General Information on low dose

Siemens has always believed that even the farthest technical horizons were temporary and could be surpassed with consistent dedication to improved healthcare. This visionary approach has made Siemens the undisputed innovation leader in CT over the past 35 years. Our innovative philosophy is based solidly upon the assumption that achieving the highest technical performance is only important when it meets the needs of the patient and our customers. From the very beginning, one of the most frequent demands of our end users has been patient safety. And in Computed Tomography, patient safety translates primarily into dose reduction.

For this reason, we have, from the earliest days, developed many significant products and protocols that follow the “As Low as Reasonably Achievable” (ALARA) principle to reduce radiation dose to the lowest possible level. This desire for as little radiation exposure as possible lies at the heart of our CARE (Combined Applications to Reduce Exposure) research and development philosophy. Over the years, Siemens has been highly successful in integrating many innovations into the Siemens scanners that significantly reduce radiation dose in comparison to other systems available on the CT market.

For example, Siemens eliminates pre- and post spiral over-radiation with the Adaptive Dose Shield introduced in 2007. This saves up to 25% dose in addition to all other dose savings.

The SOMATOM Definition Flash launched in 2008 is another prime example. Its core innovation – the revolutionary Flash Spiral – reduces dose to unprecedented levels. Consider how ground-breaking it is to acquire, for example, the whole heart in the blink-of-an-eye with less than 1 mSv.

Another benchmark for low dose CT was introduced at this year’s RSNA. With Iterative Reconstruction in Image Space (IRIS), the Siemens SOMATOM Definition scanners routinely achieve up to 60% additional dose reduction in a wide range of CT applications while maintaining excellent image quality.

A final proof of Siemens CT’s undisputed low-dose leadership comes from our customers. For the first time in CT history, Siemens encourages users to participate in the International Image Contest and share their best, low-radiation images acquired while utilizing all available low-dose solutions.

Results may vary. Data on file.

The Adaptive Dose Shield - available on the SOMATOM Definition AS and SOMATOM Definition Flash - eliminates over-radiation pre- and post-spiral to the patient (marked in red). It is unique to the CT industry and part of the innovative new STRATON X-ray tube design. By dynamically moving shields into place on the X-ray tube it blocks unnecessary dose. The Adaptive Dose Shield dynamically opens at the beginning of a spiral range and then dynamically closes at the end. Now all clinically irrelevant dose is eliminated. Not only for dedicated applications, but for every single spiral acquisition. Giving you the ability to save an additional 25% of dose in routine exams like abdominal CT.


Results may vary. Data on file.

For quite some time, iterative reconstruction has been heavily discussed in the CT community as a highly promising method to achieve significant dose reduction without compromising image quality. And once again Siemens has set the benchmark on low dose imaging with the introduction of the first raw-data based iterative reconstruction – SAFIRE (Sinogram Affirmed Iterative Reconstruction). For the first time, raw data (or sinogram data) are actually being utilized in the iterative image improvement process. With this, SAFIRE can achieve a radiation dose reduction of up to 60%*. Or instead improve image quality (contrast, sharpness and noise), even surpassing the already impressive image quality realized with IRIS.

SAFIRE in 3 steps:

1. SAFIRE allows up to 60% dose reduction in a wide protocol spectrum
2. Provides a superior image quality 
3. Fast and customizable workflow with >20 images per second






* In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software:. Noise, CT numbers, homogenity, low-contast resolution and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file.

Because at Siemens dose reduction has continued to be given top priority, assuring both patients and medical personnel the best in medical care with the least possible risk, we can now introduce another low dose solution – once again Siemens has set the benchmark on low dose imaging with the introduction of iterative reconstruction. With IRIS the Siemens high-end SOMATOM Definition scanners deliver excellent diagnostic image quality with levels of dose lower than ever before. With IRIS, Siemens’ smart approach to iterative reconstruction, up to 60% additional dose reduction can be achieved in a wide range of daily routine CT applications.

Dose reduction with CT has been limited by the currently used filtered back projection reconstruction algorithm as displayed on the left. When using this conventional reconstruction of acquired raw data into image data, a trade-off between spatial resolution and image noise has to be considered. Higher spatial resolution increases the ability to see the smallest detail; however, it is directly correlated with increased image noise.

In an iterative reconstruction, a correction loop is introduced into the image generation process as shown on the right. To avoid long reconstruction times the new Iterative Reconstruction in Image Space first applies a raw data reconstruction only once. During this initial raw data reconstruction, a so-called and newly developed master volume is generated that contains the full amount of raw data information, but at the expense of significant image noise. During the following iterative corrections the image noise is removed without degrading image sharpness. The new technique results in increased image quality or dose savings of up to 60 % for a wide range of clinical applications.

Iterative Reconstruction in Image Space Brochure


Results may vary. Data on file.

In a continual commitment to patient care and radiation reduction in computed tomography (CT), Siemens Healthcare has launched SIERRA (Siemens Radiation Reduction Alliance) and has established an expert panel to advance the cause of dose reduction in CT. The new Low Dose Expert Panel includes 15 specialists in radiology, cardiology and physics, who are internationally recognized for their publications on the subject of CT dose. The panel’s objective is to generate proposals for how manufacturers may continue to develop their technology and to help users better adapt their procedures in order to bring about further dose reduction in CT. One of the most important suggestions from the first meeting of the Low Dose Expert Panel in May concerns methods to increase utilization in clinical practice of the many CT dose reduction technologies that are already available.