High-Resolution Gamma-Ray Imaging with Columnar Scintillators and CCD/CMOS Sensors, and FastSPECT III: A Third-Generation Stationary SPECT Imager
AuthorMiller, Brian William
AdvisorFurenlid, Lars R
Barrett, Harrison H
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractA new class of scintillation detector has emerged that combines columnar scintillators and CCD/CMOS sensors for high-resolution imaging. Originally developed for single-photon gamma-ray imaging, these detectors provide better than an order-of-magnitude improvement in spatial resolution compared to conventional photomultiplier tube (PMT)-based gamma cameras; sub-100 micron detector resolutions have been achieved. This work reviews the several detector configurations developed in recent years, with a specific emphasis on a type of CCD/CMOS detector developed at the Center for Gamma-Ray Imaging, which we call BazookaSPECT, that amplifies scintillation light using an image intensifier to achieve both high spatial resolution and high event-rate capability.Ongoing research into scintillator deposition techniques has led to a new form of scintillation material where crystallites are organized into columns. Similar to optical fibers, this columnar structure helps to channels scintillation light towards an exit face while restricting lateral light spread. However, because they are not perfect optical fibers, light spreads laterally and is absorbed by an amount relating to the interaction depth. Taking advantage of this phenomenon, we discuss the use of maximum-likelihood methods to estimate the 3D position and energy of gamma-ray interactions in columnar CsI(Tl)/EMCCD-based detectors.Finally, we present new imaging applications that have arisen from BazookaSPECT. These include the the development of a gamma-ray microscope using micro-coded apertures, feasibility studies for photon-counting digital mammography and eventually X-ray CT, and FastSPECT III -- a third generation small animal stationary SPECT imager. FastSPECT III system design, fabrication methods, data acquisition system, system calibration procedure, and initial tomographic reconstructions are presented.
Degree ProgramGraduate College
Degree GrantorUniversity of Arizona
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Adaptive Imaging and SPECTKupinski, Matthew A.; Lin, Alexander Liway; Furenlid, Lars R; Clarkson, Eric W. (The University of Arizona., 2020)Single-photon emission computed tomography (SPECT) systems are widely used in the field of medical imaging as a tool to perform a variety of imaging tasks, ranging from basic biological studies to pre-clinical drug development. However, different imaging tasks require different types of images---for example, one task may benefit from images with high contrast and another task may prefer images with low noise. This leads to a multitude of SPECT systems, each having a unique set of imaging parameters that have been specifically chosen to generate good images based on the task. Computer simulations are used to model and test different imaging configurations to determine the optimal imaging parameters. This optimization task, however, becomes more challenging when the number of possible configurations becomes very large. In this dissertation, we present a collection of methods that can be used to model and optimize SPECT systems with a large parameter space. Two imaging systems are examined in detail: the synthetic collimator SPECT system and an adaptive imager known as AdaptiSPECT. A task-based approach is used to provide an objective measure of the imaging performance. Under this framework, system configurations are defined as being better based on how well a particular imaging task is accomplished by using the images generated, rather than other image metrics like resolution and contrast. The synthetic-collimator SPECT system is used to estimate the uptake of dopamine in different mouse brain regions. Multi-pinhole apertures are used to generate images with both high-resolution and high-sensitivity. However, multi-pinhole apertures can also introduce image multiplexing, which has been shown to result in artifacts in reconstructions, possibly degrading imaging performance. To mitigate these effects, a pair of semi-conductor detectors are used to simultaneously acquire two images of the object at the same projection angle, but at different magnifications. The data acquired by the front detector have low levels of multiplexing and can be used to resolve some of the uncertainty in the data collected by the rear detector, which suffers from greater multiplexing. Different system configurations are constructed by varying the two detector distances as well as the separation between the multiple pinholes. The Wiener estimator is used to examine the performance of each configuration. Because the Wiener estimator only requires the first- and second-order statistics of the object ensemble and projection images, we are able to efficiently and quickly scan through the possible parameter configurations to determine good imaging configurations. We also demonstrate that the optimal detector distances of the synthetic-collimator SPECT system are closely related to the amount of multiplexing present on each detector. The AdaptiSPECT system is a state-of-the-art imager that is capable of changing its imaging parameters in real-time during the imaging acquisition. The system consists of 16 NaI(Tl) gamma cameras which are allowed to move independently of one another, changing their distance relative to the system's aperture. The aperture also has several adjustable components, allowing for variations to the pinhole radius and aperture distance, measured relative to the center of the field-of-view. The aperture can also switch between single- and multi-pinhole configurations. Different configurations to the AdaptiSPECT system are uniquely defined by a system operator and the process of generating the system operator is discussed in detail. The ability to change the parameters of AdaptiSPECT make the system uniquely suitable for adaptive imaging. Adaptive imaging is the process of customizing the imaging parameters of a system based on the unique properties of objects, in an effort to improve imaging performance. The imaging task of interest is the estimation of the strength of a spherical signal located in a noisy background. Our adaptive strategy consists of two imaging scans: a scout scan and a diagnostic scan. Image data acquired from the scout scan are reconstructed to estimate object features such as object support and distribution of activity. The object features are then used to determine the optimal system parameters for the diagnostic scan. The diagnostic scan collects data from both single- and multi-pinhole configurations of AdaptiSPECT and the combined dataset is reconstructed by using the Alternating List-mode Maximum-Likelihood Expectation-Maximization algorithm (A-LMMLEM). A region-of-interest estimator is then used to estimate the signal strength. We show that an adaptive system using our optimization algorithm outperforms a system with fixed parameters. While the algorithm does not identify the best possible system configuration, it can be performed in real-time and results in system configurations that perform close to the best system, without the need of an exhaustive search.
Applications of iQID CamerasHan, Ling; Miller, Brian W.; Barrett, Harrison H.; Barber, H. Bradford; Furenlid, Lars R.; Univ Arizona, Coll Opt Sci; Univ Arizona, CGRI, Dept Med Imaging (SPIE-INT SOC OPTICAL ENGINEERING, 2017)iQID is an intensified quantum imaging detector developed in the Center for Gamma-Ray Imaging (CGRI). Originally called BazookaSPECT, iQID was designed for high-resolution gamma-ray imaging and preclinical gamma-ray single-photon emission computed tomography (SPECT). With the use of a columnar scintillator, an image intensifier and modern CCD/CMOS sensors, iQID cameras features outstanding intrinsic spatial resolution. In recent years, many advances have been achieved that greatly boost the performance of iQID, broadening its applications to cover nuclear and particle imaging for preclinical, clinical and homeland security settings. This paper presents an overview of the recent advances of iQID technology and its applications in preclinical and clinical scintigraphy, preclinical SPECT, particle imaging (alpha, neutron, beta, and fission fragment), and digital autoradiography.
Fisher Information in X-ray/Gamma-ray Imaging Instrumentation DesignFurenlid, Lars R.; Salcin, Esen; Barrett, Harrison H.; Barber, H. Bradford; Kupinski, Matthew A.; Furenlid, Lars R. (The University of Arizona., 2015)Signal formation in a photon-counting x-ray/gamma-ray imaging detector is a complex process resulting in detector signals governed by multiple random effects. Recovering maximum possible information about event attributes of interest requires a systematic collection of calibration data and analysis provided by estimation theory. In this context, a likelihood model provides a description of the connection between the observed signals and the event attributes. A quantitative measure of how well the measured signals can be used to produce an estimate of the parameters is given by Fisher Information analysis. In this work, we demonstrate several applications of the Fisher Information Matrix (FIM) as a powerful and practical tool for investigating and optimizing potential next-generation x-ray/gamma-ray detector designs, with an emphasis on medical-imaging applications. Using FIM as a design tool means to explore the physical detector design choices that have a relationship with the FIM through the likelihood function, how are they interrelated, and determining whether it is possible to modify any of these choices to yield or retain higher values for Fisher Information. We begin by testing these ideas by investigating a new type of a semiconductor detector, a Cadmium Telluride (CdTe) detector with double-sided-strip geometry developed by our collaborators at the Japan Aerospace Exploration Agency (JAXA). The statistical properties of the detector signals as a function of interaction positions in 3D (x, y, z) are presented with mathematical expressions as well as experimental data from measurements using synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory. We show the computation of FIM for evaluating positioning performance and discuss how various detector parameters, that are identified to affect FIM, can be used in detector optimization. Next, we show the application of FIM analysis in a detector system based on multi-anode photomultiplier tubes coupled to a monolithic scintillator in the design of smart electronic read-out strategies. We conclude by arguing that a detector system is expected to perform the best when the hardware is optimized jointly with the estimation algorithm (simply referred to as the "software" in this context) that will be used with it. The results of this work lead to the idea of a detector development approach where the detector hardware platform is developed concurrently with the software and firmware in order to achieve optimal performance.