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This paper shows the viscoelastic and nonlinear liver model for organ model based needle insertion, in which the deformation of an organ is estimated and predicted, and the needle trajectory is decided with organ deformation taken into consideration. An organ model including detailed material characteristics is important in order to achieve the proposed method. Firstly, the material properties of the liver are modeled from the measured data and its viscoelastic characteristics are represented by differential equations, including the term of the fractional derivative. Nonlinearity in terms of the stiffness was measured, and modeled using the quadratic function of strain. Next, a solution of an FE(Finite element) model using such material properties is shown. We use the sampling time scaling property as the solution for the viscoelastic system, while the solution for a nonlinear system using the Euler method and the Modified Newton-Raphson method is also shown. Finally, the deformation of liver model is calculated and pig liver of in vivo situation is obtained from medical ultrasound equipment. Comparing the relationship between needle displacement and force on real liver and liver model, we validate the proposed model. [ABSTRACT FROM AUTHOR]

Vibration-controlled transient elastography (VCTETM) technique is routinely used in clinical practice to assess non-invasively the liver stiffness which is correlated to hepatic fibrosis. Adequate use of the VCTETM probe requires the knowledge of the distance between the skin and the liver parenchyma. This paper compares two methods to estimate this distance using spatial variations of the spectral content of ultrasound radiofrequency (RF) lines, obtained from a probe consisting of a single element ultrasound transducer placed in front of the liver right lobe. Results on a database of 188 patients, including normal-weight and obese persons, show that the spectral variance can accurately discriminate the subcutaneous fat from the liver tissue. The proposed algorithm works in real-time and is suitable for VCTETM scanning protocol setup. [ABSTRACT FROM AUTHOR]

Radiofrequency Ablation (RFA) assisted liver resection results in lesser blood loss during liver resections. It involves a time consuming and error prone process of alternating coagulation and cutting until the line of transaction is completed to finally divide the liver. We proposed a new robotic mechanism to automate the ablation and division process. The robotic device comprises a 2-link manipulator, an x-y translator, a flexi-arm as well as a liver ablation and division device. The process of precise linear motion ablation and cutting has been integrated with the guidance of a robotic mechanism to uniformly coagulate and slit areas of the parenchymal. A prototype of the robotic device has been evaluated on its ability to uniformly target a large region. [ABSTRACT FROM AUTHOR]

In vivo aspiration experiments on human livers are analyzed and material parameters for a non-linear-viscoelastic constitutive model are determined. A novel procedure is applied for the inverse analysis that accounts for the initial tissue deformation in the experiment and for the non-homogeneity of liver tissue. A numerical model is used consisting of a surface layer (capsule) and an underlying non-linear-viscoelastic solid (parenchyma). The capsule is modeled as hyperelastic membrane using data from measurements on bovine and human tissue. In a two step optimization procedure the set of constitutive model parameters for the ˵average″ response of liver parenchyma is obtained. The proposed model is in line with literature values of high strain rate elastic modulus obtained from dynamic elastography. The model can be used to predict the nonlinear, time dependent behavior of human liver in computer simulations related to surgery training and planning. [ABSTRACT FROM AUTHOR]