LASER TOMOGRAPHY OF EXTRACTED HUMAN TEETH USING COHERENT DETECTION IMAGING

近年来，用于生物组织功能监测的光学传感方法受到了广泛关注。光学方法的新兴应用之一是它在成像方面的潜在用途。光具有非电离性质，相对安全，能够对患者的结构和功能状态进行非侵入性和非破坏性的监测。提出的生物组织光谱光学成像技术之一是基于光外差检测的相干检测成像(CDI)方法[1，2]。CDI方法在检测组织中的相干保留和最小散射光子方面具有很高的灵敏度和方向选择性。在本研究中，我们使用该测量系统获得了亚毫米分辨率的人体拔除牙齿的光学层析图像。采用连续波单频半导体激光器(532 Nm)作为…更多的光源。激光器的输出分为信号光束和参考光束。它们被一对声光调制器分别频移到80 MHz和100 MHz。入射光束直径为200μm，将牙齿对侧的透射光叠加到参照光上，入射到光电二极管上，产生20 MHz的中频。该测量系统的动态范围为~90分贝。牙齿安装在平移-旋转(T-R)步进器上，扫描方式类似于传统的计算机断层扫描。每次图像采集大约需要20分钟。图像重建采用滤波反投影(FBP)。光学测量后，薄片(厚度约500μm)在测量平面上对根部进行了测量。将牙齿的激光CT图像与显微镜下的横断面进行比较和评价。在水平图像上可以反映牙齿、牙髓腔和牙髓管的内部结构，还可以定位透明牙本质的位置。牙本质是一种高度散射的组织，入射光具有严重的散射和衰减特性。这似乎是很困难的，比如X射线成像。我们早些时候已经证明，CDI具有选择性地检测从牙本质片传输的最小前向散射光的能力(J Dent RES 74：IADR Abstration 423,1995)。在本研究中，这种出射光分量被用来重建断层图像。结果表明，CDI获得的CT图像是检测牙齿内部结构的可靠方法。牙髓腔、根管和透明牙本质的光衰减相对较低。其他波长较短的光源可以提供更多关于监测牙齿功能的信息，如牙髓中的循环。作为一种远程检测方法，CDI方法具有优势。有一种可能是将探测器布置在口腔之外。CDI方法是显示牙齿内部结构的可靠方法。该方法也可应用于纸浆循环的检测。较少

Optical sensing methods for the functional monitoring of biological tissues are recently receiving widespread attention. One of the emerging application of optical methods is its potential use in imaging. Light being non-ionizing nature, is relatively safe has capabilities for the non-invasive and non-destructive monitoring of the structural and functional states of patients. One of the proposed technique for spectroscopic optical imaging of biological tissues is referred to as the coherent detection imaging (CDI) method that is based on optical heterodyne detection [1,2]. The CDI method possesses high sensitivity and directional selectivity in detecting the coherence retaining and the least scattering photons from tissues. In this study, we used this measurement system to obtain optical tomographic images of extracted human teeth with submillimeter resolution.Ten human extracted teeth were used in this study. Continuous wave, single frequency, semiconductor laser (532nm) were used as … More the light sources. The output of the laser was split into signal and reference beams. They were frequency shifted by a pair of acousto-optic modulators to 80 MHz and 100 MHz, respectively. The diameter of the incident beam was 200μm. The transmitted beam from opposite side of the tooth was superposed on the reference beam and impinged on a photodiode generating an intermediate frequency at 20MHz. The measurement system has a dynamic range of 〜90dB. The tooth was mounted on a translational-rotational (T-R) stepper and the scanning was performed in the T-R mode similar to that of the conventional computed tomography. Approximately 20 min was required for each image acquisition. The image reconstruction was done using the filtered back projection (FBP). After the optical measurement, thin sections (500μm thickness, approx.) of the root, at the measurement plane were made. Laser CT images of teeth were compared to the microscopic cross sections and assessed. The internal structure of teeth, pulp cavities and canals were reflected in the horizontal images, and also the site of the transparent dentine could be located.Dentine is a highly scattering tissue, and the incident light is heavily dispersed and attenuated. It seems to be difficult that such as X-ray imaging. We had earlier demonstrated that the CDI has the capability to selectively detect the least forward scattered light transmitted from dentine slabs (J Dent Res 74 : IADR abstract 423, 1995). This component of the emergent light was used to reconstruct the tomographic images in the present study. Our results indicate that the CT images obtained by CDI is reliable to detect the internal structure of the tooth. Relative low light attenuation is observed in the pulp cavity, canals and transparent dentine. The light sources with other shorter wavelengths could provide more information on the monitoring of teeth functions such as the circulation in the pulp. The CDI method has an advantage as a remote detection method. There is a possibility to arrange detectors outside of the oral cavity. The CDI method is reliable to visualize the internal structure of the tooth. This method may also be applicable to the detection of the circulation in the pulp. Less