Optimized vertical stereo base radiographic setup for the clinical three-dimensional reconstruction of the human spine

A Review of 3D Modalities Used for the Diagnosis of Scoliosis

Spine radiographs in the standing position are the recommended standard for diagnosing idiopathic scoliosis. Though the deformity exists in 3D, its diagnosis is currently carried out with the help of 2D radiographs due to the unavailability of an efficient, low-cost 3D alternative. Computed tomography (CT) and magnetic resonance imaging (MRI) are not suitable in this case, as they are obtained in the supine position. Research on 3D modelling of scoliotic spine began with multiplanar radiographs and later moved on to biplanar radiographs and finally a single radiograph. Nonetheless, modern advances in diagnostic imaging have the potential to preserve image quality and decrease radiation exposure. They include the DIERS formetric scanner system, the EOS imaging system, and ultrasonography. This review article briefly explains the technology behind each of these methods. They are compared with the standard imaging techniques. The DIERS system and ultrasonography are radiation free but have limitations with respect to the quality of the 3D model obtained. There is a need for 3D imaging technology with less or zero radiation exposure and that can produce a quality 3D model for diseases like adolescent idiopathic scoliosis. Accurate 3D models are crucial in clinical practice for diagnosis, planning surgery, patient follow-up examinations, biomechanical applications, and computer-assisted surgery.

Survey of methods and principles in three-dimensional reconstruction from two-dimensional medical images

Three-dimensional (3D) reconstruction of human organs has gained attention in recent years due to advances in the Internet and graphics processing units. In the coming years, most patient care will shift toward this new paradigm. However, development of fast and accurate 3D models from medical images or a set of medical scans remains a daunting task due to the number of pre-processing steps involved, most of which are dependent on human expertise. In this review, a survey of pre-processing steps was conducted, and reconstruction techniques for several organs in medical diagnosis were studied. Various methods and principles related to 3D reconstruction were highlighted. The usefulness of 3D reconstruction of organs in medical diagnosis was also highlighted.

Generative Adversarial Network (GAN) for Automatic Reconstruction of the 3D Spine Structure by Using Simulated Bi-Planar X-ray Images

In this study, we modified the previously proposed X2CT-GAN to build a 2Dto3D-GAN of the spine. This study also incorporated the radiologist’s perspective in the adjustment of input signals to prove the feasibility of the automatic production of three-dimensional (3D) structures of the spine from simulated bi-planar two-dimensional (2D) X-ray images. Data from 1012 computed tomography (CT) studies of 984 patients were retrospectively collected. We tested this model under different dataset sizes (333, 666, and 1012) with different bone signal conditions to observe the training performance. A 10-fold cross-validation and five metrics—Dice similarity coefficient (DSC) value, Jaccard similarity coefficient (JSC), overlap volume (OV), and structural similarity index (SSIM)—were applied for model evaluation. The optimal mean values for DSC, JSC, OV, SSIM_anteroposterior (AP), and SSIM_Lateral (Lat) were 0.8192, 0.6984, 0.8624, 0.9261, and 0.9242, respectively. There was a significant improvement in the training performance under empirically enhanced bone signal conditions and with increasing training dataset sizes. These results demonstrate the potential of the clinical implantation of GAN for automatic production of 3D spine images from 2D images. This prototype model can serve as a foundation in future studies applying transfer learning for the development of advanced medical diagnostic techniques.

Three-dimensional reconstruction of In Vivo human lumbar spine from biplanar radiographs

We present a method for three dimensional (3D) reconstruction of in vivo human lumbar spine from biplanar radiographs with comparable results to Computerised Tomography (CT) scans or Magnetic Resonance Imaging (MRI) models. In this work, we used uncalibrated radiographs to reconstruct the 3D vertebrae and a priori information stored in an Active Shape Model (ASM) that is constructed using the Spherical Demons Algorithm. The method is semi-automatic as bounding boxes are required to delimit the positions of the vertebrae on biplanar radiographs of a patient. Optimisation is based on comparisons between simulated and actual radiographs. Finally, we compare the results to the models generated from MRI and CT scans. The results show the feasibility of generating personalised models of patients from biplanar radiographs.

Reconstruction of three-dimensional lumbar vertebrae from biplanar x-rays

Objective. Vertebrae models from computer tomographic (CT) imaging are extensively used in image-guided surgical systems to deliver percutaneous orthopaedic operations with minimum risks, but patients may be exposed to excess radiation from the pre-operative CT scans. Generating vertebrae models from intra-operative x-rays for image-guided systems can reduce radiation exposure to the patient, and the surgeons can acquire the vertebrae's relative positions during the operation; therefore, we proposed a lumbar vertebrae reconstruction method from biplanar x-rays.Approach. Non-stereo-corresponding vertebral landmarks on x-rays were identified as targets for deforming a set of template vertebrae; the deformation was formulated as a minimisation problem, and was solved using the augmented Lagrangian method. Mean surface errors between the models reconstructed using the proposed method and CT scans were measured to evaluate the reconstruction accuracy.Main results. The evaluation yielded mean errors of 1.27 mm and 1.50 mm inin vitroexperiments on normal vertebrae and pathological vertebrae, respectively; the outcomes were comparable to other template-based methods.Significance. The proposed method is a viable alternative to provide digital lumbar to be used in image-guided systems, where the models can be used as a visual reference in surgical planning and image-guided applications in operations where the reconstruction error is within the allowable surgical error.

3D posture visualisation from body shape measurements using physics simulation, to ascertain the orientation of the pelvis and femurs in a seated position

BACKGROUND AND OBJECTIVE

The paper presents a novel technique for the visualisation and measurement of anthropometric features from patients with severe musculoskeletal conditions. During a routine postural assessment, healthcare professionals use anthropometric measurements to infer internal musculoskeletal configuration and inform the prescription of Custom Contoured Seating systems tailored to individual needs. Current assessment procedures are not only time consuming but also do not readily facilitate the communication of musculoskeletal configuration between healthcare professionals nor the quantitative comparison of changes over time. There are many techniques measuring musculoskeletal configurations such as MRI, CT or X-ray. However, most are very resource intensive and do not readily lend themselves to widespread use in, for example, community based services. Due to the low volume of patient data and hence small datasets modern machine learning techniques are also not feasible and a bespoke solution is required.

METHODS

The technique outlined in this paper uses physics simulation to visualise the orientation of the pelvis and femurs when seated in a custom contoured cushion. The input to the algorithm is a body shape measurement and the output is a visualised pelvis and femurs. The algorithm was tested by also outputting a multi-label classification of posture (specific to the pelvis and femurs).

RESULTS

The physics simulation has a classification accuracy of 72.9% when labelling all 9 features of the model; when considering 6 features (excluding rotations about the x-axis) the accuracy is increased to 92.8%.

CONCLUSIONS

This study has shown that a mechanical shape sensor can be used to capture the unsupported seated posture of an individual during a clinic. The results have demonstrated the potential of the physics simulation to be used for anthropometric feature extraction from body shape measurements leading to a better posture visualization. Capturing and visualising the seated posture in this way should enable clinicians to more easily compare the effects of clinical interventions over time and document postural changes. Overall, the algorithm performed well, however, in order to fully evaluate its clinical benefit, it needs to be tested in the future using data from patients with severe musculoskeletal conditions and complex body shapes.

3D Reconstruction of Scoliotic Spines from Stereoradiography and Depth Imaging

Spine shape can be reconstructed from stereoradiography, but often requires specialized infrastructure or fails to account for subject posture. In this paper a protocol is presented for stereo reconstructions that integrates surface recordings with radiography and naturally accounts for variations in patient posture. Low cost depth cameras are added to an existing radiographic system to capture patient pose. A statistical model of human body shape is learned from public datasets and registered to depth scans, providing 3D correspondence across images for stereo reconstruction of radiographic landmarks. A radiographic phantom was used to validate these methods in vitro with RMS 3D landmark reconstruction error of 2.0 mm. Surfaces were automatically and reliably registered, with SD 12 mm translation disparity and SD .5° rotation. The proposed method is suitable for 3D radiographic reconstructions and may be beneficial in compensating for involuntary patient motion.

Iterative approach for 3D reconstruction of the femur from un-calibrated 2D radiographic images

Three-dimensional reconstruction of the femur is important for surgical planning in patients with cerebral palsy. This study aimed to reconstruct the three-dimensional femur shape from un-calibrated bi-planar radiographic images using self-calibration to allow for low-dose preoperative planning. The existing self-calibration techniques require anatomical landmarks that are clearly visible on bi-planar images, which are not available on the femur. In our newly developed method, the self-calibration is performed so that the contour of the statistical shape matches the image contour while the statistical shape is concomitantly optimized. The proposed approach uses conventional radiograph systems and can be easily incorporated into existing clinical protocols, as compared to other reconstruction methods.

Improving Visibility of Stereo-Radiographic Spine Reconstruction with Geometric Inferences

Complex deformities of the spine, like scoliosis, are evaluated more precisely using stereo-radiographic 3D reconstruction techniques. Primarily, it uses six stereo-corresponding points available on the vertebral body for the 3D reconstruction of each vertebra. The wireframe structure obtained in this process has poor visualization, hence difficult to diagnose. In this paper, a novel method is proposed to improve the visibility of this wireframe structure using a deformation of a generic spine model in accordance with the 3D-reconstructed corresponding points. Then, the geometric inferences like vertebral orientations are automatically extracted from the radiographs to improve the visibility of the 3D model. Biplanar radiographs are acquired from five scoliotic subjects on a specifically designed calibration bench. The stereo-corresponding point reconstruction method is used to build six-point wireframe vertebral structures and thus the entire spine model. Using the 3D spine midline and automatically extracted vertebral orientation features, a more realistic 3D spine model is generated. To validate the method, the 3D spine model is back-projected on biplanar radiographs and the error difference is computed. Though, this difference is within the error limits available in the literature, the proposed work is simple and economical. The proposed method does not require more corresponding points and image features to improve the visibility of the model. Hence, it reduces the computational complexity. Expensive 3D digitizer and vertebral CT scan models are also excluded from this study. Thus, the visibility of stereo-corresponding point reconstruction is improved to obtain a low-cost spine model for a better diagnosis of spinal deformities.

Computational Biomechanical Modeling of Scoliotic Spine: Challenges and Opportunities

BACKGROUND

Biomechanical computer models of the spine have important roles in the treatment and correction of scoliosis by providing predictive information for surgeons and other clinicians.

OBJECTIVES

This article reviews computational models of intact and scoliotic spine and its components; vertebra, intervertebral disc, ligament, facet joints, and muscle. Several spine models, developed using multi-body modelling and finite element modelling schemes, and their pros and cons are discussed.

CONCLUSIONS

The review reveals that scoliosis modelling is performed for 3 main applications: 1) brace simulation; 2) analysis of surgical correction technique; and 3) patient positioning before surgical instrumentation. The models provide predictive information for a priori choice of brace configurations and mechanically effective surgical correction techniques and the expected degree of correction. However, they have many shortcomings: for instance, they do not fully reproduce the active behaviour of the spine and the models' properties are not personalized.

A fast method for spine localization in x-ray images

Detection of spines in medical images are important tasks in medical applications. These tasks are relatively easy for CT/MR images because the bones are easily distinguishable from other tissues. However, they are difficult for x-ray images due to bone and soft tissue overlapping. This paper illustrates a method for detecting the medial axis of spine in x-ray images. Given an initial point on the spine in the x-ray image manually or automatically, the method iteratively searches for good feature points on the spine to locate the medial axis. As a result, the effort of determining the relevant medical information, such as Cobb's angle, can be minimized. The proposed method is fast and efficient. In average it took less than 1 second for localizing the spine on a 3000×1000 gray scale x-ray image.

Accessing 3D Location of Standing Pelvis: Relative Position of Sacral Plateau and Acetabular Cavities versus Pelvis

The goal of this paper is to access to pelvis position and morphology in standing posture and to determine the relative locations of their articular surfaces. This is obtained from coupling biplanar radiography and bone modeling. The technique involves different successive steps. Punctual landmarks are first reconstructed, in space, from their projected images, identified on two orthogonal standing X-rays. Geometric models, of global pelvis and articular surfaces, are determined from punctual landmarks. The global pelvis is represented as a triangle of summits: the two femoral head centers and the sacral plateau center. The two acetabular cavities are modeled as hemispheres. The anterior sacral plateau edge is represented by an hemi-ellipsis. The modeled articular surfaces are projected on each X-ray. Their optimal location is obtained when the projected contours of their models best fit real outlines identified from landmark images. Linear and angular parameters characterizing the position of global pelvis and articular surfaces are calculated from the corresponding sets of axis. Relative positions of sacral plateau, and acetabular cavities, are then calculated. Two hundred standing pelvis, of subjects and scoliotic patients, have been studied. Examples are presented. They focus upon pelvis orientations, relative positions of articular surfaces, and pelvis asymmetries.

Geometric Structure of 3D Spinal Curves: Plane Regions and Connecting Zones

This paper presents a new study of the geometric structure of 3D spinal curves. The spine is considered as an heterogeneous beam, compound of vertebrae and intervertebral discs. The spine is modeled as a deformable wire along which vertebrae are beads rotating about the wire. 3D spinal curves are compound of plane regions connected together by zones of transition. The 3D spinal curve is uniquely flexed along the plane regions. The angular offsets between adjacent regions are concentrated at level of the middle zones of transition, so illustrating the heterogeneity of the spinal geometric structure. The plane regions along the 3D spinal curve must satisfy two criteria: (i) a criterion of minimum distance between the curve and the regional plane and (ii) a criterion controlling that the curve is continuously plane at the level of the region. The geometric structure of each 3D spinal curve is characterized by the sizes and orientations of regional planes, by the parameters representing flexed regions and by the sizes and functions of zones of transition. Spinal curves of asymptomatic subjects show three plane regions corresponding to spinal curvatures: lumbar, thoracic and cervical curvatures. In some scoliotic spines, four plane regions may be detected.

TOWARDS THE SELF-CALIBRATION OF A MULTIVIEW RADIOGRAPHIC IMAGING SYSTEM FOR THE 3D RECONSTRUCTION OF THE HUMAN SPINE AND RIB CAGE

The main objective of this study was to develop a 3D reconstruction technique of the spine and rib cage of idiopathic scoliotic patients using the self-calibration of the imaging system. The proposed approach computes the intrinsic and extrinsic parameters of the radiographic setup with respect to the global coordinate system used at Ste-Justine Hospital. Our approach determines an optimal estimate of the geometrical parameters of the imaging system from a nonlinear minimization of the mean square distance between the observed and analytical projections of a set of matched points identified on a pair of radiographic views. The accuracy of the optimal estimate for the intrinsic parameters was significantly improved when geometric knowledge such as the known length of detectable straight bars is incorporated as a set of equality constraints in the optimization process. Furthermore, in order to retrieve the 3D structure of interest in the global coordinate system, a reference plane including the origin of the global coordinate system is specified. Computer simulations were performed to evaluate the self-calibration procedure and to determine the minimum knowledge required to obtain an accurate 3D reconstruction for clinical applications. An in vitro validation on real images of a dry cadaveric human spine showed that the method is feasible and reaches the expected accuracy.

IN VIVO LOCATION OF JOINT CENTERS OF THE SHOULDER SYSTEM: GLENO-HUMERAL AND SCAPULO-THORACIC JOINTS BETWEEN TWO POSTURES DESCRIBING THE ARM ELEVATION IN THE PLANE OF SCAPULA USING TECHNIQUES BASED UPON BIPLANAR RADIOGRAPHY

In biomechanics, the knowledge of accurate location of a joint center is essential because equilibration of the external loads and muscular forces about the joint is performed about this specific point. This paper focuses on the location of centers of gleno-humeral joint and scapulo-thoracic joint in a subject moving their arm in the scapular plane with a magnitude of 120°. Biplanar radiography with successive exposures has been used locating anatomical axes of bones. Geometric models of bones were defined allowing access to bone morphology by superposing model projections onto X-ray imaged bone contours. Functional models were used so as to represent the behavior in motion of shoulder joints. These techniques allowed us to access to results describing the linear and angular relative displacements of the shoulder bones between two different postures. The gleno-humeral and scapulo-thoracic finite joint centers (F H and F S ) are first defined through the location of the corresponding helical axis of motion (HAM) moving the joint from positions occupied in initial and final postures. The gleno-humeral and scapulo-thoracic mean joint centers (M H and M S ) are then calculated using a new technique, which defines that each joint center has the point having the smallest migrations while moving continuously from initial to final postures. This allows for the analysis of the linear and angular clearances, which affect joint center migration. The whole continuous movement has been parsed into several steps to test the stability of the mean joint center throughout the motion.

Classification of pelvic and spinal postural patterns in upright position. Specific cases of scoliotic patients

The 3D analyses of spinal shapes and postural features give a great number of data. The global patient posture includes his pelvic morphology and tilting, and his pelvic and spinal balance. In some scoliotic spines, the spinal curve belongs to a unique plane. In other scoliotic patients, the spinal curve shows several plane regions. The spinal structures are modeled from parameters locating the structural planes and by values of maximum curvatures. Some parameters have been introduced for describing the postural patterns and the spinal deformities. For each tested patient, each major parameter has been characterized by an index of class.

A review of methods for quantitative evaluation of spinal curvature

The aim of this paper is to provide a complete overview of the existing methods for quantitative evaluation of spinal curvature from medical images, and to summarize the relevant publications, which may not only assist in the introduction of other researchers to the field, but also be a valuable resource for studying the existing methods or developing new methods and evaluation strategies. Key evaluation issues and future considerations, supported by the results of the overview, are also discussed.

A review of methods for quantitative evaluation of axial vertebral rotation

Quantitative evaluation of axial vertebral rotation is essential for the determination of reference values in normal and pathological conditions and for understanding the mechanisms of the progression of spinal deformities. However, routine quantitative evaluation of axial vertebral rotation is difficult and error-prone due to the limitations of the observer, characteristics of the observed vertebral anatomy and specific imaging properties. The scope of this paper is to review the existing methods for quantitative evaluation of axial vertebral rotation from medical images along with all relevant publications, which may provide a valuable resource for studying the existing methods or developing new methods and evaluation strategies. The reviewed methods are divided into the methods for evaluation of axial vertebral rotation in 2D images and the methods for evaluation of axial vertebral rotation in 3D images. Key evaluation issues and future considerations, supported by the results of the overview, are also discussed.

3D reconstruction of the spine from biplanar X-rays using parametric models based on transversal and longitudinal inferences

Reconstruction methods from biplanar X-rays provide 3D analysis of spinal deformities for patients in standing position with a low radiation dose. However, such methods require an important reconstruction time and there is a clinical need for fast and accurate techniques. This study proposes and evaluates a novel reconstruction method of the spine from biplanar X-rays. The approach uses parametric models based on longitudinal and transversal inferences. A first reconstruction level, dedicated to routine clinical use, allows to get a fast estimate (reconstruction time: 2 min 30 s) of the 3D reconstruction and accurate clinical measurements. The clinical measurements precision (evaluated on asymptomatic subjects, moderate and severe scolioses) was between 1.2 degrees and 5.6 degrees. For a more accurate 3D reconstruction (complex pathologies or research purposes), a second reconstruction level can be obtained within a reduced reconstruction time (10 min) with a fine adjustment of the 3D models. The mean shape accuracy in comparison with CT-scan was 1.0 mm. The 3D reconstruction method precision was 1.8mm for the vertebrae position and between 2.3 degrees and 3.9 degrees for the orientation. With a reduced reconstruction time, an improved accuracy and precision and a method proposing two reconstruction levels, this approach is efficient for both clinical routine uses and research purposes.

Reliability of 3D reconstruction of the spine of mild scoliotic patients

STUDY DESIGN

A reliability study was conducted in quantitative 3-dimensional (3D) measurements for mild scoliosis.

OBJECTIVE

To evaluate the intrarater and interrater reliability of a computer tool used for 3D reconstruction of the spine.

SUMMARY OF BACKGROUND DATA

No reliability study of spinal in vivo 3D medical imaging measurements has been performed in the literature.

METHODS

This study included 30 patients (mean age 13 years) with mild idiopathic scoliosis. Spinal 3D reconstruction was performed using a new technique called semiautomatic 3D reconstruction, which requires only the location of the corners of each vertebral body on 2 orthogonal views. Three raters performed the 3D reconstruction procedure on the 30 pairs of radiographs in random order. One of the raters repeated the procedure for the 30 patients 15 days later. Inter-reliability and intra-reliability were estimated for different parameters: thoracic kyphosis, lumbar lordosis, Cobb's angle, pelvic morphologic and positional parameters, and axial rotation.

RESULTS

Intraclass correlation coefficient showed good or very good agreement for most of the measurements. The 95% prediction limits are approximately 4 degrees for the measurements of spinal curves, 2 degrees for pelvic parameters, and axial vertebral rotation.

CONCLUSIONS

The reliability of 3D reconstruction of the spine is acceptable, and this technique can be used for clinical studies.

Modelling Skin Pelvic Landmark Coordinates Into Corresponding Internal Bone for Wheelchair Users

The purpose of this study was to investigate the relationships, by linear regression, between internal and external pelvic landmarks identified by two techniques: manual digitization or skin markers. It was hypothesized that the body mass index or the skinfold thickness are significant variables in these relationships. The internal pelvic landmarks were obtained with a stereoradiographic method. Results showed that the external coordinates are generally statistically different from the internal ones; manual digitization of the landmark reduces the soft tissue artifacts compared to the use of skin markers. Different regression models were obtained according to the external acquisition method. Body mass index or skinfold thickness was generally included as a significant variable in models along the direction of the soft tissue thickness: postero-anterior direction for the anterior-superior iliac spine, medio-lateral direction for the apex of the iliac crests. With the use of skin markers, models obtained for a specific internal landmark coordinate include generally many variables, such as the other two coordinates of the landmark, body mass index, or skinfold measurements. This study presented preliminary results on the relationships between internal and external pelvic landmark coordinates. More research is needed before the full relationships are understood and adequate models are developed.

Three-dimensional easy morphological (3-DEMO) classification of scoliosis, part I

BACKGROUND

While scoliosis has, for a long time, been defined as a three-dimensional (3D) deformity, morphological classifications are confined to the two dimensions of radiographic assessments. The actually existing 3-D classification proposals have been developed in research laboratories and appear difficult to be understood by clinicians.

AIM OF THE STUDY

The aim of this study was to use the results of a 3D evaluation to obtain a simple and clinically oriented morphological classification (3-DEMO) that might make it possible to distinguish among different populations of scoliotic patients.

METHOD

We used a large database of evaluations obtained through an optoelectronic system (AUSCAN) that gives a 3D reconstruction of the spine. The horizontal view was used, with a spinal reference system (Top View). An expert clinician evaluated the morphological reconstruction of 149 pathological spines in order to find parameters that could be used for classificatory ends. These were verified in a mathematical way and through computer simulations: some parameters had to be excluded. Pathological data were compared with those of 20 normal volunteers.

RESULTS

We found three classificatory parameters, which are fully described and discussed in this paper: Direction, the angle between spinal pathological and normal AP axis; Shift, the co-ordinates of the barycentre of the Top View ; Phase, the parameter describing the spatial evolution of the curve. Using these parameters it was possible to distinguish normal and pathological spines, to classify our population and to differentiate scoliotic patients with identical AP classification but different 3D behaviors.

CONCLUSION

The 3-DEMO classification offers a new and simple way of viewing the spine through an auxiliary plane using a spinal reference system. Further studies are currently under way to compare this new system with the existing 3-D classifications, to obtain it using everyday clinical and x-rays data, and to develop a triage for clinical use.

Analysis of structural features of deformed spines in frontal and sagittal projections

In the study of spine, two approaches exist. Clinicians still measure directly, either on X-ray films or on digitized images, a small number of angular values characterizing the profile of deformed spines. 3D software programs exist, but they describe the spinal features calculated from a large set number of inputs. An alternative approach is proposed for clinical applications. Frontal and sagittal radiographs are treated separately. Neutral curves are drawn from a small number of records in a small amount of time. Feature parameters accurately describe the spinal shape, and they are the basis for drawing the modeled curve of the spine. These parameters facilitate the follow up of evolutive back pathologies. Several examples display the new technique.

3D reconstruction of the pelvis from bi-planar radiography

3D personalized models are more and more requested for clinical and biomechanical studies. Techniques based on bi-planar X-rays present the advantage of a low radiation dose for the patient. However, up to now, such techniques have shown limited accuracy in the case of pelvis reconstruction. This study proposes and validates a method providing accurate 3D personalized model of the pelvis from bi-planar X-rays. The algorithm is based on the fast computation of an initial solution followed by local deformations based on 2D anatomical points and contours that are digitized in both radiographs. Results were close to CT-scan reconstructions (mean difference 1.6 mm and differences under 4.3 mm for 95% of the points). Moreover, 3D morphometry of the pelvis could be obtained with an accuracy of 5%. This technique provides 3D patient specific model with a low radiation dose.

Three-dimensional in vivo displacements of the shoulder complex from biplanar radiography

The goal of this study was to adapt roentgen photogrammetry to in vivo studies of shoulder skeletal motion during arm elevation in the scapular plane. Numerous in vitro and in vivo studies have been published describing shoulder bone movements. They involve plain radiographic measurements and utilize a three-dimensional (3D) approach. Measurements are either direct using pins implanted in bones, or indirect recording points on medical images. Roentgen photogrammetry locates points in space from two projections obtained from two different radiographic incidences. The technique has been applied in vivo by implanting metallic balls in bones. However, to be used as a standard clinical procedure, the technique must be adapted to be less invasive. In vivo photogrammetric reconstruction of known points in 3D space requires that the subject is strictly motionless between the successive radiographic exposures or that the exposures are obtained simultaneously. Methods used in this study were developed to allow subsequent exposures to be used for analysis. Numerical tools have been developed to align the two projections of a point in 3D space which have moved slightly between two successive exposures. The standard photogrammetric technique is completed by geometric modeling of the shoulder complex and humerus, and by the control of their mutual proximity at the level of joints. Bones are modeled as a set of simple volumes linked together using geometric shapes described by shape parameters. The coincidence between real bone contours and radiographic projections of the modeled bone gives the values of the shape parameters and the accurate location in space. Results focus on two different topics: errors related to the use of roentgen photogrammetry with successive exposures, and results obtained by applying roentgen photogrammetry to the in vivo shoulder complex. Results describing shoulder bone and joint displacements are presented for comparison with previously published results. The technique of roentgen photogrammetry can successfully be applied to patients. The radiographic protocol is simple, and data can be obtained easily and quickly from the digitized films. The data obtained from asymptomatic shoulders compared favorably with published values. Future research will focus on comparisons between kinematics of the symptomatic and asymptomatic contralateral limbs in volunteers.

Three-Dimensional (3-D) Reconstruction of the Spine From a Single X-Ray Image and Prior Vertebra Models

The lateral bending test is routinely used by clinicians for the preoperative assessment of spinal mobility. The evaluation of bending motion is usually based on the qualitative analysis of a two-dimensional (2-D) antero-posterior X-ray image. The aim of this paper is to introduce a novel three-dimensional (3-D) reconstruction technique that is a prerequisite for the quantitative 3-D analysis of lateral bending motion. An algorithm was developed for the 3-D reconstruction of the spine from a single X-ray image. The X-ray is calibrated using a small calibration object and an explicit calibration algorithm. The information contained in the single X-ray is completed by registering a priori 3-D geometric models of individual vertebrae. Part of the error yielded by the 3-D/2-D registration is corrected by a vertebral alignment constraint that aims to minimize intervertebral dislocations. Three-dimensional models of 15 different scoliosis patients, obtained from a standard stereo-radiographic 3-D reconstruction, were used in simulation and validation experiments. Experimental results show that the new method is robust and accurate. With pessimistic levels of simulated noise, the average root mean square reconstruction error is 2.89 mm, which is appropriate for common clinical applications.

Validation of the relative 3D orientation of vertebrae reconstructed by bi-planar radiography

The three dimensional (3D) reconstruction of the spine can be obtained by stereoradiographic techniques. To be safely used on a routine clinics basis, stereoradiography must provide both accurate vertebral shape and coherent position. Although the accuracy of the reconstructed morphology of the vertebrae is well documented, only few authors studied the accuracy of the vertebral orientation. Therefore, this paper focuses on the evaluation of the orientation accuracy of the reconstructed vertebrae (obtained by non-stereo corresponding point technique) considering either a 178 point vertebral model or a 6 point vertebral model (previously proposed in the literature). Five dried vertebrae were fixed on holders containing four markers each. The 3D reconstruction of both vertebrae and markers were obtained by stereoradiographic techniques. Using least square method matching from one position to another, the relative orientation was computed for the vertebral models (6 or 178 points) and the four markers. These vertebral and holder orientations were compared (considering the holder's one as reference). The repeatability of these relative orientations (vertebrae and holders) was also evaluated. The mean (RMS) orientation error of 178 point vertebral model was 0.6 degrees (0.8 degrees ), for lateral rotation, 0.7 degrees (1.0 degrees ) for sagittal rotation and 1.4 degrees (1.9 degrees ) for axial rotation. The intra-observer repeatability was 0.5 degrees (0.7 degrees ) for lateral rotation, 0.7 degrees (0.8 degrees ) for sagittal rotation and 0.9 degrees (1.2 degrees ) for axial rotation. The orientation was found more accurate and precise when using the 178 point vertebral model than when using the basic 6 point vertebral model. The relative orientation (in post-operative follow-up with respect to the pre-operative examination) of the vertebrae of one scoliotic patient was performed as an example of clinical application. The stereoradiographic method is a reliable 3D quantitative tool to assess the spine deformity, that can be used in clinics for the follow-up of scoliotic patients.

Correlation between nucleus zone migration within scoliotic intervertebral discs and mechanical properties distribution within scoliotic vertebrae

Correlations between intervertebral disc degeneration and bone mass were investigated previously, but never on scoliotic patients. Using MRI measurements of intervertebral discs behavior and vertebral bone tomodensitometry, correlations between nucleus zone displacement within intervertebral discs and mechanical center migration within vertebral bodies were investigated in vivo on scoliotic patients. The protocol, performed on eleven scoliotic girls, was composed of a CT scan acquisition of apical and adjacent vertebrae followed by a MRI acquisition of the thoracolumbar spine. The displacement between the vertebral body centroid and inertia center was computed from the CT images and called the mechanical migration. The displacement between nucleus zones and vertebral body centroids was quantified from MRI and called the nucleus zone migration. For apical vertebrae, a significant correlation was found in the coronal plane (r = 0.766, p < 0.01), but not in the sagittal plane (r = -0.349, p > 0.05). For adjacent vertebrae, significant correlations were found in both coronal (r = -0.633, p < 0.05) and sagittal (r = -0.797, p < 0.01) planes. The nucleus zone migration occurred in the convexity of the curvature whereas the mechanical migration occurred in the concavity.Known secondary mechanical phenomenon of scoliosis was quantified using new parameters describing intervertebral discs and vertebral bodies. Further investigations should be performed to explain the mechanical evolution of scoliosis and to use these parameters in predictive criteria of scoliosis.

Fast accurate stereoradiographic 3D-reconstruction of the spine using a combined geometric and statistic model

OBJECTIVE

To describe and evaluate a fast accurate stereoradiographic 3D-reconstruction method of the spine.

BACKGROUND

Stereoradiographic methods based on anatomical landmarks identification are the only ones providing information on 3D-deformities of the spine in a standing position, but require 2-4 h for the whole spine, making the method inadequate for clinical routine.

METHODS

The proposed semi-automated method is based on (1) vertebral body volume reconstruction, (2) definition of a local referential associated to this volume, (3) reliable a priori knowledge of the vertebral shape using eight morphologic descriptors of the vertebral body to estimate, from a multiple linear regression, 21 3D-point coordinates per vertebra, (4) kriging of a 2000 points model with regard to the 21 points. The method was evaluated for vertebral orientation and shape accuracy.

RESULTS

3D models of the whole spine are obtained within 15 min. Manual vs. semi-automated reconstruction comparison yield similar accuracy regarding the CT-scan references. For vertebrae orientation, results were slightly different from the manual reconstruction method (however an absolute reference is lacking).

CONCLUSION

The stereoradiographic 3D-reconstruction method allows for a significant reduction of the whole reconstruction time, with regard to previously described methods. Moreover, the accuracy was evaluated and was found to be comparable to the accuracy of previous methods. The results of this study show that stereoradiography could now be employed in routine clinical environment.

RELEVANCE

3D spine reconstruction from biplanar radiographs in standing position can be obtained using a fast and accurate method.

Evidence of three-dimensional variability in scoliotic curves

In the current study, 98 patients with idiopathic scoliosis were selected for analysis. The object of this study was to determine whether three-dimensional variability exists within each class of the King classification, and to evaluate the currently used King classification in its ability to categorize different scolioses adequately. Anteroposterior and lateral radiographs were digitized, and three-dimensional models were reconstructed for each spine. Several parameters were recorded for each individual: age, gender, four Cobb angles, (1) anteroposterior, (2) lateral, (3) maximum (Cobb angle at the plane of maximum deformity), and (4) minimum (Cobb angle at the plane of minimum deformity), and the orientation of the planes of maximum and minimum deformity. Most of the curves were kyphotic, but a small percentage in each class were hypokyphotic or lordotic. This was not seen in the analysis in which the individual King classes were compared. It was seen, however, when the authors reanalyzed the data after having pooled the subjects and reclassified them according to presence or absence of kyphosis. The King classification was shown to be inadequate for describing spinal deformities in three dimensions, because different variants of sagittal spine configurations were seen which can look identical on the anteroposterior view. Therefore, the need for a new three-dimensional classification, which takes this variability into account, is established.

Explicit calibration method and specific device designed for stereoradiography

The three-dimensional geometry of the human spine is noteworthy information that can be obtained by stereoradiographic methods. These methods are based on the identification of anatomical structures in several views which are obtained by rotation of a patient standing on a turntable. Calibration algorithms for computer vision or photogrammetry are well documented, but they generally yield calibration devices which are cumbersome for the use in clinical stereoradiography. This paper presents a calibration method adapted to a two-view stereoradiography calibration (frontal and lateral incidences) and based on a simplified geometric modeling of the radiological environment. The a priori knowledge yields four calibration equations related to the vertical and horizontal planes of both views, leading to a specific calibration procedure and device. Moreover this device is attached to the stereoradiographic system (directly integrated on the turntable) in order to facilitate clinical applications. A validation was performed on 26 dried lumbar vertebrae in order to evaluate clinical situation. The mean accuracy of the stereoradiographic reconstruction was 1.2mm.

A biplanar reconstruction method based on 2D and 3D contours: application to the distal femur

A three-dimensional (3D) reconstruction algorithm based on contours identification from biplanar radiographs is presented. It requires, as technical prerequisites, a method to calibrate the biplanar radiographic environment and a surface generic object (anatomic atlas model) representing the structure to be reconstructed. The reconstruction steps consist of: the definition of anatomical regions, the identification of 2D contours associated to these regions, the calculation of 3D contours and projection onto the radiographs, the associations between points of the X-rays contours and points of the projected 3D contours, the optimization of the initial solution and the optimized object deformation to minimize the distance between X-rays contours and projected 3D contours. The evaluation was performed on 8 distal femurs comparing the 3D models obtained to CT-scan reconstructions. Mean error for each distal femur was 1 mm.

Is Cobb angle progression a good indicator in adolescent idiopathic scoliosis?

STUDY DESIGN

A retrospective follow-up study of spine geometry after posterior instrumentation and fusion for adolescent idiopathic scoliosis (AIS).

OBJECTIVES

To evaluate 1) if Cobb angle progression is a reliable indicator of the crankshaft phenomenon; 2) if significant growth of the spine can occur after surgery without the development of a crankshaft phenomenon?

SUMMARY OF BACKGROUND DATA

Anterior fusion of the spine is often recommended for skeletally immature scoliotic patients to avoid the risk of a crankshaft phenomenon, a long-term loss of curve correction caused by residual growth of the spine combined with the constraints of a posterior fusion. The crankshaft phenomenon is usually assessed indirectly by documenting progression of the Cobb angle on frontal radiographs. Thus far, no study has directly measured the three-dimensional growth of the spine after surgery in AIS.

METHODS

Cobb angle, spine length and spine height were obtained from three-dimensional radiographic reconstructions of the spine in 48 adolescent scoliotic patients undergoing posterior instrumentation and fusion. Measurements were done before surgery, after surgery and at skeletal maturity. A significant growth of the spine was defined as a > or = 10 mm increase in spine length, while a significant curve progression was defined as a > or = 10 degrees increase in Cobb angle at skeletal maturity.

RESULTS

In the majority of patients (56%), there was no significant change in spinal length or in Cobb angle measurements at an average 2.4 years post surgery. A crankshaft phenomenon was detected in 6 patients (12%) for which significant increases both in spinal length and Cobb angle measurement were found. Significant curve progression without any change in spine length was noted in 9 patients (19%) while an increase in spine length with no evidence of curve progression was present in 6 patients at last follow-up.

CONCLUSION

Spinal growth as indicated by an increase in spinal length can be measured in a significant proportion of adolescents with idiopathic scoliosis after posterior instrumentation and fusion. Some of these study participants will develop a crankshaft phenomenon but Cobb angle progression is not a reliable indicator of this complication, since it may occur without any detectable growth of the spine.

Reconstruction of laser-scanned 3D torso topography and stereoradiographical spine and rib-cage geometry in scoliosis

Assessments of scoliosis are routinely done by means of clinical examination and full spinal x-rays. Multiple exposure to ionization radiation, however, can be hazardous to the child and is costly. Here, we explain the use of a noninvasive imaging technique, based on laser optical scanning, for quantifying the three-dimensional (3D) trunk surface topography that can be used to estimate parameters of 3D deformity of the spine. The laser optical scanning system consisted of four BIRIS laser cameras mounted on a ring moving along a vertical axis, producing a topographical mapping of the entire torso. In conjunction with the laser scans, an accurate 3D reconstruction of the spine and rib cage were developed from the digitized x-ray images. Results from 14 scoliotic patients are reported. The digitized surfaces provided the foundation data to start studying concordance of trunk surface asymmetry and spinal shape in idiopathic scoliosis.

Tomodensitometry measurements for in vivo quantification of mechanical properties of scoliotic vertebrae

OBJECTIVE

This in vivo study investigated the mechanical properties of scoliotic vertebrae especially in the apical zone.

DESIGN

A method based on computed tomography images and finite element meshing had been developed to quantify and visualise the bone density distribution of scoliotic vertebrae.

BACKGROUND

Most of scoliotic studies performed considered only geometrical parameters.

METHOD

Computed tomography examination had been performed on 11 girls presenting idiopathic scoliosis. Using in-house image processing software and the pre-post processor Patran, a finite element mesh of each vertebral body and a mapping of each cancellous bone slice were proposed allowing the bone density distribution to be visualised. The mechanical properties were derived from predictive relationships between Young's modulus and computed tomography number. Geometrical (unit mass) and mechanical centres were calculated and compared in order to quantify the role of mechanical property distribution on the apex zone of the scoliotic spine.

RESULTS

In the coronal plane, compared to the geometrical centre, the mechanical centre was shifted forward in the concavity (0.54 mm) of the curvature except for two vertebrae. In the sagittal plane, the mechanical centre was shifted forward in the back (0.26 mm) except for three vertebrae. The shift forward by slice was made in a same way for each slice (0.63 mm), except at the end plates (0.58 mm).

DISCUSSION

The result values obtained were small but significant because the curvatures were low and the vertebrae were not wedged. Besides, one can observe that the scoliotic deformation evolution seemed to modify the mechanical property distribution.

RELEVANCE

This study suggested the following question: Could these CT measurements be a predictive tool in scoliosis treatment?

Validation of the non-stereo corresponding points stereoradiographic 3D reconstruction technique

Several 3D reconstruction techniques deriving from stereoradiographic DLT have been presented during the last 15 years, but these techniques have usually been limited in accuracy because of the small number of corresponding anatomical landmarks identified on both radiographs. A new technique has recently been proposed to perform 3D reconstruction of the spine using not only the stereo-corresponding anatomical landmarks (seen on both frontal and sagittal X-ray films) but also some non-stereo-corresponding ones. This technique (called non-stereo-corresponding points or NSCP) has already been used for cervical dry vertebrae. In the present study, we focus on the validation of this technique for lumbar vertebrae by comparing four techniques: direct measurement, CT scan, 3D reconstruction by stereoradiography using a direct linear transformation (DLT) algorithm and the NSCP technique. The accuracy of the NSCP technique was also evaluated on different vertebral regions. The global results show mean errors of 1.1 mm and maximum of 7.8 mm with regard to direct measurements. These mean errors are close to those obtained using 3D reconstructions from CT scan using 1 mm cuts.

In vivo geometrical evaluation of Cheneau-Toulouse-Munster brace effect on scoliotic spine using MRI method

OBJECTIVES

The aim was to quantify the immediate effect of the Cheneau-Toulouse-Munster brace (worn at night) on scoliotic curvatures in vivo.Design. A three-dimensional geometrical model of the spine was developed using magnetic resonance images.

BACKGROUND

Many corrective ortheses were proposed for the orthopaedic treatment of idiopathic scoliosis. Simple radiographs were not sufficient to analyse the three-dimensional spinal deformations. So, three-dimensional geometrical models were developed using stereoradiography and axial tomography. MRI has been only used clinically for investigation of intervertebral disc disorders.

METHOD

MRI examination had been performed on 14 girls having an idiopathic scoliosis and wearing a first Cheneau-Toulouse-Munster brace. The protocol investigated was performed with and without brace. Using an in-house image processing software and the pre-post processing software Patran, two geometrical models of the spine (spine without brace and spine with brace correction) were obtained, respectively, for each patient, the models including the vertebral bodies.

RESULTS

Our method reproducibility was found to be 0.5 mm on the displacements and 2.5 degrees on the rotations. The Cheneau-Toulouse-Munster brace decreased the coronal shift forward, the coronal tilt, the axial rotation, and increased the sagittal shift forward and the sagittal vertebral tilt.

DISCUSSION

The results showed that the Cheneau-Toulouse-Munster brace had a three-dimensional and personalised action on vertebrae. This technique using MRI provides no irradiation and allows the soft tissue visualisation, but actually is not dedicated for clinical use and is limited to the lying position.

RELEVANCE

The qualitative and quantitative data obtained allowed a better description of the Cheneau-Toulouse-Munster brace effect on scoliotic spine, and will help the orthopaedist in the brace design and the clinician in the scoliosis comprehension.

Pre-, intra-, and postoperative three-dimensional evaluation of adolescent idiopathic scoliosis

The authors measured and compared the pre-, intra-, and postoperative three-dimensional shape of the spine during corrective surgery to quantify the specific contribution of positioning, anesthesia, surgical exposure, surgical instrumentation, and postural adaptation of the thoracic and lumbar spine. In 58 adolescent girls with idiopathic scoliosis undergoing corrective surgery by a posterior approach, the three-dimensional geometry of the thoracic and lumbar spine was documented in the standing position before and after surgery using a three-dimensional reconstruction technique based on multiplanar radiography, and the intraoperative three-dimensional geometry was measured using a three-dimensional magnetic digitizer before and after installation of the first rod. Prone positioning, anesthesia, and surgical exposure are responsible for a considerable decrease in all curves in the frontal and sagittal plane. Instrumentation with the first rod produces additional substantial and favorable three-dimensional changes with partial restoration of the normal sagittal curves and sagittal shift of the plane of maximum deformity. Although no loss of correction was observed in the frontal plane when patients resumed their standing position, a "spring-back" effect on the spine was noted in the sagittal plane and a loss of three-dimensional correction was seen in the orientation of the plane of maximum deformity. Surgeons can use the knowledge of these various changes to achieve better results by more careful attention to the preoperative positioning of patients and to curve correction in the sagittal plane when instrumentation is applied to the spine.

3D reconstruction method from biplanar radiography using non-stereocorresponding points and elastic deformable meshes

Standard 3D reconstruction of bones using stereoradiography is limited by the number of anatomical landmarks visible in more than one projection. The proposed technique enables the 3D reconstruction of additional landmarks that can be identified in only one of the radiographs. The principle of this method is the deformation of an elastic object that respects stereocorresponding and non-stereocorresponding observations available in different projections. This technique is based on the principle that any non-stereocorresponding point belongs to a line joining the X-ray source and the projection of the point in one view. The aim is to determine the 3D position of these points on their line of projection when submitted to geometrical and topological constraints. This technique is used to obtain the 3D geometry of 18 cadaveric upper cervical vertebrae. The reconstructed geometry obtained is compared with direct measurements using a magnetic digitiser. The order of precision determined with the point-to-surface distance between the reconstruction obtained with that technique and reference measurements is about 1 mm, depending on the vertebrae studied. Comparison results indicate that the obtained reconstruction is close to the actual vertebral geometry. This method can therefore be proposed to obtain the 3D geometry of vertebrae.

A three-dimensional radiographic comparison of Cotrel-Dubousset and Colorado instrumentations for the correction of idiopathic scoliosis

STUDY DESIGN

A prospective clinical study comparing two instrumentation systems for the correction of idiopathic scoliosis.

OBJECTIVES

To measure the short-term three-dimensional changes in the shape of the spine after corrective surgery and compare the Cotrel-Dubousset instrumentation to the more recent Colorado instrumentation to determine whether one system provides better three-dimensional correction.

SUMMARY OF BACKGROUND DATA

Adequate three-dimensional correction of scoliotic deformities has been reported with the Cortrel-Dubousset instrumentation system. During the past decade, a new generation of more versatile and user-friendly spinal implants has appeared, but there are no reports available to indicate whether similar or better correction can be obtained with these newer systems.

METHODS

The three-dimensional geometry of the thoracic and lumbar spine was documented in the standing position using a three-dimensional reconstruction technique based on multiplanar radiography in 67 adolescents with idiopathic scoliosis undergoing correction by a posterior approach. Changes in spinal shape were measured 3 days before and 1 month after the surgery in 31 patients with Cotrel-Dubousset instrumentation and 36 patients with Colorado instrumentation.

RESULTS

In both groups, adequate three-dimensional correction of the scoliotic deformities was documented for thoracic and lumbar curves, with significant changes in the frontal plane, in the plane of maximum curvature, and in its orientation. When comparing both groups, better correction was obtained in the frontal plane with the Colorado instrumentation (65% vs. 48% with Cotrel-Dubousset), a finding that may be explained by the significantly greater proportion of pedicle screws used in this group.

CONCLUSION

Both instrumentation techniques achieve an effective and comparable three-dimensional correction of the scoliotic deformities.