Evaluation of elastic structural change in coronary atherosclerosis using scanning acoustic microscopy

Coronary atherosclerotic lesions were observed by scanning acoustic microscopy (SAM), a technique which can visualize regions of differing elasticity. Three regions, i.e., dark (dR), intermediate (iR) and bright (bR) demonstrating differences in acoustic reflection intensity and the velocity of surface acoustic waves, were seen in the lesions. Furthermore, lipid-positive areas were found to be dR and iR and fatty crystalline areas were observed only in iR regions by polarizing microscope. These phase transitions of fat affected the acoustic properties in each region. According to SAM images, intimal structural changes were classified into three types, minimum structural change (type I), the overcrowded net-like dR structure (type II) and markedly disturbed structure with a decrease of dR (type III). The medial structure change was also classified into three types paralleling the decrease of dR (types M1, M2 and M3). Intimal type II with a large degree of thickening and intimal type III with medial type M3 were highly prominent in the acute myocardial infarction (AMI) group (P less than 0.01). Therefore these results suggest that the anisotropic elasticity induced by micro-elastic changes in the arterial wall may be associated with functional disturbance of the vascular wall.