[Advances in gammaencephalography for the study of intercranial lesions]

Simultaneously to the development of new techniques such as the computerized axial tomography, the gamma-angioencephalography is progressing in the field of cerebral investigation in its original way, keeping on non invasing character. In view to analyze this evolution we shall examine first its technical possibilities, then the extractible data of the various techniques. Finally we will consider in which way we must bring most of our effort for the best utilization of the gamma-angioencephalography in the routine work, on one hand, and for progressing in the knowledge of the physiopathology of some lesions, specially vascular accidents, on the other hand. Technical modalities are multiple. Besides the standard technique (pertechnetate angiography with rapid sequential views, regional transit curves, early and late static views) it is possible to replace or to repete the injection: --changing the patient's position, --using another radiopharmaceutical labelled with technetium -or another isotope, or two tracers for two compartments; --carrying out a pharmacodynamic or CO2 test, --using radioxenon, and secondly a pure vascular tracer, to measure relative regional blood pool and relative regional blood flow. a) morphological ones (vascular tracks, regional blood pool, radioactive areas: number, form, homogeneity, outline), b) dynamic and quantitative ones (transit times, blood flow, extravascular diffusion, changes of these parameters when changing the radiopharmaceutic, or when using a test). Progresses can take place in three ways, very closely related to each other: a) In the methodology, to precise --relative merit of the different radiocompounds according to the various cerebral lesions, --methods for examination according to the clinical problems, --computing and date processing techniques. b) In the indications, to choose the best, the simplest, though the surest method for the daily clinical problems, and the best one to assemble special information escaping to the morphological radiological techniques. This choice needs frequent and close discussions between clinicians and nuclear specialists. c) In the signification of the data, to interprate correctly: --preferential uptakes in lesions or in compartments, --changes in the relative volumes of vascular bed and extravascular space in lesions, --vascular reactivity to an hemodynamic test, --accumulation or clearance of a diffusible tracer such as xenon. It is not always easy to reach a non equivocal interpretation of a whole group of data. It can be better to give a descriptive analysis which brings together elements for the diagnosis and physiopathological observations helpful for a therapeutic action and to follow up the disease at short and long term.