ELASTOGRAPHY OFFERS NEW INSIGHTS INTO PLAQUE IMAGING
Elastography has been used for many years to differentiate malignant from benign lesions, especially in the breast or liver. Experience in carotid artery disease is limited, but recent studies have shown that elastography may help to stratify plaque and reduce the risk of unnecessary surgery, as a Greek expert will show during a New Horizons session today at the ECR.
Stroke is one of the leading causes of death in developed countries; one third of cases are fatal and survival can come with considerable disabilities. In Europe alone, experts estimate that there are one million new ischaemic strokes per year and they expect this number to rise by 12% by 2020, as the population ages1. A wide spectrum of carotid artery diseases can lead to stroke, but atherosclerosis accounts for a significant percentage – about 20 to 30% of cases. Stenosis is typically a cause for atherosclerosis and is now being measured using ultrasound in symptomatic patients, who are usually treated with atherectomy. But it is not so clear how asymptomatic patients should be managed, according to Dr. Nikos Liasis, medical director of Affidea Greece, a pan-European medical service provider specialising in diagnostics investigations, clinical laboratories and cancer treatment services. “Despite many randomised clinical trials, there is a surprising lack of consensus regarding the treatment of asymptomatic patients,” he said ahead of his presentation during the session today. There is widespread agreement among physicians that many procedures are probably being performed with risks that are higher than the risk of the actual indications. “Ninety-two per cent of all atherectomies in the U.S. are undertaken in asymptomatic patients. On average, we operate on 16 patients to prevent one stroke in just five years, so we perform surgery on 15 people who may not need it, which is quite a high risk,” he said. The degree of stenosis is not the only predictive parameter for myocardial infarction or stroke. Therefore it has become crucial to be able to understand and stratify plaque morphology. The majority of myocardial infarctions and strokes are actually caused by plaque rupture. Thanks to histological findings, physicians know that unstable, vulnerable plaques, which are prone to rupture and distal embolisation, are those with a large lipid core and intraplaque haemorrhage. Inflammation is also a high risk factor for plaque rupture. Researchers have tried to establish whether it would be suitable to use ultrasound in everyday clinical practice to stratify plaque morphology, but the results combined with histopathological findings were poor. Liasis and his team at Affidea Greece, together with the University of Athens Medical School and the National Technical University of Athens, decided to conduct a prospective study in order to determine the contribution of ultrasound elastography to the description of plaque morphology. “Ultrasound elastography is based on the principle that so tissue deforms more than hard tissue. So plaques that are hard and stable deform less than so, vulnerable plaques,” he said. So far the few available papers on the topic focused on either shear wave or strain elastography. In his study, Liasis has compared both techniques against histopathological findings and he will present his results today. He estimates that the potential of both techniques for stratifying plaque is significant, and that they may be complementary in many ways as they offer information that is not accessible through B mode or Doppler flow and other US techniques. “Elastography enables the detection of the fibrous cap, the thickness or thinness of which is an indication of plaque instability, but it remains challenging to spot with traditional ultrasound. It also provides information about plaque smoothness and more accurate information on what is outside of the plaque. We have all the features that are characteristics of plaque morphology and which make plaque unstable,” he said. Elastography offers other benefits to consider for daily practice; it is radiation free, accessible and widely available. Furthermore, it does not require any patient preparation and the costs are low. Examination times are short compared with MRI and, unlike CT, there are no allergy risks linked to contrast agents use. However a number of technical limitations remain to be overcome and reproducibility is still challenging. “When plaque is calcified, we are not able to describe it because of the acoustic shadow. Our biggest disadvantage is subjectivity. Reproducibility is still an issue, but using appropriate examination protocols may help,” Liasis said. It will also be necessary to adapt the technique, which has been developed for lesions in superficial organs, to small pulsating vessels. “We need more prospective studies to evaluate its potential. US elastography in carotid plaque imaging is only a few years old. But our research is very promising to describe plaque,” he concluded.
1 Data gathered by Brainomix, Oxford University h‑ps://ec.europa.eu/easme/en/ sme/4065/brainomix-limited BY MÉLISANDE ROUGER