Detecting small low emission radiating sources

The article addresses the possibility of robust detection of geometrically small, low emission sources on a significantly stronger background. This problem is important for homeland security. A technique of detecting such sources using Compton type cameras is developed, which is shown on numerical examples to have high sensitivity and specificity and also allows to assign confidence probabilities of the detection. 2D case is considered in detail

Development and optimization of the control software for a mobile computed tomography system for cultural heritage.

In quest’elaborato sono descritti l’ottimizzazione e lo sviluppo del software di controllo di un apparato tomografico con sorgente di raggi X per analisi nel campo di Beni Artistici e Culturali. In particolare, il lavoro è stato effettuato sul software preesistente di un sistema mobile in uso presso il Dipartimento di Fisica e Astronomia per indagini tomografiche. Il sistema, sviluppato nell’arco di più anni, consiste di un tubo a raggi X, un detector flat-panel e una tavola rotativa per la tomografia. Tre assi traslazionali consentono il movimento di detector e sorgente, ottenendo un'area scansionabile di 1,5×1,5 m². Il software di controllo si occupa dell’intero processo di acquisizione: gestisce il movimento degli assi, effettua la rotazione della tavola che sostiene l’oggetto durante la tomografia e controlla la scheda di acquisizione in comunicazione con il detector per la cattura delle immagini. Con l’upgrade sviluppato in questo lavoro vengono introdotte diverse routine automatizzate e una più comoda gestione delle regioni di interesse per la scansione radio-tomografica, con lo scopo di alleggerire il carico dell’operatore e ridurre i tempi di acquisizione. Il lavoro di tesi si conclude con un’indagine presso Palazzo Vecchio a Firenze in cui sono state effettuate analisi radiografiche e tomografiche di una serie di dipinti su tavola attribuiti in buona parte al Pontormo. In quest’occasione il software aggiornato è stato testato sul campo per verificarne la praticità e l’efficienza delle nuove funzioni. L’esperienza ha messo in evidenza alcuni problemi e carenze del software e del sistema stesso che suggeriscono l’opportunità di un certo numero di aggiornamenti e di una eventuale riscrittura del codice. Nonostante ciò, l’automatizzazione delle operazioni di acquisizione radiografica e tomografica si è rivelata efficace, riducendo il numero di interventi manuali richiesti e con essi il tempo necessario per l’analisi stessa

Optimising the benefits of spectral x-ray imaging in material decomposition

The extra energy information provided by spectral x-ray imaging using novel photon counting x-ray detectors may allow for improved decomposition of materials compared to conventional and dual-energy imaging. The information content of spectral x-ray images, however, depends on how the photons are grouped together. This thesis deals with the theoretical aspect of optimising material discrimination in spectral x-ray imaging. A novel theoretical model was developed to map the confidence region of material thicknesses to determine the uncertainties in thickness quantification. Given the thickness uncertainties, photon counts per pixel can be optimised for material quantification in the most dose efficient manner. Minimisation of the uncertainties enables the optimisation of energy bins for material discrimination. Using Monte Carlo simulations based on the BEAMnrc package, material decomposition of up to 3 materials was performed on projection images, which led to the validation of the theoretical model. With the inclusion of scattered radiation, the theoretical optima of bin border energies were accurate to within 2 keV. For the simulated photon counts, excellent agreement was achieved between the theoretical and the BEAMnrc models regarding the signal-to-noise ratio in a decomposed image, particularly for the decomposition of two materials. Finally, this thesis examined the implementation of the Medipix detector. The equalisation of pixel sensitivity variations and the processing of photon counting projection images were studied. Measurements using the Medipix detector demonstrated promising results in the charge summing and the spectroscopic modes of acquisition, even though the spectroscopic performance of the detector was relatively limited due to electronic issues known to degrade the equalisation process. To conclude, the theoretical model is sufficient in providing guidelines for scanning parameters in spectral x-ray imaging and may be applied on spectral projection measurements using e.g. the redesigned MedipixRX detector with improved spectroscopic performance, when it becomes available

Development of a simulation platform for the evaluation of PET neuroimaging protocols in epilepsy

Monte Carlo simulation of PET studies is a reference tool for the evaluation and standardization of PET protocols. However, current Monte Carlo software codes require a high degree of knowledge in physics, mathematics and programming languages, in addition to a high cost of time and computational resources. These drawbacks make their use difficult for a large part of the scientific community. In order to overcome these limitations, a free and an efficient web-based platform was designed, implemented and validated for the simulation of realistic brain PET studies, and specifically employed for the generation of a wellvalidated large database of brain FDG-PET studies of patients with refractory epilepsy