In the past, luminography of a desired arterial segment had been the method of choice to evaluate atherosclerosis. This still commonly used in the setting of coronary angiography by which atherosclerosis is graded by the percent stenosis of the vessel.
However, it has become more and more apparent that most atherosclerotic plaques by outward remodelling of the vessel wall grow without occluding the lumen and the fact that the plaques most prone to rupture and to form thrombosis, and thereby inducing myocardial infarction and stroke, are only causing a stenosis of some 30-50%. Furthermore, it has been shown that most of those “vulnerable” plaques contain a large lipid-rich necrotic core, a thin fibrous cap and a high degree of inflammation caused by infiltration of macrophages and other immuno-competent cells. Thus, imaging in the future has not only have to show the part of the plaque that is not occluding the artery and thereby not visible at luminography, but also have to be able to image the composition of the plaques, including the degree of inflammation.
In the PIVUS study including 1016 subjects aged 70 from the general population of Uppsala, atherosclerotic plaques were found in one of the carotid arteries by ultrasound in about one-third of the population, while bilateral plaques were found in another third of the population. These plaques were generally quite small and only some 2-3% showed plaques being significantly blood flow limiting. The majority of these plaques were rather echolucent at visual inspection. When applying a digitalized technique to quantify the echogenecity in the plaques, the echogenecity was related to BMI, HDL, a marker of lipid oxidation and glutathion, a marker of ROS generation. When the echogenecity was measured also in the “normal” carotid artery wall, the intima-media complex, the echogenecity at this location was related to the same set of risk factors and was also related to the echogenecity in the overt plaques. Furthermore, when evaluated in another cohort, the ULSAM study of males aged 75 years, those with an echolucent intima-media complex showed an increased risk of CV death over 5 years follow-up compared to those belonging to the middle-tertile of echogenecity values.
