Multiresolution features of carotid artery wall and plaque toward identifying vulnerable asymptomatic cases from B-mode ultrasound

Efficient management of asymptomatic carotid atherosclerosis remains a crucial issue in clinical practice, because the currently used determinant for deciding surgical or medical treatment, namely the stenosis degree, has proven inadequate. Various features derived from ultrasound image analysis have shown promise for enhancing the effectiveness of decision making. Among these, multiresolution, i.e. wavelet-transform-based, texture analysis has been shown to adequately characterise atheromatous tissue, especially in terms of horizontally oriented texture in longitudinal B-mode sections. We sought to investigate the horizontally-oriented multiresolution textural properties of arterial wall and plaque in a carefully selected sample of asymptomatic male subjects. Of the 19 carotid arteries that were interrogated, 7 had low stenosis degrees (50-69%) and 12 had high stenosis degrees (70-100%); the two groups had similar ages. Multiresolution analysis was performed using wavelet packets and the coiflet 1 wavelet, for three levels of decomposition. Seven features were derived from the resulting approximation (A) and horizontal detail (Dh) images, for two segments in each artery, namely plaque and the adjacent intima-media complex (IM). All features were statistically similar between low and high stenosis cases, suggesting that stenosis degree may not be sufficient to characterise the two case types. Differences between IM and plaque were observed for most multiresolution features. The differences were more prominent for higher decomposition levels. The feature Dh3A2A1 was different between plaque and IM in the low stenosis cases but was not different in the high stenosis cases. The opposite was observed for Dh₂Dh₁. Such differences suggest discontinuities in tissue properties and therefore increased vulnerability. In conclusion, multiresolution texture analysis may provide valuable information about normal and atheromatous tissue, because certain tis- ue properties are revealed at high decomposition levels.