Time resolution of the plastic scintillator strips with matrix photomultiplier readout for J-PET tomograph

Recent tests of a single module of the Jagiellonian Positron Emission Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips have proven its applicability for the detection of annihilation quanta (0.511 MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved resolution is almost by a factor of two better with respect to the current TOF-PET detectors and it can still be improved since, as it is shown in this article, the intrinsic limit of time resolution for the determination of time of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much lower. As the major point of the article, a method allowing to record timestamps of several photons, at two ends of the scintillator strip, by means of matrix of silicon photomultipliers (SiPM) is introduced. As a result of simulations, conducted with the number of SiPM varying from 4 to 42, it is shown that the improvement of timing resolution saturates with the growing number of photomultipliers, and that the 2 x 5 configuration at two ends allowing to read twenty timestamps, constitutes an optimal solution. The conducted simulations accounted for the emission time distribution, photon transport and absorption inside the scintillator, as well as quantum efficiency and transit time spread of photosensors, and were checked based on the experimental results. Application of the 2 x 5 matrix of SiPM allows for achieving the coincidence resolving time in positron emission tomography of $\approx$ 0.170 ns for 15 cm axial field-of-view (AFOV) and $\approx$ 0.365 ns for 100 cm AFOV. The results open perspectives for construction of a cost-effective TOF-PET scanner with significantly better TOF resolution and larger AFOV with respect to the current TOF-PET modalities.Comment: To be published in Phys. Med. Biol. (26 pages, 17 figures

GATE : a simulation toolkit for PET and SPECT

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols, and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at the address http://www-lphe.epfl.ch/GATE/

Application of Silicon Photomultipliers to Positron Emission Tomography

Historically, positron emission tomography (PET) systems have been based on scintillation crystals coupled to photomultipliers tubes (PMTs). However, the limited quantum efficiency, bulkiness, and relatively high cost per unit surface area of PMTs, along with the growth of new applications for PET, offers opportunities for other photodetectors. Among these, small-animal scanners, hybrid PET/MRI systems, and incorporation of time-of-flight information are of particular interest and require low-cost, compact, fast, and magnetic field compatible photodetectors. With high quantum efficiency and compact structure, avalanche photodiodes (APDs) overcome several of the drawbacks of PMTs, but this is offset by degraded signal-to-noise and timing properties. Silicon photomultipliers (SiPMs) offer an alternative solution, combining many of the advantages of PMTs and APDs. They have high gain, excellent timing properties and are insensitive to magnetic fields. At the present time, SiPM technology is rapidly developing and therefore an investigation into optimal design and operating conditions is underway together with detailed characterization of SiPM-based PET detectors. Published data are extremely promising and show good energy and timing resolution, as well as the ability to decode small scintillator arrays. SiPMs clearly have the potential to be the photodetector of choice for some, or even perhaps most, PET systems

Threonine utilization is high in the intestine of piglets

The whole-body threonine requirement in parenterally fed piglets is substantially lower than that in enterally fed piglets, indicating that enteral nutrition induces intestinal processes in demand of threonine. We hypothesized that the percentage of threonine utilization for oxidation and intestinal protein synthesis by the portal-drained viscera (PDV) increases when dietary protein intake is reduced. Piglets (n = 18) received isocaloric normal or protein-restricted diets. After 7 h of enteral feeding, total threonine utilization, incorporation into intestinal tissue, and oxidation by the PDV, were determined with stable isotope methodology [U-(13)C threonine infusion]. Although the absolute amount of systemic and dietary threonine utilized by the PDV was reduced in protein-restricted piglets, the percentage of dietary threonine intake utilized by the PDV did not differ between groups (normal protein 91% vs. low protein 85%). The incorporation of dietary threonine into the proximal jejunum was significantly different compared with the other intestinal segments. Dietary, rather than systemic threonine was preferentially utilized for protein synthesis in the small intestinal mucosa in piglets that consumed the normal protein diet (P < 0.05). Threonine oxidation by the PDV was limited during normal protein feeding. In protein-restricted pigs, half of the total whole-body oxidation occurred in the PDV. We conclude that, in vivo, the PDV have a high obligatory visceral requirement for threonine. The high rate of intestinal threonine utilization is due mainly to incorporation into mucosal protein

Cisgenesis and intragenesis as new strategies for crop improvement

Cisgenesis and intragenesis are emerging plant breeding technologies which offer great promise for future acceptance of genetically engineered crops. The techniques employ traditional genetic engineering methods but are confined to transferring of genes and genetic elements between sexually compatible species that can breed naturally. One of the main requirements is the absence of selectable marker genes (such as antibiotic resistance genes) in the genome. Hence the sensitive issues with regard to transfer of foreign genes and antibiotic resistance are overcome. It is a targeted technique involving specific locus; therefore, linkage drag that prolongs the time for crop improvement in traditional breeding does not occur. It has great potential for crop improvement using superior alleles that exist in the untapped germplasm or wild species. Cisgenic and intragenic plants may not face the same stringent regulatory assessment for field release as transgenic plants which is a clear added advantage that would save time. In this chapter, the concepts of cis/intragenesis and the prerequisites for the development of cis/intragenesis plants are elaborated. Strategies for marker gene removal after selection of transformants are discussed based on the few recent reports from various plant species

Arachidonic Acid but not Eicosapentaenoic Acid (EPA) and Oleic Acid Activates NF-κB and Elevates ICAM-1 Expression in Caco-2 Cells

In patients with inflammatory bowel disease (IBD), intestinal activation of the transcription factor NF-κB as well as intercellular adhesion molecule (ICAM)-1 expression, which is involved in recruiting leukocytes to the side of inflammation is increased. Moreover, colonic arachidonic acid (ARA) proportions are increased and oleic acid (OA) proportions are decreased. Fish oils are protective in IBD patients however, a side-by-side comparison between effects of fish oils, ARA and OA has not been made. We therefore, compared effects of eicosapentaenoic acid (EPA) versus ARA and OA on ICAM-1 expression in Caco-2 enterocytes. To validate our model we showed that dexamethasone, sulfasalazine and PPARα (GW7647) or PPARγ (troglitazone) agonists significantly lowered ICAM-1 expression. ICAM-1 expression of non-stimulated and cytokine stimulated Caco-2 cells cultured for 22 days with ARA was significant higher as compared to EPA and OA. Furthermore, ARA increased NF-κB activation in a reporter cell-line as compared to EPA. Antibody array analysis of multiple inflammatory proteins particularly showed an increased monocyte chemotactic protein (MCP)-1 and angiogenin production and a decreased interleukin (IL)-6 and IL-10 production by ARA as compared to EPA. Our results showed that ARA but not EPA and OA activates NF-κB and elevates ICAM-1 expression in Caco-2 enterocytes. It suggests that replacement of ARA by EPA or OA in the colon mucosa might have beneficial effects for IBD patients. Finally, we suggest that the pro-inflammatory effects of ARA versus EPA and OA are not related to PPARγ activation and/or eicosanoid formation