Mapping of Kidney Stone by Far-Infrared Spectroscopy

Kidney stones are mainly composed of calcium oxalate (CaOx) minerals, and the understanding of the polymorphisms of CaOx is essential in establishing the pathogenesis of kidney stone formation. CaOx polymorphs are predominantly calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD). In this study, we employ reflection-mode Fourier transform infrared spectroscopy in the far-infrared region to map the spatial distribution of the main CaOx phases in a thin section of kidney stone. A higher reflectance band is observed on the COD-rich areas of the kidney stone compared to COM-rich areas in the spectral region between 5-10 THz. The spatial distribution of COM and COD phases is demonstrated herein based on the reflectance map utilizing the selected frequency of 8 THz. Our results show that THz waves could be useful in kidney stone analysis without an invasive sample preparation, thereby preserving the spatial information of the stone which contains the history of the stone formation process.