Three dimensional elastic modulus reconstruction for non-invasive, quantitative monitoring of tissue scaffold mechanical property changes

The field of tissue engineering requires improved methods to monitor tissue growth and function as well as the degradation of biomaterial scaffolds following implantation. Invasive methods of monitoring, such as histology or direct mechanical measurements, are less than ideal. Non-invasive imaging techniques, such as magnetic resonance imaging (MRI), X-ray computed tomography (CT) or conventional ultrasound (US) might only provide morphological information. However, US Elasticity Imaging (UEI) can provide mechanical property information, in the form of elastic modulus images, as well as morphological information. 3D UEI will provide the spatial distribution in 3D of the mechanical property information. This information can be used to characterize and monitor the internal structure and composition of the tissue and scaffold. In order to determine the feasibility of using quantitative 3D UEI to monitor tissue scaffolds, experiments were designed to image Poly (1, 8 Octanediol-co-Citrate) (POC) scaffolds before and following chemically induced weight degradation. In the absence of tissue in growth, the amount degradation is directly related to the scaffold's elastic modulus. For each degradation state, the scaffolds were imbedded in gelatin and imaged with a 3D US scanning system while undergoing a quasi-static compression. A novel US image registration algorithm was used to estimate the displacement field and an elastic modulus reconstruction algorithm was then applied to the estimated displacements. The reconstructed elastic modulus images compared well with direct mechanical measurements and the amount of degradation.