Interlaboratory comparison of femur surface reconstruction from CT data compared to reference optical 3D scan
© The Author(s) 2018
Received: 17 May 2017
Accepted: 23 February 2018
Published: 2 March 2018
The present study contrasts the accuracy of different reconstructed models with distinctive segmentation methods performed by various experts. Seven research groups reconstructed nine 3D models of one human femur based on an acquired CT image using their own computational methods. As a reference model for accuracy assessment, a 3D surface scan of the human femur was created using an optical measuring system. Prior to comparison, the femur was divided into four areas; “neck and greater trochanter”, “proximal metaphysis”, “diaphysis”, and “distal metaphysis”. The deviation analysis was carried out in GEOMAGIC studio v.2013 software.
The results revealed that the highest deviation errors occurred in “neck and greater trochanter” area and “proximal metaphysis” area with RMSE of 0.84 and 0.83 mm respectively.
In conclusion, this study shows that the average deviation of reconstructed models prepared by experts with various methods, skills and software from the surface 3D scan is lower than 0.79 mm, which is not a significant discrepancy.
Over the past decade, the application of medical imaging technology in clinical diagnostics and therapy has expanded to diverse approaches such as evaluation of joint biomechanics, patient specific implant development and evaluation, statistical modelling, three-dimensional (3D) printing and rapid prototyping, computer-assisted surgery, and preoperative planning [1–4]. In order to examine the biomechanical behavior of human joints and tissues for all above-mentioned applications, subject specific image based finite element (FE) analysis has been used as the most commonly used method . Extracting the bone geometry from medical images, generating an optimum FE mesh, assigning proper material properties, and defining actual boundary conditions are the main inputs for FE analysis , and therefore their accuracy affects the precision of the FE analysis result . The file format for performing 3D analysis is different from medical image formats for computed topography (CT) to magnetic resonance imaging (MRI). Digital imaging and communication in medicine (DICOM) file formats must be converted to a format readable by CAD or finite element software for further 3D analyses, e.g. the stereolithography (STL) format. The first milestone of construction workflow of image-based biomechanical analysis is accurate segmentation (extracting desired bone geometry from medical image data) from source data [8–10]. Therefore, FE analysis for the aforementioned purposes requires accurate 3D shape representation of bones. This is fundamental to obtain segmented bone data as authentic as possible to the patient’s morphology. Since there are many commercial segmentation software packages and algorithms, The STL models segmented with commercially available software packages may have discrepancies compared to the actual bone, and the accuracy of the segmented bone could then vary based on the segmentation method and operator’s skills. Hence, the accuracy assessment of 3D reconstructed bone based on medical images has been recently investigated extensively [8, 11–25]. Yet, it is concerned that such segmented models do not represent the accuracy of the original bone in a FE model. Therefore, the purpose of this study is to investigate the effect of using different segmentation methodologies conducted by experts with different experiences and skills through a round robin test including seven biomechanics laboratories. The deviation of segmented bone models from the cadaver bone geometry obtained by optical 3D scanning was investigated and the discrepancies between reconstructed models from CT images and the model obtained from optical 3D scanning was quantified.
CT scan acquiring
The CT image of the right femur of a 58 year-old male cadaver was acquired from Trauma Center Murnau with a SOMATOM Definition AS + CT scanner (Siemens AG, Erlangen, Germany). This unique CT image was used by all seven laboratories for segmentation. Soft tissues were removed from the bone prior to the scan. The CT image was saved as DICOM with resolution of 0.29 × 0.29 mm and slice thickness of 0.6 mm for deviation analysis. To reduce partial volume effects, the femur was scanned in a water bath. In order to achieve a calibrated scan, a bone mineral density phantom was scanned in the same setup.
Optical 3D digitization
Optical 3D scanner system specifications
Measuring field (xyz) 500
500 × 500 (mm2)
Distance between points
MV500: 0.009/0.030/0.017 (mm)
2048 × 2048 (4 megapixels)
690 (W) × 220 (H) × 160 (D) (mm)
Reconstruction of 3D models
Segmentation information such as segmentation software, time taken for segmentation, and segmentation method for each participant
Semi-automatic + manuel editing (3-Matic v.10)
Semi-automatic + manuel editing (MeshLab 1.3.4)
YaDiv 1.0 beta 5
Semi-automatic + manuel editing (MeshLab 1.3.4)
Semi-automatic + manuel editing
Semi-automatic + manuel editing (Geomagic Studio v.2012)
Semi-automatic + manuel editing (Geomagic Studio v.2012)
Full-automatic + manual editing
Semi-automatic + manuel editing (Geomagic Studio v.2013)
Semi-automatic + manuel editing (3-Matic v.9)
Average deviation of four different parts of femur
Average deviation positive (mm)
Average deviation negative (mm)
Standard deviation (mm)
Average percentage errors of surface area (%)
Neck and greater trochanter area
Finite element models are commonly used based on specific geometrical characteristics extracted from medical imaging data. This study presents a deviation analysis to evaluate different segmentation methods based on CT scan compared to optical 3D surface scan of the same bone. Thereby, the reconstruction results of seven different biomechanics laboratories were compared to evaluate how human skills, methods of segmentation, and different software packages can cause imprecision in image-based reconstructed models.
This study investigated a variety of conditions, which may have influenced the accuracy of the segmentation process. The segmentations of “neck and greater trochanter” area and “proximal metaphysis” showed the greatest deviations with RMSE of 0.84 and 0.83 mm respectively (Table 3). Thevenot et al.  reported the accuracy of a novel method for automatically reconstructed 3D model from 2D hip radiograph and Verim et al.  evaluated the reconstructed proximal femur from different images of different devices. They both found that the greatest error happened in the trochanter area which is in good agreement with our results. Vaananen et al.  assessed the 3D shape of proximal femur using two different methods; shape template and bone mineral density image. They also found out that the maximum discrepancies are in trochanter area, ranging from 0.7 to 2.6 mm. Our results also showed the similar range of discrepancies. Schumann et al.  used clinically relevant morphometric parameters measurement of the proximal femur to examine the accuracy of their reconstructed method. In their study, the highest average deviations were also observed in trochanter area. Rathnayaka et al.  conducted a study to compare the accuracy of MRI and CT reconstructed 3D models where they also estimated the highest deviations was observed in the “neck and greater trochanter” region. The highest deviations, usually observed in the “neck and greater trochanter” area, are probably due to geometrical complications exist in this area. In the current study, the highest estimated discrepancy from the reconstructed models is 0.79 mm. The previous studies of Glaude et al. [11, 43] on accuracy assessment of reconstructed models based on medical images, suggest that the mean 3D deviation of reconstructed models should be in the range of 1 mm. Since clinical hip fractures commonly occur in the neck area , more accuracy in reconstruction of this area is required to have more precise FE analysis results. Furthermore, as observed in Fig. 5, there was no outlier in the accuracy assessment comparison, and all the reconstructed 3D models have similar range of deviations. However, if peak discrepancies are observed, they can be simply disregarded because they are local. The outer surface areas of the reconstructed models providing the surface meshes for FE analysis were also estimated in this study. Highest errors of the outer surface area were observed in “diaphysis” and “neck and greater trochanter” regions. This is also illustrated in Fig. 4 using color-coded map to show that “diaphysis” and “neck and greater trochanter” regions have the highest surface discrepancies compare to the real bone 3D optical scan. Therefore, these two regions are the most critical regions for reconstruction of 3D models based on medical images and should be processed carefully. The results also suggest, that the quality of the image segmentation is rather independent of reconstruction processing software. The differences observed in segmentation times can be associated with either individual investigator speed of segmentation or the usability of the software. For future works, the effect of the negligible discrepancies on the FE analysis results will be examined using a controlled load case in an experimental setup.
This study shows that the average deviation of CT based models, prepared by experts with different skills using various software packages, from a bone surface scan is very low. This reveals that the effect of human expertise and use of different software packages and corresponding methodologies have a negligible effect on the accuracy of the reconstruction procedure from medical images. Therefore, image-based reconstructed models are reliable to use in FE models for clinical applications.
ES: CT image segmentation, major contributor in writing the manuscript, performing the data analysis. DK: designing the study and organizing participants. PAV: CT image segmentation. RC: CT image segmentation. MS: CT image segmentation. DG: CT image segmentation. FN: Designing 3D optical scanning. DP: CT image segmentation. MW: CT image segmentation and design the study. All authors read and approved the final manuscript.
We thank Prof. Dr.-Ing. H. Seitz for support using Materialise Mimics® software. This study was organized within the structures of the Musculoskeletal Biomechanics Network (MSB-Net) of the Basic Research section within the German Society for Orthopaedics and Trauma. The human bone specimen was obtained through an anatomic gifts program (Science Care, Phoenix, AZ, USA) and its use was authorized by the responsible ethical committee (BLAEK 2011-058, Munich, Germany).
The authors declare that they have no competing interests.
Availability of data and materials
The datasets generated and/or analyzed during the current study are available in the Biomechanics and Implant Technology Research Laboratory, Department of Orthopedics, University Medicine Rostock repository. The datasets generated and/or analyzed during the current study are not publicly available but are available from the corresponding author on reasonable request.
Consent for publication
Ethics approval and consent to participate
The human bone specimen was obtained through an anatomic gifts program (Science Care, Phoenix, AZ, USA) and its use was authorized by the responsible ethical committee (BLAEK 2011-058, Munich, Germany).
We acknowledge the internal funding program of University Medicine Rostock (‘Förderung zur Vorbereitung von Anträgen der Verbundforschung’) to financially support this project.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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