Dosimetry of the PIM1 Pion Beam at the Paul Scherrer Institute for Radiobiological Studies of Mice.

Significant past work has identified unexpected risks of central nervous system (CNS) exposure to the space radiation environment, where long-lasting functional decrements have been associated with multiple ion species delivered at low doses and dose rates. As shielding is the only established intervention capable of limiting exposure to the dangerous radiation fields in space, the recent discovery that pions, emanating from regions of enhanced shielding, can contribute significantly to the total absorbed dose on a deep space mission poses additional concerns. As a prerequisite to biological studies evaluating pion dose equivalents for various CNS exposure scenarios of mice, a careful dosimetric validation study is required. Within our ultimate goal of evaluating the functional consequences of defined pion exposures to CNS functionality, we report in this article the detailed dosimetry of the PiMI pion beam line at the Paul Scherrer Institute, which was developed in support of radiobiological experiments. Beam profiles and contamination of the beam by protons, electrons, positrons and muons were characterized prior to the mice irradiations. The dose to the back and top of the mice was measured using thermoluminescent dosimeters (TLD) and optically simulated luminescence (OSL) to cross-validate the dosimetry results. Geant4 Monte Carlo simulations of radiation exposure of a mouse phantom in water by charged pions were also performed to quantify the difference between the absorbed dose from the OSL and TLD and the absorbed dose to water, using a simple model of the mouse brain. The absorbed dose measured by the OSL dosimeters and TLDs agreed within 5-10%. A 30% difference between the measured absorbed dose and the dose calculated by Geant4 in the dosimeters was obtained, probably due to the approximated Monte Carlo configuration compared to the experiment. A difference of 15-20% between the calculated absorbed dose to water at a 5 mm depth and in the passive dosimeters was obtained, suggesting the need for a correction factor of the measured dose to obtain the absorbed dose in the mouse brain. Finally, based on the comparison of the experimental data and the Monte Carlo calculations, we consider the dose measurement to be accurate to within 15-20%.

Optimized light sharing for high-resolution TOF PET detector based on digital silicon photomultipliers.

The majority of current whole-body PET scanners are based on pixelated scintillator arrays with a transverse pixel size of 4 mm. However, recent studies have shown that decreasing the pixel size to 2 mm can significantly improve image spatial resolution. In this study, the performance of Digital Photon Counter (DPC) from Philips Digital Photon Counting (PDPC) was evaluated to determine their potential for high-resolution whole-body time of flight (TOF) PET scanners. Two detector configurations were evaluated. First, the DPC3200-44-22 DPC array was coupled to a LYSO block of 15 × 15 2 × 2 × 22 mm(3) pixels through a 1 mm thick light guide. Due to light sharing among the dies neighbour logic of the DPC was used. In a second setup the same DPC was coupled directly to a scalable 4 × 4 LYSO matrix of 1.9 × 1.9 × 22 mm(3) crystals with a dedicated reflector arrangement allowing for controlled light sharing patterns inside the matrix. With the first approach an average energy resolution of 14.5% and an average CRT of 376 ps were achieved. For the second configuration an average energy resolution of 11% and an average CRT of 295 ps were achieved. Our studies show that the DPC is a suitable photosensor for a high-resolution TOF-PET detector. The dedicated reflector arrangement allows one to achieve better performances than the light guide approach. The count loss, caused by dark counts, is overcome by fitting the matrix size to the size of DPC single die.

[Changes in the methods of cesarean section]. / Zmiany w technice operacji ciecia cesarskiego.

OBJECTIVE: To evaluate the effects of leaving the visceral peritoneum open and hysterotomy closing by a one-layer continuous locked. MATERIALS AND METHODS: The analysis of 868 women underwent caesarean section had been performed. All operated patients were divided into three compared groups. 268 women operated between 01.05.96 and 31.01.97, belonged into I group, which had the visceral peritoneum sutured during caesarean section, in comparison to the II group operated between 01.05.97-31.01.98 (n = 280), which had only one modification in surgical procedure--the visceral peritoneum was left unsutured and to the group operated between 01.05.98-31.01.99 (n = 320) with second modification--the hysterotomy was closed by a one-layer continuous locked. RESULTS: The average operating time was significantly shorter at group II and III. After surgery we have not observed significant differences in frequency of febrile morbidity (6.34% in I group, 8.93% in second group and 8.44% in third group) and postoperative complications (respectively 9.33; 11.07 and 10.63%). CONCLUSIONS: Non-closure of the visceral peritoneum and closure of the hysterotomy by a one-layer continuous locked has no influence on the number of the post surgical complications. Modifications method of cesarean section showed significantly decreased operative time and chirurgical materials use.

A pseudomass on pelvic computed tomography: a pitfall to avoid.

Reported here is a patient with celiac disease in whom a spurious pelvic mass was suggested by computed tomography. This pitfall can be prevented by an awareness of the normal appearance of the small bowel following intravenous contrast enhancement and by monitoring of the examination by a radiologist. Delayed scanning or real-time ultrasound examination will confirm that the initial computed tomography appearance is due to small bowel loops.