Reconstruction 3D personnalisée de la colonne vertébrale à partir d'images radiographiques non-calibrées

Les systèmes de reconstruction stéréo-radiographique 3D -- La colonne vertébrale -- La scoliose idiopathique adolescente -- Évolution des systèmes de reconstruction 3D -- Filtres de rehaussement d'images -- Techniques de segmentation -- Les méthodes de calibrage -- Les méthodes de reconstruction 3D -- Problématique, hypothèses, objectifs et méthode générale -- Three-dimensional reconstruction of the scoliotic spine and pelvis from uncalibrated biplanar X-ray images -- A versatile 3D reconstruction system of the spine and pelvis for clinical assessment of spinal deformities -- Simulation experiments -- Clinical validation -- A three-dimensional retrospective analysis of the evolution of spinal instrumentation for the correction of adolescent idiopathic scoliosis -- Auto-calibrage d'un système à rayons-X à partir de primitives de haut niveau -- Segmentation de la colonne vertébrale -- Approche hiérarchique d'auto-calibrage d'un système d'acquisition à rayons-X -- Personalized 3D reconstruction of the scoliotic spine from hybrid statistical and X-ray image-based models -- Validation protocol

Three-Dimensional Biplanar Reconstruction of the Scoliotic Spine for Standard Clinical Setup

Tese de Doutoramento. Engenharia Informática. Faculdade de Engenharia. Universidade do Porto. 201

Analyse de la relation entre les déformations scoliotiques du tronc et celles des structures osseuses sous-jacentes

RÉSUMÉ La scoliose idiopathique adolescente est une déformation tridimensionnelle complexe de la colonne vertébrale et de la cage thoracique qui entraine des déformations visibles à la surface du tronc. On remarque généralement une asymétrie des épaules, des omoplates, de la taille et du bassin ainsi qu’une bosse dans le dos. Ces déformations esthétiques constituent, d’une part, les premiers signes d’une scoliose, et d’autre part, la principale préoccupation des jeunes patients qui voient leur corps se développer différemment des jeunes de leur âge. Les outils cliniques utilisés pour quantifier les déformations du tronc, comme le scoliomètre ou le fil à plomb, sont peu fiables. C’est pourquoi, aujourd’hui, l’évaluation de la scoliose repose principalement sur des radiographies de face et de profil du tronc complet. Celles-ci permettent d’apprécier le type de courbure rachidienne et de quantifier son degré de sévérité, en fonction de quoi une stratégie de traitement sera décidée. Cependant, une exposition répétée des patients aux rayons X peut entrainer des effets indésirables sur leur santé. De plus, ces paramètres radiographiques ne permettent pas de documenter les déformations esthétiques. Cette différence notable entre ce que le patient perçoit, et ce que le clinicien est capable d’évaluer, peut mener à l’insatisfaction des patients suite au traitement. Comparativement aux radiographies, la surface du tronc reconstruite par les systèmes de numériseurs optiques 3D représente mieux les déformations que les patients observent et dont ils se soucient principalement, comme la gibbosité. De plus, l’absence de rayonnement ionisant est un avantage majeur de ces systèmes optiques, qui favorise une évaluation aussi fréquente que souhaité. Toutefois, l’absence de consensus sur un ensemble de mesures des déformations de la surface du tronc fait en sorte qu’elles restent encore considérées comme secondaires dans l’évaluation clinique; pourtant elles sont au coeur des préoccupations des patients. De cette double problématique, découle la question de recherche globale de cette thèse : comment compléter, voire remplacer, les évaluations clinique et radiographique actuelles de la scoliose par de l’information quantitative obtenue de manière non irradiante et qui permet de prendre davantage en considération les préoccupations des patients par rapport à leurs déformations esthétiques du tronc ? Parmi les premiers signes de scoliose, la gibbosité est une déformation esthétique qui ne peut être évaluée sur des radiographies, ni sur une reconstruction 3D de la colonne vertébrale.----------ABSTRACT Adolescent idiopathic scoliosis is a complex three-dimensional deformation of the spine and rib cage which leads to visible deformations at the trunk surface. The first signs of scoliosis include a hump on the back, a lateral shift of the trunk and asymmetries of the shoulders, the scapula, the waist and the hips. These esthetic deformities constitute major concern of patients and the reason for which they seek treatment. Currently, the tools available in clinical practice to quantify trunk deformations have limited reliability. For this reason, current scoliosis assessment is mainly based on frontal and lateral radiographs of the entire spine. These images allow clinicians to determine the type of the spinal curvature and its severity, according to which the treatment strategy is decided. However, the repeated exposure of patients to X-ray radiation can be harmful. Moreover, these radiographic measures do not give an indication as to the esthetic deformities of the trunk. This significant difference between what patients perceive and what clinicians are able to evaluate can lead to patient dissatisfaction following treatment. Compared to X-rays, the trunk surface acquired and reconstructed in 3D using optical digitizers better represents the deformations that patients observe and are primarily concerned with, such as the rib hump. In addition, the major advantage of these optical systems is their lack of ionizing radiation, thus allowing for a more frequent scoliosis assessment when compared to X-rays. However, there is currently no consensus on a set of indices that optimally quantifies trunk surface deformations. For this reason, trunk surface indices are still considered as secondary in the clinical evaluation, even though they are at the heart of the patients’ preoccupations. These problems lead to the main research question of this thesis: How can we complete, or even replace, the current clinical and radiographic evaluations of scoliosis with quantitative information obtained without ionizing radiation that takes more into account the patients’ concerns about their cosmetic trunk deformities? Among the first signs of scoliosis, the rib hump is a cosmetic deformity that cannot be assessed on radiographs, nor on a 3D reconstruction of the spine. It is mainly associated with rib cage deformity. It is therefore intuitive to suppose that the axial rotations of the ribs and of the back surface are highly correlated. Nevertheless, previous works have failed to demonstrate a strong relationship between these measurements. This might be explained by the limited accuracy of the technique used for the 3D reconstruction of the ribs. Consequently, in this work, a novel metho

Combined numerical and morphological study of the lumbar spine: parametric finite element model and evaluation of dynamic implants

Low back pain is a major cause of disability and requires the development of new devices to treat pathologies and improve prognosis following surgery. Finite Element (FE) Methods represent an appealing solution to provide mechanical evaluations of new devices speeding up the design process, as well as evaluating several anatomical scenarios. The aim of this thesis was to develop an accurate FE of the lumbar spine and the evaluation of the variability introduced by morphological and material parameters. The generation of the geometrical model were implemented in a toolbox, the LMG (Lumbar Model Generator), with dimensions based on correlation analyses or subject-specific measurements. It allows the automatic preparation of the FE model, performing the mesh generation and evaluation, assigning material properties, boundary conditions and analysing the results. The FE model of a functional unit (L1-L2) was evaluated and the FE results were in agreement with studies available in literature. Sensitivity analyses on the material properties and morphological parameters were performed and the most influential parameters identified. Moreover, the mechanical behaviour of two devices, the BDyn (S14 Implants (Pessac, France)) and the GsDyn (a device for the paediatric scoliosis developed as part of the Spinal Implant Design project) were evaluated

Investigating the ability to use the CT scan projection radiograph to monitor adolescent idiopathic scoliosis

Introduction: Adolescent idiopathic scoliosis (AIS) is a spinal deformity that causes the spine to bend laterally. Patients with AIS undergo frequent X-ray examinations to monitor the progression of the deformity through the measurement of the Cobb angle, increasing the risk of developing radiation-induced cancer. The aim of this study was to investigate the use of scan projection radiograph (SPR) in computed tomography (CT) to assess AIS by quantifying radiation dose from the SPR acquisitions and comparing it to those of digital radiography (DR) and a dedicated scoliosis imaging system (EOS) and by evaluating the accuracy of Cobb angle measurements on SPR images using a bespoke validated phantom. Methods: A dosimetry phantom representing a 10-year-old child and thermoluminescent dosimeters were used for measuring organ dose to calculate effective dose (ED) and effective risk (ER). Twenty-seven CT SPR protocols were used. A comparison was made to doses from imaging protocols using DR and the EOS system. The effectiveness of a scoliosis shawl for selected projections was also tested. To test the accuracy of Cobb angle measurements on SPR images, a scoliotic phantom was constructed and validated. Poly-methyl methacrylate (PMMA) and plaster of Paris (PoP) were used to represent human soft tissue and bone tissue, respectively, to construct a phantom exhibiting a 15° lateral curve of the spine. The phantom was validated by comparing the Hounsfield unit (HU) of its vertebrae with those of a human and an animal. Additionally, comparisons of signal-to-noise ratio (SNR) to those from a commercially available phantom were made. The angle of the curve in the phantom was measured directly to confirm that it was 15°. The constructed phantom was scanned in CT SPR mode, and the resulting images were visually evaluated against set criteria to determine their suitability for Cobb angle measurements. Those deemed of insufficient quality were excluded. Cobb angle measurements were then performed on the remaining images (n = 10) by 13 observers.Results: EOS had the lowest ED and ER when it was used to irradiate the phantom in AP positions. Five SPR AP imaging protocols and seven PA imaging protocols delivered significantly lower radiation dose and risk than their corresponding imaging positions in DR (p < 0.05). The scoliosis shawl significantly lowered the ED and ER of SPR and DR AP imaging protocols (p < 0.05). The validation of the PoP phantom revealed that the HU of the PoP vertebrae was 628 (SD= 56), human vertebrae was 598 (SD= 79) and sheep vertebra was 605 (SD= 83). The SNR values of the two phantoms correlated strongly (r = 0.93 [(p < 0.05]). The measured scoliosis angle was 14 degrees. When the phantom was imaged using SPR, the difference between the measured Cobb angle and the known angle was, on average, –2.75° (SD = 1.46°). The agreement among the observers was good (p = 0.861, 95% CI [0.70–0.95]) and comparable to similar studies on other imaging modalities which are used for Cobb angle estimation.Conclusion: EOS had the lowest dose. Where this technology is not available, there is a potential for organ dose (OD) reduction in AIS imaging using CT SPR compared with DR. The PoP phantom has physical characteristics (in terms of spinal deformity) and radiological characteristics (in terms of HU and SNR values) of the spine of a 10-year-old child with AIS. CT SPR images can be used for AIS assessment with the 5° margin of error that is clinically acceptable. A few SPR imaging protocols (CT4, 8 and 11) had the lower radiation risk compared with the DR and provided the most accurate Cobb angle measurements.Implications for practice: The bespoke phantom can be used to investigate new X-ray imaging techniques and technology in the assessment of scoliosis and has utility for the optimisation of X-ray imaging techniques in 10-year-old children. Overall, the outcome is promising for patients and health providers because it provides an opportunity to reduce patient dose and achieve clinically acceptable Cobb angle measurements whilst using existing CT technology