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Protoporphyrin IX concentrations in skull base meningioma. Scatter plot of PpIX concentrations in normal and tumor tissue (mean 4.81 ± 1.49 μg/ml, range 0.11–19.15 μg/ml). Tumor tissue accumulated significantly more PpIX than normal tissue. Concentrations in normal dura were all below the level of quantification and outside the axis limits.
