Mueller polarimetric imaging through a rigid endoscope

Mueller polarimetry has been shown to effectively detect multiple pathologies on a striking variety of biological tissues. The ongoing challenge is to implement Mueller polarimetry into the clinical practice in-vivo. This technique is suitable for this purpose since it provides wide field images (up to 20 cm²) well adapted to the exploration of entire organs while revealing information on their microstructure. In addition, it is non-invasive, label-free and non-destructive. One instrument of great interest for biomedical diagnostics in vivo is the conventional rigid endoscope, also called laparoscope. This instrument is used to explore the inner cavities of the human body and is a standard in many minimally invasive surgery applications. However, it is implemented by using conventional white light intensity imaging which does not provide enough contrast to identify, for example, tumor margins during surgical resection. Mueller polarimetric imaging could provide useful contrast which can considerably improve the definition of these margins. However, to adapt a conventional laparoscope to Mueller polarimetric imaging is an instrumental challenge due to its complex polarimetric response. In this work, we provide a detailed characterization of the polarimetric properties of a conventional laparoscope. It is shown that a conventional laparoscope is characterized at the same time by birefringence and strong spectral depolarization that can be reduced by reducing the spectral bandwidth. The origin of these polarimetric effects have been investigated and modeled. Our work provides useful knowledge about implementing rigid endoscopes in polarimetric applications.