牙齿组织光热动态特性仿真与试验研究

调制激光作用牙齿组织发生散射形成光子密度波, 而由于光热效应产生热波, 基于一维介质辐射传输漫射近似方程与一维热传导方程建立了调制激光作用牙齿组织半透明混合介质的一维热波数学模型. 利用该模型仿真分析了牙齿龋损特性参数(牙釉质龋损层光吸收系数、散射系数、热扩散系数及龋损深度)对光热辐射动态响应特性的影响与规律. 利用红外探测器(HgCdTe, 2–12 μm)记录808 nm半导体激光激发牙齿组织产生的热波信号, 由锁相放大器计算热波信号的幅值与相位. 通过频率扫描试验获得了牙齿组织的光热动态响应, 利用多参数最佳统计拟合方法得到了牙齿组织特性参数. 结果表明光热辐射测量对牙齿组织不均匀性和龋损特性均具有较高敏感性与特异性.     

无吸收光栅的X射线相位衬度成像实验研究

通过对基于空间相干源和具有分析光栅功能的X射线转换屏的微分干涉X射线相位衬度成像 系统的理论分析, 利用线发射体阵列结构阳极X射线管和光助电化学刻蚀技术 研制的相位光栅和具有分析光栅功能的X射线转换屏, 组建了一种无吸收光栅的X射线微分干涉相衬成像系统. 在此系统上开展了生物样品的实验研究, 获得了较传统吸收成像更为清晰和更多样品结构信息的相位衬度图像. 从而试验验证了该系统方案设计的可行性, 为X射线相衬成像技术从实验室走向临床应用提供了有效途径.     

X射线相位成像的最佳衬度

根据Zernike相衬观察法的基本思想和Fresnel–Kirchhoff衍射理论,采用傅里叶变换和卷积处理,考虑到临床实际,利用振幅近似和相位缓变条件,将X射线经过生物组织产生的相位改变转换成强度分布.在所导出的理论公式的基础上,作出相位衬度和吸收衬度与物平面到像平面距离的关系曲线.分析得到X射线相位衬度成像的最佳物像距离,并通过微聚焦X射线成像装置对蟑螂成像的实验加以验证,其结果表明理论所预言的成像最佳位置符合度较高.     

基于迭代重建算法的X射线光栅相位CT成像

基于光栅干涉仪的X射线成像技术可以同时获得样品内部的吸收信息、相位信息和散射信息,既保持了传统X射线衰减成像的优点,又拥有相衬成像和散射成像的优势.然而基于传统CT重建算法的X射线光栅成像需要采集大量完整的原始投影数据,数据采集时间过长从而使得物体接受很大的辐射剂量,难以在实际中应用.提出基于传统代数迭代重建算法的光栅成像技术.该方法利用现有X射线光栅成像系统采集少量原始投影数据,基于传统代数迭代重建算法,对旋转变化的相位数据进行CT重构,同时基于傅里叶变换的方法对微分相位数据进行相位恢复.模拟和实验结果表明,基于少量或不完备的原始投影数据,该方法能够准确重构成像对象的吸收、柑位和散射三维信息,同时还能对微分相位切片进行高信噪比的相位恢复,得到样品折射率实部衰减率,为X射线光栅成像技术在工业、生物和医学诊断等领域的应用提供理论和技术支撑.     

同步辐射相位衬度成像医学应用初探

近年来,相位衬度成像技术医学领域应用的发展引人瞩目.同步辐射相位衬度成像无须使用对比剂就能显示传统X射线无法显示的肌腱、软骨、韧带、脂肪、血管及神经等软组织.文章作者应用包括类同轴相衬成像和衍射增强成像在内的相位衬度成像技术进行了肝胆、肺脏、肾脏、胃肠道、心脏、血管、骨关节组织与肿瘤成像,证实了同步辐射相位衬度成像较传统X射线成像图像清晰,分辩率明显提高,特别适用于软组织、血管等的成像.     

线缆系统电磁脉冲效应测量系统研制和试验

分析了实验室瞬态X射线产生的系统电磁脉冲(SGEMP)效应测试所面临的技术问题,提出了解决方法、措施以及实验室模拟瞬态X射线的SGEMP模拟试验方法。通过电子屏蔽、电磁屏蔽、光电隔离、信号对称提取等特殊技术处理,解决了SGEMP效应模拟试验方法和测量系统抗X射线、抗电磁辐射等技术问题,并在大型瞬态X射线模拟源上,测出了瞬态X射线辐照时金属腔内线缆的SGEMP效应波形及幅值。     

X射线衍射增强成像中吸收、折射以及散射衬度的计算层析

X射线相位衬度成像是一种新型的X射线成像技术,通过记录射线穿过物体后相位的改变对物体进行成像,可以提供比传统的X射线吸收成像更高的图像衬度以及空间分辨力。衍射增强成像方法(Diffraction enhancedimaging,DEI)是X射线相位衬度成像方法之一,利用一块放置在物体和探测器之间的分析晶体提取物体的吸收、折射以及散射信息并进行成像。将衍射增强成像方法与计算机断层成像技术(Computerized Tomography)进行结合,利用吸收、散射以及折射信息,分别采用滤波反投影以及雷登(Radon)变换,对昆虫样品——蜜蜂进行计算层析重建,获得了好于X射线吸收计算层析的重建结果,验证了衍射增强成像信息分离计算层析的优越性。     

X射线衍射增强成像中的定量测量

提出了一种基于X射线衍射增强成像(DEI)断层计算机X射线层析术(CT)图像的物体尺寸精确测量方法.X射线衍射增强成像是一种基于相位衬度的成像技术.通过建立DEI的简化模型,研究衍射成像过程中品体转角、投影图像谷点位置、成像系统等效模糊等因素之间关系,由此具体探讨了系统模糊效应对圆物体边界成像带来的位置偏移,并以圆形被测样品为例.提出可精确测定直径的简单有效算法.通过理论仿真模型数据和北京同步辐射装置上的实测数据验证了该算法的精度.该方法实现了利用DEI图像对被测物体几何尺寸的精确测量,可用于对牛物组织样品等物体内部微小结构的尺寸的精确测量.     

复合组分材料的X射线定量相衬成像研究

对复合组分材料的应用和需求日益广泛,但如何精确地测量其定量结构信息仍是一个亟待解决的难题.建立了复合组分结构模型,利用X射线同轴相衬成像和相位恢复方法,分别进行了计算机模拟和实验研究,系统地分析了复合组分材料不同的密度差异对X射线相衬成像和相位恢复精度的影响以及噪声对定量相位恢复的影响.实验结果表明,利用X射线定量相衬...     

X射线光栅相位成像的理论和方法

通过对X射线光栅相位衬度成像实验装置的理论分析,提出了光栅位移曲线的表达式,推导出了X射线光栅相位衬度成像方程.根据该成像方程,提出了基于光栅成像相位提取方法.这些理论结果将简化光栅相位衬度成像实验步骤,提高信息获取效率,并为X射线光栅相位衬度成像和计算机断层成像的结合,进一步提出光栅相位衬度CT的简化理论奠定基础. 关键词： X射线 相位衬度成像 光栅衍射 Talbot效应     

Interproximal dental caries detection using Photothermal Radiometry (PTR) and Modulated Luminescence (LUM)

Frequency-domain photothermal radiometry (FD-PTR or PTR) has been used to detect mechanical holes and demineralized enamel in the interproximal contact area of extracted human teeth. Thirty four teeth were used in a series of experiments. Preliminary tests to detect mechanical holes created by dental burs and 37% phosphoric acid etching for 20 s on the interproximal contact points showed distinct differences in the signal. Interproximal contact areas were demineralized by using a partially saturated acidic buffer system. Each sample pair was examined with PTR before and after micro-machining or treating at sequential treatment periods spanning 6 hours to 30 days. Dental bitewing radio graphs showed no sign of demineralized lesion even for samples treated for 30 days. μ-CT, TMR and SEM analyses were performed. Although μ-CT and TMR measured mineral losses and lesion depths, only SEM surface images showed visible signs of treatment because of the minimal extent of the demineralization. However, the PTR amplitude increased by more than 300% after 80 hours of treatment. Therefore, PTR has been shown to have sufficient contrast for the detection of very early interproximal demineralized lesions. The technique further exhibited excellent signal reproducibility and consistent signal changes in the presence of interproximal demineralized lesions, attributes which render PTR a reliable probe to detect early interproximal demineralization lesions. Modulated luminescence was also measured simultaneously, but it showed a lower ability to detect these interproximal demineralized lesions than PTR.     

Dental biothermophotonics: How photothermal methods are winning the race with X-rays for dental caries diagnostic needs of clinical dentistry

Recent trends in biothermophotonics of teeth are presented. The presentation is centered on the development of clinical-level frequency-domain photothermal radiometry and modulated luminescence to address issues associated with the early diagnosis of demineralization caries in human teeth. Biothermophotonic principles and applications to the detection of the carious state in human teeth as embodied by laser photothermal radiometry are presented and further supported by modulated luminescence. The emphasis is on recent developments with regard to abilities of these techniques to diagnose interproximal lesions between teeth, etching with phosphoric acid and with an artificial demineralization gel in order to simulate early demineralization, as well as demineralization and remineralization of dental crown enamel and root dentin. These are lesions which normally go undetected by X-ray radiographs. Comparisons with X rays, Micro-Computed Tomography (μ-CT) and Transverse Micro-Radiography (TMR) are discussed. A theoretical model involving coupled diffuse photon density and thermal-wave fields is developed and applied to frequency scans from demineralized artificial lesions to produce quantitative values for optical and thermophysical parameters of teeth as well as the thickness of the induced lesion.     

牙本质龋的太赫兹成像研究

牙本质龋与牙髓感染状态及活力密切相关,龋损深度则决定临床治疗方案,但目前牙本质龋的检测及诊断方法如：视诊、探诊容易受到主观因素影响;X线辅助检查对龋病灵敏度低等,都有一定缺陷,可靠性及有效性仍有待提高。太赫兹时域光谱可以利用不同的物理参数成像,在牙本质龋在体、无损检测方面有较大应用潜力。为探索牙本质龋损的太赫兹光谱图像开展本研究。实验通过搭建透射、反射式扫描太赫兹平台,对15枚含牙本质龋离体牙磨片扫描,通过数据二维重构,获得了不同参数的太赫兹透射和反射图像,再将太赫兹图像与实验室研究龋病的光镜图像与X线图像对比、拟合并进行光镜下、太赫兹图像下龋损面积评价。结果表明：太赫兹图像与光镜图像相符,较X线图像灵敏度更高。反射模式下由于太赫兹反射信号较弱,使得样品厚度,表面粗糙程度以及系统噪声对实验结果影响较大,图像仅能辨识样本轮廓,不能用于区分牙釉质、牙本质及牙本质龋。透射模式下的频域1.4 THz相位差成像、时域信号最小值对应的时间成像都能区分牙釉质,牙本质和牙本质龋,可以用来鉴别三者,其中最小值对应的时间成像效果最佳。对光镜下测得牙本质龋损面积与太赫兹透射模式下的时域信号最小值对应的时间图...     

牙齿龋齿损伤可见-近红外光谱偏振检测研究

针对不同龋齿损伤程度有效表征问题,探究一种光谱偏振无损低耗的检测方法,作为对常规检测方法如化学分析法、表面轮廓测定法、显微放射照相术的有益补充。牙齿龋齿损伤由脱矿溶解牙釉质与牙本质的钙与磷酸盐造成,牙齿组织表面微观结构发生了不同程度的变化,结构的变化导致其对光波散射特性与相位改变呈现不同程度的差异。基于偏振光谱对观测样本表面微观结构敏感的特征,不同龋齿损伤样本其表面微观结构变化与偏振信息强烈关联,提出一种光谱偏振有效表征牙齿龋齿损伤度的方法。分别选取450,550,670和860 nm四个不同观测光谱研究波段,选择六个不同龋坏程度的实验样本,选取偏振度参量描述不同牙齿样本的光谱偏振特性。实验结果表明,同一观测光谱波段随着牙齿龋坏程度的加深其偏振度表征参量呈现增加趋势,同时,对于同一观测样本450 nm光谱波段的偏振特性强于其他波段,呈现观测光谱波段与其偏振特性负相关关系。为进一步定量刻画偏振光谱与牙齿龋坏损伤等级的表征关系,构建光谱偏振特征参量与不同损伤等级牙齿样本的指数关联数学模型,通过数学模型解译其内在耦合关联。为有效验证构建模型的稳健性,对模型仿真预测结果与实测数据进行定量化验证,选取和方差（SSE）、模型确定系数（R-square）、均方根（RMSE）等评价因子对构建的模型进行定量评判。结果表明,四个不同光谱波段的模型确定系数均接近于1,和方差与均方根数值均较小,且450nm观测光谱波段接近于0,定量评价结果验证了构建模型的稳健性与有效性,构建模型可有效解译不同龋齿样本与光谱偏振特征的耦合关联。该研究内容有效扩展了牙齿龋齿检测方式,揭示了光谱偏振可有效表征龋齿损伤,发展了一种无损低耗的新型偏振光谱检测技术手段。     

Proton µ‐PIXE mapping,AFM imaging and size statistics of mineral granules in a dental composite

We applied proton microbeam particle‐induced X‐ray emission (µ‐PIXE) for mapping Ca, Zr, Ba and Yb, and atomic force microscopy (AFM) for imaging the surface landscape of a dental composite which releases Ca²⁺ and F^? for the protection of hard dental tissues. Three areas ～250 × 250 µm² located ～0.5–2 mm apart on a smooth surface specimen were mapped with 3.1 MeV protons focused to a ～3.0 µm spot and at ～3.9 µm pixel size sampling. The maps evidenced particles with diameters of 3.2–32 µm (Ca), 20–60 µm (Zr), ≤ 4 µm (Ba) and 10–50 µm (Yb). Cross‐section area histograms of Ca‐rich particles fitted with 2–6 Poisson functions revealed a polydisperse size distribution and substantial differences from an area to another, possibly implying large local variations of Ca²⁺ released in the hard tissue near a dental filling of a few millimeters in diameter. Such imbalances may lead to low local Ca²⁺ protection of the dental tissue, favoring the onset of secondary caries. Similarly, AFM images showed high zone‐dependent differences in the distributions of grains with apparent diameters of 1–4 µm, plausibly recognized as Ca‐ and Ba‐containing particles. In a simple model based on demineralization data, lateral diffusion of Ca²⁺ between adjacent domains containing high‐ and low‐area Ca‐rich grains is described by exponential concentration gradients. These gradients may generate appreciable electromotive forces, which may enhance electrochemically the local tissue demineralization. Similar effects are to be expected in the protective action of F^? ions released from microgranules of YbF₃ and of Ba fluoroaluminosilicate glass. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface configuration properties of partially demineralized bio-derived compact bone scaffolds

To further improve surface characteristics of bio-derived compact bone scaffolds (BDCBS), 20% surface demineralization in a controlled manner was applied to the scaffolds. The surface configuration properties and roughness of the partially demineralized BDCBS and non-demineralized BDCBS (n = 12 in each group) were investigated with SEM and atomic force microscopy (AFM) in this study. The result demonstrated that the surface configuration of partially demineralized BDCBS exhibited specific porous micro-structure when compared to the compact structure of non-demineralized BDCBS. Furthermore, the result showed that the surface roughness of the partially demineralized BDCBS was significantly higher than that of BDCBS (P < 0.01). These results revealed that the partial demineralization could improve the surface configuration characteristics of BDCBS.     

Mechanical heterogeneity of dentin at different length scales as determined by AFM phase contrast

In this study we sought to gain insights of the structural and mechanical heterogeneity of dentin at different length scales. We compared four distinct demineralization protocols with respect to their ability to expose the periodic pattern of dentin collagen. Additionally, we analyzed the phase contrast resulting from AFM images obtained in tapping mode to interrogate the viscoelastic behavior and surface adhesion properties of peritubular and intertubular dentin, and partially demineralized dentin collagen fibrils, particularly with respect to their gap and overlap regions. Results demonstrated that all demineralization protocols exposed the gap and overlap zones of dentin collagen fibrils. Phase contrast analyses suggested that the intertubular dentin, where the organic matrix is concentrated, generated a higher phase contrast due a higher contribution of energy dissipation (damping) than the highly mineralized peritubular region. At increasing amplitudes, viscoelasticity appeared to play a more significant contribution to the phase contrast of the images of collagen fibrils. The overlap region yielded a greater phase contrast than the more elastic gap zones. In summary, our results contribute to the perspective that, at different length scales, dentin is constituted of structural features that retain heterogeneous mechanical properties contributing to overall mechanical performance of the tissue. Furthermore, the interpretation of phase contrast from images generated with AFM tapping mode appears to be an effective tool to gain an improved understanding of the structure and property relationship of biological tissues and biomaterials at the micro- and nano-scale.     

Characterization of enamel caries lesions in rat molars using synchrotron X‐ray microtomography

Dental caries is a ubiquitous infectious disease with a nearly 100% lifetime prevalence. Rodent caries models are widely used to investigate the etiology, progression and potential prevention or treatment of the disease. To explore the suitability of these models for deeper investigations of intact surface zones during enamel caries, the structures of early‐stage carious lesions in rats were characterized and compared with previous reports on white spot enamel lesions in humans. Synchrotron X‐ray microcomputed tomography non‐destructively mapped demineralization in carious rat molar specimens across a range of caries severity, identifying 52 lesions across the 30 teeth imaged. Of these lesions, 13 were shown to have intact surface zones. Depth profiles of fractional mineral density were qualitatively similar to lesions in human teeth. However, the thickness of the surface zone in the rat model ranges from 10 to 58 µm, and is therefore significantly thinner than in human enamel. These results indicate that a fraction of lesions in rat caries possess an intact surface zone and are qualitatively similar to human lesions at the micrometer scale. This suggests that rat caries models may be a suitable analog through which to investigate the structure of surface zone enamel and its role during dental caries.     

Alterations in enamel remineralization in vitro induced by blue light

Blue light, especially from LED devices, is a very frequently used tool in dental procedures. However, the investigations of its effects on dental enamel are focused primarily on enamel demineralization and fluoride retention. Despite the fact that this spectral region can inhibit enamel demineralization, the effects of the irradiation on demineralized enamel are not known. For this reason, we evaluated the effects of blue LED on remineralization of dental enamel. Artificial lesions were formed in bovine dental enamel blocks by immersing the samples in undersaturated acetate buffer. The lesions were irradiated with blue LED (455 nm, 1.38 W/cm², 13.75 J/cm², and 10 s) and remineralization was induced by pH-cycling process. Cross-sectional hardness was used to asses mineral changes after remineralization. Non-irradiated enamel lesions presented higher mineral content than irradiated ones. Furthermore, the mineral content of irradiated group was not significantly different from the lesion samples that were not submitted to the remineralization process. Results obtained in the present study show that the blue light is not innocuous for the dental enamel and inhibition of its remineralization can occur.