L. J. Harkness

GAMOS: An easy and flexible way to use GEANT4

The wide range of physics models available in GEANT4, as well as its outstanding geometry and visualization tools, has made it gain widespread use in several fields of physics, like high energy, medical, space, etc. Nevertheless the use of GEANT4 often requires a long learning-curve, which implies a good knowledge of C++ and the GEANT4 code itself. GAMOS facilitates the use of GEANT4 by avoiding the need to use C++, providing instead a set of user commands. One of the novelties of GAMOS with respect to similar simulation codes lies in its flexibility, which makes it appropriate for simulation in many physics fields. This flexibility is sustained by the wide range of geometrical configurations, primary generators and physics lists supported and by the comprehensive set of tools that help the user in extracting detailed information from the simulation through user commands. The use of the plug-in technology contributes to this flexibility, as it facilitates the extension of the framework to include extra functionality not foreseen by the framework authors. GAMOS counts already with several hundreds registered users in the five continents; while it is more frequently used in the medical physics field, its use has also been extended to other fields, like high energy physics, space physics, neutron shielding, etc.

Development of the ProSPECTus semiconductor Compton camera for medical imaging

The ProSPECTus project is the development of a prototype semiconductor Compton camera for use in nuclear medical imaging applications. The proposed system has the potential to improve the sensitivity of conventional mechanically col-limated Single Photon Emission Computed Tomography (SPECT) systems through the use of electronic collimation techniques. In addition, the use of compatible semiconductor technology within a Magnetic Resonance Imaging (MRI) system could potentially lead to simultanous SPECT/MRI data acquisition. This paper outlines the consideration of key design features for the new system. Such design factors include the geometrical setup, suitable energy and position resolution values for the detectors and the ability of the system to function in a magnetic field. The ProSPECTus protoype imaging system will now be built according to optimised specifications.

Semiconductor detectors for Compton imaging in nuclear medicine

An investigation is underway at the University of Liverpool to assess the suitability of two position sensitive semiconductor detectors as components of a Compton camera for nuclear medical imaging. The ProSPECTus project aims to improve image quality, provide shorter data acquisition times and lower patient doses by replacing conventional Single Photon Emission Computed Tomography (SPECT) systems. These mechanically collimated systems are employed to locate a radioactive tracer that has been administered to a patient to study specifically targeted physiological processes. The ProSPECTus system will be composed of a Si(Li) detector and a High Purity Germanium (HPGe) detector, a configuration deemed optimum using a validated Geant4 simulation package. Characterising the response of the detectors to gamma irradiation is essential in maximising the sensitivity and image resolution of the system. To this end, the performance of the HPGe ProSPECTus detector and a suitable Si(Li) detector has been assessed at the University of Liverpool. The energy resolution of the detectors has been measured and a surface scan of the Si(Li) detector has been performed using a finely collimated 241Am gamma ray source. Results from the investigation will be presented.

Prospectus: Development of a Compton Camera for Medical Imaging

Single Photon Emission Computed Tomography (SPECT) is an established method of studying physiological functions. However, novel gamma-ray Compton camera systems which provide electronic collimation have the potential to greatly improve the sensitivity of this technique. Compton cameras have been employed in high energy applications but have not yet been fully implemented for clinical applications at low energies. This paper describes the optimization of imaging efficiency for the ProSPECTus medical imaging Compton camera system with 99mTc. Experimental factors which degrade the image quality will also be assessed and quantified.

Compton imaging with AGATA and SmartPET for DESPEC

DESPEC (DEcay SPECtroscopy) is a spectrometer, currently under construction, which is to be used at the FAIR (Facility for Antiproton and Ion Research) facility at GSI Darmstadt, Germany, as part of the NuSTAR (Nuclear STructure, Astrophysics and Reactions) project. Its goal is to analyse the decay of exotic nuclei produced via the Super-FRS (SUPERconducting FRagment Separator). The optimal configuration of certain elements of the spectrometer, namely a HPGe (High Purity Germanium) tracking array, is still under consideration. Work currently being carried out at the University of Liverpool using a segmented, coaxial HPGe detector (AGATA B009) and a pixelated, planar HPGe detector (SmartPET 1) in a Compton camera configuration aims to inform this process by providing insight into the potential performance of such a configuration. This will determine its suitability for the intended purpose, i.e. Compton reconstruction of gamma rays emitted from exotic nuclei implanted into the DESPEC implantation detector, AIDA (Advanced Implantation Detector Array). Preliminary results from this investigation, along with plans for the future direction of this work, are presented.

Status and Performance of an AGATA asymmetric detector

High‐resolution gamma‐ray detectors based on high‐purity germanium crystals (HPGe) are one of the key workhorses of experimental nuclear science. The technical development of such detector technology has been dramatic in recent years. Large volume, high‐granularity, electrically segmented HPGe detectors have been realised and a methodology to improve position sensitivity using pulse‐shape analysis coupled with the novel technique of gamma‐ray tracking has been developed. Collaborations have been established in Europe (AGATA) [1] and the USA (GRETA/GRETINA) [2] to build gamma‐ray tracking spectrometers. This paper discusses the performance of the first AGATA (Advanced GAmma Tracking Array) asymmetric detector that has been tested at the University of Liverpool. The use of a fully digital data acquisition system has allowed detector charge pulse shapes from a selection of well defined photon interaction positions to be analysed, yielding important information on the position sensitivity of the detector.

Design Considerations Of A Compton Camera For Low Energy Medical Imaging

Development of a Compton camera for low energy medical imaging applications is underway. The ProSPECTus project aims to utilize position sensitive detectors to generate high quality images using electronic collimation. This method has the potential to significantly increase the imaging efficiency compared with mechanically collimated SPECT systems, a highly desirable improvement on clinical systems. Design considerations encompass the geometrical optimisation and evaluation of image quality from the system which is to be built and assessed.

Compton imaging with a planar semiconductor system using pulse shape analysis

Homeland security agencies have a requirement to locate and identify nuclear material. Compton cameras [1, 2] offer a more efficient method of gamma-ray detection than collimated detector systems. The resolution of the interaction positions within the detectors greatly influences the accuracy of a reconstructed Compton image. Utilizing digital electronics and applying pulse shape analysis [3] allows the spatial resolution to be enhanced beyond the pixel granularity in three dimensions. Analytically reconstructed Compton images from a range of radiation sources shall be presented with and without pulse shape analysis showing the improvements gained along with a discussion of our analysis methods.

Quantification of the experimental limitations of a semiconductor PET camera

An investigation of the applicability of semiconductors to small animal positron emission tomography has been conducted. The SmartPET collaboration has been responsible for successful experimental work demonstrating how these detectors could enhance small animal imaging devices. Highly encouraging experimental results present an improvement in image resolution to 2mm (full width at half maximum). In order to understand current experimental limitations and overcome these in future systems, we have carried out a Monte Carlo study to systematically quantify experimental image distortions in terms of the image resolution of a point source. With a full understanding of experimental sources of error, the full potential of the existing SmartPET system can be understood. This ground work will allow the imaging of more complex phantom geometries to assist a transition into preclinical trials. This work also permits an optimized system to be designed in future.

A Semiconductor‐Based Positron Emission Tomography System

This paper shall summarize the research conducted employing the high‐purity germanium based small animal imaging system, SmartPET (SMall Animal Reconstructive Tomograph for Positron Emission Tomography). Geant4 simulations of the experimental setup were carried out in order to derive novel analysis procedures and quantify the system limitations. In this paper, we will focus on a gamma ray tracking approach devised to overcome germaniums high Compton scattering cross‐section and on imaging challenging and complex phantom geometries. The potential of the developed tools and of the system itself will be discussed.