XMEA: A New Hybrid Diamond Multielectrode Array for the In Situ Assessment of the Radiation Dose Enhancement by Nanoparticles.

This work presents a novel multielectrode array (MEA) to quantitatively assess the dose enhancement factor (DEF) produced in a medium by embedded nanoparticles. The MEA has 16 nanocrystalline diamond electrodes (in a cell-culture well), and a single-crystal diamond divided into four quadrants for X-ray dosimetry. DEF was assessed in water solutions with up to a 1000 µg/mL concentration of silver, platinum, and gold nanoparticles. The X-ray detectors showed a linear response to radiation dose (r2 ≥ 0.9999). Overall, platinum and gold nanoparticles produced a dose enhancement in the medium (maximum of 1.9 and 3.1, respectively), while silver nanoparticles produced a shielding effect (maximum of 37%), lowering the dose in the medium. This work shows that the novel MEA can be a useful tool in the quantitative assessment of radiation dose enhancement due to nanoparticles. Together with its suitability for cells' exocytosis studies, it proves to be a highly versatile device for several applications.

Low-Cost Fetal Magnetocardiography: A Comparison of Superconducting Quantum Interference Device and Optically Pumped Magnetometers.

Background Fetal magnetocardiography (fMCG) is a highly effective technique for evaluation of fetuses with life-threatening arrhythmia, but its dissemination has been constrained by the high cost and complexity of Superconducting Quantum Interference Device (SQUID) instrumentation. Optically pumped magnetometers (OPMs) are a promising new technology that can replace SQUIDs for many applications. This study compares the performance of an fMCG system, utilizing OPMs operating in a person-sized magnetic shield, to that of a conventional fMCG system, utilizing SQUID magnetometers operating in a magnetically shielded room. Methods and Results fMCG recordings were made in 24 subjects using the SQUID system with the mother lying supine in a magnetically shielded room and the OPM system with the mother lying prone in a person-sized, cylindrical shield. Signal-to-noise ratios of the OPM and SQUID recordings were not statistically different and were adequate for diagnostic purposes with both technologies. Although the environmental noise was higher using the small open-ended shield, this was offset by the higher signal amplitude achieved with prone positioning, which reduced the distance between the fetus and sensors and improved patient comfort. In several subjects, fMCG provided a differential diagnosis that was more precise and/or definitive than was possible with echocardiography alone. Conclusions The OPM-based system was portable, improved patient comfort, and performed as well as the SQUID-based system at a small fraction of the cost. Electrophysiological assessment of fetal rhythm is now practical and will have a major impact on management of fetuses with long QT syndrome and other life-threatening arrhythmias.

Patient-specific neurosurgical phantom: assessment of visual quality, accuracy, and scaling effects.

BACKGROUND: Training in medical education depends on the availability of standardized materials that can reliably mimic the human anatomy and physiology. One alternative to using cadavers or animal bodies is to employ phantoms or mimicking devices. Styrene-ethylene/butylene-styrene (SEBS) gels are biologically inert and present tunable properties, including mechanical properties that resemble the soft tissue. Therefore, SEBS is an alternative to develop a patient-specific phantom, that provides real visual and morphological experience during simulation-based neurosurgical training. RESULTS: A 3D model was reconstructed and printed based on patient-specific magnetic resonance images. The fused deposition of polyactic acid (PLA) filament and selective laser sintering of polyamid were used for 3D printing. Silicone and SEBS materials were employed to mimic soft tissues. A neuronavigation protocol was performed on the 3D-printed models scaled to three different sizes, 100%, 50%, and 25% of the original dimensions. A neurosurgery team (17 individuals) evaluated the phantom realism as "very good" and "perfect" in 49% and 31% of the cases, respectively, and rated phantom utility as "very good" and "perfect" in 61% and 32% of the cases, respectively. Models in original size (100%) and scaled to 50% provided a quantitative and realistic visual analysis of the patient's cortical anatomy without distortion. However, reduction to one quarter of the original size (25%) hindered visualization of surface details and identification of anatomical landmarks. CONCLUSIONS: A patient-specific phantom was developed with anatomically and spatially accurate shapes, that can be used as an alternative for surgical planning. Printed models scaled to sizes that avoided quality loss might save time and reduce medical training costs.

Influence of photon beam energy on the dose enhancement factor caused by gold and silver nanoparticles: An experimental approach.

PURPOSE: Noble metal nanoparticles have found several medical applications in the areas of radiation detection; x-ray contrast agents and cancer radiation therapy. Based on computational methods, many papers have reported the nanoparticle effect on the dose deposition in the surrounding medium. Here the authors report experimental results on how silver and gold nanoparticles affect the dose deposition in alanine dosimeters containing several concentrations of silver and gold nanoparticles, for five different beam energies, using electron spin resonance spectroscopy (ESR). METHODS: The authors produced alanine dosimeters containing several mass percentage of silver and gold nanoparticles. Nanoparticle sizes were measured by dynamic light scattering and by transmission electron microscopy. The authors determined the dose enhancement factor (DEF) theoretically, using a widely accepted method, and experimentally, using ESR spectroscopy. RESULTS: The DEF is governed by nanoparticle concentration, size, and position in the alanine matrix. Samples containing gold nanoparticles afford a DEF higher than 1.0, because gold nanoparticle size is homogeneous for all gold concentrations utilized. For samples containing silver particles, the silver mass percentage governs the nanoparticles size, which, in turns, modifies nanoparticle position in the alanine dosimeters. In this sense, DEF decreases for dosimeters containing large and segregated particles. The influence of nanoparticle size-position is more noticeable for dosimeters irradiated with higher beam energies, and dosimeters containing large and segregated particles become less sensitive than pure alanine (DEF < 1). CONCLUSIONS: ESR dosimetry gives the DEF in a medium containing metal nanoparticles, although particle concentration, size, and position are closely related in the system. Because this is also the case as in many real systems of materials containing inorganic nanoparticles, ESR is a valuable tool for investigating DEF. Moreover, these results alert to the importance of controlling the size-position of nanoparticles to enhance DEF.

Assessment of the post-prandial distribution of intragastric contents using an automated technique.

The distribution of intragastric contents has been studied using operator-dependent methods. We devised an automated technique for determining post-prandial intragastric distribution of radiolabeled meals, based on the calculation of the 'center of activity' (CA) of the radioactivity contained in the stomach in any given scintigraphic image. Twelve healthy volunteers and eleven functional dyspepsia (FD) patients ingested a liquid meal (320 mL, 450 kcal) labeled with (99m)Technetium-phytate. Images of the stomach were acquired every 5-10 min for 2 h, and counted to determine the percentage of total activity retained in the upper half of the stomach, as visually delineated. Each image was then processed using an algorithm for calculating a CA value representing the average of image-forming points corrected by pixel number. The relative CA position along the main longitudinal axis of the stomach, as defined by a digital 'skeletonizing' process, was expressed in a '0 to 1' scale. In the FD patients, the average of all CA determinations was significantly higher than in the controls (0.56, 0.30-0.80 versus 0.48, 0.33-0.68, p < 0.05) and correlated significantly with proximal stomach retention values assessed by a visual method (R = -0.64, p < 0.001). Assessing post-prandial intragastric distribution by a novel automated method is feasible and yields reliable data, while being much less operator dependent.