Blood velocity is a functional parameter that is not easily assessed noninvasively, especially in small animals. A new noninvasive method that uses magnetic resonance angiography (MRA) to measure blood flows is proposed. This method is based on the time-of-flight (TOF) phenomenon. By initially suppressing the signal from the stationary spins in the area of interest, it is possible to sequentially visualize only the signal from the moving spins entering a given volume. With this method, 3D cine images of the blood flow can be generated by positive contrast, with unparalleled spatial (<200 microm) and temporal resolutions (<10 ms/image). As a result, it is possible to measure flow in sinuous paths. The present method was applied in vivo to measure the blood velocity in mouse carotid arteries. Because of its robustness and simplicity of implementation, this method has numerous potential applications for fundamental studies in small animal models. 相似文献
Summary
The introduction of fast gradient systems allows a reliable visualization of the extracranial carotid vessels by the magnetic
resonance angiography (MRA) which meanwhile is implemented into clinical routine. By the mainly applied time-of-flight (TOF)
technique, vessels can be imaged without contrast agent (CA). Due to the application of ultra-fast gradient-echo-sequences,
the first-pass evaluation of an intravenous bolus-injection of Gadolinium in the carotids from the aortic arch up to the skull
base can be performed in less than 30 s. In this study, advantages and disadvantages of both techniques are discussed. For
a qualitatively optimal contrast enhanced MRA (CE-MRA) timing parameters like injection delay, flow rate and the adjustment
of sequence parameters have to be considered in relation to the fast venous return from the sinus to the jugular veins. First,
the optimal time point of the data acquisition have been determined at a model and with a computer simulation in reference
to the presence of CA in the arteries. As a result, 90 % of the contrast contribution is defined by 16 % of the symmetrically
acquired central k-space lines. A measuring protocol for clinical use was obtained by a gradual variation of spacial resolution,
measuring time and CA-injection parameters and was proved in normal volunteers and patients. An exact determination of the
bolus-arrival-time by means of a test-bolus injection was acquired. The best qualitative results were achieved by a double-dose
injection at 2 ml/s injection rate. The temporal reserves of ultra-fast sequences should be invested in the improvement of
the spatial resolution. To date, further investigations related to the problem of optimal CA-application may improve the potentials
of CE-MRA procedures.
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Summary: The chromatographic analysis of hydrophilic copolymers is complicated due to the fact that in most cases aqueous eluents must be used. In aqueous eluents different polar and ionic effects may disturb the selective interactions between the macromolecules and the stationary phase making it impossible to separate such copolymers with regard to chemical composition. Therefore, 2D chromatography combining a separation according to composition with a separation according to molar mass has been applied mostly to polymers that are soluble in organic solvents. The present contribution describes experimental approaches to analyze such hydrophilic copolymers by 2D‐chromatography. For a model polymer system resulting from the copolymerization of methacrylic acid and a poly(ethylene glycol) macromonomer, it is shown that different analytical techniques including SEC, LC‐CC, MALDI‐TOF MS and 2D chromatography can be used to analyze the different parameters of molecular heterogeneity of such copolymers.
2D separation of poly(MPEG‐MM 2), 1st dimension: LC‐CC, 2nd dimension: SEC. 相似文献
Two out of 47 patients with sporadic tetralogy of Fallot (TOF), the most common cyanotic conotruncal heart defect (CTD), showed heterozygous missense mutations of the ZFPM2/FOG2 gene. Knockout mice carrying mutations in the ZFPM2/FOG2 gene have similarly been found to exhibit TOF. While both mutant ZFPM2/FOG2 proteins, E30G (c.88A>G) and S657G (c.1968A>G), retain the ability to bind the partner protein GATA4 and repress GATA4 mediated gene activation, the S657G, but not the E30G, mutation is subtly impaired in this function. ZFPM2/FOG2 gene mutations may contribute to some sporadic cases of TOF. 相似文献
Summary: Sarcosine‐N‐carboxyanhydride (Sar‐NCA), L ‐alanine‐NCA and D,L ‐alanine‐NCA were polymerized with benzylamine as initiator in three different solvents: dichloromethane (CH2Cl2), 1,4‐dioxane and dimethylformamide (DMF). The isolated polyaminoacids were characterized by 1H NMR spectroscopy and MALDI‐TOF mass spectrometry. High conversions and degrees of polymerization s close to the monomer‐initiator (M/I) ratios were found for all polypeptides. For polysarcosine which was soluble under the given reaction conditions a narrow monomodal frequency distribution was found. In contrast, a broad frequency distribution was observed, when L ‐alanine NCA was polymerized in dioxane and DMF. These results were attributed to a partial precipitation of oligopeptides in the β‐sheet structure, which reduces the reactivity of endgroups for steric reasons. The polymerizations of D,L ‐alanine‐NCA showed features in between the extremes of Sar‐NCA and L ‐Ala‐NCA.
Schematic illustration of the secondary structures formed in a primary amine initiated polymerization of L ‐Ala‐NCA. 相似文献
ObjectivesMatrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) is becoming the method of choice for bacterial identification. However, correct identification by MALDI-TOF of closely related microorganisms such as viridans streptococci is still cumbersome, especially in the identification of S. pneumoniae. By making use of additional spectra peaks for S. pneumoniae and other viridans group streptococci (VGS). We re-identified viridans streptococci that had been identified and characterized by molecular and phenotypic techniques by MALDI-TOF.MethodsVGS isolates (n = 579), 496 S. pneumoniae and 83 non-S. pneumoniae were analysed using MALDI-TOF MS and the sensitivity and specificity of MALDI-TOF MS was assessed. Hereafter, mass spectra analysis was performed. Presumptive identification of proteins represented by discriminatory peaks was performed by molecular weight matching and the corresponding nucleotides sequences against different protein databases.ResultsUsing the Bruker reference library, 495 of 496 S. pneumoniae isolates were identified as S. pneumoniae and one isolate was identified as non-S. pneumoniae. Of the 83 non-S. pneumoniae isolates, 37 were correctly identified as non-S. pneumoniae, and 46 isolates as S. pneumoniae. The sensitivity of the MALDI-TOF MS was 99.8% (95% confidence interval (CI) 98.9–100) and the specificity was 44.6% (95% CI 33.7–55.9). Eight spectra peaks were mostly present in one category (S. pneumoniae or other VGS) and absent in the other category and inversely. Two spectra peaks of these (m/z 3420 and 3436) were selected by logistic regression to generate three identification profiles. These profiles could differentiate between S. pneumoniae and other VGS with high sensitivity and specificity (99.4% and 98.8%, respectively).ConclusionsSpectral peaks analysis based identification is a powerful tool to differentiate S. pneumoniae from other VGS species with high specificity and sensitivity and is a useful method for pneumococcal identification in carriage studies. More research is needed to further confirm our findings. Extrapolation of these results to clinical strains need to be deeply investigated. 相似文献
Poly(methyl methacrylate)s (PMMA)s and poly(methyl acrylate)s (PMA)s are prepared by atom transfer radical polymerization (ATRP) or single electron transfer‐living radical polymerization (SET‐LRP) using methyl dichloroacetate (MDCA) and ethyl dibromoacetate (EDBA) as bifunctional initiators. The chain‐end functionality is determined by MALDI‐TOF mass spectrometry. The target PMMA (Mn = 2000 g mol?1) and PMA (Mn = 2000 g mol?1) samples obtained by ATRP of MMA and MA with MDCA as initiator have 12 and 81 mol% bis‐chloro end groups, respectively; those prepared by SET‐LRP have 57 and 100 mol% bis‐chloro end groups, respectively. The PMMAs obtained by ATRP or SET‐LRP with EDBA have no bromine end groups.