the Somatom Definition to find a role in acute care as well. The scanner will be able to handle a broad range of applications from trauma, including stroke, to the assessment of patients with chest or abdominal pain, he said.

The foundation for this development was laid two years ago with the Straton x-ray tube (DI SCAN 10/29/03), a compact, highly efficient tube compatible with the z-Sharp. The Sensation 64 platform, launched in 2004, delivers improved spatial resolution through the integration of these two key technologies, creating two nearly simultaneous images of each point along the axial rotation of the imaging chain (DI SCAN 1/8/04). Combining two such imaging chains doubles temporal resolution and cuts acquisition time in half.

Somatom Definition delivers one slice every 83 msec, an accomplishment achieved without the use of segmentation algorithms that vendors commonly use to draw data from sequential rotations to "compile," or enhance, an image. If Siemens were to use such algorithms, temporal resolution would double again to about 42 msec. Ohnesorge does not expect such mathematical manipulations to be necessary, however.

"It has been shown in EBT (electron-beam tomography) that if you are able to go below 100 msec, there is no motion artifact in coronary artery imaging," he said.

Using the scanner's inherent power keeps scan time to a minimum. When applied to the heart, the Somatom Definition might acquire as much data in a beat or two as current scanners do in the five or more now required. Consequently, x-ray exposure to the patient is expected to drop by half, according to Ohnesorge, at the same time that power doubles.

"We can get incredible scan speed, because the Somatom Definition can utilize power reserves up to 160 kW, driven by two 80-kW tubes and generators," he said. "We can utilize these power reserves to scan always at top speed and get high image quality independent of patient size and weight. So even with obese patients, we can get maximum quality and maximum speed."

Siemens has designed the scanner to deliver two simultaneous but different energies. Each imaging chain can be tuned to deliver separate energies that optimize different types of tissues.

Dual-energy scanning might be used in cardiovascular imaging to differentiate the vessel wall from surrounding tissue. It could be used to isolate bone and blood vessels, as in the case of complex vasculature near the skull or across the knee. It may also be used in the lung to characterize pulmonary arteries and nodules or in the liver to differentiate fatty lesions from carcinoma.

The true potential of dual-energy scanning, however, has yet to be determined through clinical studies. Some have begun at the University of Erlangen, and others will take shape at the dozens of clinical sites expected to begin using the Somatom Definition in the year ahead.

Editor's note: A detailed description of Somatom Definition, its development and operation, will be published in the Nov. 21 issue of DI SCAN.