3D Volumetric Reconstruction for Light-Field SPECT

Preclinical research on single-photon emission computed tomography (SPECT) imaging is now well acknowledged for its critical role. It is fundamental for functional imaging and is a well-researched area of nuclear medicine emission tomography. Numerous efforts were made to provide an optimized SPECT collimator and detector design. However, these approaches suffer from limited sensitivity and resolution, demanding an efficient reconstruction algorithm development. Moreover, due to the image deterioration induced by the non-stationary collimator-detector response and the single-photon emitting nature of SPECT, it is difficult to quantify the 3D radiopharmaceutical distribution within the patient quantitatively. This dissertation's primary incentive is to design and develop a complete computational framework for the newly proposed L-SPECT scan procedure from the image acquisition to the image reconstruction. Using this framework, I solve several challenging problems related to implementing a dedicated novel 3D L-SPECT image reconstruction algorithm. In particular, a volumetric reconstruction algorithm for L-SPECT system is developed by considering the system configurations. Also, an in-depth analysis of the SPECT imaging system based on the light field concept using the micro pinhole range collimator is presented in this thesis. Moreover, I evaluate the performance of the developed reconstruction algorithms under various imaging circumstances in terms of image quality, computational complexity, and resolution. A Monte Carlo simulation environment for L-SPECT was developed by modelling the properties of the SPECT imaging setup. By examining the existing limitations in the proposed L-SPECT, an improved collimator-detector geometry for the micro-pinhole arrays was introduced in this thesis as one of the main contributions. The modular L-SPECT with the detector heads in a partial ring geometry achieved higher sensitivity and resolution than the planer L-SPECT. The modular L-SPECT was further improved by shifting the centre of the scanning detectors to eliminate the artifacts in the reconstructed images. A dedicated reconstruction algorithm for the modular L-SPECT was developed as proof of concept. In SPECT reconstruction, identification of uncertainty information would help to enhance and mitigate the limitations of the existing reconstruction algorithms. The critical contribution of this thesis is manifested in the development of an image reconstruction algorithm based on Bayesian probabilistic programming for SPECT and L-SPECT. A NUTS based MCMC algorithm is used for probabilistic programming-based reconstruction. The uncertainty associated with the radiation measurement is identified as a distribution from the posterior samples generated using the MCMC algorithm. The performance of the NUTS algorithm improved by using reverse-mode automatic differentiation and distributed programming. The automatic differentiation variational inference-based SPECT reconstruction algorithm is developed to reduce the computational cost in NUTS based reconstruction and uncertainty analysis. Further in this thesis, the L-SPECT simulations are calibrated by comparing with GATE simulations, which are the gold standard in this field. The projection results of MATLAB based simulations are comparable with GATE simulations. The system performance for the proposed different configurations was investigated and contrasted against the existing SPECT modalities and systems, such as LEHR and Inveon SPECT, respectively. The performance analysis of the L-SPECT revealed the system is able to achieve improved sensitivity and better field of view compared to the existing systems. The essential characteristics of this L-SPECT system based on the reconstructed images were assessed with pinhole radii of 0.1 mm and 0.05 mm. In addition, the system sensitivity, spatial resolution, and image quality are appraised from the 3D reconstructed images. The maximum achieved system’s sensitivity was 1000 Cps/Bbq using arrays with a pinhole radius of 0.1 mm at 1 mm pitch, while the highest resolution was obtained using arrays with 0.05 mm pinhole and 3 mm pitch. The designed L-SPECT with different configurations and the developed 3D reconstruction algorithms yielded superior image quality compared with LEHR reconstructions

Design and Evaluation of a Novel Lens-Based SPECT System Based on Laue Lens Gamma Diffraction: GEANT4/GAMOS Monte Carlo Study

Abstract While improvements in SPECT imaging techniques constitute a significant advance in biomedical science and cancer diagnosis, their limited spatial resolution has hindered their application to small animal research and early tumour detection. Using recent breakthroughs established by the high-energy astrophysics community, focusing X-ray optics provides a method to overcome the paradigm of low resolution and presents the possibility of imaging small objects with sub-millimetre resolution. This thesis aims to tackle the constraints associated with the current SPECT imaging designs by exploiting the notion of focusing high energy photons through Laue lens diffraction and developing a means of performing gamma rays imaging that would not rely on parallel or pinhole collimators. The gradual development of the novel system is discussed, starting from the single, modular, and multi-Laue lens-based SPECT. A customized 3D reconstruction algorithm was developed to reconstruct an accurate 3D radioactivity distribution from focused projections. A plug-in implementing the Laue diffraction concept was developed and used to model gamma rays focusing in the GEANT4 toolkit. The plug-in will be incorporated into GEANT4 upon final approval from its developers. The single lens-based, modular lens-based and multi lens-based SPECT models detected one hit per 42 source photons (sensitivity of 790 ⁄), three hits per 42 source photons (sensitivity of 2,373 ⁄), and one hit per 20 source photons (sensitivity of 1,670 ⁄), respectively. Based on the generated 3D reconstructed images, the achievable spatial resolution was found to be 0.1 full width at half maximum (FWHM). The proposed design’s performance parameters were compared against the existing SIEMENS parallel LEHR and multi-pinhole (5-MWB-1.0) Inveon SPECT. The achievable spatial resolution is decoupled from the sensitivity of the system, which is in stark contrast with the existing collimators that suffer from the resolution-sensitivity trade-off and are limited to a resolution of 2 . The proposed system allows discrimination between adjacent volumes as small as 0.113 , which is substantially smaller than what can be imaged by any existing SPECT or PET system. The proposed design could lay the foundation for a new SPECT imaging technology akin to a combination of tomosynthesis and lightfield imaging

Molecular Imaging

The present book gives an exceptional overview of molecular imaging. Practical approach represents the red thread through the whole book, covering at the same time detailed background information that goes very deep into molecular as well as cellular level. Ideas how molecular imaging will develop in the near future present a special delicacy. This should be of special interest as the contributors are members of leading research groups from all over the world

Perspectives on Nuclear Medicine for Molecular Diagnosis and Integrated Therapy

nuclear medicine; diagnostic radiolog

YAP-(S)PET: a small animal PET/SPECT scanner. Performance and applications in oncology, cardiology and neuroscience

Aims: Molecular imaging can be defined as the visual representation, characterization, and quantification of biological processes at the cellular and sub-cellular levels within intact living organisms. It is a novel multidisciplinary field, in which the produced images reflect cellular and molecular pathways and in vivo mechanisms of disease present within the context of physiological environments. The emergence of molecular imaging strategies is largely due to recent unprecedented advances in molecular and cell biology techniques, the use of transgenic animal models, availability of newer imaging drugs and probes that are highly specific, and successful development of small-animal imaging instrumentation. The YAP-(S)PET small animal scanner is part of this environment. It is a specifically built scanner able to perform both Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) and simultaneous PET/SPECT acquisitions. Materials and Methods: The scanner was originally developed at the Department of Physics of the Universities of Ferrara and Pisa, Italy. From 2003, a fully engineered version of the scanner have been produced and commercialized by the small italian company I.S.E. s.r.l., Pisa, Italy. This thesis deals with the physical calibration and characterization and with pre-clinical applications of the new version the YAP-(S)PET originally developed, the YAP-(S)PET II. It is made up of four detector heads, each one composed of a 4 × 4 cm2 YAP:Ce matrix of 27 × 27 elements, 1.5 × 1.5 × 20 mm3 each, coupled to a Position Sensitive-Photomultiplier (PS-PMT). The heads can be positioned at different distances ranging from 10 to 20 cm. The four modules are positioned on a rotating gantry and opposing detectors are in time coincidence when used in PET mode. The scanner can be switched between PET and SPECT modalities simply replacing the tungsten septum used in PET with a high-resolution parallel hole collimator in front of each crystal. The peculiar YAP-(S)PET architecture provides also the capability to perform simultaneous PET/SPECT acquisitions. The hardware calibrations concerned both electronics and mechanics settings such as adjustment of PMT gain or precise positioning of the center of rotation, while the software calibrations were related to definition of crystal and energy maps, and to efficiency corrections. In PET mode, the performance of the YAP-(S)PET scanner have been evaluated following the standards proposed by the PET National Electric Manufacturers Association (NEMA) task force for small animal scanners. Since the lack of small animal SPECT performance, the SPECT performance has been evaluated by rescaling the clinical SPECT NEMA reference standards NU1-1994. For both PET and SPECT modalities, the performance were evaluated at different head-to-head distances: 10, 12.5 and 15 cm. The simultaneous PET/SPECT dual imaging acquisition modality was realized by independently acquiring single events with two opposing heads equipped with the collimators (SPECT mode), while the other couple of heads detects coincident events (PET mode). Different animal models and various isotopes and tracers have been used in the experiments performed in collaborations with several research groups. In this thesis only some of these studies are reported in order to point out the YAP-(S)PET imaging capabilities, particularly in neuro-pharmacology, psychiatry and oncology. Conclusions: In PET mode the performance evaluation has regarded the spatial resolution, sensitivity, scatter fraction and count rate. The best compromise between spatial resolution and sensitivity was obtained with a head-to-head distance of 10 cm. In this configuration, the volume resolution is about 8 microliters, the sensitivity reaches 3% at the center fo the Field of View (CFOV), the scatter fraction is 27% and the peak Noise Equivalent Count rate is about 38 kcps at an activity concentration in the FOV of about 370 kBq/ml. Also in SPECT modality, the best results are obtained for 10 cm head-to-head distance. The spatial resolution is about 2.8 mm at CFOV and the sensitivity is (3.7 E-3)% for 140-250 keV energy window. Due to reduced working space at 10 cm, particularly evident in rats experiments, the best compromise between scanner performance and rats experiments is 12.5 cm for both PET and SPECT modality. On the contrary, mice experiments can be better performed at 10 cm head-to-head distance

Hydrodynamics study of the bubble columns with intense vertical heat-exchanging tubes using gamma-ray computed tomography and radioactive particle tracking techniques

Understanding the hydrodynamics of bubble columns with and without vertical heat-exchanging tubes is a necessity for the proper design, scale-up, and operation of these reactors. To achieve this goal, systematic experiments were performed to visualize and quantify the influence of the presence of vertical internal tubes on the gas holdup distributions and their profiles, axial liquid velocity, and turbulent parameters (i.e., normal and shear stresses; turbulent kinetic energy) by using advanced gamma-ray computed tomography (CT) and radioactive particle tracking (RPT). In this study, the experiments were conducted in 6- and 18-inch bubble columns with an air-water system as the working fluid, under a wide range of superficial gas velocities (5-45 cm/s). Three configurations of vertical internals (i.e., hexagonal, circular without a central tube, and circular with a central tube plus vertical internals), as well as the vertical internals sizes, were examined in this study. These three configurations were designed to cover 25% of the column\u27s cross-sectional area (CSA) to represent the percentage of the covered area utilized in the Fischer-Tropsch process. Reconstructed CT images reveal that the configurations of the vertical internal tubes significantly impacted the gas holdup distribution over the CSA of the column. Additionally, the bubble column equipped with 1-inch vertical internals exhibited a more uniform gas holdup distribution than the column with 0.5-inch internals. Moreover, a remarkable increase in the gas holdup values at the wall region was achieved in the churn turbulent flow regime due to the insertion of vertical internals inside the column. Furthermore, pronounced peaks of the gas holdup and axial liquid velocity were observed in the inner gaps between the vertical internals --Abstract, page iv