Low temperature techniques in biomedical microanalysis.

Many diseases are associated with a change in the distribution of diffusible ions at the cell or tissue level. These diseases can profitably be studied by X-ray microanalysis. This technique for the study of ion distribution requires the use of cryoprepared specimens. Analysis at low or medium resolution can be carried out on thick or semi-thick cryosections, or on frozen-hydrated or freeze-dried embedded bulk samples. Such analyses are particularly useful in the initial stages of an investigation, or when many data from a large number of samples have to be acquired. Quantitative analysis is then usually carried out with the peak-to-local background method: by taking the background in the same energy range as the characteristic peak, an intrinsic correction for absorption of X-rays within the sample is made. X-ray microanalysis of cultured cells prepared by freeze-drying can also be carried out in this way. Analysis at high resolution has to be carried out on thin sections: cryosections, or sections of freeze-substituted or freeze-dried embedded tissue. For the latter type of specimens, the use of low-temperature embedding methods may have important advantages. Quantitative analysis of thin sections is carried out by the established continuum method.