3D <Emphasis Type="Italic">T</Emphasis><Subscript>2</Subscript>-weighted imaging at 7T using dynamic k<Subscript>T</Subscript>-points on single-transmit MRI systems

Objectives

For turbo spin echo (TSE) sequences to be useful at ultra-high field, they should ideally employ an RF pulse train compensated for the B ₁ ⁺ inhomogeneity. Previously, it was shown that a single k_T-point pulse designed in the small tip-angle regime can replace all the pulses of the sequence (static k_T-points). This work demonstrates that the B ₁ ⁺ dependence of T ₂-weighted imaging can be further mitigated by designing a specific k_T-point pulse for each pulse of a 3D TSE sequence (dynamic k_T-points) even on single-channel transmit systems

Materials and methods

By combining the spatially resolved extended phase graph formalism (which calculates the echo signals throughout the sequence) with a gradient descent algorithm, dynamic k_T-points were optimized such that the difference between the simulated signal and a target was minimized at each echo. Dynamic k_T-points were inserted into the TSE sequence to acquire in vivo images at 7T.

Results

The improvement provided by the dynamic k_T-points over the static k_T-point design and conventional hard pulses was demonstrated via simulations. Images acquired with dynamic k_T-points showed systematic improvement of signal and contrast at 7T over regular TSE—especially in cerebellar and temporal lobe regions without the need of parallel transmission.

Conclusion

Designing dynamic k_T-points for a 3D TSE sequence allows the acquisition of T ₂-weighted brain images on a single-transmit system at ultra-high field with reduced dropout and only mild residual effects due to the B ₁ ⁺ inhomogeneity.

     

Pulsed arterial spin labelling at ultra-high field with a <Emphasis Type="Italic">B</Emphasis><Stack><Subscript>1</Subscript><Superscript>+</Superscript></Stack>-optimised adiabatic labelling pulse

Objective

Arterial spin labelling (ASL) techniques benefit from the increased signal-to-noise ratio and the longer T ₁ relaxation times available at ultra-high field. Previous pulsed ASL studies at 7 T concentrated on the superior regions of the brain because of the larger transmit radiofrequency inhomogeneity experienced at ultra-high field that hinders an adequate inversion of the blood bolus when labelling in the neck. Recently, researchers have proposed to overcome this problem with either the use of dielectric pads, through dedicated transmit labelling coils, or special adiabatic inversion pulses.

Materials and methods

We investigate the performance of an optimised time-resampled frequency-offset corrected inversion (TR-FOCI) pulse designed to cause inversion at much lower peak B ₁ ⁺ . In combination with a PICORE labelling, the perfusion signal obtained with this pulse is compared against that obtained with a FOCI pulse, with and without dielectric pads.

Results

Mean grey matter perfusion with the TR-FOCI was 52.5 ± 10.3 mL/100 g/min, being significantly higher than the 34.6 ± 2.6 mL/100 g/min obtained with the FOCI pulse. No significant effect of the dielectric pads was observed.

Conclusion

The usage of the B ₁ ⁺ -optimised TR-FOCI pulse results in a significantly higher perfusion signal. PICORE–ASL is feasible at ultra-high field with no changes to operating conditions.

     

Quantitative T<Subscript>1</Subscript> and T<Subscript>2</Subscript> MRI signal characteristics in the human brain: different patterns of MR contrasts in normal ageing

Objective

The objective of this study was to examine age-dependent changes in both T₁-weighted and T₂-weighted image contrasts and spin-echo T₂ relaxation time in the human brain during healthy ageing.

Methods

A total of 37 participants between the ages of 49 and 87 years old were scanned with a 3 Tesla system, using T₁-weighted, T₂ weighted and quantitative spin-echo T₂ imaging. Contrast between image intensities and T₂ values was calculated for various regions, including between individual hippocampal subfields.

Results

The T₁ contrast-to-noise (CNR) and gray:white signal intensity ratio (GWR) did not change in the hippocampus, but it declined in the cingulate cortex with age. In contrast, T₂ CNR and GWR declined in both brain regions. T₂ relaxation time was almost constant in gray matter and most (but not all) hippocampal subfields, but increased substantially in white matter, pointing to an age effect on water relaxation in white matter.

Conclusions

Changes in T₁ and T₂ MR characteristics influence the appearance of brain images in later life and should be considered in image analyses of aged subjects. It is speculated that alterations at the cell biology level, with concomitant alterations to the local magnetic environment, reduce dephasing and subsequently prolong spin-echo T₂ through reduced diffusion effects in later life.

     

Microwave dielectric properties of Na<Superscript>+</Superscript> and M<Superscript>3+</Superscript>-doped Ba(Mg<Subscript>0.5</Subscript>W<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> ceramics

In this study, phase evolution, microstructure, and microwave dielectric properties of (Ba_0.98Na_0.02)(Mg_0.48M³⁺_0.02W_0.5)O₃ (M³⁺?=?Al, Ga, Sc, In, Yb, Y, Dy, Gd, and Sm) ceramics sintered at 1700 °C for 1 h were investigated. All the compounds exhibited an ordered cubic perovskite structure. Regardless of the ionic radius of the doped M³⁺ ions, BaWO₄ was detected as the secondary phase in all the compounds. The field emission scanning electron microscopy (FE-SEM) images revealed a dense microstructure in all the compounds, except in the Al-doped compound, which exhibited an insufficient grain growth. The large and irregularly shaped grains indicated that the liquid phase sintering occurred. Splitting of the A_1g(O) mode was observed in the Raman spectra of large M³⁺ ion-doped compounds. Splitting of the F_2g modes did not occur and the bands were sharp, indicating that the cubic symmetry was retained. As the ionic radius of the doped M³⁺ ions increased, the dielectric constant (ε_r) increased slightly. The compounds doped with M³⁺?=?Sc, In, Yb, and Y exhibited a very high quality factor (Q?×?f₀) in the range of 250,000 ~ 280,000 GHz. In the case of the compounds doped with M³⁺?=?Al, Ga, Sc, In, Yb, Y, and Dy, the value of the temperature coefficient of resonant frequency (τ_f) was in the range of ?24 ~ ?19 ppm/°C, while the Gd and Sm-doped compounds exhibited positive values of 2.8 and 31.2 ppm/°C, respectively. The dielectric constant, quality factor, and temperature coefficient of resonant frequency of the In-doped compound, i.e., (Ba_0.98Na_0.02)(Mg_0.48In_0.02W_0.5)O₃, were 18.7, 286,557 GHz, and???24.4 ppm/°C, respectively.     

A novel alternative to classify tissues from <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript> and <Emphasis Type="Italic">T</Emphasis><Subscript>2</Subscript> relaxation times for prostate MRI

Objective

To segment and classify the different attenuation regions from MRI at the pelvis level using the T ₁ and T ₂ relaxation times and anatomical knowledge as a first step towards the creation of PET/MR attenuation maps.

Materials and methods

Relaxation times were calculated by fitting the pixel-wise intensities of acquired T ₁- and T ₂-weighted images from eight men with inversion-recovery and multi-echo multi-slice spin-echo sequences. A decision binary tree based on relaxation times was implemented to segment and classify fat, muscle, prostate, and air (within the body). Connected component analysis and an anatomical knowledge-based procedure were implemented to localize the background and bone.

Results

Relaxation times at 3 T are reported for fat (T ₁ = 385 ms, T ₂ = 121 ms), muscle (T ₁ = 1295 ms, T ₂ = 40 ms), and prostate (T ₁ = 1700 ms, T ₂ = 80 ms). The relaxation times allowed the segmentation–classification of fat, prostate, muscle, and air, and combined with anatomical knowledge, they allowed classification of bone. The good segmentation–classification of prostate [mean Dice similarity score (mDSC) = 0.70] suggests a viable implementation in oncology and that of fat (mDSC = 0.99), muscle (mDSC = 0.99), and bone (mDSCs = 0.78) advocates for its implementation in PET/MR attenuation correction.

Conclusion

Our method allows the segmentation and classification of the attenuation-relevant structures required for the generation of the attenuation map of PET/MR systems in prostate imaging: air, background, bone, fat, muscle, and prostate.

     

Acoustic noise reduction in <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript>- and proton-density-weighted turbo spin-echo imaging

Objective

To reduce acoustic noise levels in T ₁-weighted and proton-density-weighted turbo spin-echo (TSE) sequences, which typically reach acoustic noise levels up to 100 dB(A) in clinical practice.

Materials and methods

Five acoustic noise reduction strategies were combined: (1) gradient ramps and shapes were changed from trapezoidal to triangular, (2) variable-encoding-time imaging was implemented to relax the phase-encoding gradient timing, (3) RF pulses were adapted to avoid the need for reversing the polarity of the slice-rewinding gradient, (4) readout bandwidth was increased to provide more time for gradient activity on other axes, (5) the number of slices per TR was reduced to limit the total gradient activity per unit time. We evaluated the influence of each measure on the acoustic noise level, and conducted in vivo measurements on a healthy volunteer. Sound recordings were taken for comparison.

Results

An overall acoustic noise reduction of up to 16.8 dB(A) was obtained by the proposed strategies (1–4) and the acquisition of half the number of slices per TR only. Image quality in terms of SNR and CNR was found to be preserved.

Conclusions

The proposed measures in this study allowed a threefold reduction in the acoustic perception of T ₁-weighted and proton-density-weighted TSE sequences compared to a standard TSE-acquisition. This could be achieved without visible degradation of image quality, showing the potential to improve patient comfort and scan acceptability.

     

The Similar Defect Chemistry of Highly-Doped SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> and SrBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>

The equilibrium electrical conductivities of undoped SrBi₂Ta₂O₉ (SBT) and SrBi₂Nb₂O₉ (SBN) have been shown to behave quite differently. SBT has the behavior expected for a 1% acceptor-doped oxide, while SBN behaves like a 1% donor-doped oxide. This difference has been related to the substantial cation place exchange that occurs between the Bi^{+ 3} and Sr^{+ 2} ions in the alternating layers of the structure. It was proposed that this place exchange is not entirely self-compensating, as would be expected for a simple, isotropic oxide, but that there is some local compensation within each layer by lattice and/or electronic defects. It is now shown that the equilibrium conductivity of 3% donor-doped SBT is similar to that of undoped SBN, while the equilibrium conductivity of 3% acceptor-doped SBN resembles that of undoped SBT. Thus the defect chemistrys of the two compounds are quite similar, but the equilibrium conductivities are displaced along a doping axis.     

Effects of Al<Superscript>3+</Superscript> substitution on the luminescence properties of LuNbO<Subscript>4</Subscript> doped with Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript> ions

The effect of Al³⁺ substitution on the enhancement of the luminescence of Lu_1–xAl_xNbO₄:Eu³⁺ and Lu_1–xAl_xNbO₄:Tb³⁺ was investigated. X-ray diffraction patterns confirmed that the Eu³⁺, Tb³⁺, and Al³⁺ ions were fully incorporated into the Lu³⁺ sites. In the case of Lu_1–xAl_xNbO₄:Eu³⁺, the predominant red emission (614 nm) was assigned to the ⁵D₀?→?⁷F₂ transition of Eu³⁺ and for x?=?0–0.05, its intensity increased up to ~125 and 108% under 395 nm (⁷F₀ → ⁵L₆) and a charge transfer band excitation, respectively. For Lu_1–xAl_xNbO₄:Tb³⁺, the strongest emission band peaking at 551 nm was attained in the green region among multiple emission bands corresponding to the ⁵D₄?→?⁷F_J transitions of Tb³⁺. Increasing the x values from 0 to 0.05 increased the green emission significantly by ~137%. These phenomena were explained by the local structural distortions and crystal field asymmetry surrounding Eu³⁺ and Tb³⁺, which were attributed to a large difference in the ionic radii of Al³⁺ and Lu³⁺.     

Preparation of superconductive P3 cobalt oxyhydrates Na<Subscript>x</Subscript>(H<Subscript>2</Subscript>O)<Subscript>y</Subscript>CoO<Subscript>2</Subscript> with three-layered CoO<Subscript>2</Subscript> using NaMnO<Subscript>4</Subscript> solution

We report the synthesis of the superconductive P3 cobalt oxyhydrates by immersing α-NaCoO₂ in aqueous NaMnO₄ solution for the first time. It is a novel route to form the superconductive phase of cobalt oxyhydrates without resort to the commonly used Br₂/CH₃CN solution. Topotactic transformation of the parent compound α-NaCoO₂ results in water intercalation and hence a significant expansion of the c-axis in the unit cell. The P3 cobalt oxyhydrates exhibits an onset superconducting transition at about 4.2 K.     

Effect of O<Superscript>2-</Superscript> migration in Pt/HfO<Subscript>2</Subscript>/Ti/Pt structure

In this paper, we study the post-fabrication phenomenon of natural oxidation of the Ti layer observed in a Pt/HfO₂/Ti/Pt Resistive Random Access Memory (OxRRAM) stack with no external influence. We identify that the resistance ratio decreases by 100 × in a month time period due to the natural oxidation of the Ti layer in contact of the HfO₂ layer. We then propose two paths to control both the final properties of the device and the aging process. The first approach consists in carefully optimizing the thickness of the Ti layer to reduce the aging effect. However, the resistance ratio is proportional to the thickness of the layer, leading to an unwanted trade-off between device properties and aging effect. The second approach consists in adding a TiO₂ inter-layer, creating a Pt/HfO₂/TiO₂/Ti/Pt OxRRAM stack that is more stable over time with similar resistive states. The obtained OxRRAM stack presents a resistance ratio in the order of 10⁴ with no observable post-fabrication aging degradation.     

Properties and crystallization kinetics of low temperature co-fired Li<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> electroceramics

The glass-ceramic in the Li₂O-Al₂O₃-SiO₂ system has been prepared by melt quenching route. The crystallization kinetics was studied by differential scanning calorimetry. The effects of sintering temperature on the phase transformation, sintering behavior, bulk density, microstructure, thermal expansion, bending strength and dielectric properties were also investigated by X-ray diffractometry and scanning electron microscopy. (Li, Mg, Zn)_1.7Al₂O₄Si₆O₁₂ is the first crystalline phase forming in the glass-ceramic and transforms to LiAlSi₃O₈ phase at 800 °C. The other two crystalline phases of ZrO₂ and CaMgSi₂O₆ precipitate at 700 and 750 °C, respectively. The densification of this LAS glass-ceramic starts at around 730 °C and stops at about 805 °C. The coefficient of thermal expansion increases with the increasing sintering temperature. The sample sintered at 800 °C for 30 min exhibited excellent properties. The nonisothermal activation energy of crystallization is 149 kJ/mol and the values of Avrami constant (n) are in the range of 3.2 to 3.9. The LAS glass-ceramic sintered at 800 °C for 30 min showed excellent properties. This makes that this material suitable for a number of LTCC applications.     

Hyperpolarized <Superscript>3</Superscript>He lung ventilation imaging with <Emphasis Type="Italic">B</Emphasis><Subscript>1</Subscript>-inhomogeneity correction in a single breath-hold scan

The signal-to-noise ratio (SNR) of hyperpolarized noble gas MR images is sensitive to the flip angle used. Variations in flip angle due to B ₁-inhomogeneity of the RF coil cause intensity variation artifacts in lung ventilation images which may mask or mimic disease. We show these artifacts can be minimized by using the optimal flip angle and corrected if the local flip angle is known. Hyperpolarized ³He lung images were obtained in ten healthy subjects using both a conventional gradient-echo sequence and a new hybrid pulse sequence designed to simultaneously acquire lung ventilation images and corresponding flip-angle maps in comparable imaging time. Flip-angle maps and corrected images were calculated from the hybrid scan and compared with conventional images. The qualitative theoretical dependence of flip angle on SNR was verified. Ventilation images and flip-angle maps were successfully obtained with the hybrid sequence. Corrections to image intensity calculated from the flip-angle maps appeared reasonable for images acquired using an average flip angle near optimal. Use of the optimal flip angle is crucial to the quality of lung ventilation images. Artifactual intensity variations due to RF-coil inhomogeneity may be identified and potentially corrected using our hybrid sequence. Acknowledgement The authors thank John M. Christopher, RT(R)(MR) for valuable assistance performing the studies, and Jaime F. Mata, MS, Jing Cai, MS, and Andrew G. Reish, BS, for excellent operation of the ³He polarization system. We gratefully acknowledge support for this research from the Commonwealth of Virginia Technology Research Fund (Grant No. IN2002-01), Siemens Medical Solutions and Amersham Health.     

Formation of a KNbO<Subscript>3</Subscript> single crystal using solvothermally synthesized K<Subscript>2-m</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6-m/2</Subscript> pyrochlore phase

A K_2-mNb₂O_6-m/2 single crystal with a pyrochlore phase formed when the Nb₂O₅?+?x mol% KOH specimens with 0.6?≤?x?≤?1.2 were solvothermally heated at 230 °C for 24 h. They have an octahedral shape with a size of 100 μm, and the composition of this single crystal is close to K_1.3Nb₂O_5.65. The single-crystal KNbO₃ formed when the single-crystal K_2-mNb₂O_6-m/2 was annealed at a temperature between 600 °C and 800 °C with K₂CO₃ powders. When annealing was conducted at 600 °C (or with a small amount of K₂CO₃), the KNbO₃ single crystal has a rhombohedral structure that is stable at low temperatures (< ? 10 °C). The formation of the rhombohedral KNbO₃ structure can be explained by the presence of the K⁺ vacancies in the specimen. The KNbO₃ single crystal with an orthorhombic structure formed when the K_2-mNb₂O_6-m/2 single crystal was annealed at 800 °C with 20 wt% of K₂CO₃.     

Microwave Dielectric Properties of CuO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Doped ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript> Ceramics with Low Sintering Temperature

Microwave dielectric properties of low temperature sintering ZnNb₂O₆ ceramics doped with CuO-V₂O₅-Bi₂O₃ additions were investigated systematically. The co-doping of CuO, V₂O₅ and Bi₂O₃ can significantly lower the sintering temperature of ZnNb₂O₆ ceramics from 1150 to 870C. The secondary phase containing Cu, V, Bi and Zn was observed at grain boundary junctions, and the amount of secondary phase increased with increasing CuO-V₂O₅-Bi₂O₃ content. The dielectric properties at microwave frequencies (7–9 GHz) in this system exhibited a significant dependence on the relative density, content of additives and microstructure of the ceramics. The dielectric constant ( _r) of ZnNb₂O₆ ceramics increased from 21.95 to 24.18 with increasing CuO-V₂O₅-Bi₂O₃ additions from 1.5 to 4.0 wt%. The quality factors (Q× f) of this system decreased with increasing CuO-V₂O₅-Bi₂O₃ content and ranged from 36118 to 67100 GHz for sintered ceramics, furthermore, all Q× f values of samples with CuO-V₂O₅-Bi₂O₃ additions are lower than that of un-doped ZnNb₂O₆ ceramics sintered at 1150C for 2 h. The temperature coefficient of resonant frequency ( _f) changed from –33.16 to –25.96 ppm/C with increasing CuO-V₂O₅-Bi₂O₃ from 1.5 to 4.0 wt%     

3D single point imaging with compressed sensing provides high temporal resolution <Emphasis Type="Italic">R</Emphasis><Subscript>2</Subscript>* mapping for in vivo preclinical applications

Objective

Purely phase-encoded techniques such as single point imaging (SPI) are generally unsuitable for in vivo imaging due to lengthy acquisition times. Reconstruction of highly undersampled data using compressed sensing allows SPI data to be quickly obtained from animal models, enabling applications in preclinical cellular and molecular imaging.

Materials and methods

TurboSPI is a multi-echo single point technique that acquires hundreds of images with microsecond spacing, enabling high temporal resolution relaxometry of large-R ₂* systems such as iron-loaded cells. TurboSPI acquisitions can be pseudo-randomly undersampled in all three dimensions to increase artifact incoherence, and can provide prior information to improve reconstruction. We evaluated the performance of CS-TurboSPI in phantoms, a rat ex vivo, and a mouse in vivo.

Results

An algorithm for iterative reconstruction of TurboSPI relaxometry time courses does not affect image quality or R ₂* mapping in vitro at acceleration factors up to 10. Imaging ex vivo is possible at similar acceleration factors, and in vivo imaging is demonstrated at an acceleration factor of 8, such that acquisition time is under 1 h.

Conclusions

Accelerated TurboSPI enables preclinical R ₂* mapping without loss of data quality, and may show increased specificity to iron oxide compared to other sequences.

     

Improvement of Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Co<Subscript>2</Subscript>O<Subscript>y</Subscript> thermoelectric performances by Na doping

Bi₂Sr_2-xNa_xCo₂O_y thermoelectric materials with x = 0, 0.025, 0.05, 0.075, 0.10, 0.125, and 0.15 have been prepared by the classical solid state reaction. Microstructure has shown an important grain growth when Na is added, leading to very high bulk densities confirmed through density measurements. These modifications have produced a drastic decrease of electrical resistivity without significant modification of Seebeck coefficient. As a consequence, Power Factor has been increased in all Na-doped samples, reaching the maximum value (0.21 mW/K².m at 650 °C) for 0.075 Na samples, which is fairly close to the reported for single crystals.     

Structure and properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Bi(Mg<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>-0.38PbTiO<Subscript>3</Subscript> ceramics with MPB composition

0.62Bi(Mg_1/2Ti_1/2)O₃-0.38PbTiO₃-xwt%Bi₂O₃ (BMT-0.38PT-xBi₂O₃) ceramics were prepared by conventional powder-processing method. It indicated that the morphotropic phase boundary (MPB) region located in 0.0?≤?x?≤?0.3. For x?=?0.3, it exhibited good piezoelectric properties, d₃₃ ~245pC/N and k_p ~40 %. With the increase of Bi₂O₃ content, the Curie temperature (T_c) was found to increase, and the dielectric loss was found to decrease above 200 °C compared with BMT-0.38PT sample. Finally, it can be found that depolarization temperature was around 350 °C by thermal depoling method.     

Effects of MnO<Subscript>2</Subscript> addition on microstructure and electrical properties of (Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>) <Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> ceramics

In this letter, MnO₂-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT-6) lead-free piezoelectric ceramics were synthesized by solid state reaction, and the microstructure and electrical properties of the ceramics were investigated. X-ray diffraction (XRD) reveals that all specimens take on single perovskite type structure, and the diffraction peaks shift to a large angle as the MnO₂ addition increases. Scanning electron microscopy shows that the grain sizes increases, and then decreases with increasing the MnO₂ content. The experiment results indicate that the electrical properties of ceramics are significantly influenced by the MnO₂ content, and the ceramics with homogeneous microstructure and excellent electrical properties are obtained with addition of 0.3 wt% MnO₂ and sintered at 1160°C. The piezoelectric constant (d₃₃), the electromechanical coupling factor (k _p ), the dissipation factor (tan δ) and the dielectric constant (ɛ _r ) reach 160 pC/N, 0.29, 0.026 and 879, respectively. These excellent properties indicate that the MnO₂-doped BNBT-6 ceramics can be used for actuators.     

Coke-tolerant La<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript>-Ni-Gd<Subscript>0.1</Subscript>Ce<Subscript>0.9</Subscript>O<Subscript>1.95</Subscript> composite anode for direct methane-fueled solid oxide fuel cells

Direct CH₄-fueled solid oxide fuel cells (SOFCs) have been studied for a few decades, but carbon depositions on the Ni-based anodes are still remained as a major problem. In order to enhance coke tolerances and durability of SOFCs, La₂Sn₂O₇ nano-powders are prepared by co-precipitation. The SOFCs with the different amounts of the La₂Sn₂O₇ nano-powders in the Ni-GDC anodes are tested under dry CH₄, and the 0.3 wt.% La₂Sn₂O₇-Ni-GDC (0.3LNG) anodes show the highest cell performances of all anodes. The maximum power density of the cell is approximately 0.55 W cm^?2 at 650 °C. The durability of the 0.3LNG cell is significantly enhanced without any carbon formations, showing approximately 0.69 V over 600 h at 0.3 A cm^?2, whereas the conventional Ni-GDC cell is stopped only after 90 h. It suggests that the 0.3LNG is a promising anode material to enhance coke-tolerances and durability of direct-methane fuel cells.     

Detection of myocardial viability in acute infarction using contrast-enhanced <Superscript>1</Superscript>H magnetic resonance imaging

Background Reperfusion strategies salvage myocardium at risk in acute myocardial infarction (MI). This clinical study was performed to determine whether areas without evidence of delayed MRI contrast enhancement in MI correspond to viability by means of percent systolic wall thickening (%SWT) and enddiastolic wall thickness (EDWT) in chronic infarction. Methods Twenty MRI studies were performed in ten patients within 6 days of MI and 3 months post-MI. On a segmental basis the percentage of viable myocardium as defined by contrast-enhanced MRI (no delayed MRI contrast enhancement) in acute MI was measured and was compared with %SWT and EDWT in chronic MI. Results Of the 1718 segments in acute infarction in which the percentage of viable myocardium was measured 1333 were found to be completely viable by means of contrast-enhanced MRI (no delayed MRI contrast enhancement). All of these segments revealed %SWT on day 90 post-MI, and 97% of segments were viable by means of an EDWT of more than 5.5 mm. In 85 segments the proportion of viable myocardium was 50–99% (mean 56±8%), with 92% segments found to be viable by means of %SWT and 92% by EDWT, and of 156 segments with viable myocardium between 1–49% (36±8%) 79% were found to be viable by means of %SWT and 82% by EDWT. Corresponding proportions of 144 segments with transmural delayed MRI contrast enhancement in acute MI were 45% and 17%. Conclusions In acute reperfused MI viable myocardium as delineated by contrast-enhanced MRI is correlated with clinical parameters of viability. Delayed MRI contrast enhancement resolves nontransmural MI and may become a valuable clinical tool when planning revascularization procedures.