EH@ESC_2015

CARDIOLOGY www.healthcare-in-europe.com 5 n Nuclear Cardiology and Cardiac CT s in cardiac CThave many more options to do so,’ Achenbach said. The first strategy to limit exposure is to modify the mode of acquisi- tion and to avoid spiral or helical scanning with continuous radiation exposure, which results in a dose in the 25-30 mSv range. ‘That is really inappropriate for most patients who undergo CTA and can easily be modified because, in most cases, we want image reconstruction only in diastole. Most technology enables limitation of the full output of the X-ray tube during the diastolic seg- ment of the cardiac cycle, thanks to ECG-correlated tube current modu- lation, often called ECG pulsing,’ he explained. Achenbach recommends using ECG pulsing systematically when spiral/helical acquisition is per- formed, as this will lead to a dose reduction of 40 to 50%. Prospectively ECG triggered acquisition avoids spiral acquisition and combines step-wise table move- ments with short periods of data acquisition, typically in diastole. Therefore the dose is low, between 3 and 5 mSv. High-pitch spiral acquisition, sometimes called Flash mode, is a combination of spiral l acquisi- tions and prospective ECG trig- gering. Thhis is only possible with dual source scanners and spends low dose, between 1.5 and 2 mSv. However, it requires low and very regular heart rates. Lowering tube voltage also helps to reduce dose. Traditionally 120 kV were used in cardiac CT, but in many cases this can be lowered to 100 kV. Doing so will reduce the dose by 40%, even in patients who have high body mass index (BMI), according to Achenbach. ‘100 kV should be used in patients less than 85 to 100 kg – some say with BMI < 30 or 25, some combine the two, there are no strict guidelines,’ he pointed out. By combining 100 kV tube voltage with prospectively ECG triggered axial acquisition, dose can be lowered to 2-3 mSv, and to as little as 0.9 mSv with high-pitch acquisition. 80 kVp work in very thin patients (<70 kg), and can lower dose to 0.6 mSv. Some studies have combined all possible modes for dose reduction and performed coronary CTA with doses as low as 0.1 mSv. However, image quality can be seriously ham- pered in such an approach. ‘Very low doses are possible, but I have to say I am not a fan for continuing this race for lower doses because we really risk sacrificing image quality and makinf misdiag- nosis if we put too much weight on dose. Cardiac CT imaging is not a race to achieve the lowest possible dose; you always have to make sure you retain image quality to evalu- ate even those patients who have complex situations such as calcified plaque, etc. Marc Dewey MD is the Heisenberg Professor of Radiology and Vice Chair of the Department of Radiology at Charité University Hospital, Berlin, Germany. He studied medicine at Charité and Johns Hopkins universities. His research focused on non-invasive cardiovascular imaging, cardiac MRI and CT, radiation dose, experimental radiology, meta-analyses, cost-effectiveness and patient-centred imaging. Publications number over 150 and he has produced 65 original papers as first or last author, and given more than 70 invited lectures, including at the RSNA and ECR. hybrid imaging techniques such as PET/CT, are most promising to com- prehensively assess CAD.’ For further information please go to: DISCHARGE Trial www.dischargetrial.eu Department of Radiology http://radiologie.charite.de Prof. Marc Dewey MD www.marcdewey.de EU-Project DISCHARGE http://ec.europa.eu/research/health/ medical-research/cardiovascular-diseases/ projects/discharge_en.html

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