engleski

Directivity Pattern of Neurosurgical Endoscopic Ultrasonic Probes

The objective of this paper is to present recent investigations of the characteristics of the sound field generated by neurosurgical endoscopic ultrasonic prbes for minimally invasive surgery. The importance of this information has been investigated and discussed taking into account following facts: 1. According to the international standard IEC 61847:1998 basic acoustical output characteristics of ultrasonic surgical equipment is declared for and measured in the free acoustic field. The Standard treats the ultrasonic probe as an omnidirectional point source or the zero order (monopole source). 2. In real conditions, operations with neurosurgical endoscopic ultrasonic probes are performed within the near sound field. Having in mind that the cavitation and hydrodynamic effcts are dominant, two theoretical boundary conditions can be presented. The first on takes place when operarations are performed near the "soft" acoustic boundary (tissue/bone). Reflections of sound waves from boundaries have influenced on the characteristics of the ultrasonic probe (transducer) and on the sound field. In such cases spherical waves of the first order are generated, so the sound can be described as an acoustic dipole. Directivity of sound sources takes shape in the far field and has to be measured there. On the basis of measured directivity patterns influence of different operational conditions (immersion depth of the probe tip, boundary type,acoustic impedance of the medium etc.)to the radiated sound power and spatial distribution of sound pressure can be estimated.

surgery; directivity pattern; monopole source

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