Dosage for Cardiac Dual-Source CT Can Be Significantly Lowered

A new study reveals that by using dual-source computed tomography (DSCT), the effective dosage for a heart examination can be significantly lowered, in comparison to conventional CT. The study also demonstrated that stenoses could be diagnosed with similar high accuracy as with invasive X-ray angiography.

At the University Hospital Zürich (Switzerland), 120 patients with suspected coronary heart disease were scanned with the world's first CT scanner with two X-ray tubes, a Somatom Definition system, developed by Siemens Healthcare (Erlangen, Germany). The Siemens application, Adaptive Cardio Sequence with a step-and-shoot mode, was also used for the first time with a dual-source CT. The results of the study were published in the June 2008, issue of the journal Heart.

Angiography is a diagnostic procedure used to determine coronary arterial occlusion. Typically, this examination is conducted using angiography devices in the catheter laboratory and CT images. However, with CT, the question of the radiation dosage plays a huge role. Researchers at the University Hospital now want to see whether the dose used during CT angiography can be reduced.

The research team used Adaptive Cardio Sequence, which was recently developed by Siemens for all Somatom Definition Scanners. The application is based on the step-and-shoot method, in which the next respective diastole is calculated, and only this phase of the cardiac cycle is used to obtain image data. The combination of Adaptive Cardio Sequence and the DSCT's maximum time resolution of 83 ms facilitate this technique in a particularly effective manner and permits a further significant reduction in dosage.

"The results show that CT coronary angiography with a dual-source CT in step-and-shoot mode produces images of excellent diagnostic quality in patients with stable heart rates up to 70 bpm. The dosage reduction achieved in comparison to previous CT angiography is also remarkable. In our study, we required an effective dose of 2.5 mSv on average with a deviation of plus or minus 0.8 mSv. In the literature, a normal average effective dose for heart scans of between 9 mSv and 21 mSv is reported,” said Dr. Hatem Alkadhi, specialist in radiology at the Institute for Diagnostic Radiology, University Hospital Zürich.

The Adaptive Cardio Sequence supplements the step-and-shoot method with intelligent algorithms, which monitor the heart frequency of patients, and if necessary, respond to arrhythmia, such as extra systoles (i.e., additional heart beats). In this case, the recording phase is automatically postponed to avoid image errors due to the sudden movement. Moreover, the recording window can be widened a little more if required so that, using the Adaptive Cardio Sequence, the robustness of the CT scan can be increased significantly overall.

"For Siemens, the safety of the patients has always been the primary focus of the developments in CT. At the same time, we consider our highest obligation to be to give doctors the best diagnostic image quality and to support them in making their workflow as efficient as possible. With this outlook and constant further development, Siemens has positioned itself as a market leader in CT technology,” said Dr. Sami Atiya, CEO, Computed Tomography, Siemens Healthcare. "Innovations for dose reduction, in conjunction with improved diagnostic image quality, are therefore of the utmost importance to us. This is why we have also further developed our Adaptive Cardio Sequence, now for the dual-source CT. The study from Zurich confirms to us that the combination of step-and-shoot and dual-source computed tomography does significantly reduce the dosage required during heart scans.”

Related Links:
University Hospital Zurich
Siemens Healthcare