[Study of circulation of cerebro-spinal fluid using indium 111 DTPA. Apropos of 300 cases]

A study of the C.S.F. circulation by intrathecal injection of radioactive tracers has become a common technic of neurological exploration. Among the molecules used at present, Indium111 DTPA has numerous advantages for this type of study. It is a chelating agent, the renal clearance of which is rapid and which has no toxicity at the dose injected. Indium111 is a product of the cyclotron and the physical period (2.8 days) is compatible with the duration of the examination. Finally the dose of radioactivity delivered by this isotope is less than that Iodine131, Technetium99m and Ytterbium169. In normal subjects after injection by the lumbar route, the average biological period measured by external counting lies between 20 and 28 hours. A study of the circulation of the C.S.F. is particularly useful in patients suspected of hydrocephalus. It permits finer diagnosis and shows the indications and type of by pass operation that may be neccssary. A marked increase in the biological period of Indium111-DTPA seems to be a good indication for such an operation. Our experience of 300 patients has shown the interest of the use of Indium111-DTPA which now seems to be the best radio-isotope for the study of the subarachnoid space.

Optical surface roughness determination using speckle correlation technique

Two speckle patterns produced from the same rough surface by two different illuminations are correlated. The correlation depends on the surface roughness. The two illuminations were obtained here by varying the angle of incidence of a coherent plane wave on the surface. The speckle patterns are recorded on the same film by double exposure. By placing this film in a convergent laser beam, Young fringes are observed in the Fourier plane. The correlation of the speckle patterns is obtained by measuring the visibility of the fringes. The theoretical calculations have been performed for a normally distributed surface. The experimental results are in good agreement with theory.