Optical imaging of biological tissue using speckle patterns of ultrasound-modulated light

为了提高生物组织光学成像的空间分辨率，提出了一种利用超声调制光的散斑模式成像的新方法。本文对该方法的实验评价结果进行了总结。提出了一种方法和实验系统：为了检测超声频率下光学散斑图案的时间变化，我们使用了传统的CCD静态相机，并介绍了频闪示波器的原理，即CCD静态相机的快门打开，被观察物体受到与曝光超声同步的脉冲光照射。实验系统采用16位对比度分辨率的冷却CCD摄像机。采用功率为600 mW、脉宽为0.1 ns的脉冲激光二极管作为照明光源，中心频率为1 MHz的聚焦超声换能器作为超声光源。透射成像：对乳腺肿瘤幻影进行一维透射成像。将光源、光体和CCD摄像机排成一条直线，利用透射光产生的散斑图进行成像。采用琼脂模体（厚度为35 mm， μs'=0.5 mm^<-1>）作为模体，在模体中心埋置模仿乳腺肿瘤（μa= 0.048 mm^<-1>, μs'=0.5 mm^<-1>）的吸收物（10x10x10 mm^3）。利用该方法成像的吸收目标轮廓比常规成像结果更陡峭，表明通过检测超声调制光提高了光学成像的空间分辨率。反射成像：一维成像也尝试使用由反射光产生的斑点图案。在本实验中，光源和CCD相机被放置在幻影的同一侧。照明光束以大约65度的角度进入幻影，并使用放置在幻影前面的CCD相机拍摄在幻影同一表面上产生的散斑图案的图像。在此情况下，采用该方法提高了空间分辨率，表明该方法具有广泛的适用性。系统的改进：在上述实验中，由于光的脉冲宽度太小，测量一维轮廓需要大约10个小时。采用大功率光源（功率为20 W，脉宽为50 ns），大大缩短了测量时间，且信噪比无下降。少

To improve spatial resolution of optical imaging of biological tissue, a new method using speckle patterns of ultrasound-modulated light was proposed. Results of experimental evaluations of the proposed method are summarized as follows.1. A proposed method and an experimental system : To detect temporal variations of optical speckle patterns in ultrasound frequency, we used a conventional CCD still camera and introduced a principle of a strobe scope, that is, the shutter of the CCD still camera is open and the object observed is illuminated by pulsed light synchronized with exposed ultrasound. The experimental system used the cooled CCD camera of 16-bits contrast resolution. A pulsed laser diode (power =600 mW, pulse width = 0.1 ns) was used as the illumination light source, and a focused ultrasound transducer of 1 MHz in center frequency was used as the ultrasound source.2. Transmission Imaging : One-dimensional transmission imaging of a breast tumor phantom was carried out. The light … More source, the phantom, and the CCD camera were placed in line and speckle patterns generated by transmitted light was used for imaging. An agar phantom (Thickness = 35 mm, μs'=0.5 mm^<-1>) was used as the phantom, and an absorbing object (10x10x10 mm^3) mimicking a breast tumor (μa= 0.048 mm^<-1>, μs'= 0.5 mm^<-1>) was buried at the center of the phantom. A profile of the absorbing object imaged by the proposed method is steeper than that of a conventional imaging result, indicating that the spatial resolution of optical imaging was improved by detecting the ultrasound modulated light.3. Reflection Imaging : One-dimensional imaging was also tried using speckle patterns generated by reflected light. In this experiment, the light source and the CCD camera were placed at the same side of the phantom. The illumination beam entered the phantom at an angle of approximately 65 degrees, and an image of the speckle pattern generated on the same surface of the phantom was taken using a CCD camera placed in front of the phantom. Also in this case, spatial resolution was improved using the proposed method, and it was shown that this method has wide applicability.4. Improvement of the system : In the above experiments, it took about 10 hours to measure a one dimensional profile because the pulse width of the light was needlessly small. A high-power light source (power =20 W, pulse width = 50 ns) was used, and measurement time was greatly reduced without S/N drop. Less