Motion measurement algorithms for MARS imaging

The goal of the MARS molecular imaging team is to advance medicine by researching, developing, and commercialising spectral CT systems. This thesis presents the work I performed to facilitate live imaging with MARS scanners. This aim was achieved by developing a gating algorithm, designing and developing a mouse holder, and creating a motorised motion phantom. My gating algorithms will contribute to improving the image quality of human data obtained by human-scale MARS scanners. I contributed to the design and development of a mouse holder with a temperature regulating system that is compatible with MARS scanners for the purpose of live animal imaging. This holder design provides simple animal handling, secure positioning, anaesthesia delivery, regulated temperature control, and physiological monitoring. I developed a post-acquisition automatic gating method based on the acquired scan data over time. This method is capable of identifying various movement phases to sort the acquired exposure images into temporal bins. To reduce the undersampling noise due to gating, a weight-based reconstruction algorithm was introduced and implemented. Instead of binning the data, this method employed all images for the reconstruction of specific time points by assigning a weight to each. The result of applying this method showed that it can improve the undersampling artefacts compared to the temporal binning method. To evaluate the gating method, a motorised motion phantom was designed and manufactured. The motion phantom could be programmed to produce periodic signals with a similar frequency and amplitude to that of a mouse or human breathing. The quantitative measurements showed that gating can reduce motion artefacts and blurring by 50% with a 1mm amplitude and 26% for a 5mm amplitude. The effect of motion on the material decomposition process in MARS imaging systems was investigated. Known contrast agents were added to the motion phantom and then scanned with movements with the amplitude of 1 to 5 mm. No clear trend between the motion amplitude and the material decomposition accuracy was observed. The gated images had lower SNR compared to the non-gated data, resulting in more misidentified voxels. This suggests that noise properties are more important than motion blur. In summary, the research documented in this thesis facilitates live imaging in MARS scanners in the future

Study of bone-metal interface in orthopaedic application using spectral CT

This thesis investigates the diagnostic potential of MARS spectral photon counting computed tomography (CT) in assessing musculoskeletal disorders such as bone fractures and crystal arthritis. The hypothesis states that the high spatial resolution, quantitative material specific information and reduced metal artefacts of spectral photon counting CT makes the MARS spectral CT scanner a promising imaging tool to confirm or rule out a diagnosis. Being a new imaging modality, a protocol to scan samples with metal implants has to be optimised, before it can be implemented clinically for patient imaging. I contributed to optimising a protocol for imaging bone-implant specimens. Different biomaterials (titanium and stainless steel) used for fracture fixation were imaged. The artefacts were evaluated in both the energy and material domain. A bone analysis tool for measuring bone morphological parameters such as trabecular thickness and spacing was developed in collaboration with the Human Interface Technology Lab. Bone healing at the bone-metal interface was studied and the results were compared with plain radiographs, dual energy x-ray absorptiometry and clinical single and dual energy CT. The advantages of photon counting spectral CT in the early assessment of bone healing due to reduced artefacts was demonstrated. This thesis also investigated the potential of spectral photon counting CT to differentiate calcium crystals present in phantoms and osteoarthritic human meniscus samples. Our results show that MARS spectral CT can moderately discriminate calcium pyrophosphate (crystals inducing pseudogout) and calcium hydroxyapatite crystals. The results were compared with plain radiographs, polarised light microscopy and x-ray diffraction methods. In conclusion, this thesis demonstrated the clinical potential of MARS preclinical spectral photon counting CT scanner for the non-invasive and non-destructive imaging of bone-metal interfaces, for early assessment of bone healing, and for the detection and characterisation of articular crystals

Development of a Monte-Carlo based tool for dosimetry studies with spectral scanners

This thesis reports on the implementation of methods to optimise the MARS scan settings and conduct a novel material-specific dosimetry simulation using the MARS small-bore scanner. This thesis was undertaken because no guideline exists on how to optimise MARS scan settings and conduct material-specific dose simulation. The MARS photon-counting spectral computed tomography (CT) scanner is at the stage of conducting the first MARS human clinical trials. Therefore, the need to perform the clinical trials with optimal MARS scan settings are crucial. Also, the MARS scanner provides material-specific information without knowing their radiation dose deposition. Hence, it is important to characterise their dose depositions and reduces the patient's exposure while maintaining the image quality. This study aims to use the As Low As Reasonably Achievable (ALARA) principle of radiation protection to determine the absorbed dose for spectral imaging of small animals that have sufficient image quality and material differentiation to meet clinical needs. Custom-built Perspex phantoms were used to measure signal-to-noise ratio and spatial resolution, and to measure radiation dose using thermoluminescent dosimeters. A multicontrast calibration phantom was used to assess material identification. Small animal imaging and dosimetry were then performed to demonstrate the study aim. The results suggest that the energy resolving capability of photon-counting CT maintains diagnostically relevant image quality with high levels of material discrimination at reduced radiation dose. The material-specific dosimetry methods were established through developing and implementing the Geant4 Application for Tomographic Emission (GATE) Monte Carlo (MC) simulation program based on the MARS small-bore scanner. The simulated MARS scanner was verified with physical measurements. Further, a method for preparing spectral attenuation CT data for three-dimensional MC dose simulation has been established. Lastly, a method for demonstrating the potential use of the spectral material image for MC dose simulation has also been developed. The methods employed in this thesis can also be applied to optimise MARS large-bore and body-parts scanners scan settings and build a strong basis for personalised dosimetry

NASA SBIR abstracts of 1990 phase 1 projects

The research objectives of the 280 projects placed under contract in the National Aeronautics and Space Administration (NASA) 1990 Small Business Innovation Research (SBIR) Phase 1 program are described. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses in response to NASA's 1990 SBIR Phase 1 Program Solicitation. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 280, in order of its appearance in the body of the report. The document also includes Appendixes to provide additional information about the SBIR program and permit cross-reference in the 1990 Phase 1 projects by company name, location by state, principal investigator, NASA field center responsible for management of each project, and NASA contract number

Research and technology, 1987

Three broad goals were presented by NASA as a guide to meet the challenges of the future: to advance scientific knowledge of the planet Earth, the solar system, and the universe; to expand human presence beyond the Earth into the solar system; and to strengthen aeronautics research and technology. Near-term and new-generation space transportation and propulsion systems are being analyzed that will assure the nation access to and presence in space. Other key advanced studies include large astronomical observatories, space platforms, scientific and commercial payloads, and systems to enhance operations in Earth orbit. Longer-range studies include systems that would allow humans to explore the Moon and Mars during the next century. Research programs, both to support the many space missions studied or managed by the Center and to advance scientific knowledge in selected areas, involve work in the areas of atmospheric science, earth science, space science (including astrophysics and solar, magnetospheric, and atomic physics), and low-gravity science. Programs and experiment design for flights on the Space Station, free-flying satellites, and the Space Shuttle are being planned. To maintain a leadership position in technology, continued advances in liquid and solid propellant engines, materials and processes; electronic, structural, and thermal investigations; and environmental control are required. Progress during the fiscal year 1987 is discussed

Neuroimaging of Epilepsy: Lesions, Networks, Oscillations

While analysis and interpretation of structural epileptogenic lesion is an essential task for the neuroradiologist in clinical practice, a substantial body of epilepsy research has shown that focal lesions influence brain areas beyond the epileptogenic lesion, across ensembles of functionally and anatomically connected brain areas. In this review article, we aim to provide an overview about altered network compositions in epilepsy, as measured with current advanced neuroimaging techniques to characterize the initiation and spread of epileptic activity in the brain with multimodal noninvasive imaging techniques. We focus on resting-state functional magnetic resonance imaging (MRI) and simultaneous electroencephalography/fMRI, and oppose the findings in idiopathic generalized versus focal epilepsies. These data indicate that circumscribed epileptogenic lesions can have extended effects on many brain systems. Although epileptic seizures may involve various brain areas, seizure activity does not spread diffusely throughout the brain but propagates along specific anatomic pathways that characterize the underlying epilepsy syndrome. Such a functionally oriented approach may help to better understand a range of clinical phenomena such as the type of cognitive impairment, the development of pharmacoresistance, the propagation pathways of seizures, or the success of epilepsy surgery

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 187

This supplement to Aerospace Medicine and Biology lists 247 reports, articles and other documents announced during November 1978 in Scientific and Technical Aerospace Reports (STAR) or in International Aerospace Abstracts (IAA). In its subject coverage, Aerospace Medicine and Biology concentrates on the biological, physiological, psychological, and environmental effects to which man is subjected during and following simulated or actual flight in the earth's atmosphere or in interplanetary space. References describing similar effects of biological organisms of lower order are also included. Emphasis is placed on applied research, but reference to fundamental studies and theoretical principles related to experimental development also qualify for inclusion. Each entry in the bibliography consists of a bibliographic citation accompanied in most cases by an abstract

Computed-Tomography (CT) Scan

A computed tomography (CT) scan uses X-rays and a computer to create detailed images of the inside of the body. CT scanners measure, versus different angles, X-ray attenuations when passing through different tissues inside the body through rotation of both X-ray tube and a row of X-ray detectors placed in the gantry. These measurements are then processed using computer algorithms to reconstruct tomographic (cross-sectional) images. CT can produce detailed images of many structures inside the body, including the internal organs, blood vessels, and bones. This book presents a comprehensive overview of CT scanning. Chapters address such topics as instrumental basics, CT imaging in coronavirus, radiation and risk assessment in chest imaging, positron emission tomography (PET), and feature extraction