Siemens unveils flagship low-dose, high-res CT

A new CT scanner built on Siemens' unique dual-source x-ray technology promises to dramatically reduce dose and eliminate motion artifact in the chest. Using two x-ray tubes and matching detectors, the Somatom Definition Flash, debuted at RSNA 2008, opens the door to routine scanning of the coronaries, according to the company.

It requires only a fraction of the radiation dose of other systems now on the market and exposes patients to just a third of the dose they naturally encounter in a year from background sources. A new filter will purify x-ray beams at high and low energies to emit only the planned spectra, enhancing tissue characterization. The FDA-cleared system with a $2 million price tag will be installed first at leading institutions in Europe, then at ones in the U.S.

Rotations every 0.28 sec provide the horsepower to cover 43 cm/sec and deliver a temporal resolution of 75 msec. Whole chests can be covered in just 0.6 sec, eliminating the need for breath-holds, according to the company. The scanner's extraordinary speed means staff will not have to sedate pediatric or trauma patients. This speed is possible because the second imaging chain, mounted in the gantry at a 90° angle to the first, provides the data that would otherwise be missed if a single tube system were used.

"With two sources and two detectors, we can fill the gaps that would be there on a conventional-source CT scanner at higher pitch," said Alexander Zimmermann, director of product marketing for Siemens CT. "We fill them with information from the second source."

Spiral heart scans can be done in a quarter of a second, or about half a heartbeat. Rather than receive an increase in dose, as might be expected, patients undergoing a heart scan on the Definition Flash receive less than 1 mSv of dose.

The selective photon shield blocks unnecessary parts of the energy spectrum to improve separation of the two simultaneous scans with low and high energy. This capability can be used to classify the chemical composition of tissues or to reconstruct unenhanced CT images without administering x-ray contrast media or having to perform an additional examination.

The X-Care application selectively reduces radiation exposure when the scanner passes over dose-sensitive organs, such as the eyes and female breast. This is done by switching off the x-ray tube assemblies during the rotation phase, when vulnerable tissues are most directly exposed to radiation, reducing radiation exposure by up to 40%, according to Zimmermann.