Ultrasound Imaging using Laser Induced Breakdown
Ultrasound Imaging using Laser Induced Breakdown
复制标题
使用激光诱导击穿的超声成像
DOI：
10.1541/ieejsmas.121.479
复制
发表时间：
2001
影响因子：
--
通讯作者：
S. Kawata
中科院分区：
文献类型：
--
作者：
O. Oshiro;Atsunori Machida;M. Doi;K. Chihara;D. Ueda;T. Sugiura;S. Kawata
超声成像技术被广泛应用，因为它可以可视化测量对象的外部结构和光学测量方法无法可视化的内部结构。因此，它在工业领域是钢管、铁路等无损检测的必备工具，在医学领域是心脏、肝脏等人体器官诊断的必备工具。此外，美国成像也用于渔业或军事领域。在传统的美国成像方法中，美国光束通过电扫描物体来重建二维（2D）图像。图像的帧率约为10-100 fps（帧每秒），但由于超声波在介质中的速度有限，例如水中的速度为1,500 m/秒，因此很难提高图像的帧率。近十年来，三维超声成像的研究一直是人们关注的热点。然而，由于超声波的速度有限，并且帧率低于10fps，因此重建三维图像需要较长的时间。我们一直在研究瞬时美国成像系统，该系统通过一次发射具有小指向性的脉冲美国，在多个点接收来自测量物体的反射波，并用合成孔径法重建测量物体的三维图像。由于只需要一次超声波传输就可以重建3D图像，因此这种成像方法有可能获得正面宽视图的3D图像，并且帧率非常高，超过1,000 fps。但是，遇到了以下问题：(1)由于换能器在传输超声时振铃（振铃现象），使得传输波形不是单峰而是多峰，导致重构图像模糊。(2)低指向性的超声波不能从例如陶瓷制成的压电装置的换能器中传输。超声波只能看到非常狭窄的区域。从上述情况来看，瞬时US成像正在等待低指向性的脉冲超声。当脉冲激光束照射到很小区域内的原子或分子时，一些原子或分子吸收光，从而引起能级升高，使原子或分子电离。这种电离引起其他原子或分子的级联电离。然后，电离的原子或分子与电子重新结合。紧接着是光发射、冲击波和空化。因此，光、热和声音从激光焦点产生。这种现象被称为“激光诱导击穿”。由于声音是从一个非常小的源产生的，它被认为具有低指向性。因此，我们首先对LIB进行了超声生成，并对超声特性进行了检测。接下来，我们利用超声和合成孔径法进行瞬时成像。本文描述了利用LIB生成超声的实验，研究了超声的波形和指向性，并利用该方法重建了三维图像。
Ultrasound (US) imaging is widely used because it visualizes the exterior structure of a measurement object and the interior structure that cannot be visualized with an optical measurement method. Therefore, it is an essential tool as non-destruction test of a steel pipe and a railway and so on in the industrial field and as diagnosis of a human organ like a heart, a liver and so on in the medical field. Furthermore, US imaging is also used in the fishery or military field. In the conventional US imaging method, a US beam scans the object electrically to reconstruct a twodimensional (2D) image . The image has about the frame rate of 10-100 fps (frame per second) but it is difficult to increase the frame rate of the image because ultrasound has the finite velocity in a media, for example, 1,500 m/sec in water. In the last decade, the research on three-dimensional (3D) ultrasound imaging is often discussed . However, it takes a longer time to reconstruct a 3D image because of the finite velocity of ultrasound and the frame rate is below 10 fps. We have been studying the instantaneous US imaging system , where pulsed US with little directivity was transmitted once, the wave reflected from a measurement object was received at several points and the 3D image of a measurement object was reconstructed with the synthetic aperture method . As only one transmission of ultrasound enables to reconstruct a 3D image this imaging method has the potential to obtain a 3D image with frontally wide view and very high frame rate above 1,000 fps. However, the following problems are encountered; ( 1 ) The transmitted waveform has not single peak but many peaks owing to the transducer ringing on transmitting ultrasound (ringing phenomenon), which results in blurring the reconstructed image. ( 2 ) Ultrasound with low directivity cannot be transmitted from a transducer of a piezoelectric device, for example, made of ceramics. The ultrasound enables to visualize only the very narrow region. Judging from the the matters mentioned above, the instantaneous US imaging is waiting for the pulsed ultrasound with low directivity. When pulsed laser beam was radiated to atoms or molecules in the very small region, some atoms or molecules absorb light, which induces to raise the energy level and to ionize the atoms or molecules. This ionization causes a cascade ionization of other atoms or molecules. Then, ionized atoms or molecules are recombined with an electron. Immediately, light emission, shock wave and cavitation follows. Consequently, light, heat and sound are generated from the laser focal point. This phenomenon is called ’laser induced breakdown (LIB)’ . As the sound is generated from a very small source, it is thought to have the low directivity. Therefore, at first, we performed the generation of ultrasound from LIB and examined the characteristics of the ultrasound. Next, we carried out the instantaneous imaging using the ultrasound and the synthetic aperture method. This paper describes the experiment to generate ultrasound from LIB, the investigation of the waveform and directivity of the ultrasound and the reconstructed 3D image using this method.