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Positron emission tomography (PET) is routinely used for medical imaging; a current surge in published geoscientific research utilizing this modality also infer increasing interest for in-situ PET imaging in core analysis. Excellent signal to noise ratio coupled with high temporal and spatial resolution suggest that PET might become the new method-of-choice for core analysis. Obstacles related to production, transfer and handling of radioactive fluids and gases must, however, be dealt with for PET to become a widely used core scale imaging technique. This paper describes an ongoing, true multidisciplinary collaboration, where pre-clinical PET imaging facilities are routinely used in core analysis to investigate dynamic fluid flow at high pressure conditions. We detail challenges and opportunities related to porous media research in established pre-clinical laboratory facilities designed for small-animal imaging, and demonstrate the significant potential of PET imaging in core scale analysis in a context related to long-term porous media carbon storage. Explicit imaging of several fluid phases is possible by PET imaging using a range of readily available radiotracers. Relevant radiotracers to carbon storage in porous media are e.g. the carbon radioisotope 11C and water-soluble tracer 18F. These are both short-lived tracers (20 - 110 min) and must be used in high doses of radiation, which present challenges related to safe transfer and handling. Although there are several obstacles to conduct advanced core analysis in hospital imaging facilities (some of which are detailed in this paper), significant advantages include trained personnel on-site to operate a local cyclotron, procedures in place to ensure safe and efficient transfer of short-lived radiopharmaceuticals from the cyclotron, and advanced image analysis capabilities available. Cyclotrons are widely available worldwide (currently more than 1200 operating cyclotrons), often located in close proximity to medical and pre-clinical imaging facilities and academic institutions. Similar collaborations may therefore also be possible elsewhere, reducing the need for allocated geophysical PET-scanners and lowering the threshold for routinely using PET imaging in core analysis.

Monte Carlo simulations of a time-of-flight Positron Emission Tomography front end readout system (TOF-PET) are performed to investigate obtainable timing resolution at different ADC sample times using LYSO scintillators. Results from simulations with different combinations of ADC sample times and analog filter time constants are presented. To determine the coincidence resolving time (CRT), a trigger system based on a digital constant fraction zero crossing discriminator (CFD) is investigated. Such a trigger system would be suitable for running real time in a field-programmable gate array (FPGA). It is seen that below a certain sample time, the time resolution is limited by the scintillator and MPPC combination, and not the readout system. [ABSTRACT FROM PUBLISHER]

Aims: We observed hitherto unreported layering of radioactivity in the bladder on PET/CT in prostate cancer (PC) when combined with contrast-enhanced CT (CECT). This effect facilitates assessment of the prostate bed in PC., Methods: Among 128 patients imaged with [ 18 F]PSMA-1007, we selected all 8 studies without and 28 studies with CECT. 20 patients also underwent PET/MR. As controls, we chose 20 and 16 males studied with [ 18 F]FDG for extrapelvic disease with and without CECT. Posterior anterior (PA) ratio was calculated as SUV post /SUV ant * 100 % based on maximal standard uptake values (SUV) in 20 mm spheres in the anterior and posterior bladder. Four nuclear physicians scored assessibility of the bladder base on a 3-point Likert scale (3 = optimal, 1 = poor). We acquired serial PET/CT over 4 hours of a flask with layering of 100 ml intravenous contrast agent and 100 ml physiological saline with 40 MBq of [ 18 F]PSMA-1007, while a control flask was shaken at the start of the experiment., Results: Layering of tracer was observed in all PET/CT studies with CE-CT, but not in studies without contrast. Median PA ratios were 44 % (interquartile range 33-62) for [ 18 F]PSMA-1007 and 73 % (52-67) for [ 18 F]FDG, respectively. Intravenous contrast improved assessibility scores in PET of the bladder base, but the effect only reached significance in the PET/MR data. In the in vitro data, radioactivity was retained in the aqueous supernatant over the entire experiment whereas there was no separation of phases in the control flask over time., Conclusion: When performing PET combined with CECT, sedimentation of contrast agent in the bladder leads to upward displacement of radioactivity, enhancing clarity of PET images in the posterior bladder and the prostate bed on both PET/CT and PET/MR., Competing Interests: The last author is consultant (unpaid) for Segami Corporation, Inc. The remaining authors have no conflicts of interest., (Thieme. All rights reserved.)