Amide I kurtosis maps cardiac amyloid in human tissue by ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS) microscopy

Abstract

Cardiac amyloidosis is caused by deposits of misfolded proteins in the heart and can lead to heart failure. Histological confirmation typically involves staining tissue sections with Congo red and examining them under polarized light for apple-green birefringence; however, achieving an interpretable, label-free, and observer-independent assessment remains challenging. Here we show that Pearson kurtosis of channel intensities within the amide I window provides an interpretable, fitting-free contrast for cardiac amyloid in unstained human cardiac tissue sections imaged by ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS). In two participants, high-kurtosis regions corresponded with Congo red-positive tissue in adjacent stained sections (descriptive spatial AUCs, 0.79 and 0.73). Across 15 fields from nine participants, including one of these two, kurtosis values did not overlap between severe-deposition and amyloid-negative tissue. Among the descriptors examined, kurtosis showed the largest standardized participant-level separation. Exploratory multivariate curve resolution yielded a deposit-associated component with aromatic-residue features shared with reagent transthyretin. Second harmonic generation (SHG), acquired simultaneously with CARS, showed a broadly inverse spatial pattern relative to kurtosis, providing complementary architectural contrast. These findings support a label-free approach to detecting cardiac amyloid deposits that combines broadband CARS-derived amide I kurtosis with SHG.