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

A needs assessment study for optimising prescribing practice in secondary care junior doctors: the Antibiotic Prescribing Education among Doctors (APED).

BACKGROUND: Appropriate antimicrobial prescribing is essential for patient care, yet up to half of antimicrobial prescriptions written in the UK are sub-optimal. Improving prescriber education has recently been promoted as a mechanism to optimise antimicrobial use, but identification of key learning objectives to facilitate this is so far lacking. Using qualitative methods we investigated junior doctor knowledge, attitudes, and behaviours around antimicrobial prescribing to identify key areas to address in future educational programmes. METHODS: A cross-sectional survey of qualified doctors in training in West London was undertaken exploring antimicrobial prescribing practices and educational needs. RESULTS: Among 140 junior doctors from 5 London hospitals, a third (34 %) reported prescribing primarily unsupervised, and two thirds (67 %) reported difficulties obtaining prescribing support outside of hours. 20 % stated not feeling confident in writing an antimicrobial prescription, but confidence was increased through having confirmatory diagnostic results (24) and obtaining advice from a senior doctor (26 %); whether this senior was from their own specialty, or an infection-specialist, varied significantly (p < 0.01) by experience. Only a small percentage (5-13 %; depending on number of years post-qualification) of participants stated their previous antimicrobial education was effective. 60 % of those in their first year post qualification reported wanting further education in antimicrobial prescribing, rising to 74 % among more experienced junior doctors. Specific areas of educational need identified were (i) principles of antimicrobial prescribing, (ii) diagnosis of infections, (iii) clinical review of patients with infections, (iv) prescribing in the context of antimicrobial resistance, and (v) laboratory testing and test results. CONCLUSIONS: A significant proportion of junior doctors report lone prescribing of antimicrobials in the context of low self-perceived confidence and knowledge in this field, and frequent difficulty in accessing help when necessary. Innovative training, targeting five specific areas identified through this needs assessment, is urgently needed by junior doctors practising in secondary care

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

Upper limb vascular occlusion in the recipient of a monochorionic twin pair

Monochorionicity is responsible for an increased rate of severe complications because of unequal splitting of the placental mass and/or an imbalance in the blood flow across placental vascular anastomoses. Vascular limb occlusion is one of the rare complications of monochorionic twins, usually occurring in the lower extremities after intra-uterine death of one twin, antenatal intervention (amnio-reduction or laser therapy) or in the presence of twin anemia-polycythemia syndrome. We report a case of vascular occlusion of the upper extremity in the recipient twin of a monochorionic pair in the absence of those predisposing factors. © 2014 Informa UK Ltd. All rights reserved: reproduction in whole or part not permitted

Physical effects of mechanical design parameters on photon sensitivity and spatial resolution performance of a breast-dedicated PET system

Purpose: This study aims to address design considerations of a high resolution, high sensitivity positron emission tomography scanner dedicated to breast imaging

High-resolution and high-sensitivity SPECT imaging of breast phantoms

A small field of view gamma camera based on a Position Sensitive Photomultiplier Tube has been used for tomoscintigraphic imaging of breast phantoms. The breast phantoms consist of small hot quantities of 99mTc placed in a plastic pot filled with a lower concentration 99mTc solution. The volume of the hot quantities varied from 0.5 to 0.25ml and the target to background activity ratio varied from 3:1 to 5:1. The impact of the acquisition time per projection and the number of projections on image quality has been investigated. © 2004 Elsevier B.V. All rights reserved