[en] Compton imaging devices employ electronic collimation to determine the direction of photons coming from a radio-tracer labeled organ. They therefore not subject to the limiting constraint imposed by mechanical collimators, for which sensitivity and spatial resolution are inversely coupled. As a result,the sensitivity can be dramatically increased for a comparable resolution. Furthermore, their performance improve rapidly with increasing photon energy, making possible to achieve spectacular gains over conventional mechanical collimation. simulations predict a great improvement over existing devices. A first prototype has been built, and images have been reconstructed. The results prove the feasibility of this technique nad its implementation using silicon detectors as electronic collimators. (Author) 5 refs

[en] Compton cameras have been developed for almost fifty years in various fields (astronomy, medical imaging, safety and industrial inspections, etc.), employing different types of detectors. Their potential use has gained renewed interest with the emergence of high light yield scintillator crystals and silicon photomultipliers (SiPMs). This combination provides good performance and operation simplicity at an affordable cost, raising again the interest in this type of systems. SiPM-based Compton cameras are being assessed for diverse applications with promising results.

[en] The goal of this work is to study the ability of the open ring PET geometries with TOF and of the proposed Compton Camera for assessing range shifts below 5 mm. All this work is part of the ENVISION project which is directed towards on-line dose monitoring in hadron therapy. (Author)

[en] Highlights: • An improved version of a Compton telescope for hadron therapy is under development. • First characterization, coincidence and imaging tests have been carried out. • Results show a general improvement of the system performance. The IRIS group of IFIC-Valencia is developing a Compton telescope for treatment monitoring in hadron therapy. The system is composed of three detector layers, each of them consisting of a monolithic LaBr${}_3$ scintillator crystal coupled to Silicon Photomultiplier (SiPM) arrays. A first version of the prototype was developed within the European project ENVISION. Tests with point-like sources and in-beam were carried out with successful results, demonstrating the feasibility of the proposed technology. The limitations of the system were also identified. A new version of the prototype is under development with the aim of improving the performance of the telescope detector planes. To this end, the initial tests of a detector plane based on a new SiPM array have been carried out. The first characterization, coincidence and imaging tests with this new version of the detector plane are presented. In addition, the suitability of CeBr${}_3$ scintillator crystals for this application is being investigated.

[en] The ability to diagnose early prostate cancer has outpaced imaging methods for accurate localization and staging of the disease. A precise determination of the extent of local disease is difficult and, unfortunately, present imaging instrumentation employing radiotracer techniques (PET, SPECT, planar scintigraphy) is limited in its ability to provide detailed information when imaging the prostate due to modest spatial resolution, often poor counting efficiency, and photon attenuation. The innovation in the work described here is the use of a silicon prostate probe based on the principle of the Compton scatter camera. Simulation studies show that the endorectal prostate probe will enhance the spatial resolution by a factor 4-5 and, simultaneously, provide a gain in efficiency of a factor 16-40 over conventional nuclear medicine cameras. The ongoing tasks are focused on the design optimization of a Compton probe prototype

[en] Detectors based on Silicon Photomultipliers (SiPMs) coupled to continuous crystals are being tested in medical physics applications due to their potential high resolution and sensitivity. To cope with the high granularity required for a very good spatial resolution, SiPM matrices with a large amount of elements are needed. To be able to read the information coming from each individual channel, dedicated ASICs are employed. The VATA64HDR16 ASIC is a 64-channel, charge-sensitive amplifier that converts the collected charge into a proportional current or voltage signal. A complete assessment of the suitability of that ASIC for medical physics applications based on continuous crystals and SiPMs has been carried out. The input charge range is linear from 0−2 pC up to 55 pC. The energy resolution obtained at 511 keV is 10% FWHM with a LaBr_3 crystal and 16% FWHM with a LYSO crystal. A coincidence timing resolution of 24 ns FWHM is obtained with two LYSO crystals

[en] Compton Cameras are electronically collimated photon imagers suitable for sub-MeV to few MeV gamma-ray detection. Such features are desirable to enable in vivo range verification in hadron therapy, through the detection of secondary Prompt Gammas. A major concern with this technique is the poor image quality obtained when the incoming gamma-ray energy is unknown. Compton Cameras with more than two detector planes (multi-layer Compton Cameras) have been proposed as a solution, given that these devices incorporate more signal sequences of interactions to the conventional two interaction events. In particular, three interaction events convey more spectral information as they allow inferring directly the incident gamma-ray energy. A three-layer Compton Telescope based on continuous Lanthanum (III) Bromide crystals coupled to Silicon Photomultipliers is being developed at the IRIS group of IFIC-Valencia. In a previous work we proposed a spectral reconstruction algorithm for two interaction events based on an analytical model for the formation of the signal. To fully exploit the capabilities of our prototype, we present here an extension of the model for three interaction events. Analytical expressions of the sensitivity and the System Matrix are derived and validated against Monte Carlo simulations. Implemented in a List Mode Maximum Likelihood Expectation Maximization algorithm, the proposed model allows us to obtain four-dimensional (energy and position) images by using exclusively three interaction events. We are able to recover the correct spectrum and spatial distribution of gamma-ray sources when ideal data are employed. However, the uncertainties associated to experimental measurements result in a degradation when real data from complex structures are employed. Incorrect estimation of the incident gamma-ray interaction positions, and missing deposited energy associated with escaping secondaries, have been identified as the causes of such degradation by means of a detailed Monte Carlo study. As expected, our current experimental resolution and efficiency to three interaction events prevents us from correctly recovering complex structures of radioactive sources. However, given the better spectral information conveyed by three interaction events, we expect an improvement of the image quality of conventional Compton imaging when including such events. In this regard, future development includes the incorporation of the model assessed in this work to the two interaction events model in order to allow using simultaneously two and three interaction events in the image reconstruction. (paper)

[en] A detector head composed of a continuous LaBr₃ crystal coupled to a silicon photomultiplier array has been mounted and tested, for its use in a Compton telescope for dose monitoring in hadron therapy. The LaBr₃ crystal has 16 mmx18 mmx5 mm size, and it is surrounded with reflecting material in five faces. The SiPM array has 16 (4 x4) elements of 3 mmx3 mm size. The SPIROC1 ASIC has been employed as readout electronics. The detector shows a linear behavior up to 1275 keV. The energy resolution obtained at 511 keV is 7% FWHM, and it varies as one over the square root of the energy up to the energies tested. The variations among the detector channels are within 12%. A preliminary measurement of the timing resolution gives 7 ns FWHM. The spatial resolution obtained with the center of gravity method is 1.2 mm FWHM. The tests performed confirm the correct functioning of the detector.

[en] Preliminary experimental results of the search for long-lived metastable μp(2s) are presented. The μp(2s) are identified via muon transfer to neon in a gas mixture of hydrogen and several percent of neon at mbar pressures. An energy-dependent 1s transfer rate to neon has been observed. The time spectra can only be explained assuming a nonzero μp(2s) population

[en] Compton collimated imaging may improve the detection of gamma rays emitted by radioisotopes used in single photon emission computed tomography (SPECT). We present a crude prototype consisting of a single 500 μm thick, 256 pad silicon detector with pad size of 1.4x1.4 mm², combined with a 15x15x1 cm³ NaI scintillator crystal coupled to a set of 20 photo multipliers. Emphasis is placed on the performance of the silicon detector and the associated read-out electronics, which has so far proved to be the most challenging part of the set-up. Results were obtained using the VATAGP3, 128 channel low-noise self-triggering ASIC as the silicon detector's front-end. The noise distribution (σ) of the spectroscopic outputs gave an equivalent noise charge (ENC) with a mean value of <σ>=137 e with a spread of 10 e, corresponding to an energy resolution of 1.15 keV FWHM for the scattered electron energy. Threshold settings above 8.2 keV were required for stable operation of the trigger. Coincident Compton scatter events in both modules were observed for photons emitted by ⁵⁷Co source with principal gamma ray energies of 122 and 136 keV