Small-angle X-ray scattering (SAXS) and nitrogen porosimetry (NP): two novel techniques for the evaluation of urinary stone hardness.

PURPOSE: To evaluate urinary stones using small-angle X-ray scattering (SAXS) and nitrogen porosimetry (NP). Traditionally, stones are categorized as hard or soft based on their chemical composition. We hypothesized that stone hardness is associated not only with its chemical composition but also with its internal architecture. SAXS and NP are well-known techniques in material sciences. We tested whether SAXS and NP are applicable for evaluating human urinary stones and whether they provide information at the nanoscale level that could be useful in clinical practice.

METHODS: Thirty endoscopically removed urinary stones were studied. Standard techniques for stone analysis were used to determine the stone composition. SAXS was used to evaluate the solid part of the stone by measuring the crystal thickness (T) and the fractal dimension (Dm /Ds ), while NP was used to evaluate the porosity of the stone, i.e., the pore radius, pore volume, and specific surface area (SSA).

RESULTS: All stones were successfully analyzed with SAXS and NP. Each stone demonstrated unique characteristics regarding T, Dm /Ds , pore radius, pore volume, and SSA. Significant differences in those parameters were seen among the stones with almost identical chemical compositions. The combination of high T, high SSA, low Dm /Ds , low pore volume, and low pore radius is indicative of a hard material and vice versa.

CONCLUSIONS: SAXS and NP can be used to evaluate human urinary stones. They provide information on stone hardness based on their nanostructure characteristics, which may be different even among stones with similar compositions.