59 research outputs found
A versatile imaging system for in vivo small animal research
In vivo small animal imaging has become an essential technique for molecular biology studies. However, requirements of spatial resolution, sensitivity and image quality are quite challenging for the development of small-animal imaging systems. The capabilities of the system are also significant for carrying out small animal imaging in a wide range of biological studies. The goal of this dissertation is to develop a high-performance imaging system that can readily meet a wide range of requirements for a variety of small animal imaging applications. Several achievements have been made in order to fulfill this goal.;To supplement our system for parallel-hole single photon emission computed tomography (SPECT) based upon a 110 mm diameter circular detector, we have developed novel compact gamma cameras suitable for imaging an entire mouse. These gamma cameras facilitate multi-head (\u3e2) parallel-hole SPECT with the mouse in close proximity to the detector face in order to preserve spatial resolution. Each compact gamma cameras incorporates pixellated Nal(Tl) scintillators and a pair of Hamamatsu H8500 position sensitive photomultiplier tubes (PSPMTs). Two types of copper-beryllium parallel-hole collimators have been designed. These provide high-sensitivity imaging of I-125 or excellent spatial resolution over a range of object-detector distances. Both phantom and animal studies have demonstrated that these gamma cameras perform well for planar scintigraphy and parallel-hole SPECT of mice.;To further address the resolution limitations in parallel-hole SPECT and the sensitivity and limited field of view of single-pinhole SPECT, we have developed novel multipinhole helical SPECT based upon a 110 mm diameter circular detector equipped with a pixellated Nal(Tl) scintillator array. A brass collimator has been designed and produced containing five 1 mm diameter pinholes. Results obtained in SPECT studies of various phantoms show an enlarged field of view, very good resolution and improved sensitivity using this new imaging technique.;These studies in small-animal imaging have been applied to in vivo biological studies related to human health issues including studies of the thyroid and breast cancer. A re-evaluation study of potassium iodide blocking efficiency in radioiodine uptake in mice suggests that the FDA-recommended human dose of stable potassium iodide may not be sufficient to effectively protect the thyroid from radioiodine contamination. Another recent study has demonstrated that multipinhole helical SPECT can resolve the fine structure of the mouse thyroid using a relatively low dose (200 muCi). Another preclinical study has focused on breast tumor imaging using a compact gamma camera and an endogenous reporter gene. In that ongoing study, mammary tumors are imaged at different stages. Preliminary results indicate different functional patterns in the uptake of radiotracers and their potential relationship with other tumor parameters such as tumor size.;In summary, we have developed a versatile imaging system suitable for in vivo small animal research as evidenced by a variety of applications. The modular construction of this system will allow expansion and further development as new needs and new opportunities arise
Evaluation of the UCL Compton camera imaging performance
This thesis presents the imaging performance of the University College London (UCL) High Purity Germanium (HPGe) Compton camera. This work is a part of an ongoing project to develop a Compton camera for medical applications. The Compton camera offers many potential advantages over other imaging modalities used in nuclear medicine. These advantages include a wide field of view, the ability to reconstruct 3D images without tomography, and the fact that the camera can have a portable lightweight design due to absence of heavy collimation.
The camera was constructed by ORTEC and the readout electronics used are based on GRT4 electronics boards (Daresbury, UK). The camera comprises two pixellated germanium detector planes housed 9.6 cm apart in the same vacuum housing. The camera has 177 pixels, 152 in the scatter detector and 25 in the absorption detector. The pixels are 4x4 mm2.
The imaging performance with different gamma-ray source energies was evaluated experimentally and compared to the theoretical estimations. Images have been taken for a variety of test objects including point, ring source and Perspex cylindrical phantom. The measured angular resolution is 7.8° ± 0.4 for 662 keV gamma-ray source at 5 cm. Due to the limited number of readout modules a multiple-view technique was used to image the source distributions from different angles and simulate the pixel arrangement in the full camera. In principle, the Compton camera potentially has high sensitivity but this is not recognized in practice due to the limited maximum count rate.
Although there are a number of limitations in the current prototype camera some potentially useful qualities have been demonstrated and distributed sources have been imaged. The key limitations in the current prototype are acquisition time, processing time and image
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reconstruction. However, techniques are available to significantly improve and overcome these limitations. This thesis presents the current state of the Compton camera performance along with a demonstration of its strengths and limitations as a potential candidate for nuclear medicine imaging
Design, construction, and test of the Gas Pixel Detectors for the IXPE mission
Due to be launched in late 2021, the Imaging X-Ray Polarimetry Explorer
(IXPE) is a NASA Small Explorer mission designed to perform polarization
measurements in the 2-8 keV band, complemented with imaging, spectroscopy and
timing capabilities. At the heart of the focal plane is a set of three
polarization-sensitive Gas Pixel Detectors (GPD), each based on a custom ASIC
acting as a charge-collecting anode. In this paper we shall review the design,
manufacturing, and test of the IXPE focal-plane detectors, with particular
emphasis on the connection between the science drivers, the performance metrics
and the operational aspects. We shall present a thorough characterization of
the GPDs in terms of effective noise, trigger efficiency, dead time, uniformity
of response, and spectral and polarimetric performance. In addition, we shall
discuss in detail a number of instrumental effects that are relevant for
high-level science analysis -- particularly as far as the response to
unpolarized radiation and the stability in time are concerned.Comment: To be published in Astroparticle Physic
Application of novel technologies for the development of next generation MR compatible PET inserts
Multimodal imaging integrating Positron Emission Tomography and Magnetic
Resonance Imaging (PET/MRI) has professed advantages as compared to other available
combinations, allowing both functional and structural information to be acquired with
very high precision and repeatability. However, it has yet to be adopted as the standard
for experimental and clinical applications, due to a variety of reasons mainly related to
system cost and flexibility. A hopeful existing approach of silicon photodetector-based MR
compatible PET inserts comprised by very thin PET devices that can be inserted in the
MRI bore, has been pioneered, without disrupting the market as expected. Technological
solutions that exist and can make this type of inserts lighter, cost-effective and more
adaptable to the application need to be researched further.
In this context, we expand the study of sub-surface laser engraving (SSLE) for
scintillators used for PET. Through acquiring, measuring and calibrating the use of a SSLE
setting we study the effect of different engraving configurations on detection
characteristics of the scintillation light by the photosensors. We demonstrate that apart
from cost-effectiveness and ease of application, SSLE treated scintillators have similar
spatial resolution and superior sensitivity and packing fraction as compared to standard
pixelated arrays, allowing for shorter crystals to be used. Flexibility of design is
benchmarked and adoption of honeycomb architecture due to geometrical advantages is
proposed. Furthermore, a variety of depth-of-interaction (DoI) designs are engraved and
studied, greatly enhancing applicability in small field-of-view tomographs, such as the
intended inserts. To adapt to this need, a novel approach for multi-layer DoI
characterization has been developed and is demonstrated.
Apart from crystal treatment, considerations on signal transmission and processing are
addressed. A double time-over-threshold (ToT) method is proposed, using the statistics of
noise in order to enhance precision. This method is tested and linearity results
demonstrate applicability for multiplexed readout designs. A study on analog optical
wireless communication (aOWC) techniques is also performed and proof of concept
results presented. Finally, a ToT readout firmware architecture, intended for low-cost
FPGAs, has been developed and is described.
By addressing the potential development, applicability and merits of a range of
transdisciplinary solutions, we demonstrate that with these techniques it is possible to
construct lighter, smaller, lower consumption, cost-effective MRI compatible PET inserts.
Those designs can make PET/MRI multimodality the dominant clinical and experimental
imaging approach, enhancing researcher and physician insight to the mysteries of life.La combinación multimodal de TomografÃa por Emisión de Positrones con la Imagen de
Resonancia Magnética (PET/MRI, de sus siglas en inglés) tiene clara ventajas en
comparación con otras técnicas multimodales actualmente disponibles, dada su capacidad
para registrar información funcional e información estructural con mucha precisión y
repetibilidad. Sin embargo, esta técnica no acaba de penetrar en la práctica clÃnica debido
en gran parte a alto coste. Las investigaciones que persiguen mejorar el desarrollo de
insertos de PET basados en fotodetectores de silicio y compatibles con MRI, aunque han
sido intensas y han generado soluciones ingeniosas, todavÃa no han conseguido encontrar
las soluciones que necesita la industria. Sin embargo, existen opciones todavÃa sin explorar
que podrÃan ayudar a evolucionar este tipo de insertos consiguiendo dispositivos más
ligeros, baratos y con mejores prestaciones.
Esta tesis profundiza en el estudio de grabación sub-superficie con láser (SSLE) para el
diseño de los cristales centelladores usados en los sistemas PET. Para ello hemos
caracterizado, medido y calibrado un procedimiento SSLE, y a continuación hemos
estudiado el efecto que tienen sobre las especificaciones del detector las diferentes
configuraciones del grabado. Demostramos que además de la rentabilidad y facilidad de
uso de esta técnica, los centelladores SSLE tienen resolución espacial equivalente y
sensibilidad y fracción de empaquetamiento superiores a las matrices de centelleo
convencionales, lo que posibilita utilizar cristales más cortos para conseguir la misma
sensibilidad. Estos diseños también permiten medir la profundidad de la interacción (DoI),
lo que facilita el uso de estos diseños en tomógrafos de radio pequeño, como pueden ser
los sistemas preclÃnicos, los dedicados (cabeza o mama) o los insertos para MRI.
Además de trabajar en el tratamiento de cristal de centelleo, hemos considerado nuevas
aproximaciones al procesamiento y transmisión de la señal. Proponemos un método
innovador de doble medida de tiempo sobre el umbral (ToT) que integra una evaluación
de la estadÃstica del ruido con el propósito de mejorar la precisión. El método se ha
validado y los resultados demuestran su viabilidad de uso incluso en conjuntos de señales
multiplexadas. Un estudio de las técnicas de comunicación óptica analógica e inalámbrica
(aOWC) ha permitido el desarrollo de una nueva propuesta para comunicar las señales del
detector PET insertado en el gantry a un el procesador de señal externo, técnica que se ha
validado en un demostrador. Finalmente, se ha propuesto y demostrado una nueva
arquitectura de análisis de señal ToT implementada en firmware en FPGAs de bajo coste.
La concepción y desarrollo de estas ideas, asà como la evaluación de los méritos de las
diferentes soluciones propuestas, demuestran que con estas técnicas es posible construir
insertos de PET compatibles con sistemas MRI, que serán más ligeros y compactos, con un
reducido consumo y menor coste. De esta forma se contribuye a que la técnica multimodal
PET/MRI pueda penetrar en la clÃnica, mejorando la comprensión que médicos e
investigadores puedan alcanzar en su estudio de los misterios de la vida.Programa Oficial de Doctorado en IngenierÃa Eléctrica, Electrónica y AutomáticaPresidente: Andrés Santos Lleó.- Secretario: Luis Hernández Corporales.- Vocal: Giancarlo Sportell
Reconstruction algorithms for multispectral diffraction imaging
Thesis (Ph.D.)--Boston UniversityIn conventional Computed Tomography (CT) systems, a single X-ray source spectrum is used to radiate an object and the total transmitted intensity is measured to construct the spatial linear attenuation coefficient (LAC) distribution. Such scalar information is adequate for visualization of interior physical structures, but additional dimensions would be useful to characterize the nature of the structures. By imaging using broadband radiation and collecting energy-sensitive measurement information, one can generate images of additional energy-dependent properties that can be used to characterize the nature of specific areas in the object of interest.
In this thesis, we explore novel imaging modalities that use broadband sources and energy-sensitive detection to generate images of energy-dependent properties of a region, with the objective of providing high quality information for material component identification. We explore two classes of imaging problems: 1) excitation using broad spectrum sub-millimeter radiation in the Terahertz regime and measure- ment of the diffracted Terahertz (THz) field to construct the spatial distribution of complex refractive index at multiple frequencies; 2) excitation using broad spectrum X-ray sources and measurement of coherent scatter radiation to image the spatial distribution of coherent-scatter form factors.
For these modalities, we extend approaches developed for multimodal imaging and propose new reconstruction algorithms that impose regularization structure such as common object boundaries across reconstructed regions at different frequencies. We also explore reconstruction techniques that incorporate prior knowledge in the form of spectral parametrization, sparse representations over redundant dictionaries and explore the advantage and disadvantages of these techniques in terms of image quality and potential for accurate material characterization.
We use the proposed reconstruction techniques to explore alternative architectures with reduced scanning time and increased signal-to-noise ratio, including THz diffraction tomography, limited angle X-ray diffraction tomography and the use of coded aperture masks. Numerical experiments and Monte Carlo simulations were conducted to compare performances of the developed methods, and validate the studied architectures as viable options for imaging of energy-dependent properties
Preparation and development of CdTe and CdZnTe detectors for gamma ray radiation applications
Tesis doctoral inédita de la Universidad Autónoma de Madrid. Facultad de Ciencias, Departamento de FÃsica de Materiales. Fecha de lectura: 20-11-201
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