Biomedical applications of proton induced X-ray emission.

Apart from studies on aerosols, the majority of applications of proton induced X-ray emission (PIXE) with a normal beam or a microprobe (micro-PIXE) is found in biology and medicine. Two aspects of broad beam PIXE are often decisive for the choice of this analytical technique. Compared to other techniques capable of analysis down beyond the ppm level, PIXE can be carried out with a very small amount of material and minute fractions of the composite samples, even in the scale of micrometers and quite often with minimal sample preparation, which are important requirements for biomedical investigations. Secondly, the speed of the total analysis opens the possibility to analyze large numbers of samples in a reasonable time, which is often necessary in biomedical studies in order to obtain sufficiently significant correlations between trace element concentrations and biomedical phenomena. Few, if any, techniques can compete with micro-PIXE; quantitative trace element analysis on a micrometer scale still represent a challenging problem. The electron microprobe normally lacks the sensitivity while the laser induced techniques suffer as yet from quantification problems. This paper describes recent developments especially in micro-PIXE in biomedical research.