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A new standard for image quality, dose reduction and Dual Energy in single source computed tomography

Somatom Definition Edge from Siemens

At this year's Congress of the Radiological Society of North America (RSNA) Siemens Healthcare is presenting a CT scanner, the Somatom Definition Edge, which makes use of innovative technologies to introduce the new reference in single source CT.

Siemens introduces a new reference in Single Source CT: the new Somatom Definition Edge with the entirely new developed Stellar Detector - the first fully integrated detector, designed to minimize electronic noise. It delivers an unprecedented spatial resolution in clinical routine and is a perfect match for low dose imaging especially in combination with iterative reconstruction solutions.

The Somatom Definition Edge is the first single source CT to make use of Siemens' recently developed Stellar Detector. In routine examinations, structures up to 0.3 mm in size are visible, and image sharpness is improved in comparison to existing single source CT scanners, without having to increase the radiation dose. With a rotation speed of 0.28 seconds, the Somatom Definition Edge is the fastest of all the single source CT scanners produced by Siemens, and acquires up to 23 centimeters per second. This allows a customary thorax-abdomen examination of an adult to be performed in around two seconds. This means that patients nearly don't need to hold their breath during a scan. In addition, Siemens has developed a new Dual Energy mode for the Somatom Definition Edge, which requires significantly less radiation than is usually the case when this scanning method is used in the Single Source CT. In Dual Energy images, two different tube voltages are generated to allow different tissue types to be recognized.

As part of Agenda 2013, a global initiative to further strengthen its innovative power and competitiveness, Siemens Healthcare has developed the CT scanner Somatom Definition Edge which is supposed to set a new benchmark for single source CT. "In 2008, Siemens took speed and dose reduction in CT operations into completely new dimensions with the Somatom Definition Flash Dual Source CT scanner. Now, with the Somatom Definition Edge, we are setting new standards in terms of image quality, low dose and Dual Energy for single source CT," explains Walter Märzendorfer, CEO Computed Tomography and Radiation Oncology for Siemens Healthcare, "and have developed a whole series of innovative technologies, such as our new Stellar Detector and a new Dual Energy mode."

Recognition of anatomical structures up to 0.3 mm

The Somatom Definition Edge employs the new TrueSignal Technology of the Stellar Detector, which for the first time enables the electronic detector components to be integrated into the photodiode. With the aid of the TrueSignal Technology, Stellar reduces significantly the electronic noise, thus improving the signal-to-noise ratio of the images. This allows ultra-thin slices of just 0.5 mm to be scanned at very low signal strength, generating images with a spatial resolution of up to 0.3 mm, without the need to increase the radiation dose. To date, a spatial resolution of up to 0.33 mm has been possible with Siemens Single Source CT scanners. However, in critical cases, such as cardio-vascular examinations or in emergency diagnostics, every additional visible micrometer can be significant. The examination of adipose patients provides a further example of how Stellar's excellent signal processing opens up new possibilities in clinical practice. An obese patient can attenuate the signal from the X-ray tube to such an extent that many CT systems can no longer generate images suitable for diagnostic purposes in the case of patients above a certain weight. Even where signals are weak, the TrueSignal technology allows to still generate image quality featuring contrasts that the physician can use for diagnostic purposes.

Increased speed in Single Source CT

One of the great challenges in CT scanning is maintaining good spatial resolution even at high gantry rotation speeds. With patients who cannot stay still for extended periods, or with fast moving organs like the heart, the shortest possible scanning time minimizes motion artifacts on the images. For this reason, the Somatom Definition Edge features a newly developed gantry, which requires just 0.28 seconds per rotation, enabling a very high spatial resolution of 142 ms. In addition, the scanner allows a pitch of 1.7, equivalent to an acquisition speed of up to 23 centimeters per second. This allows a two-meter tall patient to be scanned in around eight-and-a-half seconds.

Dose-optimized Dual Energy for Single Source CT

Until now, Dual Energy examinations with Single Source devices required the tube voltage to be changed several times during a single scan. One of the disadvantages of this is that the image quality deteriorates, as less than half of the number of projections is available for each energy level. It is also impossible to change the voltage at the same time as modulating the current, which means that the current must be permanently set for the entire duration of the scan. This results in a dose level several times higher than is the case with a customary Single Source scan.

As dose reduction has a high priority for Siemens in all its new developments in X-ray technology, the Somatom Definition Edge introduces a new scanning technique into Single Source CT examinations: During a Dual Energy examination with the new Siemens CT scanner, two scans are performed in succession with different energy levels, with each scan using only around half the dose applied in normal mode. In total, the two scans together deliver the original dose required. Also, since the voltage in each scan is fixed, all dose-reducing methods can be employed. Of particular note is Care Dose4D, a fully automatic radiation exposure control system, which adjusts the dose in real time according to the area of the body being scanned, and is thus capable of reducing overall dose levels. Safire (Sinogram Affirmed Iterative Reconstruction) is also used. This is an exceptionally rapid method for the iterative reconstruction of CT data, which likewise helps to cut dose levels. Dual Energy images can thus be generated with a Single Source system, without exposing the patient to unnecessarily high radiation levels.

Launched in November 2011, Agenda 2013 is a two-year global initiative to further strengthen the Healthcare Sector's innovative power and competitiveness. Specific measures will be implemented in four fields of action: Innovation, Competitiveness, Regional Footprint, and People Development.

The Siemens Healthcare Sector is one of the world's largest suppliers to the healthcare industry and a trendsetter in medical imaging, laboratory diagnostics, medical information technology and hearing aids. Siemens offers its customers products and solutions for the entire range of patient care from a single source – from prevention and early detection to diagnosis, and on to treatment and aftercare. By optimizing clinical workflows for the most common diseases, Siemens also makes healthcare faster, better and more cost-effective. Siemens Healthcare employs some 51,000 employees worldwide and operates around the world. In fiscal year 2011 (to September 30), the Sector posted revenue of 12.5 billion euros and profit of around 1.3 billion euros. For further information please visit:

The product Somatom Definition Edge is still under development and not commercially available yet. Its future availability cannot be ensured.

The products/features mentioned here are not commercially available in all countries. Due to regulatory reasons the future availability in any country cannot be guaranteed. Further details are available from the local Siemens organizations.

Reference Number: HIM201111003e

Ms. Marion Bludszuweit
Healthcare Sector
Siemens AG
Henkestr. 127
91052 Erlangen
Tel: +49 (9131) 84-3292

Marion Bludszuweit | Siemens Healthcare
Further information:

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