QUANTITATIVE ELECTRON SPECTROSCOPIC IMAGING IN BIO-MEDICINE - EVALUATION AND APPLICATION

Electron spectroscopic imaging (ESI) with the energy-filtering transmi ssion electron microscope enables the investigation of chemical elemen ts in ultrathin biological sections. An analysis technique has been de veloped to calculate elemental maps and quantitative distributions fro m ESI sequences. Extensive experience has been obtained with a practic al implementation of this technique. A procedure for more robust eleme nt detection has been investigated and optimized. With the use of Fe-l oaded Chelex beads, the measurement system has been evaluated with res pect to the linearity of the element concentration scale, the reproduc tibility of the measurements and the visual usage of images results. I n liver specimens of a patient with an iron storage disease the detect ability of iron was tested and we tried to characterize iron-contained components. The concentration measurement scale is approximately line ar up to a relative section thickness of approximate to 0.5. Monitorin g of this parameter is therefore considered to be important. The repro ducibility was measured in an experiment with Fe-Chelex. The iron conc entration differed by 6.4% between two serial measurements. Element di stributions are in many applications interpreted visually. For this pu rpose the frequently used net-intensity distributions are regarded as unsuitable. For the quantification and visual interpretation of concen tration differences mass thickness correction has to be performed. By contrast, for the detection of elements the signal-to-noise ratio is t he appropriate criterion. Application of ESI analysis demonstrated the quantitative chemical capabilities of this technique in the investiga tion of iron storage diseases. Based on an assumed ferritin iron loadi ng in vivo, different iron components can be discerned in liver parenc hymal cells of an iron-overloaded patient.