Near-Infrared Absorption Coefficients in Kidney Stone Minerals and Their Relation to Crystal Structure

Abstract

To quantitatively understand laser ablation of kidney stones by near-infrared (NIR) lasers, accurate measurements of physical properties related to heating and mechanical failure are needed. While light scattering varies among individual stones, absorption coefficients for the materials that form the bulk of each kidney stone are measurable when scattering is controlled. We developed methods to grow single crystals with lengths and widths >20 μm for the minerals that form kidney stones: calcium oxalate monohydrate, calcium oxalate dihydrate, calcium hydrogen phosphate dihydrate, hydroxyapatite, anhydrous uric acid, and magnesium ammonium phosphate hexahydrate. These single crystals were used with an infrared microscope to measure their NIR absorption coefficients from 1.67 to 2.5 μm. The strong correlation between single crystal NIR spectra and diffuse reflectance NIR spectra indicates little anisotropy in absorption. Most minerals absorbed more strongly at 1.94 μm than 2.12 μm, the wavelengths of thulium fiber and holmium:YAG surgical lasers, respectively. For water bearing minerals, we attribute absorption mainly to water combination modes and assign NIR absorption peaks to specific water molecules and the OH bonds thereof where possible. Reported absorption coefficients can be used to quantitatively compare both laboratory investigations of ablation and surgical experience to physical properties for the first time.

Kidney stone growth through the lens of Raman mapping

“…The appearance of layering is similar to in-vitro examples of COM growth on COD that we have observed in attempts at growing calcium oxalate stones (Figure S14 ). Region (C) shows a ≈ 100 µm long crystal with hexagonal plate morphology that can be induced by additives like citrate or by high ionic strength solutions which both inhibit growth perpedicular to the charged (100) planes of COM 59 , 60 .…”