Modeling and measurement of cryogel elasticity properties for calibrating of IVUS elasticity images

Ultrasound elastography allows the estimation of tissue elasticity and can be used to characterise atherosclerotic plaques. In order to quantify the difference in elasticity of the various plaque materials, our aim is to calibrate the intravascular elastography images. For that, we make comparison between the modeling and experiments on vessel mimicking phantoms. Use of phantoms permits one to control many parameters. The range of Young's modulus in arteries goes from 1 kPa for lipids to 1000 kPa for the axial Young's modulus of the adventicia. Experiments were done to characterise a vessel mimicking materials, polyvinyl alcohol cryogel, and were compared with arterial values. The process consists of creating a pattern on a lateral side of the homogenous sample, to apply a uniform controlled pressure loading, then a CCD camera takes a photograph of the patterned side before and after compression. Image correlation software estimates axial and lateral strain and permits one to calculate the elastic modulus. These values are then included in finite element modeling. Then we combine a finite element analysis with a simulation of ultrasound response of the phantom to generate echograms for different compression levels of the vessel. The compression is radial and uniform inside the vessel. An estimated elastogram is obtained from two images using an adaptive stretching algorithm. This study shows that cryogel is a good material to make vessel mimicking phantoms due to the similarity of its elastic modulus to that which we can find in an artery, and therefore its relative breaking resistance.