Dual-energy computed tomography (DECT) enables material decomposition for tissues and produces additional information for PET/CT imaging to potentially improve the characterization of diseases. PET-enabled DECT (PDECT) allows the generation of PET and DECT images simultaneously with a conventional PET/CT scanner without the need for a second x-ray CT scan. In PDECT, high-energy γ-ray CT (GCT) images at 511 keV are obtained from time-of-flight (TOF) PET data and are combined with the existing x-ray CT images to form DECT imaging. We have developed a kernel-based maximum-likelihood attenuation and activity (MLAA) method that uses x-ray CT images as a priori information for noise suppression. However, our previous studies focused on GCT image reconstruction at the PET image resolution which is coarser than the image resolution of the x-ray CT. In this work, we explored the feasibility of generating super-resolution GCT images at the corresponding CT resolution. The study was conducted using both phantom and patient scans acquired with the uEXPLORER total-body PET/CT system. GCT images at the PET resolution with a pixel size of 4.0 mm × 4.0 mm and at the CT resolution with a pixel size of 1.2 mm × 1.2 mm were reconstructed using both the standard MLAA and kernel MLAA methods. The results indicated that the GCT images at the CT resolution had sharper edges and revealed more structural details compared to the images reconstructed at the PET resolution. Furthermore, images from the kernel MLAA method showed substantially improved image quality compared to those obtained with the standard MLAA method.
Radioactive isotopes with energies up to 0.5 MeV are used in nuclear medicine for imaging. However several isotopes with energies up to 10 MeV exist that have interesting properties for medical applications, but conventional detectors are inefficient for these energies. A Compton camera setup, consisting of a radiator and an absorption layer, can be used to detect such high energy gamma radiation. In a Compton camera an incident gamma ray undergoes a Compton scattering in the radiator creating a high energetic Compton electron e. By determining the point of interaction and measuring the energy and the direction of the scattered gamma ray it is possible to confine the origin of the incident gamma ray to the surface of a cone. The greatest challenge lies in the coincident detection of electron and scattered gamma. Previous research proposed the use of Silicon Photomultipliers arrays (SiPM) to detect Cherenkov Light (CL) produced by e for determining es properties based on the directional properties of CL. Since only few photons of CL are produced, the high noise floor of the SiPM affects the detection negatively. In this contribution an estimation of SiPMs noise floor is presented, that bases on a behavioural simulation of noise processes in the SiPM. With the simulation it is possible to determine properties of the SiPM, to assess the effectiveness of filter and to build stimuli for other simulations.
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