摘要:

AbstractMyocardial lipid and lactate levels are sensitive indicators of biochemical status: lipid levels have been shown to increase in response to high fat diets, disease or metabolic stress and elevated lactate levels are indicative of reduced oxygen supply. Selective measurement of lactate or lipid levels by1H NMR is not straightforward since both the lactate methyl group and lipid methylene groups resonate at 1.3 ppm. We have overcome this difficulty by employing spectral editing techniques to observe both lipid methylene and lactate methyl resonances, and have measured lipid and lactate levels in perfused rat hearts during control perfusion and in response to metabolic stress. Lactate increased during ischemia and decreased during reperfusion, and the ischemia‐induced increase is inhibited by iodoacetate, as expected. In contrast, lipid levels increased during ischemia and remained elevated during reperfusion. Hearts from rats fed high fat diet show elevated lipid levels during control perfusion. Data obtained by1H NMR are consistent with biochemical data, validating the techniqu

ISSN:0740-3194    

DOI:10.1002/mrm.1910300602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractSampling of theentirebrain tissue in1H NMR metabolic studies is complicated by the presence of intense pericranial lipid and tissue water resonances, which can obscure metabolite resonances. This study extends the concept of localization by outer volume suppression (OVS) to achievefullyconformalin viuolocalization, sampling at least 95% of rat brain with complete elimination of pericranial lipids. This has permitted acquisition of lipid‐free short echo time (7.5 ms), high spatial resolution 2D spectroscopic images exhibiting high sensitivity and information content in relatively short measurement time (68 min). Incorporation ofspatially tailoredOVS into existing methods (e.g., DRESS, STEAM, PRESS) extends their localization efficiency and performance. Two single spin‐echo localization sequences have been described that attain much shorter echo times or achieve better water suppression than PRESS. One of these sequences allows editing and relaxo‐metric studies of J‐coupled spins. The methods described are suitable forin vivolocalization of most tissues and can be applied with any biologically important

ISSN:0740-3194    

DOI:10.1002/mrm.1910300603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe LCModel method analyzes anin vivospectrum as a Linear Combination ofModelspectra of metabolite solutionsin vitro.By using complete model spectra, rather than just individual resonances, maximum information and uniqueness are incorporated into the analysis. A constrained regularization method accounts for differences in phase, baseline, and lineshapes between thein vitroandin vivospectra, and estimates the metabolite concentrations and their uncertainties. LCModel is fully automatic in that the only input is the time‐domainin vivodata. The lack of subjective interaction should help the exchange and comparison of results. More than 3000 human brain STEAM spectra from patients and healthy volunteers have been analyzed with LCModel.N‐acetylaspartate, cholines, creatines,myo‐inositol, and glutamate can be reliably determined, and abnormal levels of these or elevated levels of lactate, alanine,scyllo‐inositol, glutamine, or glucose clearly indicate numerous pathologies. A computer program will be av

ISSN:0740-3194    

DOI:10.1002/mrm.1910300604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThis study reports the use of19F MRS to study halothane in the brain of eight patients recovering from halothane anesthesia of short duration. Resonances attributable to halothane were observed up to 90 min after withdrawal of the anesthetic agent. The signal‐to‐noise ratio for an unlocalized spectrum acquired using a 6 cm surface coil was typically 20 with data collection times of 2 min. In seven patients a single resonance was seen with a mean (±SD) chemical shift of +43.3 (±1.8) ppm, referenced to NaF at 0 ppm. This resonance exhibited aT1value of between 0.5 and 1 s, and aT2* (estimated from the linewidth of the resonance) between 3.5 and 10 ms. In one patient two resonances were observed with chemical shifts of +38 and +41 ppm. Because we cannot exclude the possibility that this was due to field inhomogeneity, the significance of the last finding is uncertain. However, phantom studies show that the chemical shift of halothane in different environments (such as water, olive oil, methanol, and lecithin) can vary to an extent that accounts for the two resonances seen in our patient. These results demonstrate the feasibility ofin vivo19F MRS studies of fluorinated volatile agents in humans. The potential for clinical19F MRS of fluorinated anesthetics is disc

ISSN:0740-3194    

DOI:10.1002/mrm.1910300605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractHomogeneous soft tissue, as regards its magnetic relaxation properties, is well‐modeled by solutions of cross‐linked protein (see Koenig and Brown,Prog. NMR Specfr.22,487 (1991)). Interactions at the solute‐solvent interface alter the hydrodynamics of solvent water, and also couple the solute and solvent proton Zeeman energy reservoirs, giving hydrodynamic and cross‐relaxation contributions to water proton relaxation that respond differently to deuteration of solvent. We report measurements of the magnetic field dependence of 1/T1, of water protons in cross‐linked bovine serum albumin (BSA), for partially deuterated solvent and, in order to separate these two contributions, of 1/T1, of deuterons. The major experimental finding is that, in addition to recently identified water‐binding sites on protein (covering ∼0.2% of the surface) with water lifetimes of about 1 μs, there is another group of sites with lifetimes of about 23 ns, covering ∼2% of the surface, which are evident in both proton and deuteron data. In addition, we have formulated a theory of interfacial proton‐proton magnetic interactions which—with these four parameters, plus two that quantify the protein‐water coupling at each site—can account for all the proton and deuteron data, in both nat

ISSN:0740-3194    

DOI:10.1002/mrm.1910300606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Gd3+complexes of three new phosphorus containing tetraaza macrocycles (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrakis (methylene ethylphosphonic acid), H4DOTEP; 1,4,7,10‐tetraazacyclododecane‐l,4,7,10‐tetrakis (methylene phosphonic acid monoethylester), H4DOTPME; and the corresponding n‐butyl ester, H4DOTPMB) were prepared and examined for possible use as MRI contrast agents. Although thermodynamically and kinetically less stable than Gd(DOTA)−in saline and HSA solution, the stability of these new macrocyclic complexes appears to be sufficiently high forin vivoapplications. NMRD relaxivity profiles of the three complexes indicate that the number of inner sphere water molecules for these chelates is ≤1 and that the more hydrophobic chelate, Gd(DOT‐PMB), binds to human serum albumin (HSA). Biodistribution studies of the radioactive153Sm or159Gd chelates in rats, gamma imaging of the153Sm chelates in rats, and proton MRI studies of the nonradioactive Gd3+chelates in rabbits all indicate that the DOTPMB complexes accumulate preferentially in the liver, spleen, and small intestines while the more hydrophilic DOTEP and DOTPME complexes appear to display renal clearances similar to other low molecular wei

ISSN:0740-3194    

DOI:10.1002/mrm.1910300607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe describe a cardiac‐gated MR angiographic imaging method that employs velocity‐selective preparation (VSP) pulses in conjunction with segmented gradient‐echo acquisitioin and subtraction to produce images that, ideally, contain no signal from stationary tissues and display vessels with a signal intensity that is dependent on the velocity of the blood in the vessels. The novel features of this method are a) it acquires several phase‐encoding valueslapplication of a single VSP pulse, b) it uses subtraction to eliminate signal that is not sufficiently suppressed by the VSP pulses, and c) it uses VSP pulses that are synchronized with the cardiac cycle so it can be used to produce ghost‐free images of pulsatile blood. An advantage of this sequence is that it detects a signal that, after preparation, is relatively unaffected by changes in blood velocity. This leads to a large signal‐to‐noise ratio for all the phase‐encoding values, a reduction of ghosting artifacts, and the ability to visualize blood that is in motion for only a short time during the cardiac cycle. Because the signal is prepared during peak flow, venous signal can be suppressed by making the sequence sensitive to high velocities. An additional advantage of this sequence is that it permits sampling with a shortTEbecause the velocity‐encoding gradient can be applied in a preparatory interval. Signal loss that results from dephasing during the longerTEpreparation interval can be reduced or eliminated by allowing the dephased spins to flow out of the region of complex flow, and perhaps out of the field‐of‐view, by introducing a delay between the finish of the VSP pulse and the beginnin

ISSN:0740-3194    

DOI:10.1002/mrm.1910300608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAn echo planar linewidth mapping technique,Shufflebutt, has allowed temporal measurements of changes in linewidth caused by static inhomogeneities (ΔLWSI) and transverse relaxation rate (ΔR2) in models of hypoxia and hypercapnia. We demonstrate these changes are due to intravascular susceptibility differences(ΔX) between the blood and tissue. Contrast agent injections at a /ΔXequivalent to that of deoxygenatetd blood showed a twofold difference between the contrast agent and physiological anoxia values. Hypercapnia decreased both ΔLWSIand ΔR2consistent with an increase in blood oxygenation. We attribute these findings to constant oxygen extraction during an increase in blood flow, resulting in less deoxygenated venous blood and thus reduced ΔX. Forin vivoperturbations we found that ΔR/ΔR2′ ≈ 0.33, a ratio much different from that measured in whole blood phantoms (ΔR/ΔR2′ ≈ 2). This demonstrates that signal changes in these studies are produced predominantly by dephasing of extravascular protons due to field inhomogeneities produced by intravascular deoxygenated he

ISSN:0740-3194    

DOI:10.1002/mrm.1910300609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractFlow‐ and motion‐related artifacts are problematic in clinical MR imaging. In this paper we discuss the utility of a phase‐corrected real reconstruction to reduce flow artifacts. This techinique is particularly useful when flow‐compensation pulse sequences may not be possible, such as when a very short echo delay or small field‐of‐view is desired. We will demonstrate that the phase‐corrected real reconstruction provides superior results to the magnitude reconstruction either used alone or in conjunction with existing flow‐compensa

ISSN:0740-3194    

DOI:10.1002/mrm.1910300610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractSpectrometers make use of D/A converters to generate RF and gradient shapes. This paper examines by exact simulations the time and amplitude digitization effects, inherent to the use of D/A converters, on the performance of amplitude modulated (AM) frequency selective RF pulses. By making use of Fourier theory and the small tip angle approximation, an approximate model of these effects on the magnetization slice profiles is derived and verified for several pulse types by computer simulations. This approximate model will be used to derive requirements for D/A converters with respect to spatial localization. The dynamics of the spin system allows pulse width modulation (PWM) as an alternative to AM for pulse envelope encoding. The effects of PWM on the slice profile are examined and compared with conventional AM pulses. It is shown by simulation and measurement that adiabatic PWM pulses can be found. In contrast to AM modulated adiabatic pulses, adiabatic PWM pulses have side bands with the same slice quality as the main slice and might therefore be useful as multislice selective pulses.

ISSN:0740-3194    

DOI:10.1002/mrm.1910300611

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY