EH 4_2015

CARDIOLOGY EUROPEAN HOSPITAL  Vol 24 Issue 4/15 12 From the International Conference on Dose reduction strategies During this year’s International Conference on Nuclear Cardiology and Cardiac CT, Dr Marcio Bittencourt, from Sao Paulo, Brazil, offered an overview of the newest available technology, namely GE Healthcare’s Revolution, Siemens Force, Toshiba’s Aquilion ONE ViSION, and Philips’ Brilliance and IQon Spectral Detector CT scanners. New scanners must do four things: improve image quality, acquisition speed and coverage, and reduce radiation dose, Bittencourt explained. Temporal resolution – the time needed to acquire one image – should be <15% of the cardiac cycle to minimise motion artefacts. Thus, acquisition time, a challenge in the cardiac setting, must be as low as possible. Faster rotation is one way to achieve that, and most new scan- ners have indeed increased speed up to 0.25s per rotation. Other options are dual source CT and multi segment reconstruction. To improve spatial resolution, users can either do sharper recon- struction, although some recent changes in detector technology and flying or dynamic focus spot have also improved spatial resolution. For z-axis coverage, cardiac imag- ing usually required about 14 cm. Some new scanners now allow this to be performed in a single heart- beat, though this technology is not available for all vendors, Bittencourt pointed out. New technology enables selection of the best scan mode and protocol for each individual examination, which contributes to reducing radia- tion dose. Besides protocols, other features, such as automated expo- sure control, reduced target noise and iterative reconstruction, may also lower dose significantly. One recent technology, spectral energy imaging, has the potential to do calcium subtraction, myocardial perfusion or iodine map, and beam- hardening correction for perfusion. However, not all these options are necessary if users are not doing top- notch research, Bittencourt believes. ‘If you can’t afford newer tech- nologies, any 64 detector scanner allows adequate diagnostic image quality for most patients. Anything newer will cost more. If you ask me whether any of the new scan- ners better, I think they certainly have improved temporal resolution and spatial resolution, which are interesting and may allow evalua- tion of more complex patients. So, if you can pay for these new toys, my answer is yes, they are better. But if you ask if they are a cost effective replacement for a 64 detector scan- ner, from a health perspective, the answer is probably no.’ Dr Stephan Achenbach from Erlangen, Germany, focused on methods for low-dose coronary CTA. ‘CT made its way into European guidelines on stable coronary dis- ease and acute coronary syndrome, so it should really be considered in patient management,’ he said. There is tremendous potential for dose reduction. A 2007study at 50 sites across Europe compared 1,965 CTA examinations in 2,000 individu- als. It showed tremendous differ- ences in estimated radiation dose associated with CT angiography, with some sites using doses of up to 13 mSv on average and others 4.6 mSv. Image quality, however, did not correlate to dose. ‘This study from the past clearly shows that radiation dose can be lowered without sacri- ficing image quality, and today we World-renowned cardiologists reviewed the latest trends and dose reduction strategies in cardiac CT during the International Conference on Nuclear Cardiology and Cardiac CT (ICNC) that unfolded in Madrid in May. Mélisande Rouger reports. Professor Stephan Achenbach is Chairman of the Department of Cardiology at the University of Erlangen, Germany and Vice President of Global Affairs and Communication at the European Society of Cardiology (2014-2016). With major clinical interests in cardiac CT, imaging of atherosclerosis and interventional cardiology, he was president of the Society of Cardiovascular Computed Tomography between 2007 and 2009, and is currently its secretary. He is also a fellow of the European Society of Cardiology, the American College of Cardiology and the Society of Cardiovascular Computed Tomography, and a member of the European Academy of Sciences and Arts. Dr Marcio Sommer Bittencourt is Assistant Physician at the Division of Internal Medicine, University Hospital of Sao Paulo, Brazil, where he obtained his PhD in 2014. He also gained a Masters Degree in Public Health from Harvard Medical School in 2013, and carried out a post-doctoral research fellowship in cardiovascular imaging at Brigham. His main clinical interests lie in cardiovascular disease, epidemiology, internal medicine, public health, bio- statistics, medical and biomedical image processing and cardiac MRI. He is one of the Fellow and Resident Leaders of the Society of Cardiovascular Computer Tomography SCCT and has over 100 publications to his name. Dr Bittencourt obtained a Masters in Public Health at Harvard Medical School in 2013, and gained his PhD in cardiology from Sao Paulo University in 2014. Continued from page 11 Seeking CT‘s role ber in this pan-European study. ‘Procedural complications will be a secondary outcome. ‘The study design was presented at the last ECR, during a late-break- ing clinical trial session. The study has only just begun and is being conducted in 30 sites across Europe so far. We also plan to include large and small hospitals in the project. ‘Ultimately, DISCHARGE aims to provide the basis for new guidelines in cardiac imaging. Therefore, we are collaborating closely with clini- cal sites as well as non-clinical part- ners to optimise the impact of the study for the benefit of the different European health systems. ‘This study has been granted six million euros through the 7th Framework Programme of the European Union (EC-GA 603266). It will actively recruit for two years with a maximum follow-up of four years.’ Today, where is CT placed in assessing suspected CAD? ‘Currently, CT has little role and is not reimbursed for this purpose. Despite its proven high diagnos- tic accuracy, CT’s full diagnostic potential is not being used, mainly because the comparative effective- ness of CT versus invasive coronary angiography (ICA) has not been shown in patients with stable chest pain and suspected CAD. ‘In most European countries, ICA is the final reference standard to detect CAD, but it only allows mini- mally invasive treatment of coronary stenosis during the same procedure. However, approximately two million ICAs, done in Europe every year, do not detect CAD. It is thus the focus of our research efforts to analyse in which cases CT could replace these invasive tests.’ Does CT have diagnostic value in stable chest pain and suspected CAD? ‘ICA is an invasive technique. As a diagnostic tool for patients with sus- pected CAD, especially with a low to moderate risk (10-60%), alterna- tive tests that are non-invasive might provide a better risk/benefit ratio in favour of the patient. ‘CT, because it is non-invasive, also grants potentially higher patient safety if used in appropriate clinical situations – but currently we do not know which ones. ‘Early detection and improved characterisation of coronary plaques in the entire coronary artery tree is possible with CT. Certain unique of CAD is likely, CT, with its tre- mendously improved image quality, might prove to be the best method available.’ Other imaging modalities to rule out CAD ‘We also use imaging ischemia tests, such as stress MRI, PET/CT, SPECT and stress echocardiography. These tests, while they allow the detection of CAD, are so-called functional tests and thus have a different pur- pose than CT. ‘These perfusion-imaging tests enable a search for stress-induced ischemic myocardial areas, which play an important role in clinical decision-making in case of anatomic coronary stenosis found by CT with unclear functional relevance.’ high-risk plaque features have been shown to predict subsequent events and outcomes if assessed by CT. However, it’s not known from a randomised trial whether such high-risk plaques should lead us to recommend intensified risk factor modification or certain medications. ‘Another advantage is that CT images the tissues surrounding the heart, whilst ICA is limited to the coronary arteries. Therefore, CT has the possibility to check the lungs, oesophagus and spine, which may result in a diagnosis that explains chest pain and suggests appropriate treatment, but could be overlooked by ICA. ‘In conclusion, ICA is the best way to treat known CAD; but in a situation where ruling out diagnosis Future promising techniques ‘For all the above-mentioned non- invasive techniques (CT, MRI, PET/ CT, SPECT, and echocardiography), dedicated research groups are work- ing in Europe to further improve these diagnostic tests from a techni- cal and clinical perspective. ‘The main goal would be to develop a comprehensive imaging test that would allow accurate stenosis detec- tion, characterisation of coronary plaques and myocardial perfusion assessment. Due to CT’s high diagnostic accu- racy for stenosis detection and plaque visualisation, CT itself, which is broadly available, and more costly Cardiac CT without CAD Cardiac CT with 3-D reconstruction of the chest ©Prof.MarcDewey ©Prof.MarcDewey

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