Abdelali Benali

Ex-vivo characterization of human colon cancer by Mueller polarimetric imaging

Cancerous and healthy human colon samples have been analyzed ex-vivo using a multispectral imaging Mueller polarimeter operated in the visible (from 500 to 700 nm) in a backscattering configuration with diffuse light illumination. Three samples of Liberkühn colon adenocarcinomas have been studied: common, mucinous and treated by radiochemotherapy. For each sample, several specific zones have been chosen, based on their visual staging and polarimetric responses, which have been correlated to the histology of the corresponding cuts. The most relevant polarimetric images are those quantifying the depolarization for incident linearly polarized light. The measured depolarization depends on several factors, namely the presence or absence of tumor, its exophytic (budding) or endophytic (penetrating) nature, its thickness (its degree of ulceration) and its level of penetration in deeper layers (submucosa, muscularis externa and serosa). The cellular density, the concentration of stroma, the presence or absence of mucus and the light penetration depth, which increases with wavelength, are also relevant parameters. Our data indicate that the tissues with the lowest and highest depolarizing powers are respectively mucus-free tumoral tissue with high cellular density and healthy serosa, while healthy submucosa, muscularis externa as well as mucinous tumor probably feature intermediate values. Moreover, the specimen coming from a patient treated successfully with radiochemotherapy exhibited a uniform polarimetric response typical of healthy tissue even in the initially pathological zone. These results demonstrate that multi-spectral Mueller imaging can provide useful contrasts to quickly stage human colon cancer ex-vivo and to distinguish between different histological variants of tumor.

Polarimetric imaging of uterine cervix: a case study

We present a preliminary investigation of macroscopic polarimetric imaging of uterine cervix. Orthogonal state contrast (OSC) images of healthy and anomalous cervices have been taken in vivo at 550 nm. Four ex vivo cervix samples have been studied in full Muller polarimetry, at 550 nm and 700 nm, and characterized in detail by standard pathology. One sample was totally healthy, another one carried CIN lesions at very early stage (CIN1) in its visible exocervical region, while for the other two samples more advanced (CIN3) lesions were present, together with visible glandular epithelium (ectropion). Significant birefringence has been observed in the healthy regions of all six samples, both in vivo and ex vivo. Standard treatments of the Mueller images of the ex vivo samples allowed to quantify both retardation and depolarization. Retardation reached 60° in healthy regions, and disappeared in the anomalous regions of the other three ex vivo samples. The depolarization power was largest in healthy regions, and lower in CINs and ectropion. Possible origins of the observed effects are briefly discussed.

Multispectral Mueller polarimetric imaging detecting residual cancer and cancer regression after neoadjuvant treatment for colorectal carcinomas

Abstract. This work is devoted to a first exploration of Mueller polarimetric imaging for the detection of residual cancer after neoadjuvant treatment for the rectum. Three samples of colorectal carcinomas treated by radiochemotherapy together with one untreated sample are analyzed ex vivo before fixation in formalin by using a multispectral Mueller polarimetric imaging system operated from 500 to 700 nm. The Mueller images, analyzed using the Lu-Chipmann decomposition, show negligible diattenuation and retardation. The nonirradiated rectum exhibits a variation of depolarization with cancer evolution stage. At all wavelengths on irradiated samples, the contrast between the footprint of the initial tumor and surrounding healthy tissue is found to be much smaller for complete tumor regression than when a residual tumor is present, even at volume fractions of the order of 5%. This high sensitivity is attributed to the modification of stromal collagen induced by the cancer. The depolarization contrast between treated cancer and healthy tissue is found to increase monotonously with the volume fraction of residual cancer in the red part of the spectrum. Polarimetric imaging is a promising technique for detecting short-time small residual cancers, which is valuable information for pathological diagnosis and patient management by clinicians.

Polarimetric Imaging for Cancer Diagnosis and Staging

A medical imaging technique that relies on light polarization could become a fast and accurate optical method for detecting cancer and determining the stage of the disease.

The origins of polarimetric image contrast between healthy and cancerous human colon tissue

Experimentally measured spectral Mueller matrix images of ex vivo human colon tissue revealed the contrast enhancement between healthy and cancerous zones of colon specimen compared to unpolarized intensity images. Cancer development starts with abnormal changes which being not yet visible macroscopically may alter the polarization of reflected light. We have shown with experiments and modeling that light scattering by small (sub wavelength) scatterers and light absorption (mainly due to blood hemoglobin) are the key factors for observed polarimetric image contrast. These findings can pave the way for the alternative optical technique for the monitoring and early detection of cancer.

Ex vivo photometric and polarimetric multilayer characterization of human healthy colon by multispectral Mueller imaging

Healthy human colon samples were analyzed ex vivo with a multispectral imaging Mueller polarimeter operating from 500 to 700 nm in a backscattering configuration with diffuse light illumination impinging on the innermost tissue layer, the mucosa. The intensity and polarimetric responses were taken on whole tissues first and after progressive exfoliation of the outer layers afterwards. Moreover, these measurements were carried out with two different substrates (one bright and the other dark) successively placed beneath each sample, allowing a reasonably accurate evaluation of the contributions to the overall backscattered light by the various layers. For the shorter investigated wavelengths (500 to 550 nm) the major contribution comes from mucosa and submucosa, while for the longer wavelengths (650 to 700 nm) muscular tissue and fat also contribute significantly. The depolarization has also been studied and is found to be stronger in the red part of the spectrum, mainly due to the highly depolarizing power of the muscular and fat layers.

Impact of model parameters on Monte Carlo simulations of backscattering Mueller matrix images of colon tissue

Polarimetric imaging is emerging as a viable technique for tumor detection and staging. As a preliminary step towards a thorough understanding of the observed contrasts, we present a set of numerical Monte Carlo simulations of the polarimetric response of multilayer structures representing colon samples in the backscattering geometry. In a first instance, a typical colon sample was modeled as one or two scattering “slabs” with monodisperse non absorbing scatterers representing the most superficial tissue layers (the mucosa and submucosa), above a totally depolarizing Lambertian lumping the contributions of the deeper layers (muscularis and pericolic tissue). The model parameters were the number of layers, their thicknesses and morphology, the sizes and concentrations of the scatterers, the optical index contrast between the scatterers and the surrounding medium, and the Lambertian albedo. With quite similar results for single and double layer structures, this model does not reproduce the experimentally observed stability of the relative magnitudes of the depolarizing powers for incident linear and circular polarizations. This issue was solved by considering bimodal populations including large and small scatterers in a single layer above the Lambertian, a result which shows the importance of taking into account the various types of scatterers (nuclei, collagen fibers and organelles) in the same model.

Optical fiber-based full Mueller polarimeter for endoscopic imaging using a two-wavelength simultaneous measurement method

Abstract. 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.

Use of Mueller polarimetric imaging for the staging of human colon cancer

In this paper we show the results of multi-spectral Mueller Imaging applied to the analysis of human colon cancer in a backscattering configuration with diffuse light illumination. The analyzed sample behaves as a pure depolarizer. The depolarization power, for both healthy and cancerous zones, is lower for linearly than for circularly polarized incident light for all used wavelengths and increases with increasing wavelength. Based on their visual staging and polarimetric responses, we chose specific zones which we correlated to the histology of the corresponding cuts. The histological examination shows that we see a multilayer interaction in both healthy and abnormal zones, if the light penetration depth is sufficient. The measured depolarization depends on several factors: the presence or absence of tumor, the microscopic structure of cancer (ratio between cellular density and stroma), its exophytic (budding) or endophytic (penetrating) nature, its thickness, the degree of cancer penetration in deeper layers and the nature of healthy tissue left under abnormal layers. These results demonstrate that multi-spectral Mueller imaging can provide useful contrasts for the quick staging of human colon cancer ex-vivo, with additional information about cancerous zones with different microscopic structures.

Optical biopsy of tissue with Mueller polarimetry: theory and experiments (Conference Presentation)

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.