光学相干层析术（Optical coherence tomography,OCT）是一种非侵入式、高分辨率、高灵敏度的生物组织活体断层成像技术。偏振敏感OCT（Polarization sensitive OCT,PS-OCT）技术是传统OCT的一种发展,利用偏振光成像,通过检测生物组织背向散射光中包含的偏振特性信息,以诊断生物组织内部的早期病变,在临床诊断应用中有巨大的潜力。目前PS-OCT系统存在空间光路体积过大,光纤光路算法计算量大以及无法测量生物组织样品的快轴绝对方向等问题。本文提出采用全光纤PS-OCT来实现对人体牙齿成像和生物组织双折射快轴方位测量等,主要研究内容和创新点如下:为了实现对人体牙齿的在体成像,搭建了一套手持式光纤型谱域OCT系统。其中的手持式探头采用小型扫描振镜进行横向扫描,其结构紧凑,尺寸小且成本低,可以稳定地对活体组织进行检测。对离体牙齿和在体牙齿所获得的图像中,可以清晰地看到活体牙齿的牙釉质、牙本质和釉质本质界面等组织,验证了该系统的成像性能。为了克服单偏振态输入的全光纤PS-OCT系统中单模光纤带来的偏振影响,提出了一种基于Stokes-Mueller的方法。通过偏振控制器调节系统光纤的偏振态,可以准确提取出生物组织样品正常和烧伤时的双折射相位延迟和相对快轴方向。此外,通过两束正交偏振分量的光谱相减,可以一定程度上抑制散射光中的非偏振多次散射对图像质量的影响。为了精确获得生物样品的快轴绝对方向,提出了一种基于全光纤PS-OCT系统的改进算法。首先利用偏振控制器使得系统光纤的相位延迟为π的整数倍,使从样品表面反射回来的光的斯托克斯矢量为[0,1,0]T,建立一个基于穆勒矩阵的光纤系统理论模型,得出了生物组织样品的快轴绝对方位表达式。利用该算法对标准样品快轴绝对方位的测量误差约为3°。为了无损伤评估龋变活性状态,提出了基于PS-OCT、近红外反射成像和热成像方法相结合的检验矿化层厚度减小与龋齿活性状态之间相关性的实验设计。实验结果表明金刚石砂轮抛磨后的龋变区域的反射率强度和温度随脱水时间产生明显变化（P＜0.05）。该研究结果为理解非活性龋齿病变机制提供了有关的证据,并表明亚表面龋变上方的透明矿化层极大地抑制了液体在龋变部位的扩散。

Background and Objectives: Previous studies have shown that large changes in the diffuse reflectivity of caries lesions during drying with air can be used to assess lesion activity. The largest changes occur at short wavelength infrared (SWIR) wavelengths coincident with high water absorption. The strongest water absorption in the SWIR occurs at 1950 nm. In this study changes in the reflectivity of simulated lesions with varying degrees of remineralization was measured at 1500-2340 nm and at 1950 nm as the samples were dried with air. Study Design/Materials and Methods: Twenty bovine enamel surfaces each with five treatment windows were exposed to two demineralization/remineralization regimens to produce simulated lesions of varying depth, severity, and mineral gradients. An extended range tungsten-halogen lamp with a long pass filter (1500-2340 nm) and a broadband amplified spontaneous emission source centered near the peak of the water-absorption band at 1950-nm were used as light sources and an extended range InGaAs camera (1000-2340 nm) was used to acquire reflected light images as the samples were dried with air. Lesions were also assessed using digital microscopy, polarized light microscopy, optical coherence tomography, and transverse microradiography. Results: Both wavelength ranges showed extremely high lesion contrast (>0.9) for all six lesion treatment windows in both models. The change in contrast (Delta I) was significantly higher for the 1950 nm broadband source for all the intact lesion windows compared with the 1500-2340 nm wavelength range. Conclusion: SWIR light at 1950 nm yields extremely high contrast of demineralization and appears to be the optimum wavelength for the assessment of lesion activity on tooth coronal surfaces. (c) 2020 Wiley Periodicals LLC

Improved methods are needed to assess the structure and activity of lesions on root surfaces in order to improve clinical decision making. Conventional visual and tactile methods for assessing lesion activity are not reliable, and the clinician is often unable to evaluate if the lesion is progressing or has remineralized. An important marker of an arrested lesion is a highly mineralized surface zone that forms when mineral is deposited in the outer layer of the lesion. In vitro studies have shown that a mineralized surface zone influences the kinetics of water evaporation and the surface temperature while drying. Temperature changes can be monitored by measuring the thermal emission with thermal imaging. Studies have also shown that the depth and severity of demineralization and the thickness of the highly mineralized transparent surface zone on arrested lesions can be measured nondestructively with optical coherence tomography (OCT). Thermal imaging at 8-mu m to 13-mu m wavelengths was completed on 30 test subjects with a suspected active root caries lesion by monitoring thermal emission from the tooth surfaces during 30 s of air drying. Lesions were also evaluated using cross-polarization OCT (CP-OCT) during lesion dehydration to identify transparent surface zones indicative of arrested lesions and determine if shrinkage occurred during drying. The overall thermal emission recorded during drying was significantly different (P< 0.001) when comparing sound tooth surfaces, lesion areas identified as arrested, and lesion areas identified as active, demonstrating that thermal imaging is a promising approach for the clinical assessment of lesion activity on root surfaces. Ten of the lesions in this study had distinct areas with transparent surface zones that were visible in CP-OCT images. Shrinkage was detected with CP-OCT during drying for 12 lesions. This study confirms that these novel approaches for assessing lesion activity on root surfaces can be implemented in vivo.

New imaging methods are needed to assess the activity of caries lesions on tooth surfaces. Recent studies have shown that thermal imaging of lesions on root surfaces during dehydration with air can be used to determine if the lesions are active or arrested. In this study changes in the thermal emission of root caries lesions on extracted teeth during dehydration with air was monitored using an imaging system with a miniature thermal camera and a 3D printed handpiece with an integrated air nozzle suitable for clinical use. This study evaluated the performance of the thermal camera for imaging root caries on extracted teeth prior to it's use for in vivo studies. There was a significant difference in the thermal response of sound and root lesion areas of human teeth under dehydration at constant airflow. © 2020 SPIE.

New imaging methods are needed to assess the activity of caries lesions on tooth surfaces. Recent studies have shown that changes in the contrast of lesions during dehydration with air at SWIR wavelengths can be used to determine if lesions are active or arrested. In this study changes in the reflectance of caries lesions during dehydration with air was monitored at 1500-1750-nm on extracted teeth using an imaging system with an InGaAs camera, a light source and a 3D printed handpiece with an integrated air nozzle suitable for clinical use. Lesion structure was also assessed with optical coherence tomography and microCT for comparison. This small preclinical study demonstrated that a 3D printed appliance with integrated air for dehydration can be used to acquire SWIR dehydration curves similar to those acquired previously for benchtop imaging systems.

New imaging technologies are needed for the clinical assessment of lesions on root surfaces. It is not sufficient to simply detect caries lesions; methods are needed to assess lesion depth, structural composition and activity to determine if chemical intervention has the potential to be effective and if remineralization has occurred. Lesions were monitored using CP-OCT during lesion dehydration to assess the lesion structure and any shrinkage. Thermal imaging at 6-10 mu m wavelengths and short wavelength-IR imaging at 1450-1750-nm were used to monitor thermal emission during lesion dehydration to assess lesion activity. Imaging probes were custom fabricated for clinical use. We present the first clinical results of a small feasibility study employing CP-OCT, thermal and SWIR imaging to assess lesion activity in vivo on thirty test subjects with suspected root caries lesions.