Axial strain imaging of vessel mimicking cryogel phantoms

Since procedures for curing atherosclerosis are predominantly mechanical in nature, knowledge of the elastic properties of the plaque and surrounding tissues can be of fundamental interest to predict an intervention outcome. These properties can be investigated by elastography, which estimates from pairs of RF ultrasound signals, the strain distribution occurring within a medium, in response to a stress. In this paper, first results obtained with vessel mimicking cryogel phantoms are presented. These phantoms, made from a polyvinyl alcohol solution, present a mechanical behavior close to that of a pig aorta, as well as a high pressure resistance. These properties make them very adapted for elastographic experiments, much more than commonly used agar-gelatine phantoms which tend to tear or crack easily under inner pressure. Investigating the mechanical properties of such phantoms has required the development of a specific experimental set-up, allowing both the application of a pressure inside the phantom lumen and acquisitions of RF data. This experimental set-up consists mainly in a CVIS ultrasound scanner with a 30 MHz mechanical rotating single element, an oscilloscope Lecroy 9374L and a self-made pressuring system. RF data were digitised at a sampling frequency of 500 MHz, stored on disc and processed off line, with a method we recently developed, based on the principle that, tissue compression produces changes in signals, comparable to local compression factors. This method had been shown to be appropriate for the computation of local scaling factors resulting from larger strains or a large spread of strain variations. And it turns out that, this method seems to be adapted for arterial mechanical properties investigation since the range of the Young modulus in blood vessels is very wide, from 1 kPa to 1000 kPa. Resulting intravascular elastograms show the potentialities of our method to investigate the mechanical properties of object like vessels.