100 research outputs found
Méthode de mesure automatique intraopératoire des déformations du rachis scoliotique
RÉSUMÉ
La scoliose idiopathique de l'adolescence est une pathologie complexe et évolutive entraînant une
déformation tridimensionnelle du rachis, de la cage thoracique et du bassin. Cette pathologie
affecte 2 à 4% de la population adolescente. Dans le cas de scolioses sévères, un traitement
chirurgical est recommandé. L’imagerie radiographique est la technique la plus répandue pour le
diagnostic et le suivi des effets de cette pathologie. De plus, des outils de reconstruction 3D du
rachis à partir de radiographies du patient sont actuellement disponibles avant la chirurgie pour
permettre une caractérisation bi- et tridimensionnelle des déformations scoliotiques ainsi que la
planification des manoeuvres d'instrumentation. Les modèles 3D préopératoires ne sont pas
directement utilisables pendant la chirurgie puisqu'il y existe un changement des courbures
scoliotiques dû à la position allongée, à l'exposition chirurgicale et à l'anesthésie.
Plusieurs systèmes de suivi ont été testés pour suivre le changement de forme du rachis et le
mouvement des vertèbres en intraopératoire : mécaniques, optoélectroniques, électromagnétiques,
ultrasons, radiographiques. Ces systèmes permettent de détecter la position des vertèbres pendant
la chirurgie et peuvent être utilisés pour la mise à jour de modèles 3D préopératoires. Pour ce
faire, ils requièrent l'installation de marqueurs sur les vertèbres ou l'identification manuelle de
points anatomiques pendant la chirurgie, ce qui peut interférer avec la procédure chirurgicale.
Ainsi, des systèmes d'imagerie et de navigation intraopératoires sont actuellement disponibles
pour visualiser les déformations 3D du rachis et guider les manoeuvres d'instrumentation de façon
sûre et précise. Cependant, à partir de ces systèmes, il n'est pas encore possible de quantifier en
intraopératoire les déformations scoliotiques et la correction résultant des manoeuvres
d'instrumentation.
Ce projet de maîtrise visait à développer une technique permettant la mesure intraopératoire
automatique des déformations scoliotiques afin de fournir au chirurgien des données quantitatives
exploitables pour évaluer et améliorer la stratégie chirurgicale. Globalement, le calcul des
déformations scoliotiques 3D a été effectué grâce à la mise à jour d'un modèle géométrique
préopératoire à partir d'images fluoroscopiques 3D intraopératoires.
De façon plus précise, un modèle géométrique préopératoire a été construit à partir de 28 repères
anatomiques vertébraux identifiés manuellement par un opérateur sur des radiographies biplanaires
en position érigée avant la chirurgie. Ces points ont été utilisés pour obtenir un modèle----------ABSTRACT
Adolescent idiopathic scoliosis (AIS) is a complex and progressive pathology leading to threedimensional
deformities of the spine, rib cage and pelvis. This pathology affects 2 to 4% of the
adolescent population. In the case of severe scoliosis, a surgical treatment is required.
Radiographic imaging is mostly used for the diagnosis and the monitoring of scoliosis. 3D
reconstruction of the spine from patient’s radiographs is currently available to enable the twoand
three-dimensional characterization of scoliotic deformities and planning of the
instrumentation maneuvers. The 3D preoperative models can’t be directly used during surgery
since there is a change in the scoliotic curvature caused by the prone positioning, the surgical
exposure and the anesthesia.
Several tracking systems have been tested to monitor the spinal shape changes and follow the
intraoperative motion of the vertebrae: optoelectronics or electromagnetics systems, ultrasounds,
radiographs. These systems enable the tracking of the intraoperative positioning of the vertebrae,
and can be used to update 3D preoperative models. This requires the installation of external
markers on vertebrae or the manual identification of anatomic points during surgery, which can
interfere with the surgical procedure. Imaging and navigation systems are then currently available
to visualize the 3D deformities of the spine and to safely and precisely guide the instrumentation
maneuvers. Nevertheless, these systems do not enable the quantification of the intraoperative
scoliotic deformities and the correction resulting from instrumentation maneuvers.
This project aimed to develop a technique that enables the automatic intraoperative measurement
of the scoliotic deformities, in order to provide the surgeon with quantitative feedback to evaluate
and improve the surgical strategy. The 3D scoliotic deformities were computed by registering a
preoperative geometric model with intraoperative 3D fluoroscopic images of the spine.
More precisely, a preoperative geometric model was constructed from 28 vertebral landmarks
manually identified by an operator on biplanar radiographs acquired preoperatively in standing
position. These landmarks were used to obtain a surface model of each vertebra though a dual
kriging interpolation technique. The intraoperative model was computed by the registration
between this preoperative geometric model and the intraoperative data, composed of a voxelized
model obtained from 3D fluoroscopic images. Each vertebra of the voxelized model was
segmented and manually identified on intraoperative 3D fluoroscopic images. A rigid registratio
Co-operative surveillance cameras for high quality face acquisition in a real-time door monitoring system
A poster session on co-operative surveillance cameras for high quality face acquisition in a real-time door monitoring syste
An Optimized Spline-Based Registration of a 3D CT to a Set of C-Arm Images
We have developed an algorithm for the rigid-body registration of
a CT volume to a set of C-arm images.
The algorithm uses a gradient-based iterative minimization of a least-squares measure
of dissimilarity between the C-arm images and projections of the
CT volume. To compute projections, we use a novel method for fast
integration of the volume along rays. To improve robustness and
speed, we take advantage of a coarse-to-fine processing of the
volume/image pyramids. To compute the projections of the volume,
the gradient of the dissimilarity measure, and the multiresolution
data pyramids, we use a continuous image/volume model based on
cubic B-splines, which ensures a high interpolation accuracy and a
gradient of the dissimilarity measure that is well defined
everywhere. We show the performance of our algorithm on a human
spine phantom, where the true alignment is determined using a set
of fiducial markers
Advanced capabilities for planar X-ray systems
Mención Internacional en el título de doctorThe past decades have seen a rapid evolution towards the use of digital detectors
in radiology and a more flexible robotized movement of the system components,
X-ray tube and detector. This evolution opened the possibility for incorporating
advanced capabilities in these planar X-ray systems, and for providing new valuable
diagnostic information compared to the previous technology. Some of the current
challenges for radiography are to obtain more quantitative images and to reduce the
inherent superposition of tissues because of the 2D nature of the technique.
Dual energy radiography, based on the acquisition of two images at different
source voltages, enables a separate characterization of soft tissue and bone structures.
Its benefits over conventional radiography have been proven in different applications,
since it improves information content without adding significant extra
acquisition time or radiation dose.
In a different direction, a really disruptive advance would be to obtain 3D imaging
with systems designed just for planar images. The incorporation of tomographic
capabilities into these systems would have to deal with the acquisition of a limited
number of projections, with non-standard geometrical configurations.
This thesis presents original contributions in these two directions: dual energy
radiography and 3D imaging with X-ray systems designed for planar imaging. The
work is framed in a line of research of the Biomedical Imaging and Instrumentation
Group from the Bioengineering and Aerospace Department of University Carlos III
de Madrid working jointly with the University Hospital Gregorio Marañón, focused
on the advance of radiology systems. This research line is carried out in collaboration
with the group of Computer Architecture, Communications and Systems (ARCOS),
from the same university, the Imaging Research Laboratory (IRL) of the University
of Washington and the research center CREATIS, France. The research has a clear
focus on technology transfer to the industry through the company Sedecal, a Spanish
multinational among the 10 best world companies in the medical imaging field.
The first contribution of this thesis is a complete novel protocol to incorporate
dual energy capabilities that enable quantitative planar studies. The proposal is
based on the use of a preliminary calibration with a very simple and low-cost phantom
formed by two parts that represent soft tissue and bone equivalent materials.
This calibration is performed automatically with no strict placement requirements.
Compared to current Dual-energy X-ray Absorptiometry (DXA) systems, 1) it provides
real mass-thickness values directly, enabling quantitative planar studies instead
of relative comparisons, and 2) it is based on an automatic preliminary calibration without the need of interaction of an experienced technician.
The second contribution is a novel protocol for the incorporation of tomographic
capabilities into X-ray systems originally intended for planar imaging. For this purpose,
we faced three main challenges.
First, the geometrical trajectory of equipment follows non-standard circular orbits,
thus posing severe difficulties for reconstruction. To handle this, the proposed
protocol comprises a new geometrical calibration procedure that estimates all the
system parameters per-projection.
Second, the reconstruction of a limited number of projections from a reduced angular
span leads to severe artifacts when using conventional reconstruction methods.
To deal with these limited-view data, the protocol includes a novel advanced reconstruction
method that incorporates the surface information of the sample, which
can be extracted with a 3D light surface scanner. These data are introduced as an
imposed constraint following the Split Bregman formulation. The restriction of the
search space by exploiting the surface-based support becomes crucial for a complete
recovery of the external contour of the sample and surroundings when the angular
span is extremely reduced. The modular, efficient and flexible design followed for its
implementation allows for the reconstruction of limited-view data with non-standard
trajectories.
Third, the optimization of the acquisition protocols has not yet explored with
these systems. This thesis includes a study of the optimum acquisition protocols
that allowed us to identify the possibilities and limitations of these planar systems.
Using the surface-constrained method, it is possible to reduce the total number of
projections up to 33% and the angular span down to 60 degrees.
The contributions of this thesis open the way to provide depth and quantitative
information very valuable for the improvement of radiological diagnosis. This could
impact considerably the clinical practice, where conventional radiology is still the
imaging modality most used, accounting for 80-90% of the total medical imaging
exams. These advances open the possibility of new clinical applications in scenarios
where 1) the reduction of the radiation dose is key, such as lung cancer screening or
Pediatrics, according to the ALARA criteria (As Low As Reasonably Achievable),
2) a CT system is not usable due to movement limitations, such as during surgery
or in an ICU and 3) where costs issues complicate the availability of CT systems,
such as rural areas or underdeveloped countries.
The results of this thesis has a clear application in the industry, since it is part
of a proof of concept of the new generation of planar X-ray systems that will be
commercialized worldwide by the company SEDECAL (Madrid, Spain).Los últimos años están viendo un rápido avance de los sistemas de radiología hacia el
uso de detectores digitales y a una mayor flexibilidad de movimientos de los principales
componentes del sistema, el tubo de rayos X y el detector. Esta evolución abre
la posibilidad de incorporar capacidades avanzadas en sistemas de imagen plana por
rayos X proporcionando nueva información valiosa para el diagnóstico. Dos retos en
radiografía son obtener imágenes cuantitativas y reducir la superposición de tejidos
debida a la naturaleza proyectiva de la técnica.
La radiografía de energía dual, basada en la adquisición de dos imágenes a diferente
kilovoltaje, permite obtener imágenes de tejido blando y hueso por separado.
Los beneficios de esta técnica que aumenta la cantidad de información sin añadir
un tiempo de adquisición o de dosis de radiación extra significativos frente al uso de
radiografía convencional, han sido demostrados en diferentes aplicaciones.
En otra dirección, un avance realmente disruptivo sería la obtención de imagen
3D con sistemas diseñados únicamente para imagen plana. La incorporación de capacidades
tomográficas en estos sistemas tendría que lidiar con la adquisición de un
número limitado de proyecciones siguiendo trayectorias no estándar.
Esta tesis presenta contribuciones originales en esas dos direcciones: radiografía
de energía dual e imagen 3D con sistemas de rayos X diseñados para imagen plana.
El trabajo se encuadra en una línea de investigación del grupo de Imagen Biomédica
e Instrumentación del Departamento de Bioingeniería e Ingeniería Aerospacial de
la Universidad Carlos III de Madrid junto con el Hospital Universitario Gregorio
Marañon, centrada en el avance de sistemas de radiología. Esta línea de investigación
se desarollada en colaboración con el grupo Computer Architecture, Communications
and Systems (ARCOS), de la misma universidad, el grupo Imaging Research Laboratory
(IRL) de la Universidad de Washington y el centro de investigación CREATIS,
de Francia. Se trata de una línea de investigación con un claro enfoque de transferencia
tecnológica a la industria a través de la compañía SEDECAL, una multinacional
española de entre las 10 líderes del mundo en el campo de la radiología.
La primera contribución de esta tesis es un protocolo completo para incorporar
capacidades de energía dual que permitan estudios cuantitativos de imagen plana.
La propuesta se basa en una calibración previa con un maniquí simple y de bajo coste
formado por dos materiales equivalentes de tejido blando y hueso respectivamente.
Comparado con los sistemas actuales DXA (Dual-energy X-ray Absorptiometry),
1) proporciona valores reales de tejido atravesado, 2) se basa en una calibración
automática que no requiere la interacción de un técnico con gran experiencia. La segunda contribución es un protocolo nuevo para la incorporación de capacidades
tomográficas en sistemas de rayos X originariamente diseñados para imagen
plana. Para ello, nos enfrentamos a tres principales dificultades.
En primer lugar, las trayectorias que pueden seguir la fuente y el detector en
estos sistemas no constituyen órbitas circulares estándares, lo que plantea retos importantes
en la caracterización geométrica. Para solventarlo, el protocolo propuesto
incluye una calibración geométrica que estima todos los parámetros geométricos del
sistema para cada proyección.
En segundo lugar, la reconstrucción de un número limitado de proyecciones
adquiridas en un rango angular reducido da lugar a artefactos graves cuando se
reconstruye con algoritmos convencionales. Para lidiar con estos datos de ángulo
limitado, el protocolo incluye un nuevo método avanzado de reconstrucción que incorpora
la información de superficie de la muestra, que se puede se obtener con un
escáner 3D. Esta información se impone como una restricción siguiendo la formulación
de Split Bregman, para compensar la falta de datos. La restricción del espacio
de búsqueda a través de la explotación del soporte basado en superficie, es crucial
para una recuperación completa del contorno externo de la muestra cuando el rango
angular es extremadamente pequeño. El diseño modular, eficiente y flexible de la
implementación propuesta permite reconstruir datos de ángulo limitado obtenidos
con posiciones de fuente y detector no estándar.
En tercer lugar, hasta la fecha, no se ha explorado la optimización del protocolo
de adquisición con estos sistemas. Esta tesis incluye un estudio de los protocolos
óptimos de adquisición que permitió identificar las posibilidades y limitaciones de
estos sistemas de imagen plana. Gracias al método de reconstrucción basado en
superficie, es posible reducir el número total de proyecciones hasta el 33% y el rango
angular hasta 60 grados.
Las contribuciones de esta tesis abren la posibilidad de proporcionar información
de profundidad y cuantitativa muy valiosa para la mejora del diagnóstico radiológico.
Esto podría impactar considerablemente en la práctica clínica, donde la radiología
convencional es todavía la modalidad de imagen más utilizada, abarcando el 80-
90% del total de los exámenes de imagen médica. Estos avances abren la posibilidad
de nuevas aplicaciones clínicas en escenarios donde 1) la reducción de la dosis de
radiación es clave, como en screening de cáncer de pulmón, de acuerdo con el criterio
ALARA (As Low As Reasonably Achievable), 2) no se puede usar un sistema
TAC por limitaciones de movimiento como en cirugía o UCI, o 3) el coste limita la
disponibilidad de sistemas TAC, como en zonas rurales o en países subdesarrollados.
Los resultados de esta tesis presentan una clara aplicación industrial, ya que
son parte de un prototipo de la nueva generación de sistemas planos de rayos X que
serán distribuidos mundialmente por la compañía SEDECAL.This thesis has been developed as part of several research projects with public funding:
- DPI2016-79075-R. ”Nuevos escenarios de tomografía por rayos X”, IP: Mónica
Abella García, Ministerio de Economía y Competitividad, 01/01/2017-31/12/2019,
147.620 e.
- ”Nuevos escenarios de tomografía por rayos X (NEXT) DPI2016-79075-R.
Ministerio de Economía”, Industria y Competitividad. (Universidad Carlos
III de Madrid). 30/12/2016-29/12/2019. 147.620 e.
(…)
- FP7-IMI-2012 (GA-115337), ”PreDict-TB: Model-based preclinical development
of anti-tuberculosis drug combinations”. FP7-IMI - Seventh Framework
Programme (EC-EFPIA). Unión Europea. (Universidad Carlos III de Madrid).
01/05/2012-31/10/2017.
(…)
- TEC2013-47270-R, ”Avances en Imagen Radiológica (AIR)”, Ministerio de
Economía y Competitividad”, 01/01/2014-31/12/2016. IP: Mónica Abella Garcia
and Manuel Desco Menéndez. 160.204 e
(…)
- RTC-2014-3028-1, ”Nuevos Escenarios Clínicos con Radiología Avanzada (NECRA)”,
Ministerio de Economía y Competitividad, 01/06/2014-31/12/2016 IP: Mónica
Abella García. 2014-2016. 219.458,96 e
- IDI-20130301, ”Nuevo sistema integral de radiografía (INNPROVE: INNovative
image PROcessing in medicine and VEterinary)”, IP: Mónica Abella García
and Manuel Desco Menéndez. Ministerio de Economía y Competitividad.
Subcontratación CDTI, 14/01/2013-31/03/2015. Total: 1.860.629e (UC3M:
325.000e). (Art. 83)
- IPT-2012-0401-300000 INNPACTO 2012, ”Tecnologías para Procedimientos
Intraoperatorios Seguros y Precisos. XIORT. MINECO. (Universidad Carlos
III de Madrid). 01/01/2013-31/12/2015.Programa Oficial de Doctorado en Ingeniería MatemáticaPresidente: Doménec Ros Puig.- Secretario: Cyril Riddell.- Vocal: Yannick Boursie
Measurement of intervertebral cervical motion by means of dynamic X-ray image processing and data interpolation
Accurate measurement of intervertebral kinematics of the cervical spine can support the diagnosis of widespread diseases related to neck pain, such chronic whiplash dysfunction, arthritis, segmental degeneration. The natural inaccessibility of the spine, its complex anatomy and the small range of motion only permit concise measurement in-vivo. Low dose X-ray fluoroscopy allows time-continuous screening of cervical spine during patient’s spontaneous motion. To obtain accurate motion measurements, each vertebra was tracked by means of image processing along a sequence of radiographic images. To obtain a time-continuous representation of motion and to reduce noise in the experimental data, smoothing spline interpolation was used. Estimation of intervertebral motion for cervical segments was obtained by processing patient’s fluoroscopic sequence: intervertebral angle and displacement and the instantaneous centre of rotation were computed. The RMS value of fitting errors resulted about 0.2 degree for rotation and 0.2 mm for displacement
Overview of the 2005 cross-language image retrieval track (ImageCLEF)
The purpose of this paper is to outline efforts from the 2005 CLEF crosslanguage image retrieval campaign (ImageCLEF). The aim of this CLEF track is to explore
the use of both text and content-based retrieval methods for cross-language image retrieval. Four tasks were offered in the ImageCLEF track: a ad-hoc retrieval from an historic photographic collection, ad-hoc retrieval from a medical collection, an automatic image annotation task, and a user-centered (interactive) evaluation task that is explained in the iCLEF summary. 24 research groups from a variety of backgrounds and nationalities (14 countries) participated in ImageCLEF. In this paper we describe the ImageCLEF tasks, submissions from participating groups and summarise the main fndings
Measurement of intervertebral cervical motion by means of dynamic X-ray image processing and data interpolation
Accurate measurement of intervertebral kinematics of the cervical spine can support the diagnosis of widespread diseases related to neck pain, such as chronic whiplash dysfunction, arthritis, and segmental degeneration. The natural inaccessibility of the spine, its complex anatomy, and the small range of motion only permit concise measurement in vivo. Low dose X-ray fluoroscopy allows time-continuous screening of cervical spine during patient's spontaneous motion. To obtain accurate motion measurements, each vertebra was tracked by means of image processing along a sequence of radiographic images. To obtain a time-continuous representation of motion and to reduce noise in the experimental data, smoothing spline interpolation was used. Estimation of intervertebral motion for cervical segments was obtained by processing patient's fluoroscopic sequence; intervertebral angle and displacement and the instantaneous centre of rotation were computed. The RMS value of fitting errors resulted in about 0.2 degree for rotation and 0.2 mm for displacements
Recalage et mise en correspondance d’images tomographiques et de projection: Résultats préliminaires d’une solution hybride en radiochirurgie
A new method for 2D/3D registration, applied to Magnetic Resonance Imaging (3D) and to X-Ray angiography (2D), has
been adapted and used for planning treatment in radiosurgery. The imaging flow needed for planning radiosurgery is
considerable and using registration technique would make lighter the imaging protocol without restricting planning. We
describe the preliminary results of the evaluation giving criteria to compare registration technique and localization using
stereotactic frame, which is the gold standard method. Preliminary results obtained during this first step in validating
registration put forward which kind of MRI sequence are more suitable to registration.Une méthode de recalage d’images multimodales 2D/3D entre Imagerie par Résonance Magnétique (3D) et
à l’angiographie par rayons X (2D) est appliquée à la planification dosimétrique en radiochirurgie. Le flux d’images
nécessaires à la réalisation du traitement en radiochirurgie est considérable. La fusion de ces images
multimodales dans un espace commun est requise pour la planification. Ainsi, elles nécessitent d’être acquises en
utilisant un référentiel dit «stéréotaxique». Cependant, l’utilisation d’algorithmes de recalage dans la phase de
planification permet de simplifier les procédures d’imagerie en diminuant l’usage du cadre sans contraindre la
planification. Nous proposons ici les résultats préliminaires de l’application du recalage dans un contexte
radiochirurgical par comparaison avec la méthode basée sur un repérage stéréotaxique qui constitue le gold
standard. Les résultats préliminaires obtenus lors de cette première phase de validation permettent de conclure
sur la compatibilité de certaines séquences d’images IRM avec le recalage d’images tomographique et de
projectio
Synthèse d’images tomodensitométriques à partir d’IRM par des réseaux adverses génératifs pour le recalage 3D/2D de la colonne vertébrale
L’information structurelle tridimensionnelle apporte une aide précieuse aux procédures or-thopédiques qui, le plus souvent, n’ont à portée de main que des modalités d’imagerie bi-dimensionnelles pour se guider. Non seulement cela aide-t-il à améliorer la précision des manoeuvres, mais cela permet aussi, dans plusieurs cas, de rendre les procédures moins in-vasives. La modalité d’imagerie bidimensionnelle sur laquelle se concentre ce mémoire est la fluoroscopie de bras en C. Celle-ci est très répandue dans les salles opératoires et permet une acquisition rapide et versatile pour guider les procédure orthopédiques. Cette modalité est le plus souvent fusionnée avec la tomodensitométrie par un recalage 2D/3D. Ces deux modalités reposent sur le principe d’absorption de rayons X, ce qui fait que l’on retrouve des similarités dans la géométrie et dans les intensités d’une modalité à l’autre. Cela simplifie le problème. Toutefois, la tomodensitométrie n’o˙re pas les meilleurs contrastes pour visualiser les organes, les nerfs et les tissus mous ; d’autant plus qu’elle cause une irradiation non né-gligeable au patient. En revanche, l’IRM se prête mieux à la visualisation des organes et des tissus mous. Elle a aussi l’avantage de ne pas irradier le patient. Le contraste de celle-ci est très di˙érent de la tomodensitométrie, surtout au niveau de la colonne vertébrale ; ce qui rend le problème de recalage 2D/3D avec la fluoroscopie de bras en C plus diÿcile. Les dernières avancées en apprentissage profond montrent des résultats très prometteurs pour la tache de translation d’image. Ceci est applicable à la génération de tomodensitométrie synthétique à partir d’IRM pour un recalage 2D/3D subséquent.
Nous proposons une méthode de recalage 2D/3D par Digitally Reconstructed Radiograph (DRR) entre l’imagerie par résonance magnétique et la fluoroscopie de bras en C, basée sur la synthèse de tomodensitométrie par des méthodes d’apprentissage profond. En premier lieu, nous explorons plusieurs architectures de réseaux adverses génératifs. Ces architectures-là ont montré d’impressionnants résultats pour la translation d’images non médicales. Nous expérimentons avec un ensemble de données public constitué de 18 volumes d’IRM et de CT. Nous constatons que l’architecture CycleGAN généralise mieux à des données non-observées que l’architecture cGAN, et que celle-ci tend à sur-apprendre. Nous introduisons aussi deux nouvelles composantes à l’architecture CycleGAN pour améliorer la résolution tridimension-nelle ainsi que la distribution des intensités pour les CT synthétiques. Enfin, nous e˙ectuons un recalage 2D/3D par DRR en utilisant les tomodensitométries synthétiques, avec une er-reur de recalage de 2.1 ± 0.2mm pour valider notre méthode. La méthode proposée, de par ses composantes que par son application, présente un fort potentiel tant pour la synthèse d’images médicales que pour le recalage multimodal.----------ABSTRACT
The structural information in three dimensions brings valuable insight and added precision to orthopedic interventions, which may otherwise only rely on bidimensional imaging modalities. Not only does 3D imaging help improve surgical accuracy, but it also helps reduce invasive-ness. The bidimensional imaging modality on which we focus in this work is the C-Arm fluroscopy. The latter is very common in operating theaters and allows for real-time versatile image acquisition to help guide interventions. That modality is often fused with CT scans to bring the added precision from the third dimension and lift the projective uncertainty on depth. CT and C-Arm fluoroscopy both rely on the physical principle of X-Ray absorption, which allows for their respective geometry and intensity distributions to be strongly corre-lated, and makes the registration problem relatively easier. However, computed tomography does not have the best contrast to visualize organs, nerves and soft tissue. It also involves a non-negligeable radiation dose. On the other hand, MRI allows itself to a better visualization of those organs and of soft tissue. It also has the advantage of not exposing the patient to ionizing radiation. The MRI contrast being very di˙erent than that of the CT, especially for the spine, makes the 2D/3D registration problem much harder.
The latest advances in deep learning show promising results for the task of image translation, which is applicable to the generation of a synthetic CT from an MRI, for a subsequent 2D/3D registration to C-Arm fluoroscopy through Digitally Reconstructed Radiographs (DRR). We propose such a method for 2D/3D registration between magnetic resonance imaging and C-Arm fluoroscopy, based on synthetic CT generation using deep learning methods. First, we explore numerous generative adversarial network architectures. Those architectures have shown impressive results for non-medical image translation. We experiment with a public dataset of 18 MRI and CT volumes. We notice that the CycleGAN architecture generalizes better to unseen data than the cGAN architecture does. The latter tends to overfit. We also introduce two new components to the CycleGAN architecture, which improves the tridimen-sional resolution as well as the voxel intensity distribution of the synthetic data. Finally, we perform DRR-based 2D/3D registration using the synthetic CT, and validate our method with a registration error of 2.1 ± 0.2mm. The proposed method, through its components and through its application, o˙ers a strong potential for medical image synthesis as well as multimodal registration
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