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Roser, J., Barrientos, L., Bello, P., Borja-Lloret, M., Calatayud, J. M., Casaña, J. V., et al. (2025). Radiopharmaceutical imaging of phantoms and patients with MACACO III Compton camera. Phys. Medica, 132, 104928–8pp.
Abstract: Background and purpose: The use of Compton cameras for imaging radioisotopes in nuclear medicine offers potential advantages over conventional gamma cameras in some aspects. In this work, we present the first results in this field with the Compton camera prototype MACACO III after a measurement campaign in La Fe Hospital (Valencia, Spain). Methods: Images of Derenzo-like phantoms filled with 18F-FDG and 131I-NaI have been obtained with MACACO III and, in the latter case, with gamma cameras available in the hospital. Subsequently, a metastatic lesion in a patient treated with 131I-NaI after thyroid gland resection was imaged. Results: The 18F-FDG phantom images show the prototype capability of identifying up to 4 mm diameter rods. The measurements with 131I-NaI-filled phantoms demonstrate the clear improvement of the spatial resolution attainable with MACACO III when compared with images obtained with the gamma cameras available in the hospital. Finally, the image of the patient metastatic lesion obtained with the Compton camera was found to be consistent with the gamma camera inspection image. Conclusion: These encouraging results demonstrate MACACO III's capability for radiopharmaceutical imaging and open a door for its application to nuclear medicine.
Keywords: Compton cameras; Gamma cameras; Radiopharmaceutical imaging
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Kasprzak, J., Roser, J., Werner, J., Kohlhase, N., Bolke, A., Kaufmann, L. M., et al. (2025). Regularized origin ensemble with a beam prior for range verification in particle therapy with Compton-camera data. Phys. Med. Biol., 70(7), 075009–24pp.
Abstract: Objective. In particle therapy (PT), several methods are being investigated to help reduce range margins and identify deviations from the original treatment plan, such as prompt-gamma imaging with Compton cameras (CC). To reconstruct the images, the Origin Ensemble (OE) algorithm is commonly used. In the context of PT, artifacts and strong noise often affect CC images. To improve the ability of OE to identify range shifts, and also to enhance image quality, we propose to regularize OE using beam a-priori knowledge (beam prior). Approach. We implemented the beam prior to OE using the class of Gibbs' distribution functions. For evaluation, Monte-Carlo simulations of centered and off-center beams with therapeutic energies impinging on a PMMA target were conducted in GATE. To introduce range shifts, air layers were introduced into the target. In addition, the effect of a bone layer, closer to a realistic scenario, was investigated. OE with the beam prior (BP-OE) and conventional OE (reference) were compared using the spill-over-ratio (SOR) as well as shifts in the distal falloff in projections using cubic splines with Chebyshev nodes. Main results. BP-OE improved the shift estimates by up to 11% compared to conventional OE for centered and up to 250% with off-centered beams. BP-OE decreased the image noise level, improving the SOR significantly by up to 96%. Significance. BP-OE applied to CC data can improve shift estimations compared to conventional OE. The developed Gibbs-based regularization framework also allows further prior functions to be included into OE, for instance, smoothing or edge-preserving priors. BP-OE could be extended to PET-based range verification or multiple-beam scenarios.
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Llosa, G. (2019). SiPM-based Compton cameras. Nucl. Instrum. Methods Phys. Res. A, 926, 148–152.
Abstract: 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.
Keywords: Compton camera; Silicon photomultiplier (SiPM)
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Muñoz, E., Barrio, J., Bernabeu, J., Etxebeste, A., Lacasta, C., Llosa, G., et al. (2018). Study and comparison of different sensitivity models for a two-plane Compton camera. Phys. Med. Biol., 63(13), 135004–19pp.
Abstract: Given the strong variations in the sensitivity of Compton cameras for the detection of events originating from different points in the field of view (FoV), sensitivity correction is often necessary in Compton image reconstruction. Several approaches for the calculation of the sensitivity matrix have been proposed in the literature. While most of these models are easily implemented and can be useful in many cases, they usually assume high angular coverage over the scattered photon, which is not the case for our prototype. In this work, we have derived an analytical model that allows us to calculate a detailed sensitivity matrix, which has been compared to other sensitivity models in the literature. Specifically, the proposed model describes the probability of measuring a useful event in a two-plane Compton camera, including the most relevant physical processes involved. The model has been used to obtain an expression for the system and sensitivity matrices for iterative image reconstruction. These matrices have been validated taking Monte Carlo simulations as a reference. In order to study the impact of the sensitivity, images reconstructed with our sensitivity model and with other models have been compared. Images have been reconstructed from several simulated sources, including point-like sources and extended distributions of activity, and also from experimental data measured with Na-22 sources. Results show that our sensitivity model is the best suited for our prototype. Although other models in the literature perform successfully in many scenarios, they are not applicable in all the geometrical configurations of interest for our system. In general, our model allows to effectively recover the intensity of point-like sources at different positions in the FoV and to reconstruct regions of homogeneous activity with minimal variance. Moreover, it can be employed for all Compton camera configurations, including those with low angular coverage over the scatterer.
Keywords: Compton camera imaging; MLEM; Monte Carlo simulations; image quality
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Barrientos, L., Borja-Lloret, M., Casaña, J. V., Hueso-Gonzalez, F., Ros, A., Roser, J., et al. (2023). System characterization and performance studies with MACACO III Compton camera. Radiat. Phys. Chem., 208, 110922–13pp.
Abstract: The IRIS group of IFIC-Valencia has developed a Compton camera prototype. The system detectors are made of Lanthanum (III) bromide scintillator crystals coupled to silicon photomultipliers. Two models of silicon photomultipliers arrays with different micro pixel pitch (25 and 50 μm) have been chosen as possible candidates to improve the response of the new system. Characterization studies with a 22Na point-like source have indicated that the 25 μm photodetector provided better performance in terms of energy resolution (5.2% FWHM at 511 keV) and angular resolution (6.9 degrees FWHM at 1275 keV), and more stability with temperature variations. In addition, MACACO III imaging capabilities have been assessed using a structure composed of thirty-seven 22Na point-like sources. Furthermore, in order to evaluate possible ways of improving the system performance, several studies have been carried out by means of simulations both in realistic and performance improved conditions. In this work, the system performance is evaluated for its future application in different areas.
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