Development of In Vivo Constitutive Models for Liver: Application to Surgical Simulation

Abstract

Advancements in real-time surgical simulation techniques have provided the ability to utilize more complex nonlinear constitutive models for biological tissues which result in increased haptic and graphic accuracy. When developing such a model, verification is necessary to determine the accuracy of the force response as well as the magnitude of tissue deformation for tool-tissue interactions. In this study, we present an experimental device which provides the ability to obtain force-displacement information as well as surface deformation of porcine liver for in vivo probing tasks. In addition, the system is capable of accurately determining the geometry of the liver specimen. These combined attributes provide the context required to simulate the experiment with accurate boundary conditions, whereby the only variable in the analysis is the material properties of the liver specimen. During the simulation, effects of settling due to gravity have been taken into account by a technique which incorporates the proper internal stress conditions in the model without altering the geometry. Initially, an Ogden model developed from ex vivo tension and compression experimentation is run through the simulation to determine the efficacy of utilizing an ex vivo model for simulation of in vivo probing tasks on porcine liver. Subsequently, a method for improving upon the ex vivo model was developed using different hyperelastic models such that increased accuracy could be achieved for the force characteristics compared to the displacement characteristics, since changes in the force variation would be more perceptible to a user in the simulation environment, while maintaining a high correlation with the surface displacement data. Furthermore, this study also presents the probing simulation which includes the capsule surrounding the liver.

Porohyperviscoelastic Model Simultaneously Predicts Parenchymal Fluid Pressure and Reaction Force in Perfused Liver

“…The model was found to have initial shear and bulk moduli of 200 Pa and 606 Pa, respectively. These values are in the low end of the wide range of liver tissue moduli reported in the literature [25,26,[48][49][50][51]; however, they are comparable to the modulus reported in Liu et al [52] for liver testing at a low shear rate E < 100Pa ð Þ . One possible explanation for the softer moduli found in this work is that, since the moduli are being implemented in a perfused PHVE model, they are representative of the solid phase only.…”

Isotropic incompressible hyperelastic models for modelling the mechanical behaviour of biological tissues: a review

“…It was successfully used for modelling abdominal tissues, like porcine, bovine, and human liver [13,30,62,64,111,113,114], porcine kidney [101,112], and porcine spleen [112]. Most of the mechanical test data available for brain tissue are fitted today with an Ogden hyperelastic model [15,52,53,57,[90][91][92].…”

“…The Yeoh model was applied successfully for the characterisations of human breast tissue [85], porcine muscular tissue [67], rat lung parenchyma [5,93], porcine and rat brain [52,53], and porcine liver [62]. Zaeimdar [122] applied this model together with the Mooney-Rivlin and the Neo-Hookean models through compression of eight animal tissues (chicken breast, cow fat, cow muscle, veal kidney, veal liver, pig fat, pig muscle, sheep brain) and found that the Yeoh model is the best one in capturing nonlinearity of these tissues.…”

Towards a soft-tissue cutting simulator using the cohesive zone approach

“…The experimental setup has also been used for probing tasks on in vivo porcine liver and the details pertaining to the device layout can be found in [6]. The device itself was designed to perform a controlled linear cutting motion while recording both the force imparted on the scalpel blade and the surface displacement of the surrounding tissue throughout the cutting process.…”