The use of Raman spectroscopy to identify inorganic phases in iatrogenic pathological lesions of patients with malignant pleural mesothelioma

Thin sections of pleura and lung prepared for diagnosis of Malignant Mesothelioma (MM) in patients who underwent pleurodesis were analysed by micro-Raman spectroscopy. In the pleural tissue, visual inspection under an optical microscope attached to the Raman spectroscope revealed numerous acicular crystals and several rounded particles, micrometers in size. The laser beam of the spectrometer was focused on each of the inorganic phases in turn, revealing Raman spectra attributable to talc or to clinochlore on the acicular crystals and to phosphate phases on the rounded particles. In the lung tissue, optical inspection indicated the presence of asbestos bodies, identified by micro-Raman spectroscopy as crocidolite, "asbestos" mineral, the phase of the fibre inside the coating material. The identity of the inorganic phases as determined by Raman spectroscopy was confirmed by chemical analysis using a Scanning Electron Microscope equipped with an Energy Dispersive Spectrometer (SEM/EDS). Micro-Raman spectroscopy proved effective in identifying the inorganic phases present in thin sections prepared for medical diagnosis, allowing compounds introduced during treatment (talc or clinochlore) to be distinguished from those inhaled (asbestos) or crystallized during disease progression (phosphates).