Obstacle Detection by Three Dimensional Frontal Imaging with Laser-Induced Breakdown

Abstract

Our group has been studying 3 dimensional (3D) frontal imaging with ring-arrayed sparse acoustic sensors1. Considering the requirement for suitable small-sized probes for intravascular ultrasonic (IVUS) imaging, a limited number of sensors have been used. Based on the fundamental delay-and-sum method for implementing a synthetic aperture, a simple constitution in which one transducer emits a single pulse and the rest receive echoes allows the instantaneous acquisition of frontal 3D information2. In order to obtain a higher signal-to-noise (S/N) ratio and wider angle transmission of US, some attempts to improve the constitution of the ring array probe have been made3. The smaller transmitter device allows a wider angle for ultrasound emittance, but the power of the acoustic field is limited in such a device. A miniaturized transmitter still severely limits the spatial measurement range for frontal viewing, resulting from a trade-off between the high directivity and the lower power of the US acoustic field. In order to obtain an acoustic field with less directivity, laser-induced breakdown (LIB) is introduced as an acoustic source4 that can provide an almost completely spherical US pulsed wave5,6. In this paper, we propose that LIB can be used as an acoustic source that generates a suitable acoustic field in terms of its power and low directivity for instantaneous 3D imaging with a wide angle, so as to provide information on the interior conditions of pipe-shaped objects and thus enable their navigation.