Dose-Reducing Dual-Source CT Applications Suitable for Pediatric Imaging

Based on the patient's anatomy and the type of examination, a new application automatically recommends the correct tube voltage for the selected tube current in milliamperes (mA). All other parameters are adapted automatically to the selected kV level. This optimizes the relationship between contrast and noise in the image. Moreover, dose can be reduced by up to 60%. The application is currently being evaluated by a number of pediatric radiologists.

The tube voltage to be selected in computed tomography (CT), which is known as the kV (kilovolt) level, depends on the size and weight distribution of the patient, as well as on the examination type. Selecting the respective suitable kV level means that image quality can be optimized and dose minimized significantly. If the tube voltage is changed, all other scan parameters have to be adapted accordingly. However, since the dependencies are nonlinear and their adjustment is intricate, the values have to be calculated manually using complex formulas, or estimated.

Studies have shown that users generally tend not to change the kV values for this reason, and therefore do not exploit the full dose-saving potential. While the voltage values typically used today range between 80 kV and 140 kV, the Care Child function, developed by Siemens Healthcare (Erlangen, Germany) enables to perform CT examinations at only 70 kV, resulting in considerable dose savings particularly for children and babies. This power level is possible because Siemens further enhanced its Straton tube in a way to generate these low voltages.

Safire (sinogram affirmed iterative reconstruction), a new method for iterative reconstruction of CT images based on CT raw data, is another dose-saving measure. At the end of 2009, Siemens presented IRIS (iterative reconstruction in image space), its first innovation for iterative reconstruction. With Safire, Siemens has additionally enhanced the algorithms and is also offering new hardware that enables to significantly reduce the time required to reconstruct slice images in comparison to IRIS.

At IPR 2011, radiologists and pediatric radiologists will explain how--compared to noniterative reconstruction procedures--it is possible to reduce the radiation dose for children by up to 60% using Safire.

The Somatom Definition Flash is a dual-source CT system where two X-ray tubes rotate around the body simultaneously. The highest scan speed in CT to date (45 cm per second) and a temporal resolution of 75 milliseconds enable complete thoracic scans in just 0.6 seconds. As a result, patients no longer have to hold their breath. At the same time, Somatom Definition Flash works with a much lower radiation dose. For example, a routine cardiac scan on a patient of up to 90 kg can be performed with less than one millisievert (mSv), while the average effective dose is generally between 8 and 20 mSv.

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