Echo-encephalography, described by LekseU (1955), consists in the transmission into the skull of a rather narrow beam of ultrasound, part of which is reflected to the transmitter. This technique enables one to measure the distance between the reflecting surfaces arid the transmitter, in order to derive certain conclusions about structures existing within the skull.It is obvious that this method offers certain advantages to the usual X-ray techniques, for in the latter ease the total quantity of transmitted energy is visualized on the X-ray film as a density. On a normal X-ray film the skull appears to be "empty", the differences in density of the various structures being too small to cause appreciable differences in density on the X-ray film.Only when the skull contains special struetnres with a considerably differing density (nearly always ealeifications) is it possible to visualize these structures. Therefore we are obliged to have recourse to the use of contrast media of differing density to visualize certain structures, which, however, leads to an intervention not always acceptable for the patient.By the use of echo-eneephalography such an intervention can be avoided. One could ask which structures in the skull contents are involved in the reflection of the ultrasound. It appears that such structures must be present at several places, for reflections are obtained at nearly every direction of transmission, so that it is not probable that a specific structure, for instance the pineal body, should be the unique cause of the reflections.

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