Microscopic image analysis of elastin network in samples of normal, atherosclerotic and aneurysmatic abdominal aorta and its biomechanical implications

Abstract

The aim of our work was to prepare part of the input data for a computational biomechanical model of both the active and passive elements of the tunica media of an aortic aneurysm. We analyzed tissue samples of the anterior wall of the normal, atherosclerotic and aneurysmatic subrenal abdominal aorta. We assessed the proportions of smooth muscle cells, elastin and collagen in histological sections of these samples and studied the morphological characteristics of the elastin network in the tunica media. Selected photomicrographs were studied, representing relatively well preserved areas without artifacts, ruptures, corrupted integrity of the tunica media or total elastinolysis. A new method was introduced for the assessment of structures formed by elastin membranes and fibres, using the fast Fourier transform (FFT) technique. The image was transformed into reciprocal (Fourier) space and the method made use of the fact that the FFT was very sensitive to the orientation distribution of thresholded elastin morphology. The results of this comparative study, obtained from selected samples from 24 patients, revealed that the percentage values of the constituents of the arterial wall can not distinguish between the preserved segments of normal, atherosclerotic or aneurysmatic aorta. The results of the Fourier analysis proved that the FFT provided an efficient method for evaluating cross sections of the elastin membranes and fibres, reflecting their anisotropy. The shape of the power spectrum of elastin was a simple pattern, whose description was quantified by the shape of its polar coordinates histogram. We discuss the methodological difficulties and biomechanical implications of our work as well compare it to other methods of elastin analysis.