engleski

Directivity pattern of neurosurgical endoscopic ultrasonic probes

The objective of this paper is to present recent investigations in characteristics of the sound fi eld generated by neurosurgical endoscopic ultrasonic probes (NEUPs) 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 an acoustical free fi eld. The standard generally treats the ultrasonic probe as an omnidirectional point source of the zero order (monopole source). 2. In real conditions, operations with NEUPs are performed within the acoustical near fi eld. Having in mind that the cavitational and hydrodynamic eff ects are dominant, two theoretical boundary conditions can be present. The fi rst one takes place when operations are performed near the ‘ ‘ soft’ ’ acoustical boundary (tissue/air), and the second one is near the ‘ ‘ rigid’ ’ acoustical boundary (tissue/bone). Refl ections of sound waves from boundaries have infl uence on the characteristics of the ultrasonic probe (transducer) and on the sound fi eld. In such cases spherical waves of the fi rst and second order are generated. Directivity of sound sources takes shape in the far fi eld and is easier to measure there. On the basis of measured directivity patterns, the infl uence of diff erent operational conditions (immersion depth of the probe tip, boundary type, acoustical impedance of the medium etc.) on the radiated sound power and spatial distribution of the sound pressure can be estimated.
2002 Elsevier Science B.V. All rights reserved.

Directivity pattern; Monopole; Dipole source; Surgical probe

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