Careful study and simulation of mechanical properties of biological tissues and structures for surgical planning purposes is of great importance in order to limit the damage to healthy tissue during surgery and, moreover, to allow precise restoration of anatomical details destroyed or altered due to pathologies or surgical manoeuvres. In particular, accurate modelling of the mechanical behavior of the tissues is required. To achieve accurate representation of various organs and or anatomical districts, various techniques were proposed in order to reconstruct the morphological properties of such elements. Computer-aided surgical simulation progressed significantly in the last decade. Currently, many surgical procedures on human patients are not simulated yet can be relevant in minimally invasive surgeries to protect human health and to save human lives, particularly for surgeries with high accuracy requirements. An accurate 3D anatomical reconstruction necessarily starts from MRI or CT acquired details of the patients, through imaging segmentation and proper stacking and smoothing of adjacent slices. More particularly, to gain accurate models suitable for computer-aided surgical tools, many problems must be faced. In particular: a) free form surface modelling starting from MRI or CT scans; b) FEA pre-processing in terms of proper element selection and density (shell or solid according to the surgical district type and length characteristics) loads and boundary constraints definition; c) tissue constitutive material. In this research we aim to investigate these topics to enhance physical description of organs subjected to surgical operations. Therefore, this project has as goal provide a sensitivity analysis on three different geometric models, more in detail simulations will be performed using linear-elastic model and two hyperelastic models. The results will be valuated from multidisciplinary unit, bioengineering, engineering and surgeons involved in the research.
The inherent complexity in the biological tissue¿s mechanical behaviour and difficulties to acquire the parameters to describe the relationship stress-strain, has given place to an active area of research based on realistic modelling and simulation of tissue deformation that is still a challenge. Until today there is not a standard protocol that is able to reproduce the ex-vivo and in-vivo experimental tests to characterize the mechanical behaviour of soft tissues. It is due to the biological tissues characteristics that are inhomogeneous and anisotropic with nonlinear viscoelastic behaviour. However, most of the works in the biomechanics domain are to understand the fundamental properties of various tissues.
This proposal is the natural prosecution of a research cooperation aimed to develop Computer Aided Tools for colorectal surgery suitable for planning, surgical operations. It has been started in the recent past, after the proposal of Dr. Laura Lorenzon, involving the researchers of the Department of Mechanical and Aerospace Engineering (DIMA) in different fields of interest, bioengineers (Franco Marinozzi), PhD's Andrada Pica, and Michela Franzò), mechanical engineers expert in CAD (Computer Aided Design) techniques and virtual prototyping (Francesca Campana ING-IND/15), surgeons (Renzo Pretagostini, MED/18) and anesthetists (Francesco Pugliese, MED/41).
In particular, we can explore the feasibility of reconstruction applied to specific case studies and / or innovative surgical techniques such as Transanal total mesorectal excision (taTME)Technique. taTME is a novel operative approach of the radical surgery for rectal cancer, and has been a hot topic in colorectal surgery for years. TaTME aims to solve some problems from previous TME, such as exposure of peripheral mid-lower rectal space, judge of distal cutting margin, and to carry out completely minimal invasive operation.
To our knowledge, no three dimensional representation was proposed relative to a virtual reality taTME ambient.
In the recent past many works have been focused on the shape reconstruction of real images acquired by MRI and CT scans. In this work their adoption will be studied in terms of final accuracy of the FEA simulation just to understand how they can support a better understand of the surgical practice, thanks to the strict cooperation with the surgeon involved in the work. To the best of our knowledge, this is the first study based on 3D imaging in colorectal surgery settled in our Country. Although few data are emerging in relation to MRI segmentation and implementation of diagnosis (for CRM assessing and the prediction value of variation of volumetry), literature in this field is promising but very scant. Indeed, optimizing the selection criteria for patients requiring neo-adjuvant (chemo)radiation treatments (neoCHT-RT) could impact and implement surgical and multidisciplinary management of rectal cancer patients, avoiding
e.g. unnecessary treatment with a consequent reduction of side-effects and cost. On the same extent, the prediction of response to neo-adjuvant treatments using variation in volumetry could aid in defining and in predicting complete pathologic responses which could benefit e.g. of a more conservative treatment if un-fit for extended resections.
Finally, the result of this research project, together with the investigation about tool-path simulation and planning, that is being provided by other activities of the proponents, will define the core for pre-operative surgical planning protocols and post-operative techniques supporting patient¿specific treatments.
Rapid prototyping will also used for reconstructions of organs starting from image acquisition, reproducing tissue stiffness and allowing implantability via topological optimization.