Fig. 1: Spatially-unaware spectra from Raman analysis show distinct clustering.

a Data analysis workflow, starting from data acquisition using a confocal Raman microspectroscope. b Data handling, transformation and correction. Biologically relevant spectrum between 300 and 3000 cm⁻¹ (named “whole spectrum”) was corrected for outliers and then analyzed. Raman “fingerprint” spectrum between 400 and 1800 cm⁻¹ was corrected for outliers and paraffin peaks and then analyzed. c Increasing the number of principal components concretizes cluster results for UMAP analysis of Raman data. Whole spectrum data from the section from d and e was used. d H&E (left) and Picrosirius Red Staining (right) of adjacent sections to the sample of subendocardial fibrosis which was subjected to Raman spectroscopy. Scale bar 50 µm. e Raman Intensity Image (left) and Raman TCA (right) as described in the Methods section. f Various projections after dimensionality reduction of the fingerprint spectrum from the section of d and e, including PCA, tSNE and UMAP. g Cluster-specific average spectra with characteristic peak annotations. UMAP: Uniform Manifold Approximation and Projection, TCA: True Component Analysis, PC: Principal Component, tSNE: t-distributed stochastic neighbor embedding.