ELEMENTAL AND TRACE-ELEMENT DISTRIBUTION IN MEDICAL SAMPLES - ANALYSIS BY PROTON-INDUCED X-RAY-EMISSION

The analysis of trace elements is performed by proton-induced X-ray emission. The process is most effective if the velocity of the exciting particles-protons-is similar to the velocity of the electron on its orbit in the simple atomic model of Bohr. For K-shell electrons of the elements with .ltoreq.z.ltoreq. 40 this requires proton energies of a few MeV, available from electrostatic van de Graaf accelerator machines. After knocking out the K-shell electron, the empty place is filled up by electrons jumping from higher orbits with simultaneous emission of characteristic X-rays, which are registered with a cooled Si (Li) detector. By a set of electrodes the beam can be swept across the specimen surface. Therefore this method yields an excellent correlation of trace element distribution within the morphological structure of organic tissue. In the present study the sweep went along a line perpendicular to the arterial wall layers (aortic, renal artery and heart muscle) of normotensive and spontaneously hypertensive rats. Along this line all elements and trace elements are recorded simultaneously. These are P, S, Cl, K, Ca, Zn, Br and Sr. The trace element content of the aortic wall and the renal artery, of 22 spontaneously hypertensive and 11 normotensive rats and of human heart muscle was investigated. The results demonstrate that Zn was only detected in the muscle-containing layers of the arteries. There was no different distribution between hypertensive and normotensive rats. However, Ca2+ was mainly detected in the smooth muscle-containing tunica media of hypertensive rats. Thus by comparison of Zn and Cd2+ distribution in the tissue, a better identification of the different layers of the arterial wall could be achieved. The results of this study reveal that trace element analysis with PIXE yields valuable additional information on trace element distribution in organic tissue.