CBCT在口腔正畸学的应用

锥形束CT(CBCT)作为一种新型的影像学技术,近年来被广泛应用于口腔正畸学领域。它与传统影像学技术相比,具有扫描层薄、成像精确、辐射剂量低、操作简单等独特的优势。本文就CBCT在口腔正畸学领域的应用作一综述,主要应用领域包括三维头影测量、牙根吸收诊断、微种植体支抗研究、正畸牙齿阻生诊治、颞下颌关节病诊断、软组织分析、气道分析、牙槽骨研究和隐形矫治的应用等。     

52例青少年骨性安氏Ⅱ类高角病例切牙区牙槽骨开窗和骨开裂的锥形束CT特点

目的 应用锥形束CT(CBCT）探讨52例青少年骨性安氏Ⅱ类高角错畸形切牙区骨开窗和骨开裂的发生率及分布情况，为临床正畸治疗提供一定的依据。 方法 自2013年7月至2018年1月于承德市口腔医院进行CBCT检查的患者中，随机选取临床诊断为骨性Ⅱ类高角错畸形青少年病例52例，将其扫描数据导入SIDEXIS XG 2.56软件，在测量平面上根据定义诊断上下切牙区牙槽骨骨开窗和骨开裂，并采用χ²检验的方法对其分布在性别、上下颌骨、牙位间的差异进行数据分析。 结果 在样本人群中牙槽骨缺损的发生率高达86.53%。其中骨开窗和骨开裂的发生率分别为65.38%和67.30%。416颗纳入牙中82颗牙齿出现骨开窗,107颗牙齿出现骨开裂。骨开裂发生率在牙位间差异显著（P<0.05)。骨开窗发生率上下颌骨差异无统计学意义（P>0.05）,骨开裂则主要发生于下颌骨（P<0.05)。男性与女性切牙区牙槽骨骨开窗与骨开裂的发生率差异无显著性。 结论 青少年骨性安氏Ⅱ类高角错畸形患者在正畸治疗前切牙区即存在广泛的牙槽骨缺损，正畸治疗开始前及过程中医师应密切关注患者牙槽骨解剖形态。     

固定正畸技术与坚强内固定治疗颌骨骨折的对比研究

目的：探讨固定正畸技术与坚强内固定治疗颌骨骨折的临床效果。方法收集2004年1月~2013年10月我院收治的颌骨骨折患者,分别给予固定正畸治疗、坚强内固定和坚强内固定联合颌间牵引,比较治疗效果、咬合关系、治疗时间、感染以及骨折错位发生率,为颌骨骨折临床治疗提供可参考依据。结果固定正畸治疗组患者具有较好的临床治疗效果、吻合的咬合关系,未出现感染和骨折错位病例。各组患者在治疗时间上无显著性差异。本研究中儿童患者多采用固定正畸技术治疗,治疗效果显著由于成人患者。结论固定正畸治疗可有效提高临床治疗效果,特别对于儿童患者具有较好的效果。采用固定正畸治疗可大幅减轻患者痛苦和经济负担,具有广阔的临床推广应用前景。     

牙周炎患者正畸治疗前后血清TNF-α、CRP、sICAM-1及多项白介素水平变化研究

目的:探讨牙周炎患者正畸治疗前后血清TNF-α、CRP、sICAM-1及多白介素水平变化规律。方法:选取进行正畸治疗的40例牙周炎患者为观察组,并选取同期进行治疗的40例不伴牙周炎患者为对照组,将两组患者的治疗前及治疗后1 d及7 d的血清TNF-α、CRP、sICAM-1及IL-1β、IL-6、IL-8水平进行研究比较。结果:经研究发现,治疗前观察组的血清TNF-α、CRP、sICAM-1及IL-1β、IL-6、IL-8水平高于对照组,治疗后1 d有所升高,仍高于对照组(P<0.05或P<0.01),有显著性差异或有非常显著性差异,但治疗后7 d两组患者血清TNF-α、CRP、sICAM-1及IL-1β、IL-6、IL-8水平无统计学差异(P>0.05)。结论:牙周炎患者正畸治疗患者的血清TNF-α、CRP、sICAM-1及IL-1β、IL-6、IL-8水平变化呈现一定的规律性,但是正畸联合牙周炎治疗可大大改善其水平。     

基于深度学习方法的放疗患者摆位误差预测

目的为了实现对放疗患者日常摆位误差的准确预测,优化锥形束计算机断层扫描(conebeam computed tomography,CBCT)使用频率,确保患者摆位误差处在允许范围内的同时尽可能减少其承受的额外辐射剂量,本研究基于深度学习方法能够对复杂体系进行预测的能力,构建了一种深度全连接神经网络。方法选取20名头颈部肿瘤患者累积共76次CBCT扫描结果作为研究对象。首先,根据文献调研及临床实践经验,确定患者日常治疗时的摆位误差受到不同技术人员的工作经验、患者体型、固定膜的松紧程度、靶区位置、靶区大小及形状等因素的影响,且与患者前三次治疗时的摆位误差相关性较强,因此针对患者每次CBCT扫描得到的摆位误差,从患者的治疗记录及患者CT图像中获得相关信息,得到467个特征值作为深度学习的输入值,以三个方向上最大摆位误差的分类作为深度学习的输出值,将每次摆位误差的最大值以3 mm为标准分为两类,作为深度学习的目标值。然后,将研究数据按7∶3的比例随机划分为训练集和验证集,通过训练集训练深度神经网络,再使用验证集对神经网络进行初步评估。在完成深度神经网络的训练后,将正在治疗中的新患者的数据作为测试集,使用训练好的神经网络预测新患者的摆位误差大小,并与实际结果对比,评估其准确率。最后,进行重复实验,判断神经网络的预测结果是否具有可重复性。结果本研究构建的深度神经网络对患者摆位误差的预测准确率可以达到86%,能准确预测患者摆位误差大于3 mm的情况,且预测结果的可重复性好。结论基于深度学习方法可以较准确地预测放疗患者日常摆位误差的最大绝对值是否大于3 mm,为优化CBCT扫描频率提供了可靠依据,有助于提高放疗疗效,减轻放疗副反应,具有良好的临床应用价值。     

正畸牙移动对牙槽骨形态及骨密度的影响

背景:在正畸治疗过程中部分患者出现了牙齿松动、牙槽骨形态异常情况,甚至在一定程度上牙周疾病的概率有所增加。目的:分析正畸牙移动对牙槽骨形态及骨密度的影响。方法:纳入62例正畸治疗患者,其中男34例,女28例,年龄18-30岁,正畸治疗6个月后,利用三维锥形束CT机扫描患者上、下颌骨前牙区、后牙区、中切牙牙槽区,以及两侧中切牙与侧切牙牙槽间隔的骨密度。结果与结论:正畸治疗6个月后,所有患者牙齿坚固,未见异常动度,牙龈颜色呈现健康的粉红色,质地坚韧而不活动,探诊时无出血情况。正畸治疗前,上颌不同牙槽间隔牙槽骨密度比较差异无显著性意义(P0.05),治疗6个月后比较差异也无显著性意义(P0.05),但同一牙槽间隔正畸治疗6个月后的骨密度低于治疗前(P0.05);下颌牙槽骨密度变化与上颌一致;上颌牙槽骨正畸治疗前后的骨密度均高于下颌牙槽骨(P0.05)。表明正畸治疗修复后可能出现下颌牙槽骨密度降低高于上颌牙槽骨的情况,但对整体正畸效果无明显影响,不影响牙槽骨形态和健康状况。     

正畸牙釉质脱矿与应用3种不同牙刷的比较

背景:近年来,有大量关于防正畸牙釉质脱矿方面的研究,但目前还未有学者对普通牙刷、正畸专用牙刷及牙间刷3者做过这方面的比较研究。目的:比较分别使用普通牙刷、正畸牙刷及牙间刷对正畸牙釉质脱矿的影响。方法:将12-17岁的青少年正畸患者按使用牙刷的种类不同,随机分成普通牙刷组、正畸专用牙刷组和牙间刷组。由同一正畸专科医生检查并计算矫治前和矫治1年后釉质脱矿指数和釉质脱矿增加指数。结果与结论:正畸治疗前,3组患者的釉质脱矿指数差异无显著性意义(P0.05)。治疗1年后,各组患者的釉质脱矿指数均大于其矫治前(P0.05)。矫治1年后,3组间脱矿指数及脱矿增加指数的两两比较:正畸专用牙刷组普通牙刷组牙间刷组(P0.05)。结果证实,使用正畸专用牙刷对防治正畸治疗中的釉质脱矿效果更好,更适用于正畸人群;而单独使用牙间刷并不能起到很好的防止釉质脱矿的作用。     

正畸牵引联合冠延长术后桩冠修复外伤前牙

目的分析正畸牵引联合冠延长术后桩冠修复外伤前牙的临床疗效。方法收集我院2011年11月~2012年11月诊治的需要对桩冠进行修复的患者90例作为研究对象，对所有患者实施正畸牵引联合冠延长术治疗，回顾性分析患者的临床资料，观察治疗效果。结果研究结果显示，患者经治疗牙齿松动度、龈沟出血病情得到了明显的改善，治疗后不同时间比较差异具有统计学意义(<0.05)。结论正畸牵引联合冠延长术后桩冠修复外伤前牙具有良好的临床疗效，值得在临床应用上推广。     

基于牙颌模型的正畸弓丝初始回复力口外测量技术

目的利用模拟牙颌模型实现正畸弓丝初始回复力的口外测量。方法以1例临床病例作为研究对象,通过3D打印制作与患者真实牙列分布相一致的上颌牙颌模型,并以此为基础利用Nano17 F/T力学传感器搭建矫治力测量系统,测量直径为355. 6μm标准圆镍钛弓丝佩戴在牙颌模型上后施加在患者2颗上颌中切牙上的初始回复力。结果患者上颌中切牙21受到的初始矫治力较中切牙11更大,且2颗中切牙所受到的矫治力系均不利于牙齿的理想移动,需要添加辅助装置改善牙齿受力状况。在优化正畸治疗方案后,患者在治疗18个月后获得满意的矫治效果。结论利用患者的模拟牙颌模型可以准确测量正畸弓丝作用在目标牙齿上的矫治力系,预估牙齿的移动形式,并以此为基础改进牙齿矫治方案。矫治力的口外测量技术为临床正畸治疗提供重要参考,为矫治方案的优化设计开创新思路。     

双链法对正畸牙牙间隙关闭的影响

目的 探讨双链法关闭正畸牙牙间隙的安全性及有效性。方法 选取72例不同上下颌牙列间隙的正畸患者,测量正畸治疗前后上下颌第一磨牙之间的所有牙齿的牙髓活力值,并进行统计学分析评估牙髓活力的安全性;使用双链法关闭正畸牙牙列间隙,分为拔牙组和不拔牙组各36例,观察周期为4周,测量成年组和未成年组的上下颌牙齿槽间距的治疗前后变化,计算正畸治疗前后总齿槽间距的差异,并进行统计学分析评估间隙关闭的有效性。结果 所有72例患者,治疗后未发现牙髓坏死及牙髓变性,治疗前后牙髓活力无改变,差异无统计学意义（P>0.05）;与矫治前相比,双链法矫治后4周,拔牙组和不拔牙组中的成年和未成年的病例上下颌槽间距值之和均明显减小,差异有统计学意义（P<0.05）。结论 双链法关闭正畸牙牙列间隙不会引起牙髓变性与坏死,具有临床使用的安全性;双链法关闭正畸牙牙间隙具有有效性,同时可简化临床操作,值得临床推广。     

Evaluation of sparse-view reconstruction from flat-panel-detector cone-beam CT

Flat-panel-detector x-ray cone-beam computed tomography (CBCT) is used in a rapidly increasing host of imaging applications, including image-guided surgery and radiotherapy. The purpose of the work is to investigate and evaluate image reconstruction from data collected at projection views significantly fewer than what is used in current CBCT imaging. Specifically, we carried out imaging experiments using a bench-top CBCT system that was designed to mimic imaging conditions in image-guided surgery and radiotherapy; we applied an image reconstruction algorithm based on constrained total-variation (TV)-minimization to data acquired with sparsely sampled view-angles and conducted extensive evaluation of algorithm performance. Results of the evaluation studies demonstrate that, depending upon scanning conditions and imaging tasks, algorithms based on constrained TV-minimization can reconstruct images of potential utility from a small fraction of the data used in typical, current CBCT applications. A practical implication of the study is that the optimization of algorithm design and implementation can be exploited for considerably reducing imaging effort and radiation dose in CBCT.     

基于加速器的锥形束CT系统机械精度的精确测量方法及其实现

目的:设计并实现一种锥形束CT（CBCT）机械精度的检测方法,可对CBCT的机械性能参数进行精确测量和分析（重复性在0.5 mm以内,测量误差在0.5 mm内,耗时数分钟）。方法:系统硬件包括双目红外相机、定位小球、注册笔和水平注册仪。双目红外相机可输出定位小球中心的空间坐标,利用定位小球中心位置坐标可计算出加速器机械等中心坐标,利用CBCT拍出的定位小球图像可计算出CBCT影像中心与加速器机械等中心的偏差,利用注册笔可计算出CBCT平板角度偏差。结果:在某医院加速器配备的CBCT上运用本方法进行3次测试和分析,得到加速器机械等中心坐标、CBCT影像等中心坐标、两等中心距离误差和CBCT平板打开垂直度等数据。结论:本研究提出的检测CBCT机械精度的方法操作过程较简单,结果精准,可重复性高,将复杂的质控过程数字化、自动化和简单化,给CBCT的日常质量检测带来非常大的便利,也为相关技术人员以及医护人员在临床上安全应用CBCT提供指导。 【关键词】锥形束CT;红外双目相机;定位小球;机械等中心;影像等中心     

瓦里安加速器IGRT过程中患者吸收剂量的研究

目的：测量不同图像引导方式下患者的吸收剂量。方法：采用0°和270°两个正交野,分别使用MV和kV级X线获取二维图像,测量模体中不同点的吸收剂量;采用CBCT获取三维图像,测量模体中不同点的吸收剂量。结果：MV/MV成像,模体内5个点的吸收剂量在82.08 mGy～100.99 mGy之间,中心吸收剂量为89.76 mGy;kV/kV成像,模体吸收剂量在0.461 mGy～1.044 mGy之间,中心为0.737 mGy;CBCT成像,吸收剂量在2.998 mGy～6.426 mGy之间,中心为4.676mGy,低剂量模式为标准模式的50%。结论：OBI系统比EPID系统成像剂量更低,图像质量更好。CBCT日常摆位验证是安全的。治疗过程中应选择合适的图像引导方式和扫描参数,确保患者的治疗准确和安全。     

A performance comparison of flat-panel imager-based MV and kV cone-beam CT

The use of cone-beam computed tomography (CBCT) has been proposed for guiding the delivery of radiation therapy, and investigators have examined the use of both kilovoltage (kV) and megavoltage (MV) x-ray beams in the development of such CBCT systems. In this paper, the inherent contrast and signal-to-noise ratio (SNR) performance for a variety of existing and hypothetical detectors for CBCT are investigated analytically as a function of imaging dose and object size. Theoretical predictions are compared to the results of experimental investigations employing largearea flat-panel imagers (FPIs) at kV and MV energies. Measurements were performed on two different FPI-based CBCT systems: a bench-top prototype incorporating an FPI and kV x-ray source (100 kVp x rays), and a system incorporating an FPI mounted on the gantry of a medical linear accelerator (6 MV x rays). The SNR in volume reconstructions was measured as a function of dose and found to agree reasonably with theoretical predictions. These results confirm the theoretically predicted advantages of employing kV energy x rays in imaging soft-tissue structures found in the human body. While MV CBCT may provide a valuable means of correcting 3D setup errors and may offer an advantage in terms of simplicity of mechanical integration with a linear accelerator (e.g., implementation in place of a portal imager), kV CBCT offers significant performance advantages in terms of image contrast and SNR per unit dose for visualization of soft-tissue structures. The relatively poor SNR performance at MV energies is primarily a result of the low x-ray quantum efficiencies (approximately a few percent or less) that are currently achieved with FPIs at high energies. Furthermore, kV CBCT with an FPI offers the potential of combined volumetric and radiographic/fluoroscopic imaging using the same device.     

GPU-based iterative cone-beam CT reconstruction using tight frame regularization

The x-ray imaging dose from serial cone-beam computed tomography (CBCT) scans raises a clinical concern in most image-guided radiation therapy procedures. It is the goal of this paper to develop a fast graphic processing unit (GPU)-based algorithm to reconstruct high-quality CBCT images from undersampled and noisy projection data so as to lower the imaging dose. For this purpose, we have developed an iterative tight-frame (TF)-based CBCT reconstruction algorithm. A condition that a real CBCT image has a sparse representation under a TF basis is imposed in the iteration process as regularization to the solution. To speed up the computation, a multi-grid method is employed. Our GPU implementation has achieved high computational efficiency and a CBCT image of resolution 512 × 512 × 70 can be reconstructed in ～5 min. We have tested our algorithm on a digital NCAT phantom and a physical Catphan phantom. It is found that our TF-based algorithm is able to reconstruct CBCT in the context of undersampling and low mAs levels. We have also quantitatively analyzed the reconstructed CBCT image quality in terms of the modulation-transfer function and contrast-to-noise ratio under various scanning conditions. The results confirm the high CBCT image quality obtained from our TF algorithm. Moreover, our algorithm has also been validated in a real clinical context using a head-and-neck patient case. Comparisons of the developed TF algorithm and the current state-of-the-art TV algorithm have also been made in various cases studied in terms of reconstructed image quality and computation efficiency.     

Fast Monte Carlo simulation for patient-specific CT/CBCT imaging dose calculation

X-ray imaging dose from computed tomography (CT) or cone beam CT (CBCT) scans has become a serious concern. Patient-specific imaging dose calculation has been proposed for the purpose of dose management. While Monte Carlo (MC) dose calculation can be quite accurate for this purpose, it suffers from low computational efficiency. In response to this problem, we have successfully developed a MC dose calculation code, gCTD, on GPU architecture under the NVIDIA CUDA platform for fast and accurate estimation of the x-ray imaging dose received by a patient during a CT or CBCT scan. Techniques have been developed particularly for the GPU architecture to achieve high computational efficiency. Dose calculations using CBCT scanning geometry in a homogeneous water phantom and a heterogeneous Zubal head phantom have shown good agreement between gCTD and EGSnrc, indicating the accuracy of our code. In terms of improved efficiency, it is found that gCTD attains a speed-up of ～400 times in the homogeneous water phantom and ～76.6 times in the Zubal phantom compared to EGSnrc. As for absolute computation time, imaging dose calculation for the Zubal phantom can be accomplished in ～17 s with the average relative standard deviation of 0.4%. Though our gCTD code has been developed and tested in the context of CBCT scans, with simple modification of geometry it can be used for assessing imaging dose in CT scans as well.     

应用锥形束CT研究儿童神经母细胞瘤放射治疗的摆位误差

目的：应用锥形束CT（CBCT）研究儿童腹部神经母细胞瘤放射治疗分次间（Interfraction）和分次内（Intrafraction）的摆位误差,探讨临床靶区（CTV）到计划靶区（PTV）的外放边界,为临床治疗计划的设计提供参考。方法：选取于2012年10月到2013年5月共10例接受放射治疗的儿童腹部神经母细胞瘤患者,所有患儿分别于治疗前以及治疗结束后进行CBCT扫描,CBCT扫描图像与计划CT图像进行配准,记录左右方向（Medial-Lateral,ML）,头脚方向（Superior-inferior,SI）以及胸背方向误差（Anterior-Posterior,AP）,从而得到分次间和分次内的摆位误差。结果：若按照每周一次图像验证,则摆位误差为：左右方向5.3mm,头脚方向5.7mm,胸背方向5.2mm。若按照每日CBCT图像验证,这种情况下的摆位误差仅为：左右方向2.1 mm,头脚方向1.7 mm,胸背方向1.4 mm。结论：每日CBCT图像扫描可以有效减少儿童神经母细胞瘤的摆位误差,缩小CTV到PTV的外放边界,减少正常组织的受照范围。正常组织受照范围的减少对患者特别是儿童患者有很大意义。在确定CTV到PTV的外放边界时,内边界（InternalMargin）的大小还需要进一步讨论。     

基于非线性估计的CBCT几何标定算法

针对传统的几何标定算法由标定模体位姿误差导致的CBCT成像系统参数标定精度不高的问题,提出一种基于解析几何和非线性优化的CBCT几何标定算法。首先,设计一种插帧追踪的方法,提取特征点的坐标,使得标定模体与投影图像中的特征点实现一一对应。然后,利用投影图片与设计的标定模体之间的空间几何关系,计算相关参数。最后,对检测的特征点进行非线性估计,进一步提高几何参数的计算精度。仿真数据实验表明,本文算法能够较为精确地计算出CBCT成像系统的几何参数,并在标定模体出现位姿偏差时仍然保持较高的计算精度。通过非线性估计模型,本文所提出的算法突破了现有算法标定模体位于等中心点的限制,提高了CBCT成像系统中参数标定的精度。     

Accuracy and feasibility of cone-beam computed tomography for stereotactic radiosurgery setup

Image fusion, target localization, and setup accuracy of cone-beam computed tomography (CBCT) for stereotactic radiosurgery (SRS) were investigated in this study. A Rando head phantom rigidly attached to a stereotactic Brown-Roberts-Wells (BRW) frame was utilized to study the geometric accuracy of CBCT. Measurements of distances and angular separations between selected pairs of multiple radio-opaque targets embedded in the head phantom from a conventional simulation CT provided comparative data for geometric accuracy analysis. Localization accuracy of the CBCT scan was investigated from an analysis of BRW localization of four cylindrical objects (9 mm in diameter and 25 mm in length) independently computed from CBCT and conventional CT scans. Image fusion accuracy was quantitatively evaluated from BRW localization of multiple simulated targets from the CBCT and conventional CT scan. Finally, a CBCT setup procedure for stereotactic radiosurgery treatments was proposed and its accuracy was assessed using orthogonal target verification imaging. Our study showed that CBCT did not present any significant geometric distortions. Stereotactic coordinates of the four cylindrical objects as determined from the CBCT differed from those determined from the conventional CT on average by 0.30 mm with a standard deviation (SD) of 0.09 mm. The mean image registration accuracy of CBCT with conventional CT was 0.28 mm (SD = 0.10 mm). Setup uncertainty of our proposed CBCT setup procedure was on the same order as the conventional framed-based stereotactic systems reported in the literature (mean = 1.34 mm, SD = 0.33 mm). In conclusion, CBCT can be used to guide SRS treatment setup with accuracy comparable to the currently used frame-based stereotactic radiosurgery systems provided that intra-treatment patient motion is prevented.     

X-ray scatter correction algorithm for cone beam CT imaging

Developing and optimizing an x-ray scatter control and reduction technique is one of the major challenges for cone beam computed tomography (CBCT) because CBCT will be much less immune to scatter than fan-beam CT. X-ray scatter reduces image contrast, increases image noise and introduces reconstruction error into CBCT. To reduce scatter interference, a practical algorithm that is based upon the beam stop array technique and image sequence processing has been developed on a flat panel detector-based CBCT prototype scanner. This paper presents a beam stop array-based scatter correction algorithm and the evaluation results through phantom studies. The results indicate that the beam stop array-based scatter correction algorithm is practical and effective to reduce and correct x-ray scatter for a CBCT imaging task.