Analytical procedure for mapping the distribution of 10B and 99Tc markers in cryo-sections of animal tissue samples by secondary ion mass spectrometry.

The development of a complete, standard analytical procedure for a quantitative use of SIMS to map the distribution in animal tissues of exogenous isotopes presents difficulties inherently related to sample preparation and preservation, as well as to the specific application being considered. We have tested in two very different cases a procedure based on the cryopreparation of samples and calibration standards. The applications under investigation were the mapping of 10B in mouse brain tissue, with relevance to the boron neutron capture therapy, and of the perfusion tracer 99Tc in mouse heart tissue, with relevance to the study of microcirculation and cardiovascular pathologies. SEM microscopy and ICP-MS analysis were used as reference techniques for SIMS images and analyte measurements, respectively. Cryopreparation of tissue sections for ion microscopy proved to be simple and efficient (in terms of structural and chemical integrity) for both brain and heart samples derived from fresh organs. This technique, however, turned out to be reliable only on the brain tissue when applied to the preparation of standards, which required chemical fixation of portions of organs. Brain and heart tissue showed a totally different response to chemical fixation, from both a structural and an analytical point of view. On the one hand, we were able to estimate a relative sensitivity factor for 10B in the cryo-sectioned brain matrix; on the other hand, even without the possibility of an absolute quantification of the 99Tc signal and notwithstanding the presence of an isobaric interference, SIMS mapping however proved to be capable to resolve the specific response of the cardiac tissue to the perfusion mechanism.