Beamforming for Laser Generated Leaky Acoustic Waves for Image Guidance

• Main Authors: Yi-An Wang, 王以安
• Other Authors: Pai-Chi Li
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/j5gt8w

碩士 === 國立臺灣大學 === 生醫電子與資訊學研究所 === 107 === Ultrasound-guided needle operation is widely used for real-time visualization of the needle position during tissue biopsy and localized drug delivery. Conventionally B-mode imaging is used for needle visualization. However, its practical use has been limited due to acoustic reflection at the needle surface. To overcome this problem, we previously proposed a method to exploit the laser generated guided wave and the leaky acoustic waves. Although successful, the method is only applicable to linear objects and cannot be used for nonlinear objects, thus limiting its applications in areas such as guidewire visualization. The purpose of the current research is to improve the original approach by using ultrasound array beam formation. In this case, irradiated laser pulse generates acoustic waves on the top of a needle or a guidewire. These acoustic waves propagate along the metal surface. Then, the waves leak into the surrounding medium that can be detected by an ultrasound array transducer. The main challenge of the proposed method is to account for the propagation time of the guided waves for accurate beamforming. In other words, the echo arrival time between laser irradiation and array detection consists of two parts. One is the propagation time of the guided waves. The second component is the ultrasound propagation time of the leaky waves in the tissue. In principle, an image of the needle or the guidewire can be formed based on array beam formation after the propagation times on the metal are taken into consideration. Using the proposed beamforming method, results showed that the detection depth was up to 51 mm and the insertion angle was up to 47.3 degrees with needles of different diameters. On the other hand, results of the guidewires showed that the detection depth was up to 63 mm, the insertion angle was up to 56.31 degrees and the propagation distance of the guide waves was up to 1268 mm.