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1.
The parameters that govern water proton magnetic relaxation (e.g. water exchange rates, and rotational and electronic correlation
times) of representatives of two classes of Gd(III) complexes have been estimated, using two different approaches and the
results compared with those derived for known analogs. The complexes studied are: (i) the non-ionic GdDTPA-bis(methoxyethyl-amide)
[Gd(DTPA-BMEA)], a typical small-molecule extracellular MR agent, and (ii) the ionic Gd(III) complex of 4-pentylbicyclo[2.2.2]octane-1-carboxyl-di- l-aspartyl-lysine-derived-DTPA [GdL] 4−, a prototype MR blood pool agent, which binds to serum albumin in vivo through non-covalent hydrophobic interactions. An 17O-NMR study of [Gd(DTPA-BMEA)] gives a water exchange rate constant of k
ex
298
=(0.39±0.02)×10 6 s −1, identical to that for the bismethylamide analog [Gd(DTPA-BMA)]. Both approaches yield longer rotational correlation times
for [Gd(DTPA-BMEA)], consistent with its higher molecular weight. An 17O-NMR study of [GdL] 4− gives a water exchange rate constant of k
ex
298
=(4.2±0.1)×10 6 s −1, identical to that for [Gd(DTPA)] 2−. The water exchange rate on [GdL] 4− did not decrease considerably when bound to albumin, the lowest limit is k
ex,GdL-BSA= k
ex,GdL/2. Both approaches yield identical rotational correlation times for [GdL] 4−, however, it was difficult to derive a consistent rotational constant for the albumin-bound [GdL] 4− using the different approaches (values ranged between 1.0 and 23.0 ns). 相似文献
2.
Object The sensitivity of spin echo (SE) experiments to blood oxygenation level dependent (BOLD) contrast was explored in a study
of the same six subjects carried out at 3 and 7 T.
Materials and methods Multi-slice, single shot, spin echo, echo planar images with a voxel size of 1 × 1 × 3 mm 3 were acquired at three different echo times, during execution of a simple motor task.
Results Significant activation was observed at all echo times at both field strengths. Analysis of the fractional signal change as
a function of echo time indicated that the change in relaxation rate, Δ R
2, at 7 T was −0.51 ± 0.14 s
−1, which was 1.3 times larger than the value found at 3 T. Measurements of the percentage signal change on activation and temporal
signal to noise ratio showed that there was an increase in the BOLD contrast to noise ratio (CNR) at 7 versus 3 T by a factor
of 1.9. There was no overlap of areas of significant activation in the SE data acquired at either field strength with the
site of large veins.
Conclusion SE-BOLD CNR in motor cortex was found to increase significantly at 7 T compared with 3 T. 相似文献
3.
PurposeIn this study, we aimed to measure the apparent diffusion coefficients (ADCs) of major phosphorous metabolites in the human calf muscle at 7 T with a diffusion-weighted (DW)-STEAM sequence. MethodsA DW-STEAM sequence with bipolar gradients was implemented at 7 T, and DW MR spectra were acquired in three orthogonal directions in the human calf muscle of six healthy volunteers (TE/TM/TR = 15 ms/750 ms/5 s) at three b-values (0, 800, and 1200 s/mm2). Frequency and phase alignments were applied prior to spectral averaging. Averaged DW MR spectra were analyzed with LCModel, and ADCs of 31P metabolites were estimated. ResultsFour metabolites (phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phosphate (Pi) and glycerol phosphorylcholine (GPC)) were quantified at all b-values with mean CRLBs below 10%. The ADC values of PCr, ATP, Pi, and GPC were (0.24 ± 0.02, 0.15 ± 0.04, 0.43 ± 0.14, 0.40 ± 0.09) × 10–3 mm2/s, respectively. ConclusionThe ADCs of four 31P metabolites were successfully measured in the human calf muscle at 7 T, among which those of ATP, Pi and GPC were reported for the first time in humans. This study paves the way to investigate 31P metabolite diffusion properties in health and disease on the clinical MR scanner. 相似文献
4.
Chemosensitivity of N-methyl- N-nitrosourea-induced rat mammary tumours treated with 5-fluorouracil at a dose of 100 mg kg −1 i.p. was assessed by using diffusion-weighted 1H-MRS to measure the average diffusion coefficient (ADC) of water in the tumour tissue. ADC measurements prior to any therapy
correlated positively with necrotic fraction. Tumours with low initial ADC (<0.95×10 9 m 2 s −1) showed an increase in ADC 7 days after treatment, whereas tumours with a high initial ADC (>1.2×10 9 m 2 s −1) showed a decrease. All tumours decreased significantly in volume ( P<0.05) 2, 5 and 7 days after treatment. At day 7 post-treatment, tumours with a high pre-treatment ADC started to regrow.
The initial ADC value, as well as changes after treatment predict tumour chemosensitivity, which could be clinically relevant. 相似文献
5.
Synthesis and sintering properties of the (La 0.8Ca 0.2−x
Sr
x
)CrO 3 samples doped by two alkaline earth metals in comparison to the doped only by one alkaline earth metal were evaluated by
phase analysis, sintering properties, thermal expansion behaviors, and electrical conductivity. The sintered (La 0.8Ca 0.2−x
Sr
x
)CrO 3 ( x = 0, 0.05, and 0.1) and (La 0.8Ca 0.2−x
Sr
x
)CrO 3 ( x = 0.2) were found to have orthorhombic and rhombohedral symmetries, respectively. Relative density of the (La 0.8Sr 0.2)CrO 3 sample sintered at 1500 ∘C for 5 h was lower than that of the (La 0.8Ca 0.2−x
Sr
x
)CrO 3 ( x = 0, 0.05, and 0.1) sample. TECs of the (La 0.8Ca 0.2−x
Sr
x
)CrO 3 ( x = 0, 0.05, 0.1, and 0.2) in air were 11 × 10 −6/ ∘C, 11.2 × 10 −6/ ∘C, 11.2 × 10 −6/ ∘C, and 11.3 × 10 −6/ ∘C, respectively. The electric conductivity of the (La 0.8Ca 0.2−x
Sr
x
)CrO 3 sample was determined. 相似文献
6.
In the current study the effect of increasing concentrations of superparamagnetic iron oxide labeled cells on the MRI signal decay at magnetic field strengths of 0.2, 1.5, and 3 T was evaluated. The spin echo and gradient echo cellular transverse relaxivity was systematically studied for various concentrations ( N = 1, 5, 10, 20, 40, and 80 cells/μl gel) of homogeneously suspended SH U 555A labeled SK-Mel28 human melanoma cells. For all field strengths investigated a linear relationship between cellular transverse relaxation enhancement and cell concentration was found. In the spin echo case, the cellular relaxivities [i.e., d(Δ R
2)/d N] were determined to 0.12 s −1 (cell/μl) −1 at 0.2 T, 0.16 s −1 (cell/μl) −1 at 1.5 T, and 0.17 s −1 (cell/μl) at 3 T. In the gradient echo case, the calculated cellular relaxivities (i.e., d(Δ R
2
*
)/d N) were 0.51 s −1 (cell/μl) −1 at 0.2 T, 0.69 s −1 (cell/μl) −1 at 1.5 T, and 0.71 s −1 (cell/μl) −1 at 3 T. The proposed preparation technique has proven to be a simple and reliable approach to quantify effects of magnetically labeled cells in vitro. On the basis of this quantification well suited tissue specific models can be derived. 相似文献
7.
The pyroelectric properties and temperature stability of Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3(PMN– xPT) single crystals (0.13 ≤ × ≤ 0.40) were investigated. The best choice for pyroelectric performance is [111]-oriented PMN–0.26PT
single crystal whose figures of merit for voltage responsivity and detectivity are 0.11 m 2/C and 15 × 10 −5 Pa −1/2, respectively. However, the [001]-oriented PMN–0.37PT single crystal has much better temperature stability, whose temperature
coefficient of pyroelectric property is 0.5%/K in the range of 20 °C to 55 °C, and Curie temperature is high: 175 °C. We also
found that PMN– xPT possessed low thermal diffusivity D ~ 4.4 × 10 −7 m 2/s, low volume specific heat C
v
~ 2.5 × 10 6 J/m 3 K and tunable permittivity ε ~ (300–7000). The pyroelectric performances of PMN– xPT single crystals are superior to those of conventional pyroelectric materials and promising for IR device applications. 相似文献
8.
Sr 0.7La 0.3TiO 3−α specimens were prepared in reducing atmosphere, and the structural and electrical properties were studied. The lattice parameter
of Sr 0.7La 0.3TiO 3−α at room temperature was larger than that expected from Vegard’s law between SrTiO 3 and LaTiO 3 due to the reductive expansion. The conductivity of this specimen was 100 S cm −1 at 1000°C, pO2 = 10 −13 Pa. However, the conductivity was not preserved after an oxidation-reduction cycle. Over pO2 = 10 2 Pa, the conductivity drastically dropped with increasing pO2. The thermal expansion coefficient of Sr 0.7La 0.3TiO 3−α was 11.8 × 10 −6 K −1 in 9% H 2/N 2 (room temperature – 1000°C). In this Sr 0.7La 0.3TiO 3−α, the chemical expansion on oxidation reached Δl/l o = 0.51%, when changing pO2 from 10 −11 Pa to 2 × 10 4 Pa (air) at 1000°C. 相似文献
9.
For the in vivo relaxivity of Gd-DTPA at 6.3 T in rat muscle a value of 2.7±0.5 (mM s) −1 was found, and for the in vitro value in water 3.00±0.56 (mM s) −1 at 37°C. The temperature dependence of the in vitro relaxivity was −0.087 (mM s °C) −1. The relation between 1/T
1 and the tissue Gd-DTPA concentration is linear for the normally used in vivo Gd-DTPA concentration range 相似文献
10.
The oxygen permeation flux through YSZ (Yttria-Stabilized Zirconia) in reducing Po
2 is mostly controlled by the surface-exchange kinetics in spite of very high temperature [1]. In order to study the kinetics,
the YSZ surface was coated with LaCrO 3 on feed side, permeate side, or two sides, and the oxygen fluxes were measured under controlled Po
2 gradient generated by different CO/CO 2 mixtures (permeate side: ∼3 × 10 −12 atm, feed side: 2 × 10 −10∼2 × 10 −8 atm) at 1600 ∘C. The oxygen flux was determined by measuring the change in CO 2 content of the permeate-side gas. When both feed and permeate surfaces were coated, the oxygen flux increased by ∼6 times.
For either permeate- or feed-side coating, the increases were ∼4 times and ∼1.5 times, respectively. A model was proposed
in order to estimate the surface-exchange coefficient (
) of feed and permeate side with or without coating. 相似文献
11.
Diffusion tensor imaging (DTI) was used to investigate whether tissue anisotropy in the developing brain is modified by recurrent
seizures in epileptic chickens. Twelve epileptic chickens were sorted equally into two experimental groups at 10 days old.
Until the age of 180 days, one group was photically stimulated beginning at an age of 2 weeks and repeated every 2 days while
the other group was not stimulated. The photic stimulation induced generalized tonic–clonic seizures, and the unstimulated
group did not display seizures. Both treatment groups were imaged at three time points, 45 (juvenile), 90 (adolescent), and
180 (adult) days posthatching, and maps of major and minor elements of anisotropy (η and ε), trace and fractional anisotropy
(FA) were generated. The η, ε, and trace values in the hyperstriatum, archistriatum, and optic tectum showed significant changes
as a function of developmental time point. Differences and/or interactions due to seizures were seen in the archistriatum
and optic tectum for η, ε, and trace with the largest differences between the stimulated and unstimulated birds being seen
for η in juvenile birds in the archistriatum (38.1×10 −11 m 2/s versus 18.0×10 −11 m 2/s) and the optic tectum (53.9×10 −11 m 2/s versus 27.1×10 −11 m 2/s). With the DTI parameters being sensitive to microstructure in the brain, these results demonstrate that seizures produce
measurable differences, over unstimulated chickens, in brain structure for juvenile chickens, but the differences disappear
as the brain matures. In other words, while seizure activity appears to induce atypical biophysical change (relative to unseizing
birds) in the brain at a young age, the change is apparently reversed as the brain matures. 相似文献
12.
Recently, the feasibility of the praseodymium complex of 10-(2-methoxyethyl)-1,4,7,10-tetraaza-cyclododecane-1,4,7-triacetate
(Pr[MOE-DO3A]) for non-invasive temperature measurement via 1H spectroscopy has been demonstrated. Particularly the suitability of the complex for non-invasive temperature measurements
including in vivo spectroscopy without spatial resolution as well as first spectroscopic imaging measurements at low temporal
resolution (≥4 min) and high temporal resolution (breath hold, ∼20 s) has been shown. As of today, calibration curves according
to the particular experimental conditions are necessary. This work aims to clarify whether the Pr[MOE-DO3A] probe in conjunction
with 1H-NMR spectroscopy allows non-invasive absolute temperature measurements with high accuracy. The measurement results from
two different representative media, distilled water and human plasma, show a slight but significant dependence of the calibration
curves on the surrounding medium. Calibration curves in water and plasma were derived for the temperature dependence of the
chemical shift difference (F) between Pr[MOE-DO3A]'s OCH 3 and water with F=−(27.53±0.04)+(0.125±0.001) *
T and F=−(27.61±0.02)+(0.129±0.001) *
T. respectivel, with F in ppm and T in °C. However, the differences are minuscule even for the highest spectral resolution of 0.001 ppm/pt, so that they are
indistinguishable under practical conditions. The estimated temperature errors are ±0.18°C for water and ±0.14°C for plasma
and with that only slightly worse than the measurement accuracy of the fiber-optical temperature probe (±0.1°C). It can be
concluded that the results obtained indicate the feasibility of the 1H spectroscopy method in conjunction with the Pr[MOE-DO3A] probe for absolute temperature measurements, with a maximum accuracy
of ±0.2°C. 相似文献
13.
Object Early postnatal brain maturation is closely connected to local changes of metabolite levels. Spatially resolved in vivo 1H NMR spectroscopic imaging is applied to follow absolute changes of brain metabolites in early postnatal mouse brain.
Materials and methods A short echo time semi LASER (localization by adiabatic selective refocusing) chemical shift imaging (CSI) sequence incorporating
weighted k-space averaging was implemented at high magnetic field (17.6 T). In vivo measurements were carried out on postnatal days
5, 8, 12, 16, and 20. In vivo relaxation times T
1 and T
2 were measured using variable repetition times or a CPMG sequence, respectively, combined with LASER single voxel localization.
Results Spectra were obtained with a spatial resolution of (1 × 1) mm 2 in a 1.5 mm slice as early as postnatal day 5. Maturational changes of absolute metabolite concentrations of major metabolites
were calculated in four different brain regions. A significant increase of N-acetylaspartate (NAA), total creatine (tCr), and glutamate/glutamine (Glx) concentration was paralleled by a decrease of
taurine (Tau) concentration with age ( P < 0.05). Differences between brain regions were found for NAA, tCr, and Tau ( P < 0.05). Furthermore, in vivo T
1 and T
2 of the four major brain metabolites in adult mice are reported.
Conclusion The implemented semi LASER CSI sequence allows following regional changes of metabolite levels. It is suitable for investigation
of local differences in brain metabolism and development. 相似文献
14.
We report our numerical study on the device performance of an asymmetric poly-silicon gate FinFET and FinFET with TiN metal
gate structure. Our numerical simulation revealed that the asymmetric poly-silicon FinFET structure and TiN gate FinFET structures
exhibit superior V
T tolerance over the conventional FinFET structure with respect to the variation of fin thickness. For instance, the V
T tolerance of the asymmetric poly-Si FinFET were 0.02 V while TiN gate FinFET exhibited 0.015 V tolerance for the variation
of the fin thickness of 5 nm (from 30 to 35 nm) while the conventional FinFET demonstrates 0.12 V fluctuation for the same
variation of the fin thickness. Our numerical simulation further revealed that the threshold voltage ( V
T) can be controlled within the range of −0.1∼+0.5 V through varying the doping concentration of the asymmetric poly-silicon
gate region from 1.0×10 18 to 1.0×10 20 cm −3. 相似文献
15.
1,500 °C−sintered MgTa 2O 6 ceramic exhibits microwave dielectric characteristics of ɛ
r = 30.5, Q × f = 56,900 GHz, and τ
f = 28.3 ppm/°C, whereas 1,400 °C-sintered MgNb 2O 6 ceramic exhibits microwave dielectric characteristics of ɛ
r = 21.7, Q × f = 89,900 GHz, and τ
f = −68.5 ppm/°C. In order to find the dielectric resonators with τ
f value close to 0 ppm/°C, the effects of sintering condition and composition on the microwave dielectric characteristics of
Mg(Ta 1−x
Nb
x
) 2O 6 ceramics (0.25 ≦ x ≦ 0.35) prepared under sintering temperature of 1,300–1,450 °C are investigated. The results show that as the sintering temperature
increases from 1,300 to 1,450 °C, the ɛ
r, Q × f and τ
f values of Mg(Ta 1−x
Nb
x
) 2O 6 ceramics all increase and saturate at 1,450 °C. On the other hand, as the Nb 2O 5 content decreases, the τ
f values of Mg(Ta 1−x
Nb
x
) 2O 6 ceramics will shift to near 0 ppm/°C. The optimized sintering conditions and composition to obtain the Mg(Ta 1−x
Nb
x
) 2O 6 dielectrics with τ
f close to 0 ppm/°C are sintering temperature of 1,450 °C, sintering duration of 4 h, and composition of x = 0.25, which exhibits the microwave dielectric characteristics of ɛ
r = 27.9, Q × f = 33,100 GHz, and τ
f = −0.7 ppm/°C. 相似文献
16.
Single crystals of Bi and Cu-doped Ca 3Co 2O 6were synthesized in a molten K 2CO 3flux. Using an obtained single crystal of (Ca 0.985(5)Bi 0.015(5)) 3(Co 0.990(3)Cu 0.010(3)) 2O 6elongated to the c-axis direction of the crystal structure, the electric resistivity ( ρ) and Seebeck coefficient ( S) were measured from room temperature to over 1000 K in air. The single crystal showed p-type semiconducting behavior with ρ values of 1.8 Ω cm at 303 K and 0.017 Ω cm at 1000 K. The S values were +254 μ VK − 1 at 325 K, +360 μ VK − 1 at 420 K, and +214 μ VK − 1 at 1000 K. The power factor ( S
2
ρ
− 1) increased with an increase of temperature and attained 2.70 × 10 − 4 Wm − 1K − 2 at 1000 K. 相似文献
17.
In vivo diffusion-weighted magnetic resonance imaging (MRI) was used to determine the effects of an osmotic challenge (1% NaCl) to
a freshwater fish, the common carp ( Cyprinus carpio). The imaged region covered organs such as the swimbladder, the liver, the kidney, the intestine, the spinal cord, and muscle
tissue. A striking difference between salt-treated and control fish was found in the liver. The apparent diffusion coefficient
value of livers from control fish was (0.39±0.16) 10 −9 m 2/s and of salt-treated fish was (1.23±0.14) 10 −9 m 2/s, which points to an increase in extracellular water content. These results were partially confirmed by a decrease in dry/wet
weight ratio of the liver tissue. We also found increased levels of stress proteins in liver tissue. The Q factor of the applied radiofrequency coil dropped dramatically when we performed experiments with salt-exposed fish, indicating
an increased conductivity resulting from the increased ion concentration and osmolarity of the fish. The data on plasma osmolarity
of salt-exposed fish confirm a significant osmolarity increase upon salt exposure (from 334 to 430 mOsm/kg) and exceeded the
osmolarity of the salt water (324 mOsm/kg), indicating that carp tend to cope with an increased salinity by increasing the
internal osmolarity (hyperosmotic regulation). These data demonstrate that diffusion-weighted MRI might be a useful and noninvasive
tool in the study of osmotic challenges of aquatic organisms. 相似文献
18.
We have investigated electrical and structural properties of Pt/Pd/Au ohmic contact on p-type GaN:Mg (2.5 × 10 17 cm −3) using Auger electron spectroscopy (AES) and glancing angle x-ray diffraction (GXRD) analysis. It was shown that the specific
contact resistivity improved with increasing annealing temperature. The annealing of the contact at 600 ∘C for 2 min in flowing N 2 atmosphere resulted in a specific contact resistivity of 3.1 × 10 −5 Ω cm 2. Both GXRD and AES depth profile results show that Ga 3Pt 5, Ga 2Pd 5, and Au 7Ga 2 phases are formed at the interface region between metal and GaN when annealed at temperatures 600 ∘C. Possible explanation is suggested to describe the annealing dependence of the specific contact resistivity of the Pt/Pd/Au
contacts. 相似文献
19.
Perovskite-types 0.05Pb(Mn 1/3Sb 2/3)O 2-0.95Pb- (Zr 0.5Ti 0.5)O 3 (PMS-PZT) was synthesized by conventional bulk ceramic processing technique. ZnO as a dopant up to 0.5 mol% was incorporated
into the PMS-PZT system, and the effects on piezoelectric properties were investigated. Pyrochlore phase was not detected
to form during the synthesis of the PMS-PZT system with 0–0.5 mol% ZnO addition. The highest density of 7.92 g/cm 3 was obtained when sintered at 1200 ∘C for 2 h. Piezoelectric properties as a function of ZnO content were evaluated using a gain phase analyzer. Piezoelectric
charge constant ( d
31) and piezoelectric voltage output coefficient ( g
31) increased up to −130 pC/N and −24.9 × 10 3Vm/N, respectively, with increasing ZnO content. Mechanical quality factor ( Q
m) was shown to reduce considerably with increasing ZnO content. When 0.3 mol% of ZnO was added into the system, electromechanical
coupling factor ( k
p) and relative dielectric constant (ε 33
T
/ε o) reached to the maximum of 56% and 1727, respectively. 相似文献
20.
Praseodymium-Cerium Oxide (Pr xCe 1-xO 2−δ; PCO), a potential three way catalyst oxygen storage material and solid oxide fuel cell (SOFC) cathode, exhibits surprisingly
high levels of oxygen nonstoichiometry, even under oxidizing (e.g. air) conditions, resulting in mixed ionic electronic conductivity
(MIEC). In this study we examine the redox kinetics of dense PCO thin films using impedance spectroscopy, for x = 0.01, 0.10
and 0.20, over the temperature range of 550 to 670°C, and the oxygen partial pressure range of 10 −4 to 1 atm O 2. The electrode impedance was observed to be independent of electrode thickness and inversely proportional to electrode area,
pointing to surface exchange rather than bulk diffusion limited kinetics. The large electrode capacitance (10 −2F) was found to be consistent with an expected large electrochemically induced change in stoichiometry for x = 0.1 and x = 0.2
PCO. The PCO films showed surprisingly rapid oxygen exchange kinetics, comparable to other high performance SOFC cathode materials,
from which values for the surface exchange coefficient, k
q
, were calculated. This study confirms the suitability of PCO as a model MIEC cathode material compatible with both zirconia
and ceria based solid oxide electrolytes. 相似文献
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