1,625 research outputs found
Advanced tracking and image registration techniques for intraoperative radiation therapy
Mención Internacional en el título de doctorIntraoperative electron radiation therapy (IOERT) is a technique used to
deliver radiation to the surgically opened tumor bed without irradiating healthy
tissue. Treatment planning systems and mobile linear accelerators enable
clinicians to optimize the procedure, minimize stress in the operating room (OR)
and avoid transferring the patient to a dedicated radiation room. However,
placement of the radiation collimator over the tumor bed requires a validation
methodology to ensure correct delivery of the dose prescribed in the treatment
planning system. In this dissertation, we address three well-known limitations of
IOERT: applicator positioning over the tumor bed, docking of the mobile linear
accelerator gantry with the applicator and validation of the dose delivery
prescribed. This thesis demonstrates that these limitations can be overcome by
positioning the applicator appropriately with respect to the patient’s anatomy.
The main objective of the study was to assess technological and procedural
alternatives for improvement of IOERT performance and resolution of
problems of uncertainty. Image-to-world registration, multicamera optical
trackers, multimodal imaging techniques and mobile linear accelerator docking
are addressed in the context of IOERT.
IOERT is carried out by a multidisciplinary team in a highly complex
environment that has special tracking needs owing to the characteristics of its
working volume (i.e., large and prone to occlusions), in addition to the requisites
of accuracy. The first part of this dissertation presents the validation of a
commercial multicamera optical tracker in terms of accuracy, sensitivity to
miscalibration, camera occlusions and detection of tools using a feasible surgical
setup. It also proposes an automatic miscalibration detection protocol that
satisfies the IOERT requirements of automaticity and speed. We show that the
multicamera tracker is suitable for IOERT navigation and demonstrate the
feasibility of the miscalibration detection protocol in clinical setups.
Image-to-world registration is one of the main issues during image-guided
applications where the field of interest and/or the number of possible
anatomical localizations is large, such as IOERT. In the second part of this
dissertation, a registration algorithm for image-guided surgery based on lineshaped
fiducials (line-based registration) is proposed and validated. Line-based registration decreases acquisition time during surgery and enables better
registration accuracy than other published algorithms.
In the third part of this dissertation, we integrate a commercial low-cost
ultrasound transducer and a cone beam CT C-arm with an optical tracker for
image-guided interventions to enable surgical navigation and explore image based
registration techniques for both modalities.
In the fourth part of the dissertation, a navigation system based on optical
tracking for the docking of the mobile linear accelerator to the radiation
applicator is assessed. This system improves safety and reduces procedure time.
The system tracks the prescribed collimator location to solve the movements
that the linear accelerator should perform to reach the docking position and
warns the user about potentially unachievable arrangements before the actual
procedure. A software application was implemented to use this system in the
OR, where it was also evaluated to assess the improvement in docking speed.
Finally, in the last part of the dissertation, we present and assess the
installation setup for a navigation system in a dedicated IOERT OR, determine
the steps necessary for the IOERT process, identify workflow limitations and
evaluate the feasibility of the integration of the system in a real OR. The
navigation system safeguards the sterile conditions of the OR, clears the space
available for surgeons and is suitable for any similar dedicated IOERT OR.La Radioterapia Intraoperatoria por electrones (RIO) consiste en la
aplicación de radiación de alta energía directamente sobre el lecho tumoral,
accesible durante la cirugía, evitando radiar los tejidos sanos. Hoy en día, avances
como los sistemas de planificación (TPS) y la aparición de aceleradores lineales
móviles permiten optimizar el procedimiento, minimizar el estrés clínico en el
entorno quirúrgico y evitar el desplazamiento del paciente durante la cirugía a
otra sala para ser radiado. La aplicación de la radiación se realiza mediante un
colimador del haz de radiación (aplicador) que se coloca sobre el lecho tumoral
de forma manual por el oncólogo radioterápico. Sin embargo, para asegurar una
correcta deposición de la dosis prescrita y planificada en el TPS, es necesaria una
adecuada validación de la colocación del colimador. En esta Tesis se abordan
tres limitaciones conocidas del procedimiento RIO: el correcto posicionamiento
del aplicador sobre el lecho tumoral, acoplamiento del acelerador lineal con el
aplicador y validación de la dosis de radiación prescrita. Esta Tesis demuestra
que estas limitaciones pueden ser abordadas mediante el posicionamiento del
aplicador de radiación en relación con la anatomía del paciente.
El objetivo principal de este trabajo es la evaluación de alternativas
tecnológicas y procedimentales para la mejora de la práctica de la RIO y resolver
los problemas de incertidumbre descritos anteriormente. Concretamente se
revisan en el contexto de la radioterapia intraoperatoria los siguientes temas: el
registro de la imagen y el paciente, sistemas de posicionamiento multicámara,
técnicas de imagen multimodal y el acoplamiento del acelerador lineal móvil.
El entorno complejo y multidisciplinar de la RIO precisa de necesidades
especiales para el empleo de sistemas de posicionamiento como una alta
precisión y un volumen de trabajo grande y propenso a las oclusiones de los
sensores de posición. La primera parte de esta Tesis presenta una exhaustiva
evaluación de un sistema de posicionamiento óptico multicámara comercial.
Estudiamos la precisión del sistema, su sensibilidad a errores cometidos en la
calibración, robustez frente a posibles oclusiones de las cámaras y precisión en
el seguimiento de herramientas en un entorno quirúrgico real. Además,
proponemos un protocolo para la detección automática de errores por calibración que satisface los requisitos de automaticidad y velocidad para la RIO
demostrando la viabilidad del empleo de este sistema para la navegación en RIO.
Uno de los problemas principales de la cirugía guiada por imagen es el
correcto registro de la imagen médica y la anatomía del paciente en el quirófano.
En el caso de la RIO, donde el número de posibles localizaciones anatómicas es
bastante amplio, así como el campo de trabajo es grande se hace necesario
abordar este problema para una correcta navegación. Por ello, en la segunda
parte de esta Tesis, proponemos y validamos un nuevo algoritmo de registro
(LBR) para la cirugía guiada por imagen basado en marcadores lineales. El
método propuesto reduce el tiempo de la adquisición de la posición de los
marcadores durante la cirugía y supera en precisión a otros algoritmos de registro
establecidos y estudiados en la literatura.
En la tercera parte de esta tesis, integramos un transductor de ultrasonido
comercial de bajo coste, un arco en C de rayos X con haz cónico y un sistema
de posicionamiento óptico para intervenciones guiadas por imagen que permite
la navegación quirúrgica y exploramos técnicas de registro de imagen para ambas
modalidades.
En la cuarta parte de esta tesis se evalúa un navegador basado en el sistema
de posicionamiento óptico para el acoplamiento del acelerador lineal móvil con
aplicador de radiación, mejorando la seguridad y reduciendo el tiempo del propio
acoplamiento. El sistema es capaz de localizar el colimador en el espacio y
proporcionar los movimientos que el acelerador lineal debe realizar para alcanzar
la posición de acoplamiento. El sistema propuesto es capaz de advertir al usuario
de aquellos casos donde la posición de acoplamiento sea inalcanzable. El sistema
propuesto de ayuda para el acoplamiento se integró en una aplicación software
que fue evaluada para su uso final en quirófano demostrando su viabilidad y la
reducción de tiempo de acoplamiento mediante su uso.
Por último, presentamos y evaluamos la instalación de un sistema de
navegación en un quirófano RIO dedicado, determinamos las necesidades desde
el punto de vista procedimental, identificamos las limitaciones en el flujo de
trabajo y evaluamos la viabilidad de la integración del sistema en un entorno
quirúrgico real. El sistema propuesto demuestra ser apto para el entorno RIO
manteniendo las condiciones de esterilidad y dejando despejado el campo
quirúrgico además de ser adaptable a cualquier quirófano similar.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Raúl San José Estépar.- Secretario: María Arrate Muñoz Barrutia.- Vocal: Carlos Ferrer Albiac
Improving 3D ultrasound prostate localisation in radiotherapy through increased automation of interfraction matching.
Background and purpose Daily image guidance is standard care for prostate radiotherapy. Innovations which improve the accuracy and efficiency of ultrasound guidance are needed, particularly with respect to reducing interobserver variation. This study explores automation tools for this purpose, demonstrated on the Elekta Clarity Autoscan®. The study was conducted as part of the Clarity-Pro trial (NCT02388308). Materials and methods Ultrasound scan volumes were collected from 32 patients. Prostate matches were performed using two proposed workflows and the results compared with Clarity's proprietary software. Gold standard matches derived from manually localised landmarks provided a reference. The two workflows incorporated a custom 3D image registration algorithm, which was benchmarked against a third-party application (Elastix). Results Significant reductions in match errors were reported from both workflows compared to standard protocol. Median (IQR) absolute errors in the left-right, anteroposterior and craniocaudal axes were lowest for the Manually Initiated workflow: 0.7(1.0) mm, 0.7(0.9) mm, 0.6(0.9) mm compared to 1.0(1.7) mm, 0.9(1.4) mm, 0.9(1.2) mm for Clarity. Median interobserver variation was ≪0.01 mm in all axes for both workflows compared to 2.2 mm, 1.7 mm, 1.5 mm for Clarity in left-right, anteroposterior and craniocaudal axes. Mean matching times was also reduced to 43 s from 152 s for Clarity. Inexperienced users of the proposed workflows attained better match precision than experienced users on Clarity. Conclusion Automated image registration with effective input and verification steps should increase the efficacy of interfraction ultrasound guidance compared to the current commercially available tools
Temporal Interpolation via Motion Field Prediction
Navigated 2D multi-slice dynamic Magnetic Resonance (MR) imaging enables high
contrast 4D MR imaging during free breathing and provides in-vivo observations
for treatment planning and guidance. Navigator slices are vital for
retrospective stacking of 2D data slices in this method. However, they also
prolong the acquisition sessions. Temporal interpolation of navigator slices an
be used to reduce the number of navigator acquisitions without degrading
specificity in stacking. In this work, we propose a convolutional neural
network (CNN) based method for temporal interpolation via motion field
prediction. The proposed formulation incorporates the prior knowledge that a
motion field underlies changes in the image intensities over time. Previous
approaches that interpolate directly in the intensity space are prone to
produce blurry images or even remove structures in the images. Our method
avoids such problems and faithfully preserves the information in the image.
Further, an important advantage of our formulation is that it provides an
unsupervised estimation of bi-directional motion fields. We show that these
motion fields can be used to halve the number of registrations required during
4D reconstruction, thus substantially reducing the reconstruction time.Comment: Submitted to 1st Conference on Medical Imaging with Deep Learning
(MIDL 2018), Amsterdam, The Netherland
Mesh-to-raster based non-rigid registration of multi-modal images
Region of interest (ROI) alignment in medical images plays a crucial role in
diagnostics, procedure planning, treatment, and follow-up. Frequently, a model
is represented as triangulated mesh while the patient data is provided from CAT
scanners as pixel or voxel data. Previously, we presented a 2D method for
curve-to-pixel registration. This paper contributes (i) a general
mesh-to-raster (M2R) framework to register ROIs in multi-modal images; (ii) a
3D surface-to-voxel application, and (iii) a comprehensive quantitative
evaluation in 2D using ground truth provided by the simultaneous truth and
performance level estimation (STAPLE) method. The registration is formulated as
a minimization problem where the objective consists of a data term, which
involves the signed distance function of the ROI from the reference image, and
a higher order elastic regularizer for the deformation. The evaluation is based
on quantitative light-induced fluoroscopy (QLF) and digital photography (DP) of
decalcified teeth. STAPLE is computed on 150 image pairs from 32 subjects, each
showing one corresponding tooth in both modalities. The ROI in each image is
manually marked by three experts (900 curves in total). In the QLF-DP setting,
our approach significantly outperforms the mutual information-based
registration algorithm implemented with the Insight Segmentation and
Registration Toolkit (ITK) and Elastix
Implementation of safe human robot collaboration for ultrasound guided radiation therapy
This thesis shows that safe human-robot-interaction and Human Robot Collaboration is possible for Ultrasound (US) guided radiotherapy. Via the chosen methodology, all components (US, optical room monitoring and robot) could be linked and integrated and realized in a realistic clinical workflow.
US guided radiotherapy offers a complement and alternative to existing image-guided therapy approaches. The real-time capability of US and high soft tissue contrast allow target structures to be tracked and radiation delivery to be modulated. However, Ultrasound guided radiation therapy (USgRT) is not yet clinically established but is still under development, as reliable and safe methods of image acquisition are not yet available. In particular, the loss of contact of the US probe to the patient surface poses a problem for patient movements such as breathing.
For this purpose, a Breathing and motion compensation (BaMC) was developed in this work, which together with the safe control of a lightweight robot represents a new development for USgRT. The developed BaMC can be used to control the US probe with contact to the patient. The conducted experiments have confirmed that a steady contact with the patient surface and thus a continuous image acquisition can be ensured by the developed methodology. In addition, the image position in space can be accurately maintained in the submillimeter range.
The BaMC seamlessly integrates into a developed clinical workflow. The graphical user interfaces developed for this purpose, as well as direct haptic control with the robot, provide an easy interaction option for the clinical user. The developed autonomous positioning of the transducer represents a good example of the feasibility of the approach. With the help of the user interface, an acoustic plane can be defined and autonomously approached via the robot in a time-efficient and precise manner. The tests carried out show that this methodology is suitable for a wide range of transducer positions.
Safety in a human-robot interaction task is essential and requires individually customized concepts. In this work, adequate monitoring mechanisms could be found to ensure both patient and staff safety. In collision tests it could be shown that the implemented detection measures work and that the robot moves into a safe parking position. The forces acting on the patient could thus be pushed well below the limits required by the standard.
This work has demonstrated the first important steps towards safe robot-assisted ultrasound imaging, which is not only applicable to USgRT. The developed interfaces provide the basis for further investigations in this field, especially in the area of image recognition, for example to determine the position of the target structure. With the proof of safety of the developed system, first study in human can now follow
Deformation Estimation and Assessment of Its Accuracy in Ultrasound Images
This thesis aims to address two problems; one in ultrasound elastography and one in image registration. The first problem entails estimation of tissue displacement in Ultrasound Elastography (UE). UE is an emerging technique used to estimate mechanical properties of tissue. It involves calculating the displacement field between two ultrasound Radio Frequency (RF) frames taken before and after a tissue deformation. A common way to calculate the displacement is to use correlation based approaches. However, these approaches fail in the presence of signal decorrelation. To address this issue, Dynamic Programming was used to find the optimum displacement using all the information on the RF-line. Although taking this approach improved the results, some failures persisted. In this thesis, we have formulated the DP method on a tree. Doing so allows for more information to be used for estimating the displacement and therefore reducing the error. We evaluated our method on simulation, phantom and real patient data. Our results shows that the proposed method outperforms the previous method in terms of accuracy with small added computational cost.
In this work, we also address a problem in image registration. Although there is a vast literature in image registration, quality evaluation of registration is a field that has not received as much attention. This evaluation becomes even more crucial in medical imaging due to the sensitive nature of the field. We have addressed the said problem in the context of ultrasound guided radiotherapy. Image guidance has become an important part of radiotherapy wherein image registration is a critical step. Therefore, an evaluation of this registration can play an important role in the outcome of the therapy. In this work, we propose using both bootstrapping and supervised learning methods to evaluate the registration. We test our methods on 2D and 3D data acquired from phantom and patients. According to our results, both methods perform well while having advantages and disadvantages over one another. Supervised learning methods offer more accuracy and less computation time. On the other hand, for bootstrapping, no training data is required and also offers more sensitivity
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