Ultrasound features of human carotid plaques
Atherosclerotic plaques in the carotid arteries are common in a middle-aged population. When a carotid plaque ruptures it may result in a cerebrovascular event. However, only a minor part of carotid plaques will eventually rupture. Finding those plaques is essential to decide the most appropriate treatment strategy. With non-invasive ultrasound the carotid plaques can be visualized for assessment of various features. Plaques that appear dark on the ultrasound image, i.e. echolucent plaques, are more prone to rupture. The aim of this thesis was to explore the relation between plaque features, mainly echogenicity measured as grey scale median (GSM), and some of the known risk factors for cardiovascular events, as well as treatment approaches. Measurement of GSM has in the last decades become common in research. It has not, however, been implemented in clinical practise yet. One reason could be the lack of consensus regarding measurement methods, resulting in a large variety of both range and mean values of GSM. We compared 2 softwares, using different standardization methods, for measurement of GSM in stored ultrasound images of the carotid plaques. Even though the agreement between methods was good, mean difference of GSM was large. This indicated that GSM measurements couldn’t be compared unless the same software and standardization method have been used. Subjects with diabetes have an increased risk of having a cardiovascular event. In a cohort of 100 healthy subjects, aged 70 years, we found that subjects with diabetes had increased echolucency as compared to non diabetics. This could indicate that subjects with diabetes have not only more pronounced atherosclerosis but also a different, more vulnerable, type. Treatment with metoprolol for 3 years decreased progression of intima-media thickness in the bulb. In a post hoc analysis, measuring echogenicity in ultrasound images of carotid plaques in subjects with and without metoprolol treatment, plaque in treated subjects had become more echogenic as compared to non treated. This finding suggested that treatment with beta-blockers could stabilize carotid plaques, previously attributed to statin treatment. However, the measurement of GSM is a rough method for assessing plaque features. We introduced a novel feature, namely plaque patchiness, describing the pattern of the plaque as being more or less spotty on the ultrasound image. Subjects with the combination of echolucent and spotty plaques had increased values of weight, body mass index, waist and hip. Since echolucency in plaques have been associated with increased cardiovascular risk, this finding may partly explain the increased risk of cardiovascular events among subjects with overweight and obesity. Whether the novel feature, plaque patchiness, is associated with increase in risk is still to be explored.
Clinical Medicine, atherosclerosis, carotid plaques, echogenicity, diabetes, obesity, beta-blocker, grey scale median
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Department of Clinical Sciences, Lund University