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Intima-media thickness (IMT), also called intimal medial thickness, is a measurement of the thickness of tunica intima and tunica media, the innermost two layers of the wall of an artery. The measurement is usually made by external ultrasound and occasionally by internal, invasive ultrasound catheters; see Intravascular ultrasound. Measurements of the wall thickness of blood vessels can also be done using other imaging modalities. IMT is used to detect the presence of atherosclerotic disease in humans and, more contentiously, to track the regression, arrest or progression of atherosclerosis. Ultrasound IMT measurements were first proposed and validated ''in vitro'' by Paolo Pignoli in 1984〔Pignoli P. "Ultrasound B-mode imaging for arterial wall thickness measurement". ''Atherosclerosis Reviews'' (1984) 12:177-184〕 and later publicized in a 'most cited' article.〔Pignoli P, Tremoli E, Poli A, Oreste PL, Paoletti R (Dec 1986). "Intima plus media thickness of the arterial wall: a direct measurement with ultrasound imaging". ''Circulation'' 74:1399-1495〕 The use of IMT as a non-invasive tool to track changes in arterial walls has increased substantially since the mid-1990s.〔 Although IMT is predictive of future cardiovascular events, the usefulness of measuring ''change'' in IMT over time is disputed, as meta-analyses have found that change in IMT is not predictive of cardiovascular events. As such, the use of change in IMT as a surrogate endpoint measure of drug efficacy in clinical trials, or in clinical management of cardiovascular disease, is debated.〔 IMT is occasionally used in clinical practice, but its role is not clear. After systematically reviewing the evidence base for IMT, the United States Preventive Services Task Force found no support for its routine use in stratification of risk for people at intermediate cardiovascular risk. However, in 2003 the European Society of Hypertension–European Society of Cardiology guidelines for the management of arterial hypertension recommended the use of IMT measurements in high-risk patients to help identify target organ damage and in 2010 the American Heart Association and the American College of Cardiology advocated the use of IMT on intermediate risk patients if usual risk classification was not satisfactory. ==IMT measurements in the carotid artery== Carotid IMT has been measured in numerous epidemiological and clinical studies. These have shown associations with numerous risk factors, including type 2 diabetes and impaired glucose tolerance, familial hypercholesterolemia, high-density lipoprotein cholesterol (HDL-C) and triglycerides, rheumatoid arthritis, non-alcoholic fatty liver disease, and air pollution. Since the 1990s, some small and larger scale clinical trials of lifestyle and pharmaceutical interventions have also used carotid artery IMT as a surrogate endpoint for evaluating the regression and/or progression of atherosclerotic cardiovascular disease. However the appropriateness of carotid IMT in this context is uncertain. Although carotid intima-media thickness is strongly associated with atherosclerosis, thickening of the intima-media may not always be due to atherosclerosis. Intima-medial thickening is a complex process, depending on a variety of factors, including local hemodynamics, blood pressure,〔 shear stress〔 and circumferential tensile stress.〔 Changes in shear stress may adversely affect endothelial function and particle residence time, affecting the delivery and transport of potentially atherogenic particles into the arterial wall and consequent plaque formation. Blood pressure may affect IMT through blood vessel remodelling or wall hypertrophy in response to altered circumferential stress. Variations in IMT between different locations, such as the inflow side of branches, the inner curvature at bends and opposite the flow divider at bifurcations may reflect differences in local hemodynamic forces. However, an IMT greater than 0.9-1mm is highly likely to be indicative of atherosclerosis and increased risk of cardiovascular disease. Often, the measurement of the IMT is measured in three locations: in the common carotid (typically at one cm proximal to the flow divider), at the bifurcation, and in the internal carotid artery. IMT measurements of the far (deeper) wall, by ultrasound, are generally considered more reliable than measurements performed on the near (more superficial) wall;〔 although measurement of both near and far wall IMT has also been advocated. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Intima-media thickness」の詳細全文を読む スポンサード リンク
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