IMAGING OF ELEMENTS IN TISSUE AT TRACE CONCENTRATIONS

INSTRUMENTATION ENABLING QUANTITATIVE TRACE ELEMENT-CONCENTRATION IMAGING WITH HIGH SENSITIVITY AND RESOLUTION (1 PPM, 5 ) OF BIOLOGICAL TISSUE SECTIONS OVER 2X2MM(2) WOULD BE A VALUABLE RESEARCH TOOL. SIMULTANEOUS STRUCTURAL IMAGING WOULD ENHANCE ITS UTILITY. SPUTTER-INITIATED RESONANCE IONIZATION SPECTROSCOPY (SIRIS) WILL BE ADAPTED TO PROVIDE STRUCTURAL IMAGING AND QUANTITATIVE ELEMENT-CONCENTRATION IMAGING OF BIOLOGICAL TISSUE SECTIONS. THE METHOD WILL BE TESTED BY IMAGING THE CONCENTRATIONS OF IRON AND ALUMINUM IN TISSUE SECTIONS FROM BRAINS OF ALZHEIMER'S DISEASE VICTIMS AND CORRELATING THESE IMAGES WITH SURFACE STRUCTURES VISIBLE IN SECONDARY ELECTRONIMAGES FROM THE IDENTICAL LOCATION. OPTICAL MICROSCOPY OF ADJACENT STAINED SECTIONS WILL ALSO BE PERFORMED. SIRIS UTILIZES A FOCUSED ION BEAM TO SPUTTER NEUTRAL ATOMS AND IONS FROM THE SAMPLE SURFACE. THE IONS ARE REJECTED, WHILE THE NEUTRAL ATOMS ARE IONIZED WITH NARROW-BAND LASERS TUNED TO SPECIFIC TRANSITIONS OF THE SELECTED ELEMENT. THISYIELDS A UNIFORMLY HIGH IONIZATION EFFICIENCY FOR ANY SELECTED ELEMENT, WITH ESSENTIALLY NO IONIZATION OR INTERFERENCE FROM OTHER CONSTITUENTS IN THE SAMPLE. IMAGINGWILL BE IMPLEMENTED BY RASTERING THE ION BEAM OVER THE SAMPLE WITH SYNCHRONOUS DETECTION, STORAGE, AND DISPLAY OF THE SECONDARY ELECTRON AND SIRIS ION SIGNALS. THE SYSTEM WILL ALSO BE APPLICABLE TO THE SEMICONDUCTOR INDUSTRY, SURFACE SCIENCE, AND GEOSCIENCE.