RECENT DEVELOPMENTS IN MEDICAL APPLICATIONS OF SIMS MICROSCOPY

The purpose of this review is to present the recent developments in th e medical applications of SIMS microscopy. This technique is one of th e microanalytical mass spectrometry methods which allow in theory the detection of all the elements of the Mendeleiev table as well as the s eparation of stable and radioactive isotopes. It is based on a phenome non whereby a biological sample surface is sputtered by bombardment wi th an energetic 'primary ion' beam. Part of the sputtered matter is io nized and the resulting 'secondary ions' are characteristic of the ato mic composition of the analyzed area. These secondary positive or nega tive ions are collected and separated in a mass spectrometer at low or high mass resolution, which is dependent on both the element studied and its concentration. An analytic image which conserves the tissue di stribution of the selected element is displayed on a fluorescent scree n linked to an image processing system. Local elemental concentration can also be measured. Results are highly dependent on the techniques u sed for sample preparation which should preserve both the chemical and the structural integrity of the tissue. Further, the ionic images mus t be correlated with corresponding images of the same areas of the ser ial sections observed in a photonic microscope. With our SIMS microsco pe (lateral resolution approximate to 0.5 mu m, and mass resolution 30 0 to 12,000) we have demonstrated that this microscopic imaging techni que is suitable for physiopathological studies. We revisited thyroid i odine metabolism by mapping chemical elements such as S-32 and I-127, characteristic of hormonal physiology. Newly organified iodine (radioi odine) can be evaluated in relation to previously stored iodine (I-127 ) in given follicle, thus allowing an appraisal of glandular adaptatio n to aging and iodine overload. Another area in which SIMS can be used in medicine, is for the localization of drug markers in tumor tissue (e.g. fluorine-5-fluouracil, iodine in iododeoxyrubicin). This could f acilitate the evaluation of the intratumor drug concentration at the o nset of the treatment. Likewise, SIMS can be used to localize radiopha rmaceuticals used in diagnosis (e.g. technetium) and therapy (I-131 Of metaiodobenzylguanidine). This would permit a better evaluation of th e radiation dose delivered to tissue. Further prospects are within rea ch with the imminent advent of higher lateral resolution (0.05 mu m) S IMS microscopes.