The free radical signal of pigment gallstones

Bile stones have been studied by Electron Spin Resonance (ESR) spectroscopy. Pigment containing stones show a 8.76 +/- 0.02 gauss wide free radical singlet at g approximately 2.003 region of the spectrum. Amplitude of this free radical signal linearly correlates with pigment content of the stone, which can be applied in the estimation of pigment content. The possible role of free radicals is suggested in the formation of pigment bile stones.