Three-dimensional segmentation of the upper airway using cone beam CT: a systematic review

The objectives of this study were to systematically review the literature for studies that used cone beam CT (CBCT) to automatically or semi-automatically model the upper airway (including the pharyngeal, nasal and paranasal airways), and to assess their validity and reliability. Several electronic databases (MEDLINE®, MEDLINE In-Process & Other Non-Indexed Citations, all evidence-based medicine reviews including the Cochrane database, and Scopus) were searched. Abstracts that appeared to meet the initial selection criteria were selected by consensus. The original articles were then retrieved and their references were searched manually for potentially suitable articles that were missed during the electronic search. Final articles that met all the selection criteria were evaluated using a customized evaluation checklist. 16 articles were finally selected. From these, five scored more than 50% based on their methodology. Although eight articles reported the reliability of the airway model generated, only three used intraclass correlation (ICC). Two articles tested the accuracy/validity of airway models against the gold standard, manual segmentation, using volumetric measurements; however, neither used ICC. Only three articles properly tested the reliability of the three-dimensional (3D) upper airway model generated from CBCT and only one article had sufficiently sound methodology to test the airway model''s accuracy/validity. The literature lacks proper scientific justification of a solid and optimized CBCT protocol for airway imaging. Owing to the limited number of adequate studies, it is difficult to generate a strong conclusion regarding the current validity and reliability of CBCT-generated 3D models.     

Artefacts in CBCT: a review

Artefacts are common in today's cone beam CT (CBCT). They are induced by discrepancies between the mathematical modelling and the actual physical imaging process. Since artefacts may interfere with the diagnostic process performed on CBCT data sets, every user should be aware of their presence. This article aims to discuss the most prominent artefacts identified in the scientific literature and review the existing knowledge on these artefacts. We also briefly review the basic three-dimensional (3D) reconstruction concept applied by today's CBCT scanners, as all artefacts are more or less directly related to it.     

128层螺旋CT三维重建对OSAHS患者上气道应用价值的研究

目的：评估128层螺旋 CT 上气道三维重建对阻塞性睡眠呼吸暂停低通气综合征(OSAHS)患者上气道阻塞部位的定位价值。方法采用128层螺旋 CT 对52例确诊的 OSAHS 患者清醒和 Muller 试验下及32例正常人清醒状态下进行上气道容积扫描,分别测量软腭后区、舌后区及会厌后区的气道体积和气道长度,并对各测量指标进行统计学分析。结果与正常对照组相比,清醒状态下 OSAHS 患者上气道长度显著增加(P <0.001)。与清醒状态下相比,OSAHS 患者 Muller 试验下软腭后区气道体积、舌后区气道体积、气道总体积显著减少(P <0.001)。OSAHS 患者上气道长度与平均血氧饱和度(MSaO2)呈负性相关(r=-0.33, P <0.05)。结论128层螺旋 CT 上气道三维重建能较好评估 OSAHS 患者上气道阻塞部位及阻塞的程度,对指导临床治疗有重要意义。     

Effectiveness of thyroid gland shielding in dental CBCT using a paediatric anthropomorphic phantom

Objectives:

The purpose of the study is to evaluate the effectiveness of thyroid shielding in dental CBCT examinations using a paediatric anthropomorphic phantom.

Methods:

An ATOM^® 706-C anthropomorphic phantom (Computerized Imaging Reference Systems Inc., Norfolk, VA) representing a 10-year-old child was loaded with six thermoluminescent dosemeters positioned at the level of the thyroid gland. Absorbed doses to the thyroid were measured for five commercially available thyroid shields using a large field of view (FOV).

Results:

A statistically significant thyroid gland dose reduction was found using thyroid shielding for paediatric CBCT examinations for a large FOV. In addition, a statistically significant difference in thyroid gland doses was found depending on the position of the thyroid gland. There was little difference in the effectiveness of thyroid shielding when using a lead vs a lead-equivalent thyroid shield. Similar dose reduction was found using 0.25- and 0.50-mm lead-equivalent thyroid shields.

Conclusions:

Thyroid shields are to be recommended when undertaking large FOV CBCT examinations on young patients.     

The effect of cone beam CT (CBCT) on therapeutic decision-making in endodontics

Objectives:

The aim was to assess to what extent cone beam CT (CBCT) used in accordance with current European Commission guidelines in a normal clinical setting has an impact on therapeutic decisions in a population referred for endodontic problems.

Methods:

The study includes data of consecutively examined patients collected from October 2011 to December 2012. From 2 different endodontic specialist clinics, 57 patients were referred for a CBCT examination using criteria in accordance with current European guidelines. The CBCT examinations were performed using similar equipment and standardized among clinics. After a thorough clinical examination, but before CBCT, the examiner made a preliminary therapy plan which was recorded. After the CBCT examination, the same examiner made a new therapy plan. Therapy plans both before and after the CBCT examination were plotted for 53 patients and 81 teeth. As four patients had incomplete protocols, they were not included in the final analysis.

Results:

4% of the patients referred to endodontic clinics during the study period were examined with CBCT. The most frequent reason for referral to CBCT examination was to differentiate pathology from normal anatomy, this was the case in 24 patients (45% of the cases). The primary outcome was therapy plan changes that could be attributed to CBCT examination. There were changes in 28 patients (53%).

Conclusions:

CBCT has a significant impact on therapeutic decision efficacy in endodontics when used in concordance with the current European Commission guidelines.     

Topical contrast agents to improve soft-tissue contrast in the upper airway using cone beam CT: a pilot study

The purpose of this study is to explore the topical use of radiographic contrast agents to enhance soft-tissue contrast on cone beam CT (CBCT) images. Different barium sulphate concentrations were first tested using an airway phantom. Different methods of barium sulphate application (nasal drops, syringe, spray and sinus wash) were then tested on four volunteers, and nebulized iodine was tested in one volunteer. CBCT images were performed and then assessed subjectively by two examiners for contrast agent uniformity and lack of streak artefact. 25.0% barium sulphate presented adequate viscosity and radiodensity. Barium sulphate administered via nasal drops and sprays showed non-uniform collection at the nostrils, along the inferior and/or middle nasal meatuses and posterior nasal choana. The syringe and sinus wash showed similar results with larger volumes collecting in the naso-oropharynx. Nebulized iodine failed to distribute into the nasal cavity and scarcely collected at the nostrils. All methods of nasal application failed to adequately reach or uniformly coat the nasal cavity beyond the inferior nasal meatuses. The key factors to consider for optimum topical radiographic contrast in the nasal airway are particle size, flow velocity and radio-opacity.     

Basic training requirements for the use of dental CBCT by dentists: a position paper prepared by the European Academy of DentoMaxilloFacial Radiology

Cone beam CT (CBCT) is a relatively new imaging modality, which is now widely available to dentists for examining hard tissues in the dental and maxillofacial regions. CBCT gives a three-dimensional depiction of anatomy and pathology, which is similar to medical CT and uses doses generally higher than those used in conventional dental imaging. The European Academy of DentoMaxilloFacial Radiology recognizes that dentists receive training in two-dimensional dental imaging as undergraduates, but most of them have received little or no training in the application and interpretation of cross-sectional three-dimensional imaging. This document identifies the roles of dentists involved in the use of CBCT, examines the training requirements for the justification, acquisition and interpretation of CBCT imaging and makes recommendations for further training of dentists in Europe who intend to be involved in any aspect of CBCT imaging. Two levels of training are recognized. Level 1 is intended to train dentists who prescribe CBCT imaging, such that they may request appropriately and understand the resultant reported images. Level 2 is intended to train to a more advanced level and covers the understanding and skills needed to justify, carry out and interpret a CBCT examination. These recommendations are not intended to create specialists in CBCT imaging but to offer guidance on the training of all dentists to enable the safe use of CBCT in the dentoalveolar region.     

Influence of exposure factors on the variability of CBCT voxel values: a phantom study

Objectives:

To assess the influence of milliamperage and kilovolt peak (kVp) on the variability of cone beam CT (CBCT) voxel values.

Methods:

CBCT scans were obtained from radiographic phantoms in varying concentrations of dipotassium hydrogen phosphate solutions (200–1200 mg ml⁻¹) under different protocols of milliamperage and kVp. In addition, scans were performed with and without a dental implant and exo-mass. The variability of CBCT voxel values was measured on each scan, and factorial analysis of variance and the post hoc Tukey test were performed (α = 0.05). Linear regression was performed to assess the relationship between voxel value variability and dipotassium hydrogen phosphate concentration.

Results:

milliamperage and the presence of a dental implant did not produce significant interference (p = 0.28 and 0.87, respectively) in voxel value variability. Scans at the highest kVp value presented a significant reduction (p ≤ 0.0001) in voxel value variability when only exo-mass was not present. Voxel value variability was not influenced by exo-mass in scans at the highest levels of milliamperage and kVp. The presence of exo-mass produced a significant reduction (p ≤ 0.0001) in voxel value variability in most of the scans. Higher concentrations yielded greater variations in voxel values in all scans, except for those operating at the highest levels of mAs and kVp.

Conclusions:

mAs did not influence the variability of CBCT voxel values; higher kVp reduced such variability when only the object was smaller than the field of view.     

Influence of the artefact reduction algorithm of Picasso Trio CBCT system on the diagnosis of vertical root fractures in teeth with metal posts

Objectives:

To assess the influence of the artefact reduction algorithm (AR) available on the Picasso Trio 3D^® imaging system (Vatech, Hwaseong, Republic of Korea) on image quality [greyscale values, contrast-to-noise ratio (CNR) and artefact formation] and diagnosis of vertical root fractures (VRFs) in the teeth with intracanal metal posts.

Methods:

30 uniradicular teeth had their crowns removed and their roots endodontically treated to receive intracanal metal posts. In 20 teeth, both complete (n = 10) and incomplete (n = 10) VRFs were created. Each tooth was scanned twice, with and without AR activation. The mean and variation of greyscale values, as well as CNR, were calculated for all images. Subsequently, an evaluator compared the amount of artefact (cupping, white streaks and dark bands) in all images. Five evaluators rated for VRF presence using a five-point scale.

Results:

Mean greyscale values and CNR were significantly decreased in images acquired with the AR. The usage of the algorithm promoted an overall reduction of image artefacts. Regarding the diagnosis of complete and incomplete VRFs, the use of the AR had an overall negative impact on specificity and accuracy.

Conclusions:

While indeed reducing artefact formation, the use of the AR, instead of improving the impact on the diagnosis of VRFs in teeth with intracanal metal posts, had a negative impact on the diagnosis.     

多层螺旋 CT 在小儿气管支气管异物诊断中的应用

目的：评价多层螺旋 CT 对小儿气管支气管异物的诊断价值。方法回顾性分析139例气管支气管异物的临床和 CT资料,后处理采用多平面重建(MPR)、曲面重建(CPR)、容积再现(VR)、最小密度投影(MinIP)、仿真内窥镜(VE)等技术,并与纤维支气管镜检查结果对照。结果139例中,气管异物13例,右侧支气管异物75例,左侧支气管异物48例,双侧3例。CT 正确诊断137例(98.6%),漏诊2例(1.4%);气管异物及右侧主支气管异物 CT 与纤维支气管镜检查结果有显著性差异(P <0.05),但二者总体差异无统计学意义(P =0.340)。间接伴随征象：肺气肿74例,肺炎48例,肺不张22例,纵隔移位57例,间质性肺气肿4例,纵隔及皮下积气4例,支气管扩张2例,胸腔积液4例。结论多层螺旋 CT 及其后处理技术能准确直观地显示气管支气管异物及其继发征象,具有重要的临床应用价值。     

Ex vivo comparison of Galileos cone beam CT and intraoral radiographs in detecting occlusal caries

Objective

The aim of this study was to compare the accuracy of cone beam CT (CBCT) with intraoral radiographs for detection of occlusal caries.

Methods

A set of 60 extracted teeth were imaged using a Sirona Galileos CBCT system (Sirona Dental Systems, Bensheim, Germany) and an intraoral Planmeca® system (Planmeca OY, Helsinki, Finland). Six observers looked at both modalities and used a five-point confidence scale to evaluate presence or absence of occlusal caries. Histology was used as the gold standard. Receiver operating characteristic analysis and weighted kappa statistics were used for statistical analysis. Differences in the area under the curve (AUC) values between observers and modalities were analysed using analysis of variance (ANOVA). Differences in sensitivity and specificity were analysed using the Wilcoxon test. Interobserver and intraobserver reliability was assessed by weighted kappa scores.

Results

The mean value and standard deviation of AUC was 0.719 ± 0.038 for CBCT and 0.649 ± 0.062 for the intraoral radiographs. The ANOVA results demonstrated that there was no significant difference between the modalities and the observers. The interobserver kappa for pairs of observers ranged from fair to substantial for bitewings (0.244–0.543) and CBCT (0.152–0.401). Four out of six observers reported higher sensitivity but lower specificity with CBCT. The Wilcoxon exact p-value showed no difference in sensitivity (0.175) or specificity (0.573) between the two modalities.

Conclusion

Based on the results we conclude that the Sirona CBCT unit cannot be used for the sole purpose of looking at occlusal caries.     

Influence of CBCT enhancement filters on diagnosis of vertical root fractures: a simulation study in endodontically treated teeth with and without intracanal posts

Objectives:

To evaluate the influence of CBCT enhancement filters on the diagnosis of vertical root fractures (VRFs) in teeth with and without metal posts.

Methods:

The crowns of 40 uniradicular human teeth were removed and all roots were prepared. 20 teeth were randomly selected, and VRFs were induced using a universal testing machine. The i-CAT (Imaging Sciences International, Hatfield, PA) CBCT was used to scan teeth with and without intracanal metal posts using the following parameters: 0.2 voxel size, 8 × 8-cm scan size and acquisition time of 26.9 s. Images were evaluated by three observers with and without the use of the following filters: S9, smooth, smooth 3 × 3, sharpen, sharpen-mild and sharpen 3 × 3.

Results:

Intra- and interobserver agreement ranged from poor to moderate. Images with and without CBCT filters did not show significant differences regarding the area under the receiver operating characteristic curve, as well as sensitivity (p > 0.05). As for accuracy, the sharpen-mild filter was superior to the sharpen (p = 0.03), but these filters did not differ from all others. For specificity, S9, smooth and original images were superior to sharpen (p < 0.01). Results for teeth without posts differed from those for teeth with metal posts in all cases (p < 0.05).

Conclusions:

The use of enhancement filters in CBCT images has no influence on the diagnosis of VRFs in teeth with metal posts, and their use is not justified.     

Cone beam computed tomographic evaluation of pharyngeal airway in North Indian children with different skeletal patterns

BACKGROUNDIn growing patients with skeletal discrepancies, early assessment of functional factors can be vital for the restoration of normal craniofacial growth.AIMTo compare airway volumes in patients with mandibular retrognathism with the normal anteroposterior skeletal relationship, thereby assessing the association between cephalometric variables and airway morphology.METHODSCone-beam computed tomography volume scans, and lateral cephalograms, 3-dimensional airway volume and cross-sectional areas of 120 healthy children (54 boys and 66 girls mean age 15.19 ± 1.28) which were done for orthodontic assessment were evaluated. The subjects were divided into 2 groups based on the angle formed between point A, Nasion and point B (ANB) values and cephalometric variables (such as anterior and posterior facial height, gonial angle etc.) airway volumes, and cross-sectional measurements were compared using independent t tests. Pearson’s correlation coefficient test was used to detect any relationship of different parts of the airway and between airway volume and 2-dimensional cephalometric variables.RESULTSMeans and standard deviations for cephalometric, cross-sectional, and volumetric variables were compared. ANB, mandibular body length and facial convexity were statistically highly significant (P < 0.01) whereas condylion to point A, nasal airway and total airway volume (P < 0.05) were statistically significant. The nasal airway volume and the superior pharyngeal airway volume had a positive correlation (P < 0.01), nasal airway was correlated to middle (P < 0.05) and total airway superior had a relation with middle (P < 0.05), inferior and total airway (P < 0.05), middle was related to all other airways; inferior was also related to all the airways except nasal. Lateral cephalometric values were positively correlated with the airway volume with Frankfurt Mandibular Plane Angle and facial convexity showed significant correlations with total airway volume (P < 0.05). Additionally, ANB angle was significantly correlated with total airway volume and superior airway (P < 0.05).CONCLUSIONThe mean total airway volume in patients with retrognathic mandible was significantly smaller than that of patients with a normal mandible.     

Dental cone beam CT image quality possibly reduced by patient movement

Patient artefacts in dental cone beam CT scans can happen for various reasons. These range from artefacts from metal restorations to movement. An audit was carried out in the Glasgow Dental Hospital analysing how many scans showed signs of “motion artefact”, and then to assess if there was any correlation between patient age and movement artefacts. Specific age demographics were then analysed to see if these cohorts were at a higher risk of “movement artefacts”.     

Optimization of exposure parameters for cone beam computed tomography sialography

Objectives

The assessment of image quality is a crucial step in the development of a new imaging protocol. Having proposed and reported on a preliminary protocol for sialography using cone beam CT (CBCT), the purpose of this study was to further optimize this protocol by maximizing the image signal difference-to-noise ratio (SDNR) and to relate these new data to previously published dosimetric data for CBCT sialography.

Methods

An imaging phantom was constructed using samples with different concentrations of iodine and a water-immersed mandible. The CB MercuRay (Hitachi Medical Systems, Tokyo, Japan) was used to image the phantom using different peak kilovoltage (kVp) and milliamperage (mA) settings. SDNR was then calculated using the raw images based on mean pixel values (MPV) measured in selected regions of interest (ROI). Finally, a figure of merit (FOM) was calculated to examine the trade-off between image SDNR and effective radiation dose.

Results

The SDNR demonstrated an expected increase as the kVp increased from 60 to 120. Also, images made with the higher mA setting (15) had greater SDNR. The iodine concentration also influenced the image quality such that SDNR increased with increased amounts of iodine. The calculated FOM was greatest for the technique using 80 kVp, with equivalent results for 10 mA and 15 mA.

Conclusion

An optimized protocol for CBCT sialography using CB MercuRay entails a 6 inch field of view with 80 kVp and 10 mA.     

Quantitative assessment of artefacts and identification of gaps in prosthetic crowns: a comparative in vitro study between periapical radiography and CBCT images

Objectives:To evaluate, in an in vitro study, the quantity of artefacts generated by two different restorative materials, and to determine the diagnostic accuracy of cone beam CT (CBCT) scans and periapical radiographs in identifying gaps in prosthetic crowns.Methods:A total of 30 teeth restored with metal-ceramic (n = 15) and all-ceramic (n = 15) crowns, properly adapted and with 0.30- and 0.50 mm gaps, underwent CBCT exams (with voxel sizes of 0.25 and 0.30 mm) and periapical radiographs. The artefacts generated by two different crowns were quantified and compared by the Mann–Whitney test. In addition, five examiners evaluated the presence or absence of gaps in periapical radiographs and CBCT images. The accuracy of tests was determined by the area under the receiver operatring characteristic curve and these values were compared by using the Kruskal–Wallis test.Results:There was no significant difference in artefact values between the different restorative materials and the different resolutions of CBCT images. Regarding the accuracy of the tests evaluated, periapical radiography and CBCT with voxel size 0.25 mm showed the best performance for smaller gaps (0.30 mm). For larger gaps (0.50 mm), all exams tested showed the same performance.Conclusions:Periapical radiography was still the most cost-beneficial method for the diagnosis of maladaptation in dental restorations. CBCT exams did not improve accuracy in detecting gaps in prosthetic crowns.     

CBCT in orthodontics: assessment of treatment outcomes and indications for its use

Since its introduction into dentistry in 1998, CBCT has become increasingly utilized for orthodontic diagnosis, treatment planning and research. The utilization of CBCT for these purposes has been facilitated by the relative advantages of three-dimensional (3D) over two-dimensional radiography. Despite many suggested indications of CBCT, scientific evidence that its utilization improves diagnosis and treatment plans or outcomes has only recently begun to emerge for some of these applications. This article provides a comprehensive and current review of key studies on the applications of CBCT in orthodontic therapy and for research to decipher treatment outcomes and 3D craniofacial anatomy. The current diagnostic and treatment planning indications for CBCT include impacted teeth, cleft lip and palate and skeletal discrepancies requiring surgical intervention. The use of CBCT in these and other situations such as root resorption, supernumerary teeth, temporomandibular joint (TMJ) pathology, asymmetries and alveolar boundary conditions should be justified on the basis of the merits relative to risks of imaging. CBCT has also been used to assess 3D craniofacial anatomy in health and disease and of treatment outcomes including that of root morphology and angulation; alveolar boundary conditions; maxillary transverse dimensions and maxillary expansion; airway morphology, vertical malocclusion and obstructive sleep apnoea; TMJ morphology and pathology contributing to malocclusion; and temporary anchorage devices. Finally, this article utilizes findings of these studies and current voids in knowledge to provide ideas for future research that could be beneficial for further optimizing the use of CBCT in research and the clinical practice of orthodontics.     

Cervical vertebral column morphology in patients with obstructive sleep apnoea assessed using lateral cephalograms and cone beam CT. A comparative study

Objectives:

Few studies have described morphological deviations in obstructive sleep apnoea (OSA) patients on two-dimensional (2D) lateral cephalograms, and the reliability of 2D radiographs has been discussed. The objective is to describe the morphology of the cervical vertebral column on cone beam CT (CBCT) in adult patients with OSA and to compare 2D lateral cephalograms with three-dimensional (3D) CBCT images.

Methods:

For all 57 OSA patients, the cervical vertebral column morphology was evaluated on lateral cephalograms and CBCT images and compared according to fusion anomalies and posterior arch deficiency.

Results:

The CBCT assessment showed that 21.1% had fusion anomalies of the cervical column, i.e. fusion between two cervical vertebrae (10.5%), block fusions (8.8%) or occipitalization (1.8%). Posterior arch deficiency occurred in 14% as partial cleft of C1 and in 3.5% in combination with block fusions. The agreement between the occurrence of morphological deviations in the cervical vertebral column between lateral cephalograms and CBCT images showed good agreement (κ = 0.64).

Conclusions:

Prevalence and pattern in the cervical column morphology have now been confirmed on CBCT. The occurrence of morphological deviations in the cervical vertebral column showed good agreement between lateral cephalograms and CBCT images. This indicates that 2D lateral cephalograms (already available after indication in connection with, e.g. treatment planning) are sufficient for identifying morphological deviations in the cervical vertebral column. For a more accurate diagnosis and location of the deviations, CBCT is required. New 3D methods will suggest a need for new detailed characterization and division of deviations in cervical vertebral column morphology.     

64层螺旋CT对儿童漏斗胸的心脏及小气道改变的评价

目的:通过CT观察儿童漏斗胸心脏形态及小气道改变,探讨胸廓畸形程度对心脏形态、小气道改变的影响及64层螺旋CT的价值。方法:搜集2009～2011年临床确诊漏斗胸并行胸部64层螺旋CT三维重建检查的患儿183例,测量胸廓的Haller指数、心脏旋转角度,在MPR肺窗上观察小气道改变。按Haller指数将病例分为轻、中、重度3组,比较3组间心脏旋转角、小气道改变的差异性,探讨胸骨凹陷程度对两者的影响。结果:183例漏斗胸患儿分为轻度54例(Haller指数2.86±0.31)、中度22例(3.36±0.10)、重度107例(4.61±1.27),三者间差异有统计学意义(P<0.05)。心脏旋转角分别为55.52°±8.76°、57.38°±5.03°和65.93°±7.67°,三者间差异有统计学意义(P<0.05)。随凹陷程度的增加,心脏旋转角也增加,二者有相关性(r=0.596,P<0.05)。60例患儿有小气道改变,轻、中、重度分别占22.22%(12/54)、22.73%(5/22)、40.19%(43/107),3组之间差异有统计学意义(P<0.05)。其中53例有左肺下叶小气道的改变。结论:64层螺旋CT可准确显示漏斗胸的胸廓畸形程度、心脏受压旋转及小气道改变。随着胸廓凹陷程度的加重,心脏旋转角及小气道改变也增加。