Physical methods for in vitro analytical imaging in the microscopic range in biology, using radioactive or stable isotopes (review article)

Physical methods make it possible to combine analytical imaging with isotop ic labelling in biological studies. With radioactive isotopes, track-radioa utography may be used (in parallel with conventional grain-density radioaut ography) for high lateral resolution, even with energetic beta -rays; in ma croradioautography, filmless methods (gaseous detectors, scintillation coun ters, and storage phosphor screen devices) have remarkable performances. Ne utron capture radiography is used mainly for the detection and imagine of o ne stable isotope of a few elements which have no radioisotope of practical use. With nuclear microprobes, nuclear reaction analysis and scattering an alysis may serve to discriminate between isotopes (including stable isotope s). Secondary ion mass spectrometry images any isotope of almost any elemen t with very good detection limits and a resolution better (sometimes much b etter) than 1 mum. Preventing the diffusion of mobile substances during the preparation of the biological specimens is still a difficult problem.