QUANTITATIVE X-RAY IMAGES CALCULATED ON THE BASIS OF MASS AND VOLUME

Quantitative X-ray microanalysis is used to obtain the elemental compo sitions of tissues and cells. Concentrations are calculated on the bas is of volume (mmo1L(-1) of packed cells) and mass (mmolkg(-1) dry weig ht). Elemental maps are obtained by using a computer to control the po sition of a beam in an electron microscope and to record the signals f rom the scanning transmission electron microscope (STEM) and energy di spersive X-ray spectrometer (EDS) X-ray detectors. These X-ray images provide better visualization of elemental distributions than ''spot'' mode analysis by analyzing thousands of spots sequentially. When conce ntrations are determined on the basis of volume, it is assumed that th e section thickness created during cryosectioning, and shrinkage durin g freeze-drying of a frozen section, are uniform. These assumptions ha ve been examined with a nucleated red blood cell model. Even distribut ions of cytoplasmic Fe and It, which we observed, can only occur if cr yomicrotomy produces sections with smooth surfaces and uniform thickne ss. In addition, by using bone marrow cryosections we have found that the relative shrinkage between nucleated and non-nucleated cells is si milar. Therefore, the assumptions made about volume calculations do ap pear to be reasonable under the conditions used in this study.