Abstract
Polarisation microscopy is a label-free technique whose tissue architecture profiling through anisotropy remains underinvestigated. In histology, bright-field microscopy and special stains remain the standard for investigating extracellular matrix (ECM) proteins. However, these approaches are qualitative and observer-dependent. By measuring birefringence parameters, quantitative polarisation microscopy (QPM) could offer a more objective alternative. Using dual photoelastic modulators and full Stokes parameter acquisition, QPM was applied to Congo red and picrosirius red-stained sections of human placenta, normal skin, and keloid scars. From the Stokes vectors (I, Q, U, V), polarisation azimuth, ellipticity, phase retardation, and depolarisation maps were derived, enabling quantitative characterisation of collagen organisation. QPM revealed distinct anisotropic signatures corresponding to ECM microarchitecture. Picrosirius red-stained sections demonstrated a three/four-fold in phase retardation increase compared to Congo red, confirming its collagen-specific birefringent enhancement. In placenta, spatially heterogeneous birefringence highlighted perivascular collagen arrangements. In skin, stronger phase retardation and depolarisation patterns were observed in dermal collagen bundles, with keloid scars showing markedly increased phase retardation (~ 1.4 radians) and depolarisation (~ 0.96), reflecting altered collagen density and disorganisation. QPM provides objective, spatially-resolved tissue anisotropy metrics, overcoming the qualitative limitations of traditional histological techniques. This approach offers a robust framework for assessing collagen remodelling in various pathological contexts.
Data availability
The data generated and/or analysed during the current study are available from the corresponding author on reasonable request.
Code availability
Custom Python scripts used for image acquisition and analysis, including computation of Stokes parameters, ellipticity, polarisation azimuth, depolarisation, and phase retardation, are available from the corresponding author on reasonable request.
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Acknowledgements
We wish to acknowledge the support from Spark Impact Ltd, the University of Salford Enterprise and private investors via Optimum Imaging Ltd for the development of the prototype Stokes polarimetric microscope and to thank Mr JJF Shen for his developmental work. THS would like to express his gratitude to Profs WY Liang, JV Acrivos, RH Bisby, PJ Grundy, Dr GA Jones, Prof I Morrison for their interest and encouragement and to Mr J. L. Ramos Angulo, Mr M Purdie, Dr B Prime for their participation in the early stage of the microscope development. We most sincerely thank Mr M Clegg for his invaluable technical support.
Funding
This work was generously supported by Cerebra and the UKRI QR Research Capital Investment Fund via the University of Salford.
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GM, HP, CF and TS performed experiments. Analysis and image handling were performed by GM and PM. RO, HA and MC provided technical and conceptual support. GM, NMO and TS wrote the paper. All authors contributed to the final draft.
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Mappa, G., Miklavc, P., Cummings, M. et al. Polarimetric imaging of collagen in histopathology specimens: an investigation of congo red and picrosirius red-stained placenta and skin. Sci Rep (2026). https://doi.org/10.1038/s41598-026-37711-8
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DOI: https://doi.org/10.1038/s41598-026-37711-8
