In this Letter, we report a study on the effects of spatial filtering for a transmission Mueller matrix imaging system. A spatial filter (SF) is placed on the back Fourier plane of the imaging lens in a dual-rotating-retarders Mueller matrix imaging system to select photons within a certain scattering angle. The system is then applied to three types of human cancerous tissues. When imaging with a small-aperture SF, some polarimetry basis parameters show sharp changes in contrast in the cancerous regions. Monte Carlo simulations using a simple sphere–cylinder scattering model also show that spatial filtering of the scattered photons provides extra information on the size and shape of the scattering particles. The results indicate that spatial filtering enhances the capability of polarization imaging as a powerful tool for biomedical diagnosis.

Evaluation of the mechanical properties of biological tissues has always been an important issue in the field of biomedicine. The traditional method for mechanical properties measurement is to perform in vitro tissue deformation experiments. With the fast development of optical and image processing techniques, more and more non-invasive and non-contact optical methods have been applied to the analysis of tissue mechanical features. In this study, we use Mueller matrix polarimetry to quantitatively obtain the mechanical properties of bovine tendon tissues. Firstly, to study the structural information and the changes in the optical characteristics of the tendon tissue under different stretching states, 3 × 3 Mueller matrix images of bovine tendon tissue samples are acquired by backscattering measurement setups based on a polarized camera. Then, we extract the frequency distribution histograms (FDHs) of the Mueller matrix elements to reveal the structural changes of the tendon tissue more clearly during the stretching process. Last, we calculate the Mueller matrix transformation (MMT) parameters, the total anisotropy and the anisotropy direction of the tendon tissue samples under different stretching processes to quantitatively characterize their structural changes under different mechanical states. The central moments of the MMT parameters can be used to distinguish the different stretching states of the tendon tissue. For better discrimination based on the MMT parameters, we design a multilayer neural network that takes the first-order moments of the MMT parameters as the input features. After training, a high-precision classification model of the stretching states of tendon tissue samples is finally obtained, and the total classification accuracy achieves 98%. The experimental results show that the Mueller matrix polarimetry can be a potential non-contact tool for tissue mechanical properties evaluation.

The Mueller matrix contains abundant micro- and even nanostructural information of media. Especially, it can be used as a powerful tool to characterize anisotropic structures quantitatively, such as the particle size, density, and orientation information of fibers in the sample. Compared with unpolarized microscopic imaging techniques, Mueller matrix microscopy can also obtain some essential structural information about the sample from the derived parameters images at low resolution. Here, to analyze the comprehensive effects of imaging resolution on polarization properties obtained from the Mueller matrix, we, first, measure the microscopic Mueller matrices of unstained rat dorsal skin tissue slices rich in collagen fibers using a series of magnifications or numerical aperture (NA) values of objectives. Then, the first-order moments and image texture parameters are quantified and analyzed in conjunction with the polarization parameter images. The results show that the Mueller matrix polar decomposition parameters diattenuation D, linear retardance δ, and depolarization Δ images obtained using low NA objective retain most of the structural information of the sample and can provide fast imaging speed. In addition, the scattering phase function analysis and Monte Carlo simulation based on the cylindrical scatterers reveal that the diattenuation parameter D images with different imaging resolutions are expected to be used to distinguish among the fibrous scatterers in the medium with different particle sizes. This study provides a criterion to decide which structural information can be accurately and rapidly obtained using a transmission Mueller matrix microscope with low NA objectives to assist pathological diagnosis and other applications.