Quantification of accuracy of the automated nonlinear image matching and anatomical labeling (ANIMAL) nonlinear registration algorithm for 4D CT images of lung

The performance of the ANIMAL (Automated Nonlinear Image Matching and Anatomical Labeling) nonlinear registration algorithm for registration of thoracic 4D CT images was investigated. The algorithm was modified to minimize the incidence of deformation vector discontinuities that occur during the registration of lung images. Registrations were performed between the inhale and exhale phases for five patients. The registration accuracy was quantified by the cross-correlation of transformed and target images and distance to agreement (DTA) measured based on anatomical landmarks and triangulated surfaces constructed from manual contours. On average, the vector DTA between transformed and target landmarks was 1.6 mm. Comparing transformed and target 3D triangulated surfaces derived from planning contours, the average target volume (GTV) center-of-mass shift was 2.0 mm and the 3D DTA was 1.6 mm. An average DTA of 1.8 mm was obtained for all planning structures. All DTA metrics were comparable to inter observer uncertainties established for landmark identification and manual contouring.     

The effect of automated landmark identification on morphometric analyses

Morphometric analysis of anatomical landmarks allows researchers to identify specific morphological differences between natural populations or experimental groups, but manually identifying landmarks is time‐consuming. We compare manually and automatically generated adult mouse skull landmarks and subsequent morphometric analyses to elucidate how switching from manual to automated landmarking will impact morphometric analysis results for large mouse (Mus musculus) samples (n = 1205) that represent a wide range of ‘normal’ phenotypic variation (62 genotypes). Other studies have suggested that the use of automated landmarking methods is feasible, but this study is the first to compare the utility of current automated approaches to manual landmarking for a large dataset that allows the quantification of intra‐ and inter‐strain variation. With this unique sample, we investigated how switching to a non‐linear image registration‐based automated landmarking method impacts estimated differences in genotype mean shape and shape variance‐covariance structure. In addition, we tested whether an initial registration of specimen images to genotype‐specific averages improves automatic landmark identification accuracy. Our results indicated that automated landmark placement was significantly different than manual landmark placement but that estimated skull shape covariation was correlated across methods. The addition of a preliminary genotype‐specific registration step as part of a two‐level procedure did not substantially improve on the accuracy of one‐level automatic landmark placement. The landmarks with the lowest automatic landmark accuracy are found in locations with poor image registration alignment. The most serious outliers within morphometric analysis of automated landmarks displayed instances of stochastic image registration error that are likely representative of errors common when applying image registration methods to micro‐computed tomography datasets that were initially collected with manual landmarking in mind. Additional efforts during specimen preparation and image acquisition can help reduce the number of registration errors and improve registration results. A reduction in skull shape variance estimates were noted for automated landmarking methods compared with manual landmarking. This partially reflects an underestimation of more extreme genotype shapes and loss of biological signal, but largely represents the fact that automated methods do not suffer from intra‐observer landmarking error. For appropriate samples and research questions, our image registration‐based automated landmarking method can eliminate the time required for manual landmarking and have a similar power to identify shape differences between inbred mouse genotypes.     

A population level atlas of Mus musculus craniofacial skeleton and automated image‐based shape analysis

Laboratory mice are staples for evo/devo and genetics studies. Inbred strains provide a uniform genetic background to manipulate and understand gene–environment interactions, while their crosses have been instrumental in studies of genetic architecture, integration and modularity, and mapping of complex biological traits. Recently, there have been multiple large‐scale studies of laboratory mice to further our understanding of the developmental basis, evolution, and genetic control of shape variation in the craniofacial skeleton (i.e. skull and mandible). These experiments typically use micro‐computed tomography (micro‐CT) to capture the craniofacial phenotype in 3D and rely on manually annotated anatomical landmarks to conduct statistical shape analysis. Although the common choice for imaging modality and phenotyping provides the potential for collaborative research for even larger studies with more statistical power, the investigator (or lab‐specific) nature of the data collection hampers these efforts. Investigators are rightly concerned that subtle differences in how anatomical landmarks were recorded will create systematic bias between studies that will eventually influence scientific findings. Even if researchers are willing to repeat landmark annotation on a combined dataset, different lab practices and software choices may create obstacles for standardization beyond the underlying imaging data. Here, we propose a freely available analysis system that could assist in the standardization of micro‐CT studies in the mouse. Our proposal uses best practices developed in biomedical imaging and takes advantage of existing open‐source software and imaging formats. Our first contribution is the creation of a synthetic template for the adult mouse craniofacial skeleton from 25 inbred strains and five F1 crosses that are widely used in biological research. The template contains a fully segmented cranium, left and right hemi‐mandibles, endocranial space, and the first few cervical vertebrae. We have been using this template in our lab to segment and isolate cranial structures in an automated fashion from a mixed population of mice, including craniofacial mutants, aged 4–12.5 weeks. As a secondary contribution, we demonstrate an application of nearly automated shape analysis, using symmetric diffeomorphic image registration. This approach, which we call diGPA, closely approximates the popular generalized Procrustes analysis (GPA) but negates the collection of anatomical landmarks. We achieve our goals by using the open‐source advanced normalization tools (ANT) image quantification library, as well as its associated R library (ANTsR) for statistical image analysis. Finally, we make a plea to investigators to commit to using open imaging standards and software in their labs to the extent possible to increase the potential for data exchange and improve the reproducibility of findings. Future work will incorporate more anatomical detail (such as individual cranial bones, turbinals, dentition, middle ear ossicles) and more diversity into the template.     

Alignment of CT images of skull dysmorphology using anatomy-based perpendicular axes

Rigid body registration of 3D CT scans, based on manual identification of homologous landmarks, is useful for the visual analysis of skull dysmorphology. In this paper, a robust and simple alignment method was proposed to allow for the comparison of skull morphologies, within and between individuals with craniofacial anomalies, based on 3D CT scans, and the minimum number of anatomical landmarks, under rigidity and uniqueness constraints. Three perpendicular axes, extracted from anatomical landmarks, define the absolute coordinate system, through a rigid body transformation, to align multiple CT images for different patients and acquisition times. The accuracy of the alignment method depends on the accuracy of the localized landmarks and target points. The numerical simulation generalizes the accuracy requirements of the alignment method. Experiments using a human dried skull specimen, and ten sets of skull CT images (the pre- and post-operative CT scans of four plagiocephaly, and one fibrous dysplasia patients), demonstrated the feasibility of the technique in clinical practice.     

Size and shape changes during late fetal growth (137–157 gestational days) in the pigtailed macaque (Macaca nemestrina) craniofacial complex: An application using three‐dimensional coordinate data and finite element scaling analysis

Form changes within the fetal pigtailed macaque (Macaca nemestrina) craniofacial complex was documented using finite element scaling analysis (FESA) and three‐dimensional (3D) coordinate data for 35 craniofacial landmarks. Coordinate data were digitized from 3D reconstructions of computed tomography (CT) images and 2D axial slices. Twenty‐two fetal pigtailed macaques ranging in age from 137 to 157 gestational days were included (in this species, birth is estimated at 170 gestational days). The null hypothesis that the craniofacial complex grows with isometry during late fetal growth of the craniofacial complex was tested (P < 0.05), and the prediction that morphological change along an anteroposterior axis dominates late fetal growth was also investigated. The null hypothesis was rejected, indicating that allometric growth is present during late fetal growth. Growth along an anteroposterior axis is localized in the palate and mandible. The neurocranium grows along a superoinferior axis, while the neurofacial junction displays growth along both the anteroposterior and superoinferior axes. Mediolateral changes are localized between asterions, the external auditory meati, and maxillary and mandibular alveolar points. Finally, a 3D model of craniofacial growth for this species was created, localizing size and shape changes that occur during late fetal growth for each of the 35 craniofacial landmarks defined in this study. Anat Rec 267:307–320, 2002. © 2002 Wiley‐Liss, Inc.     

Rapid automated landmarking for morphometric analysis of three‐dimensional facial scans

Automated phenotyping is essential for the creation of large, highly standardized datasets from anatomical imaging data. Such datasets can support large‐scale studies of complex traits or clinical studies related to precision medicine or clinical trials. We have developed a method that generates three‐dimensional landmark data that meet the requirements of standard geometric morphometric analyses. The method is robust and can be implemented without high‐performance computing resources. We validated the method using both direct comparison to manual landmarking on the same individuals and also analyses of the variation patterns and outlier patterns in a large dataset of automated and manual landmark data. Direct comparison of manual and automated landmarks reveals that automated landmark data are less variable, but more highly integrated and reproducible. Automated data produce covariation structure that closely resembles that of manual landmarks. We further find that while our method does produce some landmarking errors, they tend to be readily detectable and can be fixed by adjusting parameters used in the registration and control‐point steps. Data generated using the method described here have been successfully used to study the genomic architecture of facial shape in two different genome‐wide association studies of facial shape.     

Landmark Typology in Applied Morphometrics Studies: What's the Point?

Landmarks are the hallmark of biological shape analysis as discrete anatomical points of correspondence. Various systems have been developed for their classification. In the most widely used system, developed by Bookstein in the 1990s, landmarks are divided into three distinct types based on their anatomical locations and biological significance. As Bookstein and others have argued that different landmark types possess different qualities, e.g., that Type 3 landmarks contain deficient information about shape variation and are less reliably measured, researchers began using landmark types as justification for selecting or avoiding particular landmarks for measurement or analysis. Here, we demonstrate considerable variation in landmark classifications among 17 studies using geometric morphometrics (GM), due to disagreement in the application of both Bookstein's landmark typology and individual landmark definitions. A review of the literature furthermore shows little correlation between landmark type and measurement reproducibility, especially when factors such as differences in measurement tools (calipers, digitizer, or computer software) and data sources (dry crania, 3D models, or 2D images) are considered. Although landmark typology is valuable when teaching biological shape analysis, we find that employing it in research design introduces confusion without providing useful information. Instead, researchers should choose landmark configurations based on their ability to test specific research hypotheses, and research papers should include justifications of landmark choices along with landmark definitions, details on landmark collection methods, and appropriate interobserver and intraobserver analyses. Hence, while the landmarks themselves are crucial for GM, we argue that their typology is of little use in applied studies. Anat Rec, 302:1144–1153, 2019. © 2018 Wiley Periodicals, Inc.     

Measurement of acetabular version based on biplanar radiographs with 3D reconstructions in comparison to CT as reference standard in cadavers

To quantify acetabular version using 3 D reconstructions based on biplanar radiographs (BPR) with CT as reference standard. No institutional review board approval was needed. Nine dry‐bone pelvises underwent BPR in five different positions (rotation/tilt). The 3 D models of each pelvis were reconstructed by two radiologists on the basis of anatomical landmarks using semi‐automated software. Automated software was used to assess the 3 D models and to calculate acetabular versions perpendicular to the anterior pelvic plane on all levels in the craniocaudal direction in 1 mm steps. Transverse CT images perpendicular to the anterior pelvic plain were reconstructed through the acetabulum in 1 mm steps. Both readers measured acetabular version on each image. Inter‐reader agreement was calculated. Measurements based on BPR and CT were compared. Inter‐reader agreement was almost perfect for BPR‐based acetabular version measurements (ICC (intraclass correlation coefficient) = 0.920, P < 0.0005) and CT (ICC = 0.990, P < 0.0005). Correlation of acetabular versions between the five BPR‐positions was substantial/almost perfect (ICC = 0.722–0.887 and 0.749–0.872 for readers 1 and 2, respectively; most P < 0.0005). The acetabular version measurements between the ap‐positioning from BPR and CT showed moderate agreement (mean CCC (concordance correlation coefficient) = 0.733 for reader 1, CCC = 0.755 for reader 2). Acetabular version on multiple levels can be measured using BPR and dedicated post‐processing software and is relatively independent of pelvic rotation and tilt. Clin. Anat. 30:591–598, 2017. © 2017 Wiley Periodicals, Inc.     

Comparison of mandibular landmarks from computed tomography and 3D digitizer data

We recorded 3D coordinates for 28 mandibular landmarks from three-dimensional reconstructions of CT axial slices using the image analysis program eTDIPS. The images were acquired from a pediatric series of human mandibles (neonate to 13 years of age) from the Bosma collection (Shapiro and Richtsmeier, 1997, Am. J. Phys. Anthropol. 103:415-416). To test the accuracy of these coordinate data, we recorded the same 28 landmarks directly on the Bosma mandibles using a Polhemus 3Space digitizer. The directly digitized landmarks serve as a gold standard upon which to evaluate the eTDIPS data. Standard deviations of landmark placement using eTDIPS show a greater degree of variation compared to the data gathered using the digitizer, although this error is more heavily concentrated in certain types of landmarks. All possible linear distances between unique pairs of landmarks were calculated, and like linear distances were compared between the two data collection methods. The absolute difference for all like linear distances ranged from 0.001-3.9 mm (mean = 0.377 mm; SD = 1.136), with the eTDIPS data being consistently larger than the digitizer coordinates. This study demonstrates that landmark coordinate data can be reliably collected from digital CT images of the human mandible. We define a set of mandibular landmarks useful in evaluating the effects of craniofacial disorders, growth and other biological processes.     

Deformable registration of 4D computed tomography data

Four-dimensional radiotherapy requires deformable registration to track delivered dose across varying anatomical states. Deformable registration based on B-splines was implemented to register 4D computed tomography data to a reference respiratory phase. To assess registration performance, anatomical landmarks were selected across ten respiratory phases in five patients. These point landmarks were transformed according to global registration parameters between different respiratory phases. Registration uncertainties were computed by subtraction of transformed and reference landmark positions. The selection of appropriate registration masks to separate independently moving anatomical subunits is crucial to registration performance. The average registration error for five landmarks for each of five patients was 2.1 mm. This level of accuracy is acceptable for most radiotherapy applications.     

A semi-automated method using interpolation and optimisation for the 3D reconstruction of the spine from bi-planar radiography: a precision and accuracy study

The 3D reconstruction of the spine in upright posture can be obtained by bi-planar radiographic methods, developed since the 1970s. The principle is to identify 4–25 anatomical landmarks per vertebrae and per images. This identification time is hardly manageable in clinical practice. A semi-automated method is used: 3D standard vertebral models are positioned along with a 3D curve (identified all the way through the vertebral bodies). The silhouettes of the models of C7 and L5 vertebrae are first adjusted and the positions of the other vertebrae are interpolated and optimised. The inter- and intra-operator variabilities and the errors between the semi-automated method and the manual identification of six anatomical landmarks per vertebra are evaluated on 20 pairs of X-ray images of subjects with different spinal deformities. The identification time for the semi-automated method is 5 min. For scolitic subjects, the precision is under 2.2° and the accuracy is under 3.2° for all lateral, sagittal and axial rotations.     

Cross‐ and Triple‐Ratios of Human Body Parts During Development

Recently developed landmark‐based geometric morphometry has been used to depict the morphological development of organisms. In geometry, four landmarks can be mapped to any other four by Möbius transformations, if the cross‐ratio of the landmarks is invariant and vice versa. To geometrically analyze the morphological development of the human body, we examined the cross‐ratio of three consecutive body parts that are segmented by four landmarks in their configuration. Moreover, we introduced the triple‐ratio of five landmarks that segments four consecutive parts (e.g., the shoulder, upper arm, forearm, and hand) and examined their growth patterns. The cross‐ and triple‐ratios of the upper limb and shoulder girdle in fetuses were constant when biomechanical landmarks were used, although the cross‐ratio of the upper limb varied when anatomical landmarks were used. The cross‐ratios of the lower limbs, trunk, and pelvic girdles in fetuses differed from their corresponding cross‐ratios in adults. These results suggest Möbius growth in the fetal upper limb and shoulder girdle but not in the other body parts examined. However, the growth balance of the three contiguous body parts was represented by the developmental change in the cross‐ratio. Therefore, the cross‐ and triple‐ratios may be applicable for simple but significant assessments of growth balance or proportion of the body parts. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Evaluation of two 3D virtual computer reconstructions for comparison of cleft lip and palate to normal fetal microanatomy

Cleft lip and palate reconstructive surgery requires thorough knowledge of normal and pathological labial, palatal, and velopharyngeal anatomy. This study compared two software algorithms and their 3D virtual anatomical reconstruction because exact 3D micromorphological reconstruction may improve learning, reveal spatial relationships, and provide data for mathematical modeling. Transverse and frontal serial sections of the midface of 18 fetal specimens (11th to 32nd gestational week) were used for two manual segmentation approaches. The first manual segmentation approach used bitmap images and either Windows-based or Mac-based SURFdriver commercial software that allowed manual contour matching, surface generation with average slice thickness, 3D triangulation, and real-time interactive virtual 3D reconstruction viewing. The second manual segmentation approach used tagged image format and platform-independent prototypical SeViSe software developed by one of the authors (F.W.). Distended or compressed structures were dynamically transformed. Registration was automatic but allowed manual correction, such as individual section thickness, surface generation, and interactive virtual 3D real-time viewing. SURFdriver permitted intuitive segmentation, easy manual offset correction, and the reconstruction showed complex spatial relationships in real time. However, frequent software crashes and erroneous landmarks appearing "out of the blue," requiring manual correction, were tedious. Individual section thickness, defined smoothing, and unlimited structure number could not be integrated. The reconstruction remained underdimensioned and not sufficiently accurate for this study's reconstruction problem. SeViSe permitted unlimited structure number, late addition of extra sections, and quantified smoothing and individual slice thickness; however, SeViSe required more elaborate work-up compared to SURFdriver, yet detailed and exact 3D reconstructions were created.     

Impact of Resolution and Texture of Laser Scanning Generated Three-Dimensional Models on Landmark Identification

The aim of the study was to determine the impact of the resolution and texture of three-dimensional (3D) models created through laser scanning on the measurement error (ME) of craniometric landmarks. Ten skulls were scanned at five different resolutions, and the generated 3D models were exported with and without texture. The 3D coordinates of 28 landmarks were derived. Each landmark was picked five times by one observer. The ME of a definite landmark was calculated as an average of distances between the repeated placements of the landmark by the observer and the landmark centroid. One-way analysis of variance was applied for detection of significant differences in the MEs between and within landmark types recorded at different resolutions. The MEs of landmark types in textured and nontextured models were compared by a paired test. Twelve linear measurements were calculated as interlandmark distances, and their values obtained on the models of different resolution were compared. The Frankfurt horizontal plane was constructed for each model and its deviation was calculated at different resolutions. Scan resolution impacted MEs of Type 1 and Type 2 landmarks but not the precision level of Type 3 landmarks. Texture most influenced the precise identification of Type 1 landmarks. The interlandmark distances between Type 2 landmarks were most consistent in their values, those between Type 1 landmarks showed deviations in low-resolution models, and distances between Type 3 landmarks demonstrated various patterns of transition of the values throughout the resolutions. Altogether, the use of textured high-resolution models would be preferable in morphometric studies. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1950–1965, 2020. © 2019 American Association for Anatomy     

Measurement error in μCT‐based three‐dimensional geometric morphometrics introduced by surface generation and landmark data acquisition

Computed‐tomography‐derived (CT‐derived) polymesh surfaces are widely used in geometric morphometric studies. This approach is inevitably associated with decisions on scanning parameters, resolution, and segmentation strategies. Although the underlying processing steps have been shown to potentially contribute artefactual variance to three‐dimensional landmark coordinates, their effects on measurement error have rarely been assessed systematically in CT‐based geometric morphometric studies. The present study systematically assessed artefactual variance in landmark data introduced by the use of different voxel sizes, segmentation strategies, surface simplification degrees, and by inter‐ and intra‐observer differences, and compared their magnitude to true biological variation. Multiple CT‐derived surface variants of the anuran (Amphibia: Anura) pectoral girdle were generated by systematic changes in the factors that potentially influence the surface geometries. Twenty‐four landmarks were repeatedly acquired by different observers. The contribution of all factors to the total variance in the landmark data was assessed using random‐factor nested permanova s. Selected sets of Euclidean distances between landmark sets served further to compare the variance among factor levels. Landmark precision was assessed by landmark standard deviation and compared among observers and days. Results showed that all factors, except for voxel size, significantly contributed to measurement error in at least some of the analyses performed. In total, 6.75% of the variance in landmark data that mimicked a realistic biological study was caused by measurement error. In this landmark dataset, intra‐observer error was the major source of artefactual variance followed by inter‐observer error; the factor segmentation contributed < 1% and slight surface simplification had no significant effect. Inter‐observer error clearly exceeded intra‐observer error in a different landmark dataset acquired by six partly inexperienced observers. The results suggest that intra‐observer error can potentially be reduced by including a training period prior to the actual landmark acquisition task and by acquiring landmarks in as few sessions as possible. Additionally, the application of moderate and careful surface simplification and, potentially, also the use of case‐specific optimal combinations of automatic local thresholding algorithms and parameters for segmentation can help reduce intra‐observer error. If landmark data are to be acquired by several observers, it is important to ensure that all observers are consistent in landmark identification. Despite the significant amount of artefactual variance, we have shown that landmark data acquired from microCT‐derived surfaces are precise enough to study the shape of anuran pectoral girdles. Yet, a systematic assessment of measurement error is advisable for all geometric morphometric studies.     

经喙突肩胛骨关节盂螺钉内固定的最优化计算机辅助测量

目的 探讨最优化计算机辅助解剖测量技术,为经喙突肩胛骨关节盂螺钉内固定提供解剖学基础。方法 取肩胛骨CT数据30份,进行精确的三维重建得到肩胛骨数字模型。首先为使用单螺钉的内固定方法设计最优化目标函数,并在约束条件下自动计算其最佳位置;然后结合主元分析,搜索和确定使用双螺钉内固定方法的进钉位置;最后用统计方法分析测量结果,并设计新的解剖测量参考体系。结果 使用单螺钉时,进针点P到肩峰前外侧最突起点X的距离为(39.15±2.28)mm、到喙突前内点Y为(28.66±2.68)mm、到上角点Z为(61.13±6.57)mm; PX、PY 之间的夹角为(81.27±7.15)°,PX、PZ 之间的夹角为(133.27±6.84)°;对于进钉方向,螺钉与 PX的夹角为(104.08±4.41)°,与PY的夹角为(10129±351)°,与PZ 之间的夹角为(76.23±5.03)°。 使用双螺钉时,进针点E与原单螺钉的进针点之间的距离为(5.12±1.37)mm,进针点F与原单螺钉的进针点之间的距离为(3.88±0.94)mm; 两进针点的连线与长轴方向之间的夹角为(27.41±3.51)°。结论 最优化计算机辅助解剖测量是一种非常有效的新测量技术,克服了传统手工实物解剖测量的很多缺点,并且方便设计新的解剖测量参考体系和临床手术方案。     

Size and shape changes during late fetal growth (137-157 gestational days) in the pigtailed macaque (Macaca nemestrina) craniofacial complex: an application using three-dimensional coordinate data and finite element scaling analysis

Form changes within the fetal pigtailed macaque (Macaca nemestrina) craniofacial complex was documented using finite element scaling analysis (FESA) and three-dimensional (3D) coordinate data for 35 craniofacial landmarks. Coordinate data were digitized from 3D reconstructions of computed tomography (CT) images and 2D axial slices. Twenty-two fetal pigtailed macaques ranging in age from 137 to 157 gestational days were included (in this species, birth is estimated at 170 gestational days). The null hypothesis that the craniofacial complex grows with isometry during late fetal growth of the craniofacial complex was tested (P < 0.05), and the prediction that morphological change along an anteroposterior axis dominates late fetal growth was also investigated. The null hypothesis was rejected, indicating that allometric growth is present during late fetal growth. Growth along an anteroposterior axis is localized in the palate and mandible. The neurocranium grows along a superoinferior axis, while the neurofacial junction displays growth along both the anteroposterior and superoinferior axes. Mediolateral changes are localized between asterions, the external auditory meati, and maxillary and mandibular alveolar points. Finally, a 3D model of craniofacial growth for this species was created, localizing size and shape changes that occur during late fetal growth for each of the 35 craniofacial landmarks defined in this study.     

Detecting the Shape Differences of the Corpus Callosum in Behçet's Disease by Statistical Shape Analysis

The aim of this study was to assess the shape differences of the corpus callosum (CC) in patients with Behçet's disease using statistical shape analysis (SSA). Additionally, an attempt was made to investigate the changes in CC size according to disease duration. Twenty‐five adults with clinically diagnosed Behçet's disease and 25 age‐ and gender‐matched controls were examined by high‐resolution structural magnetic resonance imaging. The data obtained from the coordinate of landmarks were analyzed with Euclidean distance matrix analysis and a thin‐plate spline analysis. SSA and growth curve models were performed to investigate group differences and to fit the curves. A significant difference was determined between CC shape of Behçet patients and controls (P = 0.006). Based on the analysis, a decrease occurred in the CC size of the Behçet patients as the duration of disease increased. Maximum deformations were determined in the landmarks of interior notch of the splenium, inferior tip of the splenium, posterior‐most point of the CC, and topmost point of the CC. Similarly, the landmark of anterior‐most point of the CC was identified as having the minimum deformation. Behçet patients had significantly different CC shapes from control subjects. The results suggest that SSA is a promising tool for distinguishing Behçet patients from normal subjects, and that it can give useful information to assist clinicians. Additionally, SSA might be applied to detect shape differences in anatomical structures that are affected by a broad range of neurological diseases. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Automated Method for Computing the Morphological and Clinical Parameters of the Proximal Femur Using Heuristic Modeling Techniques

Bone morphology and morphometric measurements of the lower limb provide significant and useful information for computer-assisted orthopedic surgery planning and intervention, surgical follow-up evaluation, and personalized prosthesis design. Femoral head radius and center, neck axis and size, femoral offset and shaft axis are morphological and functional parameters of the proximal femur utilized both in diagnosis and therapy. Obtaining this information from image data without any operator supervision or manual editing remains a practical objective to avoid variability intrinsic in the manual analysis. In this article, we propose a heuristic method that automatically computes the proximal femur morphological parameters by processing the mesh surface of the femur. The surface data are sequentially processed using geometrical properties such as symmetries, asymmetries, and principal elongation directions. Numerical methods identify the axis of the shaft of femur (least squares cylinder fitting), the head surface and center (least squares sphere fitting), and the femur neck axis and radius (minimal area of the cross section by evolutionary optimization). The repeatability of the method was tested upon 20 femur (10 left + 10 right) surfaces reconstructed from CT scans taken on cadavers. The repeatability error of the automated computation of anatomical landmarks, angles, sizes, and axes was less than 1.5 mm, 2.5°, 1.0 mm, and 3.5 mm, respectively. The computed parameters were in good agreement (landmark difference: <2.0 mm; angle difference: <2.0°; axes difference: <2.5°; size difference: <1.5 mm) with the corresponding reference parameters manually identified in the original CT images by medical experts. In conclusion, the proposed method can improve the degree of automation of model-based hip replacement surgical systems.     

The accuracy of image registration for the brain and the nasopharynx using external anatomical landmarks

We investigated the accuracy of 3D image registration using markers that are repeatedly applied to external anatomical landmarks on the head. The purpose of this study is to establish a lower limit of the errors that would occur in, for instance, MRI-SPECT matching, which in some situations can only be achieved using external landmarks. Marker matching was compared with (single-modality) volume matching for 20 MRI scans. The results were compared with a published expression for the target registration error (TRE) which gives the 3D distribution of the mismatch between both scans. It was found that the main error source is reapplying the external markers on the anatomical landmarks. The published expression describes the relative distribution of the TRE in space well, but tends to underestimate the actual registration error. This deviation is due to anisotropy in the error distribution of the marker position (errors in the direction perpendicular to the skin surface are in general much smaller than errors in other directions). A simulation of marker matching with anisotropy in the errors confirmed this finding. With four reapplied markers, the TRE is 6 mm or smaller in most regions of the head.