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口腔影像学是口腔正畸学诊断的重要依据。锥形束CT（CBCT）的临床应用使正畸诊断从二维时代走向了三维时代。CBCT对于正畸治疗方案设计、治疗后的预测以及治疗效果的评价等具有重要的作用。     

锥形束CT与根尖片对牙根纵裂诊断的对比研究

目的:比较锥形束CT(CBCT)和X线根尖片在牙根纵裂诊断中的准确度,探讨CBCT对牙根纵裂诊断的价值。方法:选取临床检查中疑似牙根纵裂患牙50例,分别进行X线根尖片、CBCT检查诊断和外科手术诊断;对X线根尖片和CBCT对牙根纵裂的诊断结果进行统计分析。结果:CBCT诊断牙根纵裂的敏感度(83.33%)高于X线根尖片诊断牙根纵裂的敏感度为(47.61%),P<0.05。结论:CBCT比X线根尖片能更准确诊断牙根纵裂,有助于牙根纵裂诊断。     

多来源颅颌面三维数字化模型的建立

目的 建立一个满足临床和科研要求的可视化的多来源多精度的颅颌面三维数字化模型.方法 采用锥体束断层CT(CBCT)扫描整个头部,利用不同组织的亨氏单位(Houns Field值)的不同,提取出面部软组织、颌面部骨骼以及牙列3种组织结构,利用三维重建的方法,重构出面部、颌骨和牙齿三部分的数字化三维模型,同时采用激光扫描的方法获得带有纹理信息的面部三维模型以及高精度三维数字化牙列模型,利用三维图形学中的配准技术,将激光扫描获得的面部、三维模型转化到CT来源的重建的三维颅颌面数字化模型所在坐标系.结果 获得一个带有颜色信息的面部软组织、高精度牙列和清晰骨骼的复合三维数字化颅颌面模型.结论 多来源的三维数字化颅颌面模型是一种能够达到临床和科研要求的高精度数字化模型.     

Assessment of asymmetry in a normal occlusion sample and asymmetric patients with three-dimensional cone beam computed tomography: A study for a transverse reference plane

Objective:To characterize symmetrical features of patients with facial asymmetry and thus to find the most reliable horizontal reference lines easily used in three-dimensional images. The hypothesis was that there is a difference in the location of bilateral landmarks of the upper skull between the normal occlusion sample and skeletal Class III patients with asymmetry.Materials and Methods:Group 1 (normal occlusion sample) was composed of 20 Korean adults with normal occlusion and no noticeable asymmetry. Groups 2 through 4 were selected from patients who were diagnosed as skeletal Class III malocclusion and grouped according to the extent of asymmetry (group 2: symmetric mandible, no maxillary cant; group 3: asymmetric mandible, no maxillary cant; group 4: asymmetric mandible, more than 4 mm maxillary cant measured at maxillary first molars). Three-dimensional cone beam computed tomography images were taken before treatment, and bilateral landmarks of the skull were located and their vertical and horizontal differences compared.Results:No statistically significant difference was noted in the position of bilateral landmarks between groups, except for AG (P < .05). AG showed significant differences in vertical dimension (P < .001) and in horizontal dimension (P < .0001) between groups. The mean of the difference was clearly greatest at FM.Conclusions:The hypothesis is rejected. All groups had a similar pattern of asymmetry in the upper third of the face. Therefore, the transverse reference line of the bilateral Z or orbitale may be used even in patients with severe asymmetry of the maxilla with reference to the clinical photos.     

Accuracy of orthodontic miniscrew implantation guided by stereolithographic surgical stent based on cone-beam CT–derived 3D images

Objective:To develop surgical stents for cone-beam computed tomography (CBCT) 3-dimensional (3D) image-based stent-guided orthodontic miniscrew implantation and to evaluate its accuracy.Materials and Methods:Ten surgical stents were fabricated with stereolithographic appliances (SLAs) according to 3D CBCT image-based virtual implantation plans. Thirty self-drilling miniscrews were implanted at two to three positions on each side of the maxillary or mandibular posterior arches in three phantoms: 20 guided by 10 surgical stents in two phantoms (stent group) and 10 guided freehand in one phantom (freehand group). Six parameters (mesiodistal and vertical deviations at the corona and apex and mesiodistal and vertical angular deviations) were measured to compare variations between the groups.Results:No root damage was found in the stent group, whereas four of 10 miniscrews contacted with roots in the freehand group. In the stent group, deviations in the mesiodistal and vertical directions were 0.15 ± 0.09 and 0.19 ± 0.19 mm at the corona, respectively, and 0.28 ± 0.23 and 0.33 ± 0.25 mm at the apex, respectively; angular deviations in the mesiodistal and vertical directions were 1.47° ± 0.92° and 2.13° ± 1.48°, respectively. In the freehand group, the corresponding results were 0.48 ± 0.46 mm and 0.94 ± 0.87 mm (corona), 0.81 ± 0.61 mm and 0.78 ± 0.49 mm (apex), and 7.49° ± 6.09° and 6.31° ± 3.82°. Significant differences were found in all six parameters between the two groups (Student''s t-test, P < .05).Conclusions:3D CBCT image-based SLA-fabricated surgical stents can provide a safe and accurate method for miniscrew implantation.     

Dental age estimation in Malaysian adults based on volumetric analysis of pulp/tooth ratio using CBCT data

Forensic odontology plays an important role in human identification and dental age estimation is an integral part of this process. The aim of the study was to investigate the association between chronological age and pulp/tooth volume ratio in a Malaysian population (Malays and Chinese) from cone-beam computed tomography (CBCT) scans, enhanced with Mimics software. Three hundred CBCT scans of 153 males and 147 females, aged between 16 and 65 years were divided into 5 age groups. Volumetric analysis of the pulp/tooth ratio was performed in maxillary left canines, maxillary right canines and maxillary right central incisors. Simple linear regression and Pearson correlation analysis indicated the strongest coefficient of correlation (R) values for maxillary right central incisors (0.83) followed by maxillary right canines (0.74) and maxillary left canines (0.73). Fisher’s Z test indicated that dental age estimation is gender independent. The derived regression equations were further validated on an independent group of 126 teeth. The results indicated mean absolute error (MAE) values of 6.48 and 8.58 years for maxillary right central incisors and maxillary canines respectively. It was also noticed that MAE values were higher among the age groups ranging from 46 to 65 years. This study showed that a volumetric change in the pulp cavity with age is a valuable assessment method for dental age estimation among Malaysian population.     

Substantial CT radiation dose reduction does not affect the preference for CT over direct digital radiography to diagnose isolated zygomatic fractures – A study in human cadavers

IntroductionZygomatic fractures can be diagnosed with either computed tomography (CT) or direct digital radiography (DR). The aim of the present study was to assess the effect of CT dose reduction on the preference for facial CT versus DR for accurate diagnosis of isolated zygomatic fractures.Materials and methodsEight zygomatic fractures were inflicted on four human cadavers with a free fall impactor technique. The cadavers were scanned using eight CT protocols, which were identical except for a systematic decrease in radiation dose per protocol, and one DR protocol. Single axial CT images were displayed alongside a DR image of the same fracture creating a total of 64 dual images for comparison. A total of 54 observers, including radiologists, radiographers and oral and maxillofacial surgeons, made a forced choice for either CT or DR.ResultsForty out of 54 observers (74%) preferred CT over DR (all with P < 0.05). Preference for CT was maintained even when radiation dose reduced from 147.4 μSv to 46.4 μSv (DR dose was 6.9 μSv). Only a single out of all raters preferred DR (P = 0.0003). The remaining 13 observers had no significant preference.ConclusionThis study demonstrates that preference for axial CT over DR is not affected by substantial (∼70%) CT dose reduction for the assessment of zygomatico-orbital fractures.     

Optimal acquisition time to discriminate between breast cancer subtypes with contrast-enhanced cone-beam CT

PurposeTo identify the optimal acquisition time to best discriminate between benign and malignant breast lesions on contrast-enhanced cone beam CT (CE-CBCT) and evaluate the potential of CE-CBCT to differentiate between breast cancer subtypes.Material and methodA total of 98 women with a mean age of 49 ± 10 (SD) years (range: 29–77 years) with 100 BI-RADS 4 or 5 breast lesions were prospectively included. CE-CBCT images were obtained at 1- and 2-min after intravenous administration of iodinated contrast material. Contrast enhancement of breast lesions on CE-CBCT were evaluated and compared between different subtypes. Cut-off values for best discriminating between benign and malignant breast lesions with CE-CBCT were obtained from receiver operating characteristic curves.ResultsMalignant breast lesions showed greater enhancement than benign ones at 1-min (67.28 ± 39.79 [SD] HU vs. 42.27 ± 40.31 [SD] HU, respectively; P = 0.007) and 2-min (70.93 ± 38.05 [SD] HU vs. 48.94 ± 41.83 [SD] HU, respectively; P = 0.016) after intravenous administration of contrast material. At 1-min after intravenous administration of contrast material, an optimal cut-off value of 54.43 HU was found to best discriminate between malignant and benign breast lesions (AUC = 0.681; 95%CI: 0.558–0.805; P = 0.006) yielding 69.0% sensitivity (95%CI: 56.9–79.5%) and 69.2% specificity (95% CI: 48.2–85.7%). At 2-min, an optimal cut-off value of 72.65 HU was found to best discriminate between malignant and benign breast lesions (AUC = 0.654; 95%CI: 0.535–0.774; P = 0.020) yielding 50.7% sensitivity (95%CI: 38.6–62.8%) and 80.8% specificity (95%CI: 60.6–93.4%). CE-CBCT helped differentiate between immunohistochemical subtypes of breast lesions with lowest enhancement for triple negative lesions. No differences in enhancement were found among histopathological subtypes lesions at 1-min (P = 0.478) and 2-min (P = 0.625).ConclusionCE-CBCT helps discriminate between malignant and benign breast lesions, with best capabilities obtained at 1-min after intravenous administration of contrast material. For malignant lesions, quantitative analysis of enhancement on CE-CBCT helps differentiate between immunohistochemical subtypes.     

CBCT-guided adaptive radiotherapy using self-supervised sequential domain adaptation with uncertainty estimation

Adaptive radiotherapy (ART) is an advanced technology in modern cancer treatment that incorporates progressive changes in patient anatomy into active plan/dose adaption during the fractionated treatment. However, the clinical application relies on the accurate segmentation of cancer tumors on low-quality on-board images, which has posed challenges for both manual delineation and deep learning-based models. In this paper, we propose a novel sequence transduction deep neural network with an attention mechanism to learn the shrinkage of the cancer tumor based on patients’ weekly cone-beam computed tomography (CBCT). We design a self-supervised domain adaption (SDA) method to learn and adapt the rich textural and spatial features from pre-treatment high-quality computed tomography (CT) to CBCT modality in order to address the poor image quality and lack of labels. We also provide uncertainty estimation for sequential segmentation, which aids not only in the risk management of treatment planning but also in the calibration and reliability of the model. Our experimental results based on a clinical non-small cell lung cancer (NSCLC) dataset with sixteen patients and ninety-six longitudinal CBCTs show that our model correctly learns weekly deformation of the tumor over time with an average dice score of 0.92 on the immediate next step, and is able to predict multiple steps (up to 5 weeks) for future patient treatments with an average dice score reduction of 0.05. By incorporating the tumor shrinkage predictions into a weekly re-planning strategy, our proposed method demonstrates a significant decrease in the risk of radiation-induced pneumonitis up to 35% while maintaining the high tumor control probability.     

锥形束CT的常规检测方法和质量保证

目的探讨图像引导放疗中锥形束CT的常规检测方法和质量保证(QA)。方法从加速器中锥形束CT的相关项目验收程序入手,对锥形束CT系统进行日检、周检、月检,完成锥形束CT的系统安全、机械精度、图像质量等项目的质量保证。结果锥形束CT的系统安全性能正常,机械精度和图像质量的误差均在允许范围。锥形束CT的等中心与加速器机架等中心的误差为0.3 mm,SAD检测结果为85.2 cm,均在允许的误差范围内。锥形束CT在OBI模式下2D图像的低对比度分辨率和空间分辨率均合格,CBCT模式下CT图像空间分辨率在Ful-Fan和Half-Fan扫描模式下分别为7 lp/cm和6 lp/cm,低对比度分辨率合格,HU值的线性和一致性均合格,几何失真度小于1 mm,CT图像质量检查均为正常。结论锥形束CT的常规检测和质量保证可确保锥形束CT系统安全、精确。