Ultrasonic B-Scanning of the Brain

Abstract

U LTRASOUND restricted to one-dimensional echo-ranging can provide little information other than the location of a plane reflecting surface. I ts value in neurological diagnosis, therefore, is limited virtually to detect ion of a shift of midline structures of the brain. ',6,s,15 The purpose of the present paper is to report early experiences with a two-dimensional ultrasonic visualization system, and to discuss the possible uses of this method for more precise demonst ra t ion of various norreal and abnormal intracranial structures. The physical principles underlying the use of ultrasound as a diagnostic technique have been presented in numerous reports} ,~,7,u,n Likewise, descriptions of the instrumentation of ultrasonic methods, including those used in this study, are readily available. Therefore, only certain fundamenta l details essential to unders tanding the clinical applications of this me thod will be repeated here. Sound consists of mechanical vibrations propagated in a medium. Sinee sound travels in a wave form, it is subject to many phenomena well known in optics, including reflection, refraction, absorpt ion and diffraction. When used for the purpose of delineating an object, the resolving power of sound, as in the ease of light, is limited to about 1 wave length. Because the velocity of sound in most soft tissues, including brain, is approximately 1500 m./sec. , frequencies well above audibility, i.e., ul t rasound, must be used to achieve useful resolution in these media. For example, wi th a f requency of 1.5 !VIc./sec., the wave length in soft tissue is about 1 ram. and under opt imal conditions the depth resolution,' i.e., the resolution in