Polarization imaging techniques have been extensively employed in biomedical studies and clinical applications. As a comprehensive polarization representation, the Mueller matrix (MM) can provide abundant polarization-related information of biomedical samples. For quantitative information acquisition, groups of polarization basic parameters (PBPs) have been obtained through MM analysis and demonstrated as effective structural characterization tools of tissue samples. Recently, MM polarimetric endoscopy has shown great clinical diagnostic potential. For in-vivo polarimetry such as gastrointestinal MM endoscopy of human internal organ cavities, the complicated undulating tissue surface geometry delivers an inescapable occurrence of oblique incidence, which induces a prominent aberration to backscattering tissue polarimetry. Thus, quantitatively analyzing and reducing the polarimetric aberration induced by oblique incidence are crucial for in-vivo precision MM endoscopy. In this study, we quantitatively analyze the polarimetric aberration induced by tissue surface geometry on PBPs. A correlation heatmap is obtained as applicable criteria to select appropriate incident angle for different PBPs. Based on the analyzing results, we propose two aberration correction strategies of parameter selection and azimuth rotation, which are suitable for tissue samples with randomly and well-aligned fiber textures, respectively. Both strategies are demonstrated to be effective in the ex-vivo human gastric muscularis tissue experiment. The findings presented in this study can be useful to provide accurate polarization imaging results, widely applied on in-vivo polarimetric endoscopy for tissues with complicated surface topography.
KEYWORDS: Polarimetry, Tissues, Mueller matrices, Backscatter, Statistical analysis, Natural surfaces, Monte Carlo methods, In vivo imaging, Endoscopy, Scattering
Currently, there are two backscattering polarimetry schemes, namely the collinear reflection mode with normal incidence, and the non-collinear reflection one with obliquely incident illumination. To eliminate the surface reflection from the sample cost-effectively, the non-collinear backscattering Mueller matrix (MM) imaging setup always has an oblique incidence. Meanwhile, the uneven tissue surfaces can induce various relative oblique incidences inevitably, which can affect the polarimetry in a complicated manner. In this study, we systematically measured the MMs of experimental phantom and ex-vivo tissues under different oblique incident illuminations. Moreover, a Monte Carlo simulation program based on cylindrical scattering model was also adopted for further analysis and validation. Oblique incidence can induce various aberration on non, two and four periodic MM elements, leading to false-positive and false-negative information for tissue polarimetry. The findings presented in this study give the suggestions for appropriate incident angle selection in in vivo tissue polarimetric practices and can also be useful as valuable references for studying how to minimize the influence furtherly.
SignificanceAmong the available polarimetric techniques, backscattering Mueller matrix (MM) polarimetry provides a promising non-contact and quantitative tool for in vivo tissue detection and clinical diagnosis. To eliminate the surface reflection from the sample cost-effectively, the non-collinear backscattering MM imaging setup always has an oblique incidence. Meanwhile, for practical organ cavities imaged using polarimetric gastrointestinal endoscopy, the uneven tissue surfaces can induce various relative oblique incidences inevitably, which can affect the polarimetry in a complicated manner and needs to be considered for detailed study.AimThe purpose of this study is to systematically analyze the influence of oblique incidence on backscattering tissue polarimetry.ApproachWe measured the MMs of experimental phantom and ex vivo tissues with different incident angles and adopted a Monte Carlo simulation program based on cylindrical scattering model for further verification and analysis. Meanwhile, the results were quantitatively evaluated using the Fourier transform, basic statistics, and frequency distribution histograms.ResultsOblique incidence can induce different changes on non-periodic, two-periodic, and four-periodic MM elements, leading to false-positive and false-negative polarization information for tissue polarimetry. Moreover, a prominent oblique incidence can bring more dramatic signal variations, such as phase retardance and element transposition.ConclusionsThe findings presented in this study give some crucial criterions of appropriate incident angle selections for in vivo polarimetric endoscopy and other applications and can also be valuable references for studying how to minimize the influence further.
Recently, Mueller matrix polarimetry has received increasing attention in the field of biophotonics, because of its great potential for non-invasive, label-free detection of microstructural and optical properties of biomedical samples. In this study, we propose a method for automatic identification and quantitative evaluation of skin hair follicle structure based on Mueller matrix polarimetry combined with the K-means clustering machine learning algorithm. First, we use the transmission Mueller matrix microscope to measure the rat skin tissue sections with hair follicles. Then we derive the Mueller matrix transformation (MMT) parameters images to reveal the characteristics of the birefringent skin hair follicle structure. By taking the MMT parameters images as the identification objects, we adopt the K-means clustering algorithm to segment them and carry out image denoising processing to achieve the automatic detection of the hair follicle structure. Finally, to identify the hair follicle structure quantitatively and accurately, we conduct a comprehensive evaluation of five indexes including quantity, area, position, long axis, and short axis of the recognized regions. The results show that the method presented in this study can realize the automatic identification and quantitative evaluation of skin hair follicle structures, having great potential for the detection and clinical diagnosis of skin structures.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.