Joint image reconstruction algorithm in Compton cameras

Design and development of the DE-SPECT system: a clinical SPECT system for broadband multi-isotope imaging of peripheral vascular disease

Objective. Peripheral Vascular Disease (PVD) affects more than 230 million people worldwide and is one of the leading causes of disability among people over age 60. Nowadays, PVD remains largely underdiagnosed and undertreated, and requires the development of tailored diagnostic approaches. We present the full design of the Dynamic Extremity SPECT (DE-SPECT) system, the first organ-dedicated SPECT system for lower extremity imaging, based on 1 cm thick Cadmium Zinc Telluride (CZT) spectrometers and a dynamic dual field-of-view (FOV) synthetic compound-eye (SCE) collimator.Approach. The proposed DE-SPECT detection system consists of 48 1 cm thick 3D-position-sensitive CZT spectrometers arranged in a partial ring of 59 cm in diameter in a checkerboard pattern. The detection system is coupled with a compact dynamic SCE collimator that allows the user to select between two different FOVs at any time during an imaging study: a wide-FOV (28 cm diameter) configuration for dual-leg or scout imaging or a high-resolution and high-sensitivity (HR-HS) FOV (16 cm diameter) for single-leg or focused imaging.Main results.The preliminary experimental data show that the CZT spectrometer achieves a 3D intrinsic spatial resolution of <0.75 mm FWHM and an excellent energy resolution over a broad energy range (2.6 keV FWHM at 218, 3.3 keV at 440 keV). From simulations, the wide-FOV configuration offers a 0.034% averaged sensitivity at 140 keV and <8 mm spatial resolution, whereas the HR-HS configuration presents a peak central sensitivity of 0.07% at 140 keV and a ∼5 mm spatial resolution. The dynamic SCE collimator enables the capability to perform joint reconstructions that would ensure an overall improvement in imaging performance.Significance. The DE-SPECT system is a stationary and high-performance SPECT system that offers an excellent spectroscopic performance with a unique computer-controlled dual-FOV imaging capability, and a relatively high sensitivity for multi-tracer and multi-functional SPECT imaging of the extremities.

Gamma-ray sources imaging and test-beam results with MACACO III Compton camera

Hadron therapy is a radiotherapy modality which offers a precise energy deposition to the tumors and a dose reduction to healthy tissue as compared to conventional methods. However, methods for real-time monitoring are required to ensure that the radiation dose is deposited on the target. The IRIS group of IFIC-Valencia developed a Compton camera prototype for this purpose, intending to image the Prompt Gammas emitted by the tissue during irradiation. The system detectors are composed of Lanthanum (III) bromide scintillator crystals coupled to silicon photomultipliers. After an initial characterization in the laboratory, in order to assess the system capabilities for future experiments in proton therapy centers, different tests were carried out in two facilities: PARTREC (Groningen, The Netherlands) and the CNA cyclotron (Sevilla, Spain). Characterization studies performed at PARTREC indicated that the detectors linearity was improved with respect to the previous version and an energy resolution of 5.2 % FWHM at 511 keV was achieved. Moreover, the imaging capabilities of the system were evaluated with a line source of 68Ge and a point-like source of 241Am-9Be. Images at 4.439 MeV were obtained from irradiation of a graphite target with an 18 MeV proton beam at CNA, to perform a study of the system potential to detect shifts at different intensities. In this sense, the system was able to distinguish 1 mm variations in the target position at different beam current intensities for measurement times of 1800 and 600 s.

A stochastic alternative technique for Compton Maximum Likelihood Expectation-Maximization (MLEM) reconstruction

Even though iterative methods and particularly Maximum Likelihood Expectation-Maximization (MLEM) algorithms have been established in reconstruction with Compton data, their detailed design with respect to physical rules and processes dominate their plain implementation in the form of a system matrix. A new elementary but efficient alternative for the well-known system matrix with respect to Compton Camera image reconstruction is presented in this work. For each detected event there is a weighting factor inserted as an accumulated probability which carries all the necessary information. This probability which involves only the Compton scattering angle of the incident photon corresponds to a map that correlates all events within all possible source origins. Based on maximizing likelihood principles, the proposed model weights in a stochastic way the difference of the scatterer-to-source angle θ0, as it is determined by the deposited energy on the absorber, and any other potential scattering angle θJ, specified by the position coordinates on the reconstruction matrix. Obtained image spatial resolution, angular distortions and response to focal length determination are a few of the studied cases for the algorithms' evaluation via simulations in GEANT4/GATE with a set of radioactive sources and phantoms with in- and out-of-plane arrangement.

Hybrid PET/Compton-camera imaging: an imager for the next generation

Compton cameras can offer advantages over gamma cameras for some applications, since they are well suited for multitracer imaging and for imaging high-energy radiotracers, such as those employed in radionuclide therapy. While in conventional clinical settings state-of-the-art Compton cameras cannot compete with well-established methods such as PET and SPECT, there are specific scenarios in which they can constitute an advantageous alternative. The combination of PET and Compton imaging can benefit from the improved resolution and sensitivity of current PET technology and, at the same time, overcome PET limitations in the use of multiple radiotracers. Such a system can provide simultaneous assessment of different radiotracers under identical conditions and reduce errors associated with physical factors that can change between acquisitions. Advances are being made both in instrumentation developments combining PET and Compton cameras for multimodal or three-gamma imaging systems, and in image reconstruction, addressing the challenges imposed by the combination of the two modalities or the new techniques. This review article summarizes the advances made in Compton cameras for medical imaging and their combination with PET.