An enhancement of contrast between healthy and neoplastic zones in Mueller matrix images of excised cervical tissue was demonstrated in our prior work for the visible wavelength range. In this paper we present the statistical analysis of Mueller polarimetric data for the diagnostics of high grade cervical intraepithelial neoplasia. The results of linear and non-linear post-processing compressions of the full Mueller matrix are discussed and compared in terms of diagnostic performance. The final goal of these studies is to estimate and compare the diagnostic usefulness of 16 polarimetric measurements required for the reconstruction of complete Mueller matrix of a sample, while looking for an optimal design of future imaging protocols.
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.
Mueller polarimetric imaging appeared to be very promising to detect the modifications in the microstructure of the uterine cervix due to the development of a precancerous lesion, thus providing very useful information for diagnostics to which practitioner cannot to access with classic color imaging. The first multispectral Mueller Polarimetric Colposcope (MPC) for the in vivo analysis of the uterine cervix will be presented. It has been obtained by miniaturizing a Mueller polarimetric imaging system and “grafting” it on a conventional colposcope, which is a low magnification binocular system, currently used in medical practice to examine the uterine cervix for detection of precancerous lesions. The multispectral MPC enables to obtain reliable Mueller polarimetric images in less than 2 seconds with a spatial resolution of 100 μm simultaneously at 450, 550 and 650 nm. Currently, it is being tested in vivo in the University Hospital of Kremlin Bicêtre in France. In order to evaluate the performance of the technique, polarimetric images need to be compared with histological analyses of biopsies. The procedure developed in collaboration with medical doctors to obtain an accurate correlation between polarimetric images and biopsies will be described.
Mueller Polarimetric Imaging (MPI) showed promising results in biomedical applications, especially for early detection of precancerous lesions on biological tissues. This technique is label-free, non-invasive and can be implemented with a large field of view (up to several cm2) to image wide areas of biological tissues while providing information on its microstructure. The development of innovative (MPI) systems, able to analyze biological tissues in vivo on human patients, remains an instrumental challenge. Our goal is to build miniaturized and compact full-field MPI systems based on Ferroelectric Liquid Crystals (FLCs) capable of performing a multispectral accurate analysis of biological tissues in vivo. In this work, an innovative approach is showed to realize optimized and fast FLCs-based MPI systems able to perform full-field imaging acquisitions in the spectral range between 450 and 700nm with error less than 1% on all the elements of measured Mueller matrices. This system can be accurately calibrated by using the Eigenvalue Calibration Method (ECM) also in presence of high residual instrumental depolarization. This approach enables us to realize compact and reliable MPI systems which can be easily integrated into existing instruments currently used in medical practice.
Significant contrast in visible wavelength Mueller matrix images for healthy and pre-cancerous regions of excised cervical tissue is shown. A novel classification algorithm is used to compute a test statistic from a small patient population.
The rise of optical biopsy as an alternative to classical biopsy is dictated by ongoing technological progress: any type of measurements has to be fast, precise, non-invasive and implemented in-vivo. The use of polarized light for optical biopsy has a long history. As Mueller-Stokes formalism provides the most complete description of polarized light interaction with any type of sample (even depolarizing one) we explored the capabilities of in-house multi-wavelength Mueller imaging polarimeter for the detection of pre-malignancy and malignancy. Our studies were performed with both scattering phantom tissues (in transmission configuration) and specimens of human colon and uterine cervix (in backscattering configuration).
For the interpretation of measurement results we decomposed Mueller matrix of a sample into product of elementary Mueller matrices of homogeneous diattenuator, retarder, and depolarizer. This phenomenological approach does not require the exact solution of Maxwell equations and provides the “effective” values of polarimetric properties of sample.
Exploring differential Mueller matrix formalism for fluctuating medium we showed that depolarization in homogeneous turbid medium varied parabolically with the pathlength of transmitted light, while the standard deviation of elementary polarization properties of medium depends linearly on the concentration of scatterers.
Neither scattering phantoms nor human tissue possessed any measurable diattenuation in backscattering configuration. The polarimetric images of tissue depolarization power, scalar birefringence and orientation of optical axis were compared with the analysis of histological slides. The spectral dependence of depolarization power and scalar birefringence values ascertained the potential of imaging Mueller polarimetry to discriminate healthy and diseased tissue zones.
This paper reports a technique based on spectrally differential measurement for determining the full Mueller matrix of a biological sample through an optical fiber. In this technique, two close wavelengths were used simultaneously, one for characterizing the fiber and the other for characterizing the assembly of fiber and sample. The characteristics of the fiber measured at one wavelength were used to decouple its contribution from the measurement on the assembly of fiber and sample and then to extract sample Mueller matrix at the second wavelength. The proof of concept was experimentally validated by measuring polarimetric parameters of various calibrated optical components through the optical fiber. Then, polarimetric images of histological cuts of human colon tissues were measured, and retardance, diattenuation, and orientation of the main axes of fibrillar regions were displayed. Finally, these images were successfully compared with images obtained by a free space Mueller microscope. As the reported method does not use any moving component, it offers attractive integration possibilities with an endoscopic probe.