InitRech 2015/2016, sujet 12

Summary

This article deals with a specific reconstructive facial surgery method, called fat-filling. The main purpose of this method is to inject some fat between different layers of tissus, which compose the skin and the muscles of the face, in order to reinflate the face and to fill hemifacial deformations which can be caused by accidents or more often by diseases like the Parry-Romberg Syndrome.

The fat-filling method is kinda different compared with all the plastic surgeries that we hear about every day. Those surgeries, like the breast augmentation or other facial modifications, often use implants, and it is easy to find works ans documentations about them.

The main aim of this research is to propose an efficient model, able to simulate the final rendering of that kind of surgery and the problems that could be encountered. In fact, this model takes into account specific information about the patient, particularly his anatomy (ligaments, nerves and blood vessels), which can prove to be obstacles for the injected fat.

With those specific datas, and relying on both fluid and deformable solid models, searcher of the INRIA lab were able to make their own model. Its aim is to calculate the error which could occur during the projection of the fat, meaning that input fluxes have theoretically to be equal to output ones.

finally, the equation ruling this simulation the following :

(J+R)p=d

with : d --> vector including divergence values (error)
       p --> vector including pressure values
       J --> assembling matrix including area coefficients of the face
       R --> diagonal regularisation matrix summing the contribution of volume displacement by a pressure in the cell n°i over N cells

Some experiments were done :

The first was to simulate a fluid injection between two layers, one was a deformable solid, the other a rigid solid. The conclusion of this test was that the model was coherent with fluid general behavior.

The second was to simulate the surgery with real patient datas acquired by laser scan of his face. the aim here was to compare simulation result with the result obtained after a real fat-filling surgery. Finally, the deformations were similar, and that permitted to say that this model was realisitic, even if there was some differences between the simulation and the surgery outcome.