CORRELATIVE LIGHT MICROSCOPY AND X-RAY MICROTOMOGRAPHY OF GROUND SECTIONS OF MINERALISED TISSUES.

Starting from scratch, if one wanted to correlate light microscopical (LM) and X-ray microtomographic (XMT, micro-CT) findings from the mineralized tissues - bone and calcified cartilage in the skeleton and dentine, enamel, and cementum in teeth - one could simply examine the same, resin embedded sample with at least one flat surface by confocal scanning reflection and/or fluorescence light microscopy and XMT. However, we are frequently presented with ready-made 'ground' sections mounted in Canada balsam or DPX on 25mm wide similar to 1mm thick glass slides with 0.17mm cover slips. Many such preparations are historical or are valuable by representing archival material from rare diseases or endangered species: all are inconvenient in form for XMT. We endeavored to economize on X-ray beam time by scanning a 25mm thick stack of slides, separating the relevant data from each sample and making exact matches with transmitted ordinary and polarized light microscopy images. Samples were selected to represent a wide range of sizes and skeletal and dental tissue types, including human femoral bone, human permanent teeth, dog carnassial tooth, narwhal mandible, black rhinoceros molars, sperm whale cementum and dentine, African elephant ivory, and prairie marmot molars. XMT was conducted using the QMUL Mucat-2 system [1], nominal voxel size 20 mu m, 90kV, 24 hours. Analysis used in-house analysis software TomView, ImageJ [2] and Drishti [3] software. In each case we were able to match XMT and light microscopy. We can now report mineralization densities for all the calcified tissues in the context of classical light microscopy imagery.