X-ray transmission images of (a) paraffin-embedded kidney section fixed with Karnovsky fixative supported on ultralene foil and (c) a paraffin-only area outside the biological tissue region, with corresponding FTIR chemical images of the integration of the absorbance of the asymmetric stretching of CH3 (2960 cm−1) band (b and d, respectively). X-ray transmission images were acquired by exposing the sample to Rad1 dose. The sample regions marked with yellow, orange and red boxes were exposed to Rad2, Rad3 and Rad4 doses, respectively. (e) Optical image of the exposed area on ultralene only, as indicated in the scheme in the left subset, and (f) its corresponding chemical image obtained by using FTIRM. FTIR chemical images are false coloured with low numbers corresponding to high damage (low signal) [colour scale bar represents absorbance arbitrary units (a.u.)]. The scale bars represent 50 µm.