Quantification and validation of soft tissue deformation

We present a model for soft tissue deformation derived empirically from 10 pig carcases. The carcasses are subjected to deformation from a known single source of pressure located at the skin surface, and the deformation is quantified by means of steel markers injected into the tissue. The steel markers are easy to distinguish from the surrounding soft tissue in 3D computed tomography images. By tracking corresponding markers using methods from point-based registration, we are able to accurately quantify the magnitude and propagation of the induced deformation. The deformation is parameterised by radial basis functions with compact support. The parameterisation yields an absolute error with mean 0.20 mm, median 0.13 mm and standard deviation 0.21 mm (not cross validated). We use the parameterisation to form a statistical deformation model applying principal component analysis on the estimated deformation parameters. The model is successfully validated using leave-one-out cross validation by subject, achieving a sufficient level of precision using only the first two principal modes; mean 1.22 mm, median 1.11 mm and standard deviation 0.67 mm.