Fluorine-19 MRI at 21.1 T: enhanced spin–lattice relaxation of perfluoro-15-crown-5-ether and sensitivity as demonstrated in ex vivo murine neuroinflammation

Objective

Fluorine MR would benefit greatly from enhancements in signal-to-noise ratio (SNR). This study examines the sensitivity gain of ¹⁹F MR that can be practically achieved when moving from 9.4 to 21.1 T.

Materials and methods

We studied perfluoro-15-crown-5-ether (PFCE) at both field strengths (B₀), as a pure compound, in the form of nanoparticles (NP) as employed to study inflammation in vivo, as well as in inflamed tissue. Brains, lymph nodes (LNs) and spleens were obtained from mice with experimental autoimmune encephalomyelitis (EAE) that had been administered PFCE NPs. All samples were measured at both B₀ with 2D-RARE and 2D-FLASH using ¹⁹F volume radiofrequency resonators together. T₁ and T₂ of PFCE were measured at both B₀ strengths.

Results

Compared to 9.4 T, an SNR gain of > 3 was observed for pure PFCE and > 2 for PFCE NPs at 21.1 T using 2D-FLASH. A dependency of ¹⁹F T₁ and T₂ relaxation on B₀ was demonstrated. High spatially resolved ¹⁹F MRI of EAE brains and LNs at 21.1 T revealed signals not seen at 9.4 T.

Discussion

Enhanced SNR and T₁ shortening indicate the potential benefit of in vivo ¹⁹F MR at higher B₀ to study inflammatory processes with greater detail.

     

Measurement of substrate current in SOI MOSFETs

A new “Quasi-SOI” MOSFET structure is shown to allow direct measurement of substrate current in a fully-depleted SOI device. The holes generated by impact ionization near the drain are collected at the substrate terminal after they have traversed the source-body barrier and caused bipolar multiplication. By monitoring this hole current, direct characterization of the impact-ionization multiplication factor, M, and the parasitic bipolar gain, β, was performed. It was found that M-1 increases exponentially with V_DS and decreases with V_GS, exhibiting a drain field dependence. The bipolar gain β was found to be as high as 1000 for V_GS-V_T=0 V and V_DS=-2.5 V, but decreases exponentially as V_DS increases. Finally, it was found that β also decreases as V_GS increases     

Influence of oxygen on the photoluminescence intensity of erbium (at 1.54 µm) in erbium-doped a-Si:H films

The influence of oxygen on the photoluminescence (PL) of erbium (at 1.54 μm) in erbium-doped hydrogenated amorphous silicon (c-Si〈Er〉) is investigated. The a-Si:H〈Er〉 films studied are fabricated by cosputtering Si and Er targets using the technology of dc silane decomposition in a magnetic field. The oxygen concentration is varied from 10¹⁹ to 10²¹ cm⁻³ by increasing the partial pressure of oxygen in the chamber. It is shown that, as in the case of erbium-doped crystalline silicon (c-Si〈Er〉), oxygen has an effect on the intensity of the 1.54 μm photoluminescence in a-Si:H〈Er〉 films. The values of the erbium and oxygen concentrations at which the maximum Er PL intensity is observed are two orders of magnitude higher than in crystalline silicon. The increase in the Er PL intensity at room temperature and the weaker temperature dependence of the Er PL in comparison to c-Si〈Er,O〉 attest to the prospect of using a-Si:H〈Er〉 films in optoelectronic applications. Fiz. Tekh. Poluprovodn. 32, 1384–1389 (November 1998)     

Application of selective epitaxial silicon and chemo-mechanicalpolishing to bipolar transistors

Successful demonstration of single-polysilicon bipolar transistors fabricated using selective epitaxial growth (SEG) and chemo-mechanical polishing (CMP) is reported. The pedestal structure made possible by the SEG/CMP process combination results in significantly reduced extrinsic-base collector capacitance. Cut-off frequency (f_T) of devices with emitter stripe width of 1 μm, a base width of 110 nm, and a peak base doping of 3×10¹⁸ cm^-3 have been observed to improve from 16 GHz to 22 GHz when the extrinsic-base collector overlap is decreased from 1 μm to 0.2 μm. Leakage current, often a problem for SEG structures, has been reduced to 27 nA/cm² for the area component, and 10 nA/cm for the edge component, by (1) appropriate post-polish processing, including a high-temperature anneal and sacrificial oxidation, (2) aligning the device sidewalls along the 〈100〉 direction, and (3) the presence of the pedestal structure. Base-emitter junction nonideality in these transistors has also been investigated     

A pulsed synthesis of β-FeSi2 layers on silicon implanted with Fe+ ions

Continuous layers and fine-grained films of β-FeSi₂ were synthesized using the implantation of Fe⁺ ions into Si(100) with subsequent pulsed nanosecond ion-beam treatment of the implanted layers. The X-ray diffraction studies showed that the pulsed ion-beam treatment brings about the formation of a mixture of two phases: FeSi and β-FeSi₂ with strained crystal lattices. Subsequent rapid thermal annealing led to the complete transformation of the FeSi phase into the β-FeSi₂ phase with the formation of a textured layer. The data obtained using Raman spectroscopy corroborate the formation of the β-FeSi₂ phase with a high degree of silicon crystallinity. The results of measuring the optical absorption point to the formation of β-FeSi₂ layers and precipitates with a direct-gap structure, an optical gap of E _g≈0.83 eV, and an Urbach tail extent of E ₀≈220 meV. The photoluminescence band peaked at λ≈1.56 μm and caused by direct band-to-band transitions in β-FeSi₂ was observed at temperatures lower than 210 K. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 11, 2001, pp. 1320–1325. Original Russian Text Copyright ? 2001 by Batalov, Bayazitov, Terukov, Kudoyarova, Weiser, Kuehne.     

MOS characteristics of fluorinated gate dielectrics grown by rapidthermal processing in O2 with diluted NF3

Rapid thermal processing (RTP) was applied to the fabrication of the ultrathin (~10 nm) high-quality fluorinated oxides in O₂+NF₃. NF₃ (diluted in N₂) was used as the F source gas and was introduced either prior to rapid thermal oxidation (RTO) or with O₂ during the initial stage of RTO. The electrical characteristics of MOS capacitors have been studied and correlated with the chemical properties. It was found that SiO₂ with a small amount of F incorporated shows reduced interface state generation under F-N injection, whereas excessive F incorporation is detrimental     

The role of parenting in men's psychosocial development: A longitudinal study of early adulthood infertility and midlife generativity.

Of a sample of 343 married men, prospectively studied for four decades, 52 (15.2%) experienced infertility in their first marriage. Styles of coping with their difficulty in achieving parenthood were considered across three longitudinal phases: initial substitutes, subsequent parenting resolutions, and final marital outcomes. The ability of coping strategies used in earlier phases to predict adaptation during later phases of adjustment was considered, as was the relation between coping strategies and the subsequent achievement of generativity as defined by Erik Erikson. Results indicated that the men's parenting resolutions, marital outcomes, and midlife achievement of psychosocial generativity were predictable at statistically significant levels, on the basis of knowledge of their prior infertility coping strategies and parenting outcomes. The findings lend support to the Eriksonian idea that parenting during early adulthood is a crucial but not sufficient prior condition for the midlife achievement of psychosocial generativity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Biodegradable Laser Arrays Self-Assembled from Plant Resources

The transition toward future sustainable societies largely depends on disruptive innovations in biobased materials to substitute nonsustainable advanced functional materials. In the field of optics, advanced devices (e.g., lasers or metamaterial devices) are typically manufactured using top-down engineering and synthetic materials. This work breaks with such concepts and switchable lasers self-assembled from plant-based cellulose nanocrystals and fluorescent polymers at room temperature and from water are shown. Controlled structure formation allows laser-grade cholesteric photonic bandgap materials, in which the photonic bandgap is matched to the fluorescence emission to function as an efficient resonator for low threshold multimode lasing. The lasers can be switched on and off using humidity, and can be printed into pixelated arrays. Additionally, the materials exhibit stiffness above typical thermoplastic polymers and biodegradability in soil. The concept showcases that highly advanced functions can be encoded into biobased materials, and opens the design space for future sustainable optical devices of unprecedented function.     

Compartmentalized Jet Polymerization as a High‐Resolution Process to Continuously Produce Anisometric Microgel Rods with Adjustable Size and Stiffness

In the past decade, anisometric rod‐shaped microgels have attracted growing interest in the materials‐design and tissue‐engineering communities. Rod‐shaped microgels exhibit outstanding potential as versatile building blocks for 3D hydrogels, where they introduce macroscopic anisometry, porosity, or functionality for structural guidance in biomaterials. Various fabrication methods have been established to produce such shape‐controlled elements. However, continuous high‐throughput production of rod‐shaped microgels with simultaneous control over stiffness, size, and aspect ratio still presents a major challenge. A novel microfluidic setup is presented for the continuous production of rod‐shaped microgels from microfluidic plug flow and jets. This system overcomes the current limitations of established production methods for rod‐shaped microgels. Here, an on‐chip gelation setup enables fabrication of soft microgel rods with high aspect ratios, tunable stiffness, and diameters significantly smaller than the channel diameter. This is realized by exposing jets of a microgel precursor to a high intensity light source, operated at specific pulse sequences and frequencies to induce ultra‐fast photopolymerization, while a change in flow rates or pulse duration enables variation of the aspect ratio. The microgels can assemble into 3D structures and function as support for cell culture and tissue engineering.     

Radiofrequency antenna concepts for human cardiac MR at 14.0 T

Objective

To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx).

Materials and methods

RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study. Static and dynamic pTx were applied to enhance transmission field (B₁⁺) uniformity and efficiency in the heart of the human voxel model. B₁⁺ distribution and maximum specific absorption rate averaged over 10 g tissue (SAR_10g) were examined at 7.0 T and 14.0 T.

Results

At 14.0 T static pTx revealed a minimum B₁⁺_ROI efficiency of 0.91 μT/√kW (SGBT), 0.73 μT/√kW (BT), and 0.56 μT/√kW (FD) and maximum SAR_10g of 4.24 W/kg, 1.45 W/kg, and 2.04 W/kg. Dynamic pTx with 8 kT points indicate a balance between B₁⁺_ROI homogeneity (coefficient of variation < 14%) and efficiency (minimum B₁⁺_ROI > 1.11 µT/√kW) at 14.0 T with a maximum SAR_10g < 5.25 W/kg.

Discussion

MRI of the human heart at 14.0 T is feasible from an electrodynamic and theoretical standpoint, provided that multi-channel high-density antennas are arranged accordingly. These findings provide a technical foundation for further explorations into CMR at 14.0 T.