Reliability of anatomic structures as landmarks in three-dimensional cephalometric analysis using CBCT

Objective:To identify anatomic structures in three dimensions and examine their reliability to be used as landmarks in a three-dimensional coordinate cephalometric analysis, using cone-beam computerized tomography (CBCT).Materials and Methods:Thirty CBCT images were randomly selected for landmark location. Forty-two anatomic landmarks, which are not included in the traditional cephalometric landmarks, were chosen based on radiographic characteristics that make them pragmatic to mark in the CBCT image slices. The principal investigator marked the full set of landmarks on the software by navigating in the X, Y, and Z axes for every image three times, with each measurement trial being at least 1 week apart. One other investigator also located the landmarks once for each image for reliability purposes. Intraclass correlation coefficients (ICCs) were used to analyze the mean differences in landmark location in all axes.Results:Intra- and interexaminer reliability for x, y, and z coordinates for all landmarks had ICC greater than 0.95 with confidence interval of 0.88–0.99. Mean measurement differences found were <1.4 mm for all landmarks in all three coordinates. Mean measurement error differences obtained in the principal investigator''s trials were primarily <0.5 mm.Conclusion:The most reliable and reproducible landmarks tested for use in CBCT are mental foramina, infraorbital foramina, inferior hamulus, dens axis, foramina transversarium of atlas, medial and lateral condyles of the mandible, superior clinoid processes, and mid-clinoid.     

Reliability of 3D dental and skeletal landmarks on CBCT images

Objectives:To quantify reliability of three-dimensional skeletal landmarks and a comprehensive set of dental landmarks in cone-beam computed tomography (CBCT) and to determine the shapes of envelope of error.Materials and Methods:Three judges located 31 skeletal landmarks and 60 dental landmarks on the pre- and posttreatment CBCT images of 22 patients. Landmark error was determined by calculating the distance of deviation of landmark locations around their average. Standard deviation and mean radial spherical error were calculated. Scatterplots were constructed to characterize envelope of error.Results:The midline landmarks of the cranial base were highly reliable. Bilateral skeletal landmarks tended to have larger error than midline landmarks. Among the nonconventional landmarks, fronto-zygomatic suture, condyle, and mental foramen showed relatively high reliability. However, foramen spinosum and temporal fossa showed larger errors. Gonion was the least reliable landmark. Most dental landmarks were located more reliably than skeletal landmarks. The highest reliability was found at incisal edges. Mesiobuccal cusp of first molars also showed high reliability.Conclusions:There were differences in the size and shape of the distributions of errors of different landmarks. Most landmarks showed elongated envelopes. Bilateral structures tended to show greater errors than midline structures. Most dental landmarks were more reliable than skeletal landmarks.     

Consistency and precision of landmark identification in three-dimensional cone beam computed tomography scans

The purpose of this study was to quantify the consistency and precision of locating three-dimensional (3D) anatomic landmarks. The hypotheses tested are that these landmarks have characteristic and variable error patterns associated with their type and location. The consistency and precision of nine orthodontists identifying 32 landmarks of 19 patients were quantified. The cone beam computed tomography (CBCT) data were acquired using a Hitachi CB MercuRay system. Prior to the study, all examiners were calibrated with respect to the definitions of the landmarks and on the use of the software program (Dolphin) for identifying the landmarks. In addition, a reference guide was provided that had the definitions and sample images of the landmarks. Data were collected in spreadsheets as x, y, and z co-ordinates and statistically analysed to determine the mean and standard deviation (SD). The mean location for a given landmark on a given patient served as the reference point. The mean of the distances from the reference point was used as the consistency, while the SD of this mean was used as a measure of precision. The error in the x, y, and z planes was calculated in order to determine the specific characteristics of each landmark. The consistency in landmark location and precision did not differ significantly among the nine examiners. Sella turcica was the most consistently (0.50 mm) and most precisely (0.23 mm) identified anatomic landmark. The most inconsistent landmark was porion-right (2.72 mm) and the most imprecise landmark was orbitale-right (1.81 mm). Due to the lack of even distribution of the errors, careful use of these landmarks for analysis purposes is needed.     

Automated Identification of Cephalometric Landmarks: Part 2- Might It Be Better Than human?

ObjectivesTo compare detection patterns of 80 cephalometric landmarks identified by an automated identification system (AI) based on a recently proposed deep-learning method, the You-Only-Look-Once version 3 (YOLOv3), with those identified by human examiners.Materials and MethodsThe YOLOv3 algorithm was implemented with custom modifications and trained on 1028 cephalograms. A total of 80 landmarks comprising two vertical reference points and 46 hard tissue and 32 soft tissue landmarks were identified. On the 283 test images, the same 80 landmarks were identified by AI and human examiners twice. Statistical analyses were conducted to detect whether any significant differences between AI and human examiners existed. Influence of image factors on those differences was also investigated.ResultsUpon repeated trials, AI always detected identical positions on each landmark, while the human intraexaminer variability of repeated manual detections demonstrated a detection error of 0.97 ± 1.03 mm. The mean detection error between AI and human was 1.46 ± 2.97 mm. The mean difference between human examiners was 1.50 ± 1.48 mm. In general, comparisons in the detection errors between AI and human examiners were less than 0.9 mm, which did not seem to be clinically significant.ConclusionsAI showed as accurate an identification of cephalometric landmarks as did human examiners. AI might be a viable option for repeatedly identifying multiple cephalometric landmarks.     

Validation and reproducibility of a high-resolution three-dimensional facial imaging system

OBJECTIVE: To assess the accuracy and reproducibility of a high-resolution three-dimensional imaging system (Di3D). DESIGN: The three-dimensional imaging system was validated in vitro using 12 adult facial plaster casts, which had landmarks marked, and the positions of the landmarks on the three-dimensional images captured by Di3D were compared with those obtained by a coordinate measuring machine (CMM). METHODS: Operator error was measured by repeatedly locating landmarks on the three-dimensional image. Reproducibility error of the images was calculated by capturing three-dimensional images of the facial casts on two separate occasions; the Euclidean distance between the two matched sets of coordinates was then calculated. The Di3D system error was assessed by calculating the three-dimensional global positions of landmarks on the three-dimensional images and comparing them with those obtained by CMM (gold standard). RESULTS: The operator error in placement of landmarks on the three-dimensional model was 0.07mm, range 0.02-0.11mm. The reproducibility of the Di3D capture was 0.13mm, range 0.11-0.14mm. The mean distance between the CMM and Di3D landmarks, which constitutes the Di3D system error, was an average of 0.21mm, range 0.14-0.32mm. CONCLUSIONS: The Di3D system error was within 0.2mm, which is clinically acceptable, and offers considerable improvement in stereophotogrammetry for facial capture and analysis.     

Reproducibility of landmark identification in the jaw and teeth on 3-dimensional cone-beam computed tomography images: A preliminary study of tentative methods compared to those based on cephalometric definitions

Objective:To compare the reproducibility of landmark identification on three-dimensional (3D) cone-beam computed tomography (CBCT) images between procedures based on traditional cephalometric definitions (procedure 1) and those tentatively proposed for 3D images (procedure 2).Materials and Methods:A phantom with embedded dried human skull was scanned using CBCT. The acquired volume data were transferred to a personal computer, and 3D images were reconstructed. Eighteen dentists plotted nine landmarks related to the jaws and teeth four times: menton (Me), pogonion (Po), upper-1 (U1), lower-1 (L1), left upper-6 (U6), left lower-6 (L6), gonion (Go), condyle (Cd), and coronoid process (Cp). The plotting reliabilities of the two procedures were compared by calculating standard deviations (SDs) in three components (x, y, and z) of coordinates and volumes of 95% confidence ellipsoid.Results:All 27 SDs for procedure 2 were less than 1 mm, and only five of them exceeded 0.5 mm. The variations were significantly different between the two procedures, and the SDs of procedure 2 were smaller than those of procedure 1 in 21 components of coordinates. The ellipsoid volumes were also smaller for procedure 2 than procedure 1, although a significant difference was not found.Conclusions:Definitions determined strictly on each three sectional images, such as for procedure 2, were required for sufficient reliability in identifying the landmark related to the jaws and teeth.     

Reproducibility of facial soft tissue landmarks on 3D laser‐scanned facial images

Authors – Toma AM, Zhurov A, Playle R, Ong E, Richmond S Background – The three‐dimensional (3D) measuring technology is useful to inspect facial shape in three planes of space (X, Y, and Z). Recent work has been directed to analyse craniofacial morphology using facial soft tissue landmarks to identify facial differences among population. The reproducibility of facial landmarks is almost necessary to ensure accurate 3D facial measurements. Objective – The aim of this study is to assess the reproducibility of facial soft tissue landmarks using laser‐scan 3D imaging technology. Subjects and Methods – Facial landmarks were assessed for 30 15½‐year‐old British‐Caucasian children (15 males and 15 females). The sample was recruited from the Avon Longitudinal Study of Parents and Children (ALSPAC). The 3D facial images were acquired for each subject using two high‐resolution Konica/Minolta laser scanners. Twenty‐one facial landmarks (63 X, Y, and Z coordinates) were identified and recorded on each 3D facial image by two examiners. The reproducibility of landmarks identification at 2‐week interval was assessed for one of the examiners (intra‐examiner). In addition, the reproducibility of landmarks was assessed between the two examiners (inter‐examiner). Using Bland‐Altman plots, both intra‐ and inter‐examiner assessments had evaluated landmarks reproducibility in three dimensions for the sample divided by gender. The reproducibility of the 3D‐coordinates for each landmark was considered under three categories (< 0.5 mm, < 1 mm, and >1 mm) for both intra‐ and inter‐examiner reproducibility assessments. Results – The distribution of coordinates at the three levels of reproducibility show the following percentages: intra‐examiner: < 0.5 mm (38%), < 1 mm (51%), >1 mm (11%); inter‐examiner: < 0.5 mm (35%), < 1 mm (48%), >1 mm (17%). Generally, 10 landmarks were reproducible to less than 1 mm for both intra‐ and inter‐examiner reproducibility assessments. The Labiale Superius was the most reproducible and Palebrale Superius was the least reproducible landmark. Some landmarks showed greater reliability in certain planes of space; the Glabella was more reliable in the Z than the Y axis. Gender differences were found; Subnasale was more reproducible in the Y‐axis in males compared with females. Conclusions – The reproducibility of facial landmarks should be considered in the three planes of space. The majority of X‐Y‐Z coordinates taken to the 21 facial landmarks were reproducible to < 1 mm which is clinically acceptable. The accuracy of landmarks identification ranged from 0.39 to 1.49 mm. The reliability in identification depends on the clarity and definition of each landmark as well as gender characteristics. The different landmarks reproducibility should be considered when evaluating changes related to growth and healthcare interventions.     

The clinical significance of error measurement in the interpretation of treatment results.

The aims of this investigation were to determine the errors involved in cephalometric landmark identification and to link these to the interpretation of treatment results. Fifty cephalograms were randomly selected from patient files and the following were determined. (i) Accuracy of the digitizer--single tracing digitized on five occasions on each of 10 different positions on the digitizer by one observer. (ii) Intra- and inter-observer digitizing error--35 landmarks on the same tracing (on a fixed position) digitized on five occasions by each of four judges. (iii) Intra- and inter-observer tracing error--five separate tracings of 10 different cephalograms by four judges. There were no significant differences in the variances of the co-ordinates for each landmark between the different positions on the digitizer (mean variance x-axis 0.07 mm and y-axis 0.08 mm). (ii) One-way ANOVA showed no significant intra- or inter-observer differences in digitation. (iii) Levene's test for homogeneity of variance showed significant differences in the co-ordinates of different landmarks and between the same landmarks on different cephalograms. Two-way ANOVA showed significant differences between observers for the same landmark that were greater than the intra-observer differences. The results indicate that tracing accuracy is a limiting factor in cephalometry. The variance of each landmark is dependent on the quality of the cephalogram. Inter-observer differences were greater than intra-observer effects and these were random, rather than systematic errors. Minimal error estimation calculations enable discrimination between treatment results and measurement errors.     

Improved Lateral Cephalometric Superimposition Using an Automated Image Fitting Technique

Objective:To test the feasibility of automated lateral cephalometric radiograph (LCR) superimposition using an image fitting algorithm.Materials and Methods:Using radiopaque markers, we identified seven cephalometric landmarks on three dry skulls, took digital LCRs on each in several rotated positions, and used a custom software program (XRay3D) to automatically superimpose each rotated image on the initial image using an anterior cranial base reference. We measured superimposition error at each landmark and adjusted image brightness levels to simulate potential fitting error due to exposure variation.Results:The greatest mean error for 24 image rotation trials of less than 10° was less than 0.5 mm. Rotations of 10° or more were not reliably superimposed. Errors of 0.2–1.6 mm occurred for ±10% brightness but increased exponentially with further brightness alteration.Conclusion:Automated superimposition of LCRs, using this fitting technique, has great potential when rotation is less than 10° and brightness variation is less than 10%.     

X线头影测量人工定点的准确性研究

目的 评价X线头影测量分析中人工定点的准确性。方法 10名口腔正畸医师对同一张X线头颅定位侧位片的29个标志点进行定位获得的数据，与对照值进行对比以衡量定点误差的大小。结果 S,Ar,U1,L1的平均误差小于1.0mm，它们均为影像轮廓清晰且容易判定的标志点；Po,Mes,Co,Gs的平均误差大于4.0mm，这些标志点均为图像轮廓的最突点。结论 人工识别时，28％的标志点存在显著差异，存在显著差异的标志点主要是某一图象轮廓的最突点。     

基于深度学习的二维头影测量定点分析系统的研究

目的 探讨基于深度学习的图像高斯金字塔和卷积神经网络方法,构建和训练一种高精准度的自动化二维头影测量标志点定位与分析系统模型。方法 收集2021年1月至12月期间本院所摄的400张年龄在18至50周岁且无牙列缺损的头颅侧位影像,在3D slicer（NIH美国）上完成每张44个牙颌和颅面软硬组织结构标志点的标注,并构建和训练基于图像高斯金字塔和卷积神经网络的自动化二维头影测量标志点定位和分析系统。结果 运用图像高斯金字塔和卷积神经网络方法能高精准获取44个牙颌和颅面的软硬组织结构标志点,在 2.0 mm、2.5 mm、3.0 mm、4.0 mm 精度范围内预测的平均准确率分别为 85.61 %、90.72 %、93.82 %、96.34 %;44个牙颌和颅面软硬组织结构标志点的平均误差为 1.22 mm,平均标准差为 1.27 mm;常见头影测量项目（ANB、SNA、SNB、ODI、APDI、FHI、FMA、MW）的平均预测准确率为 85.00 % 。结论 运用图像高斯金字塔和卷积神经网络方法能高精准获取牙颌和颅面的软硬组织结构标志点,并且对牙颌和颅面形态分析诊断具有良好的准确性,该技术将有助于推进自动化头影测量的临床运用。     

Evaluation of soft tissue changes around the lips after bracket debonding using three-dimensional stereophotogrammetry

Objective:To evaluate the changes in soft tissue around the lips after orthodontic bracket debonding using three-dimensional (3-D) stereophotogrammetry.Materials and Methods:3-D facial images of 20 subjects (10 men and 10 women; mean age, 26.81 ± 7.23 years) were taken with a white light scanner before and after debonding the labial brackets. Two images acquired from each subject were superimposed, and 15 soft tissue landmarks around the lips were plotted and analyzed. Statistical analysis was performed using both paired and independent t-tests (P < .05).Results:There were no significant changes in position of any landmark on the x (left-right)- or y (vertical)-axes after removal of the brackets. However, the landmarks in the oral commissures and lower lip (LLP, −0.55 mm; Li, −0.44 mm; Ch-L, −0.56 mm, all P < .05) on the z (anteroposterior)-axis showed statistically significant differences. There were no significant positional changes of most landmarks on the x-, y-, or z- axes after bracket removal among the various genders and lip thicknesses.Conclusions:There was a slight retrusion in the oral commissure and lower lip areas after debonding, but no changes were found in the upper lip area. This study showed that 3-D stereophotogrammetry can be useful in evaluating facial soft tissue changes in orthodontic patients.     

Precision of landmark positioning on digitized models from patients with cleft lip and palate.

OBJECTIVE: To quantify the precision of landmark positioning on digitized casts of patients with unilateral cleft lip and palate. PATIENTS: Forty plaster models of newborns up to 8 months of age were selected from the archive of the Department of Orthodontics of the University of Heidelberg. MATERIAL AND METHOD: The plaster-cast models were digitized with a Micromeasure 70 three-dimensional laser scanner (Micromeasure, Bischoffen, Germany). The laser scanner used in this study operates with a precision of 0.15 mm on the x- and y-axes and 0.06 mm on the z-axis. In the intraobserver study, a single observer placed anatomical landmarks in four rounds, with at least 4 weeks between each round. In the interobserver study, four different observers each placed the same landmarks once. For the two different studies, an ideal location for each landmark was calculated by averaging the landmark positions of the four rounds or observers. The distance between each of the four landmark positions and the ideal landmark was measured. RESULTS: A 95% confidence interval for the landmark positioning error was calculated. For the intraobserver investigation, this error was 0.34 to 1.30 mm, and for the interobserver investigation it was 0.7 to 2.00 mm. CONCLUSION: Because both investigations displayed comparable error intervals, it was concluded that different observers could perform landmark positioning for the same studies.     

头影测量标志点计算机自动识别的初步研究

目的初步探讨计算机头影测量自动定点技术。方法随机选择20张头颅侧位片作为待测图像,另选1张高质量的X线片为标准图像。使用仿射变换结合模板匹配的方法来识别标志点。首先在标准图像上手工确定各标志点的位置并建立标志点的标准模板;然后用仿射变换的方法把标志点从标准图像变换到待测图像上,获得标志点的初始位置;最后经模板匹配确定标志点的准确位置。结果共识别出11个硬组织点和10个软组织点。硬组织点平均误差2.28 mm,软组织点平均误差0.77 mm。有4个硬组织标志点的定点误差<2 mm。结论初步建立了头影测量标志点自动识别系统,但整体上标志点识别的准确性尚不能满足临床应用要求。     

Accuracy of landmark identification on postero-anterior cephalograms

ObjectivesThe aim of this study was to examine accuracy in landmark identification on digital postero-anterior cephalograms, (PAC) assessing the intra-observer and the inter-observer repeatability in determining these landmarks.Materials and methodsTwenty postero-anterior digital cephalometric radiographs were randomly selected from data files of patients aged between 11 to 15 years and were used in this study. Thirty-four commonly used PAC landmarks were included in this investigation and each observer performed the determination of all landmarks on every PAC cephalograms twice (T1 and T2). Mean positions located by the three observers in the first recording session both on the x and y axes, were calculated and defined as the “best estimate” for every landmarks. Systematic differences between the two records at T1 and T2 of the same observer were evaluated using the paired t-test with P < 0.05. In order to test the hypothesis of equal mean of the vectors of differences to the “best estimate” for the three raters, a one-way ANOVA test was performed.ResultsMost landmarks showed a good reproducibility between the two recording sessions, except for some landmarks located in the zygomatic arch, mandible and dentition. As regards inter-observer reliability, there were statistically significant differences (P < 0.05) in both x and y axis.ConclusionsEach landmark has its own margin of error and there is a clear difference in the localization accuracy between the x and y coordinates. Since condylar points (CDr-CDl), coronoid points (CORr-CORl) and mental foramen points (MFr-MFl) showed to have a questionable localization accuracy, PAC cannot be strictly recommended for accurate evaluation of any asymmetry. Some dental landmarks seem to be poorly reproducible; therefore the usefulness of postero-anterior cephalometric analysis to evaluate dental discrepancies or maxillo-mandibular molar relationship is questioned.     

Reproducibility of maxillofacial landmark identification on three-dimensional cone-beam computed tomography images of patients with mandibular prognathism: Comparative study of a tentative method and traditional cephalometric analysis

Objective:To clarify the reproducibility of a tentative method for identifying maxillofacial landmarks on three-dimensional (3D) images obtained with cone-beam computed tomography (CBCT) for dental use in patients with mandibular prognathism. Also, the influence of level of experience of dentists applying the method was investigated by dividing them into two groups according to experience.Materials and Methods:Dentists with less (group A) or more (group B) than 3 years of experience of cephalometry and 3D image manipulation analyzed CBCT data from 10 patients using two different landmark identification methods: method 1 used conventional cephalometric definitions and method 2 used detailed landmark identification definitions developed for each cross-sectional plane. The plotting of nine landmarks was performed twice, and 10 coordinate values were obtained for each landmark. To assess reproducibility, the 95% confidence ellipse method was used.Results:Comparative analysis showed that method 2 was highly reproducible. Group B subjects attained smaller ellipsoid volumes than group A subjects, regardless of the landmark identification method used. With method 1, except for condyle and coronoid process, all landmarks showed a higher level of reproducibility in group A subjects than in group B subjects. With method 2, however, five landmarks showed no differences between the methods.Conclusion:The method proposed here may be highly reproducible regardless of the evaluators'' experience.     

三维测量分析单侧完全性唇腭裂术后成年患者的上颌骨形态

目的:探讨单侧完全性唇腭裂术后成年患者的上颌骨形态特征.方法:应用螺旋CT采集30例单侧完全性唇腭裂术后成年患者上颌骨数据,应用SimPlant11.04软件对数据进行三维重建、定点,建立三维坐标系,验证标记点的可重复性,测量标记点到三维坐标平面的距离.应用SAS6.12软件包对数据进行统计学分析.结果:7个居中的标记点中,A、ANS显著偏向健侧(P＜0.01);14对患健侧标记点的非对称率(Q)显示,INM’与INM 、SNM’与SNM、SPr’与SPr在到矢状面S的距离存在明显不对称畸形,而其余多数点在三维方向上无不对称畸形;患者上颌骨与正常人的主要不同是在前后方向上存在发育不足,患侧上颌骨错位较健侧明显.结论:应用螺旋CT及SimPlant 11.04软件三维测量上颌骨形态的方法,能够精确测量各标记点到坐标的三维距离,可用于评估患者患、健侧上颌骨的畸形程度.     

Relevant research from orthodontic journals

Abstract

The aim of this randomized, controlled, prospective study was to determine the reliability of computed lateral cephalometry (Fuji Medical Systems, Tokyo, Japan) in terms of landmark identification compared to conventional lateral cephalometry (CAWO, Schrobenhausen, Germany). To assess the reliability of landmark identification on lateral cephalographs, 20 computed images, taken at 30 per cent reduced radiation (70 kV, 15 mA, 0.35 s) were compared to 20 conventional images (70 kV, 15 mA, 0.5 s). The 40 lateral cephalographs were taken from 20 orthodontic patients at immediate post-treatment and 1 year after retention. The order and type of imaging was randomized. Five orthodontists identified eight skeletal, four dental and five soft tissue landmarks on each of the 40 films. The error of identification was analysed in the XY Cartesian co-ordinate following digitization. Skeletal landmarks exhibited characteristic dispersion with respect to the Cartesian co-ordinates. Root apices were more variable than crown tips. Soft tissue landmarks were more consistent in the X co-ordinate. Two-way ANOVA shows that there is no significant difference between the two imaging systems in both co-ordinates (P > 0.05). Moreover, the differences are generally small (< 0.5 mm), and are unlikely to be of clinical significance. Most of the variables attained statistical power of at least 0.8 in the X-co-ordinate while only the dental landmarks achieved statistical power of at least 0.78 in the Y-co-ordinate. Based on the results of the study: (1) computed lateral cephalographs can be taken at 30 per cent radiation reduction, compared to conventional lateral cephalograph; (2) each anatomical landmark exhibits its characteristic dispersion of error in both the Cartesian co-ordinates; (3) there is no trend between the two imaging systems, with equivocal result, and none of the landmarks attained statistical significance when both raters and imaging systems are considered as factorial variables; (4) the random error of raters in landmark identification after replicate tracing was highlighted and needs to be taken into consideration in all studies involving landmark identification.     

Reliability of a coordinate system based on anatomical landmarks of the maxillofacial skeleton: an evaluation method for three-dimensional images obtained by cone-beam computed tomography

Objectives  We propose a method for evaluating the reliability of a coordinate system based on maxillofacial skeletal landmarks and use it to assess two coordinate systems. Methods  Scatter plots and 95% confidence ellipses of an objective landmark were defined as an index for demonstrating the stability of the coordinate system. A head phantom was positioned horizontally in reference to the Frankfurt horizontal and occlusal planes and subsequently scanned once in each position using cone-beam computed tomography. On the three-dimensional images created with a volume-rendering procedure, six dentists twice set two different coordinate systems: coordinate system 1 was defined by the nasion, sella, and basion, and coordinate system 2 was based on the left orbitale, bilateral porions, and basion. The menton was assigned as an objective landmark. Results  The scatter plot and 95% ellipse of the menton indicated the high-level reliability of coordinate system 2. The patterns with the two coordinate systems were similar between data obtained in different head positions. Conclusions  The method presented here may be effective for evaluating the reliability (reproducibility) of coordinate systems based on skeletal landmarks.