Development of Sound Speed Microscope for Nano-scale Imaging of Biological Tissue Using Pico-second Ultrasonic Pulse

利用超声显微成像技术对生物组织进行观察具有非破坏性、非接触性等优点，可以定量获得声速、衰减等物理参数。我们一直在开发一种用于生物组织的超声声速显微镜。将薄切片试样放置在玻璃基板上，并将具有宽带频率的聚焦超声脉冲的反射解释为声速和其他参数。当聚焦光束点被机械扫描时，可以观察到2D图像。它的临床应用，在手术中的组织病理学检查正在考虑中。这些数据对于评估临床回声成像的起源也很重要。然而，传统的横向分辨率曾经是15微米，虽然一个具有更高的分辨率，预计将带来重要的信息，在生物和医学的观点差。在本研究计划中，我们的目标是发展一个超音波显微镜的分辨率为亚微米级。组装了使用100-500 MHz宽带脉冲扩展的超声显微镜。为了获得亚微米级的分辨率，采用了压电工作台。从强度图像和声速图像两个方面清楚地观察了从大鼠海马中取出的培养的神经细胞，并且明确了当声波从基板的后侧透射时，可以测量基板与组织之间的界面处的反射波。因此，将反射可视化为声阻抗的二维轮廓，以便在不制备薄切片标本的情况下观察组织。大鼠小脑组织的结构被清楚地观察为声阻抗图像。

Observation of biological tissue by ultrasonic micro-imaging has advantages of being non-destructive and non-contacting, making it possible to quantitatively obtain physical parameters like sound speed and attenuation. We have been developing an ultrasonic sound speed microscope for biological tissues. A thin sliced specimen is placed on a glass substrate, and the reflection of a focused ultrasound pulse with a wide band frequency is interpreted into sound speed and other parameters. A 2D image can be observed when the focal beam spot is mechanically scanned. Its clinical application to histopathological examination during surgery is being considered. The data are also important to assess the origin of clinical echographic imaging. However, the lateral resolution of conventional one used to be as poor as 15 micrometers, although one with a higher resolution was expected to bring important information in biological and medical point of view. In this research project, we aimed to develop an ultrasonic microscope with a resolution of sub-micron level. An ultrasonic microscope using a wide-band pulse spreading from 100-500 MHz was assembled. A piezo-electric stage was employed in order to obtain a resolution of sub-micron level. Cultured nerve cells taken from the hippocampus of a rat was clearly observed as both intensity and sound speed images.In addition, it was clarified that the reflected wave at the interface between the substrate and tissue can be measured when the acoustic wave was transmitted from the rear side of the substrate. Therefore the reflection was visualized as two-dimensional profile of acoustic impedance, in order to observe the tissue without preparing a thin sliced specimen. The structure of the cerebella tissue of a rat was clearly observed as an acoustic impedance image.