369 research outputs found
Theoretical and Experimental Evaluation of Spatial Resolution in a Variable Resolution X-Ray Computed Tomography Scanner
A variable resolution x-ray (VRX) computed tomography (CT) scanner can image objects of various sizes with greatly improved spatial resolution. The scanner employs an angulated discrete detector and achieves the resolution boost by matching the detector angulation to the scanner field of view (FOV) determined by the size of an object being imaged. A comprehensive evaluation of spatial resolution in an experimental version of the VRX CT scanner is presented in this dissertation. Two components of this resolution were evaluated – the pre-reconstruction spatial resolution, described by the detector presampling modulation transfer function (MTF), and the post-reconstruction spatial resolution, given by the scanner reconstruction MTF. The detector presampling MTF was modeled by the Monte Carlo simulation and measured by the moving-slit method. The modeled results showed the increase in the maximum cutoff frequency (in the detector plane) from 1.53 to 53.64 cycles per mm (cy/mm) as the scanner FOV decreased from 32 to 1 cm. The measured results supported the modeling, except for the small FOVs (below 8 cm), where the MTF could not be measured up to the cutoff frequency due to the focal-spot limitation. The scanner reconstruction MTF was measured by the special-phantom method. The measured results demonstrated the increase in the average cutoff frequency (in the object plane) from 2.44 to 4.13 cy/mm as the scanner FOV decreased from 16 to 8 cm. The MTF could not be measured at the FOVs other than 8 and 16 cm, due to the calibration-reconstruction inaccuracies and, again, the focal-spot limitation. Overall, the evaluation confirmed the potential value of the VRX CT scanner and produced results important for its further development
Advanced Image Reconstruction for Limited View Cone-Beam CT
In a standard CT acquisition, a high number of projections is obtained around the sample, generally covering an angular span of 360º. However, complexities may arise in some clinical scenarios such as surgery and emergency rooms or Intensive Care Units (ICUs) when the accessibility to the patient is limited due to the monitoring equipment attached. X-ray systems used in these cases are usually C-arms that only enable the acquisition of planar images within a limited angular range. Obtaining 3D images in these scenarios could be extremely interesting for diagnosis or image guided surgery. This would be based on the acquisition of a small number of projections within a limited angular span. Reconstruction of these limited-view data with conventional algorithms such as FDK result in streak artifacts and shape distortion deteriorating the image quality. In order to reduce these artifacts, advanced reconstruction methods can be used to compensate the lack of data by the incorporation of prior information.
This bachelor thesis is framed on one of the lines of research carried out by the Biomedical Imaging and Instrumentation group from the Bioengineering and Aerospace Department of Universidad Carlos III de Madrid working jointly with the Hospital General Universitario Gregorio Marañón through its Instituto de Investigación Sanitaria. This line of research is carried out in collaboration with the company SEDECAL, which enables the direct transfer to the industry.
Previous work showed that a new iterative reconstruction method proposed by the group, SCoLD, is able to restore the altered contour of the object, suppress greatly the streak artifacts and recover to some extend the image quality by restricting the space of search with a surface constraint. However, the evaluation was only carried out using a simulated mask that described the shape of the object obtained by thresholding a previous CT image of the sample, which is generally not available in real scenarios. The general objective of this thesis is the designing of a complete workflow to implement SCoLD in real scenarios.
For that purpose, the 3D scanner Artec Eva was chosen to acquire the surface information of the sample, which was then transformed to be usable as prior information for SCoLD method.
The evaluation done in a rodent study showed high similarity between the mask obtained from real data and the ideal mask obtained from a CT. Distortions in shape and streak artifacts in the limited-view FDK reconstruction were greatly reduced when using the real mask with the SCoLD reconstruction and the image quality was highly improved demonstrating the feasibility of the proposal.Grado en Ingeniería Biomédica (Plan 2010
Comparative linear accuracy of cone beam CT derived 3D images in orthodontic analysis.
Objective . To compare the in vitro reliability and accuracy of linear measurements between cephalometric landmarks on CBCT 3D images with varying basis projection images to direct measurements on human skulls. Methods . Sixteen linear dimensions between anatomical sites marked on 19 human skulls were directly measured. Skulls were imaged with CBCT at three settings: 153, 306, and 612 basis projections. The mean absolute error and modality mean of linear measurements between landmarks on 3D images were compared to the anatomic truth. Results . No difference in mean absolute error between the scan settings was found. The average skull absolute error between marked reference points were less than the distances between unmarked reference sites. Conclusion . CBCT measurements were consistent between scan sequences and for direct measurements between marked reference points. Reducing the number of projections for 3D reconstruction did not lead to reduced dimensional accuracy and potentially provides reduced patient radiation exposure
Comparative linear accuracy and reliability of cone beam CT derived 2-dimensional and 3-dimensional images constructed using an orthodontic volumetric rendering program.
The purpose of this project was to compare the accuracy and reliability of linear measurements made on 2D projections and 3D reconstructions using Dolphin 3D software (Chatsworth, CA) as compared to direct measurements made on human skulls. The linear dimensions between 6 bilateral and 8 mid-sagittal anatomical landmarks on 23 dentate dry human skulls were measured three times by multiple observers using a digital caliper to provide twenty orthodontic linear measurements. The skulls were stabilized and imaged via PSP digital cephalometry as well as CBCT. The PSP cephalograms were imported into Dolphin (Chatsworth, CA, USA) and the 3D volumetric data set was imported into Dolphin 3D (Version 2.3, Chatsworth, CA, USA). Using Dolphin 3D, planar cephalograms as well as 3D volumetric surface reconstructions were (3D CBCT) generated. The linear measurements between landmarks of each three modalities were then computed by a single observer three times. For 2D measurements, a one way ANOVA for each measurement dimension was calculated as well as a post hoc Scheffe multiple comparison test with the anatomic distance as the control group. 3D measurements were compared to anatomic truth using Student\u27s t test (PiÜ50.05). The intraclass correlation coefficient (ICC) and absolute linear and percentage error were determined as indices of intraobserver reliability. Our results show that for 2D mid sagittal measurements that Simulated LC images are accurate and similar to those from PSP images (except for Ba-Na), and for bilateral measurements simulated LC measurements were similar to PSP but less accurate, underestimating dimensions by between 4.7% to 17%.For 3D volumetric renderings, 2/3 rd of CBCT measurements are statistically different from actual measurements, however this possibly is not clinically relevant
Development and Implementation of Fully 3D Statistical Image Reconstruction Algorithms for Helical CT and Half-Ring PET Insert System
X-ray computed tomography: CT) and positron emission tomography: PET) have become widely used imaging modalities for screening, diagnosis, and image-guided treatment planning. Along with the increased clinical use are increased demands for high image quality with reduced ionizing radiation dose to the patient. Despite their significantly high computational cost, statistical iterative reconstruction algorithms are known to reconstruct high-quality images from noisy tomographic datasets. The overall goal of this work is to design statistical reconstruction software for clinical x-ray CT scanners, and for a novel PET system that utilizes high-resolution detectors within the field of view of a whole-body PET scanner. The complex choices involved in the development and implementation of image reconstruction algorithms are fundamentally linked to the ways in which the data is acquired, and they require detailed knowledge of the various sources of signal degradation. Both of the imaging modalities investigated in this work have their own set of challenges. However, by utilizing an underlying statistical model for the measured data, we are able to use a common framework for this class of tomographic problems. We first present the details of a new fully 3D regularized statistical reconstruction algorithm for multislice helical CT. To reduce the computation time, the algorithm was carefully parallelized by identifying and taking advantage of the specific symmetry found in helical CT. Some basic image quality measures were evaluated using measured phantom and clinical datasets, and they indicate that our algorithm achieves comparable or superior performance over the fast analytical methods considered in this work. Next, we present our fully 3D reconstruction efforts for a high-resolution half-ring PET insert. We found that this unusual geometry requires extensive redevelopment of existing reconstruction methods in PET. We redesigned the major components of the data modeling process and incorporated them into our reconstruction algorithms. The algorithms were tested using simulated Monte Carlo data and phantom data acquired by a PET insert prototype system. Overall, we have developed new, computationally efficient methods to perform fully 3D statistical reconstructions on clinically-sized datasets
Development and Application of Computational Tools for the Study and Optimization of Variable Resolution X-ray (VRX) Computed Tomography Scanners
The overall goal of this project was to develop and apply important computerized aids for the design and implementation of Variable Resolution X-ray (VRX) CT scanners developed at the University of Tennessee, Memphis. VRX scanners take advantage of the “projective compression” principle that allows the same device to image objects of very different sizes with the same level of detail by adjusting the field of view and the reconstruction resolution.
The first part of this project aimed to develop a set of computational tools specifically tailored for the design, implementation and study of VRX scanners. This included creating a reconstruction algorithm that takes into account the unique geometries of the different VRX systems that have been designed, along with improving the calibration algorithm needed to ensure a proper reconstruction. It also included the development of a computer model of VRX scanners that is an invaluable tool for the development and study of these devices.
The second part of the project was composed of a small series of experiments in which the computational tools developed proved to be fundamental in the analysis and evaluation of some aspects of VRX imaging. This included a comparison of the performance of different targeting VRX geometries in terms of spatial and contrast resolution, and a study of the effect of the VRX angle on the severity of common artifacts in single-arm images
Doctor of Philosophy
dissertationX-ray computed tomography (CT) is a widely popular medical imaging technique that allows for viewing of in vivo anatomy and physiology. In order to produce high-quality images and provide reliable treatment, CT imaging requires the precise knowledge of t
Evaluating the reliability of four-dimensional computed tomography scans of the wrist
Introduction: Four-dimensional CT (or 4D CT) scans are a novel approach to diagnosing
musculoskeletal pathology. Although still in its infancy, there has been a surge of interest
in identifying clinical applications for musculoskeletal 4D CT. The scapholunate joint has
received the most attention thus far due to the complex articulations and challenges faced
with prompt diagnosis of scapholunate injuries. The objective of this thesis is to review
current literature on musculoskeletal 4D CT and to evaluate the inter- and intra-rater
reliability of the assessment of scapholunate stability in 4D CT wrist scans.
Methodology: 4D CT scans of thirteen healthy volunteers and four patients were
prepared. Seven orthopaedic and plastic surgeons were recruited to qualitatively assess
the stability of the scapholunate joint in the 4D CT scans. Statistical analysis included
percent agreement, Fleiss’ kappa, and Gwet’s AC1 coefficient.
Results: The percent agreement amongst all raters was 0.80392 (95% CI: 0.675 - 0.932).
Fleiss’ Kappa was 0.54895 (95% CI: 0.252 - 0.846) and Gwet’s AC₁ was 0.54895 (95% CI:
0.391 - 0.915). The intraclass correlation coefficient (ICC) for intra-rater reliability was
0.71631 (95% CI: 0.5567 – 0.8423).
Conclusion: Our pilot study suggests good inter- and intra-rater reliability for the
qualitative assessment of scapholunate instability in 4D CT scans. Although further
studies are required, this thesis highlights the vast potential of 4D CT as a non-invasive
diagnostic technique of dynamic musculoskeletal injuries
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
- …