Endoscopic Mueller Imaging – IMULE

A measurement of the Mueller matrix is performed over the assembly «fiber on the forward path - target tissue - fiber on the backward path« at a given wavelength. Then it is performed on the fiber only, at a close wavelength reflected at the output. The differential analysis of the two matrices eliminates the contribution of the fiber endoscope and derives the desired polarimetric response of the target tissue.

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The goal of the "IMULE" project (for "Imagerie de Mueller Endoscopique" i.e. "Endoscopic Mueller Imaging") is to demonstrate the very first characterization of a sample of interest, by Mueller polarimetry, through an optical fibre. The main targeted applications are in the domain of the support to medical diagnosis. They concern the early detection of dysplasias, likely to degenerate in cancer, and accessible only endoscopically. The main relevant specialities are gastroenterology, gynaecology and pneumology. One of the operational results of the project will be to open the way to the development of a remote investigation tool, minimally invasive, able to reduce the numbers of required biopsies which are expensive, time consuming and often painful operations.
The main scientific challenge to take up consists in obtaining a precise information on the polarimetric response of a sample, due to light interaction in media with thicknesses between 0.1 and 1 mm, whereas the polarisation of the probing beam and that of the backscattered light are deeply modified when propagating along the meter-long fibre (10^3 to 10^4 times thicker than the sample). The modifications of the polarisation states in the fibre cannot be known and they significantly change when the fibre is manipulated (effects of bendings, pressure, twists…).
The consortium constituted for the project includes three complementary partners: the "Laboratoire de Physique des Interfaces et des Couches Minces (LPICM, UMR CNRS 7647) from Ecole Polytechnique in Palaiseau, the Photonics department of Xlim Institute (UMR CNRS 6172) in Limoges and the anathomopathology department from the "Institut Mutualiste Montsouris", a hospital in Paris.
LPICM is worldwide recognized for its work dealing with the conception of Mueller polarimeters dedicated to thin films characterisation for optics and electronics, and for its recent research on polarimetric techniques applied to cervical and colon cancer detection. For its part, for many years, Xlim has conceived, manufactured and characterised classical and non-conventional silica optical fibres and it has recently patented the very first polarimetric imaging device operating through an optical fibre (measure of degree of polarisation and of linear birefringence). At last, the anatomopathologists from IMM, already strongly involved in past and current collaborations with LPICM, will validate the studied process on biopsies characterised also by classical techniques.
The main point at the origin of the IMULE project is to simultaneously measure the Mueller matrix of the fibre and that of the sample probed through this fibre. To this end, several solutions will be explored. In addition, the decomposition techniques of Mueller matrices available at LPICM, may make it possible to recover the Mueller matrix of the sample even when the fibre matrix is not well known.
Each solution will be implemented and cross comparisons of measurable parameters, sensitivity and accuracy will be systematically achieved, first with well-known targets, then with less cooperative targets and finally with biological samples.
The IMULE project will improve Mueller imaging techniques, and it will significantly push back the limits of their application domains. In case of success, valorisation will be possible (i) by creating a novel type of microendoscope (polarimetric microendoscope) (ii) or by including the process in existing intensimetric endoscopes.