摘要:

AbstractThe aim of this work was to investigate whether 1) Rb uptake is reduced in ischemic myocardium, and 2)87Rb three‐dimensional (3D) imaging can detect the ischemic area. Hearts of domestic pigs (n= 8, 20–30 kg) were perfused retrogradely with Krebs‐Henseleit buffer in a 7‐T, 40‐cm horizontal bore magnet interfaced with Bruker MSLX spectrometer. Control (C) and ischemic (I) (45 min ligation of the left anterior descending coronary artery (LAD)) hearts were loaded with Rb+by perfusion with a Rb+‐containing solution (2–4.7 mM, 30–100% of K+substitution) for 35 min and87Rb (C) or31P (ischemic area in I) spectra were acquired. After mechanical arrest with 0.6–0.9 mMlidocaine,87Rb images (7 min each, 1 cm3resolution) were acquired (30–40 min) in the presence of Rb+‐containing perfusate. Subsequently, the hearts were stained with Evans blue (EB) and samples taken for measurements of Rb+content. In the Group C, distribution of Rb+in the left ventricle and the intensities of the 3D87Rb images were uniform. In the ischemic area (Group I), verified by the lack of EB staining and changes in31P spectra, the images showed a reduced intensity, which corresponded to decreased Rb+content (33 ± 11% of the normal). Thus,87Rb imaging reveals damaged cells detecting reduced Rb+conten

ISSN:0740-3194    

DOI:10.1002/mrm.1910400202

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

年代:1998

数据来源: WILEY

摘要:

AbstractNMR spectroscopy has been applied extensively to study metabolism noninvasively in the human brain and other tissues. However, it usually suffers from poor signal‐to‐noise ratio due to low NMR sensitivity and low metabolite concentrations. In this study, the technique of proton‐observe‐carbon‐edited (POCE) NMR spectroscopy combined with a single‐shot localization sequence was used to detect the natural abundance carbon signal of the amino acid N‐acetyl aspartate from a 12‐cm3localized volume in the occipital lobe of humans at 4 T. The results suggest that NMR spectroscopy is sensitive enough to detect signals from low concentration metabolites (<60 nmol/g) from small volumes in the human brain within several minutes of data acquisition. This reveals thatin vivoNMR spectroscopy is a promising technique for detecting small metabolite changes and low traces of13C isotopic labeling for dynamic metabolism studies aimed at investigating physiological and patholo

ISSN:0740-3194    

DOI:10.1002/mrm.1910400203

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

年代:1998

数据来源: WILEY

摘要:

AbstractFast proton magnetic resonance spectroscopic imaging (MRSI) using a multi‐element head‐coil array is examined with respect to three aspects: the coil design, the use of an appropriate signal combination method, and the design of the MRSl pulse sequence itself. An eight‐element head‐coil array has been developed to increase the signal‐to‐noise ratio (SNR) of MRSl in the human brain. The flexible wraparound design optimally fits different head sizes and thus provides high sensitivity. The signal combination of the individual coil elements is based on the approach proposed by Roemeret al. Magn. Reson. Med. 16, 192 (1990). An additional short prescan is performed to provide a good estimate of the complex coil sensitivity profiles, which are used in the signal combination procedure to correct the spectroscopic imaging data for the spatially varying intensity. The use of coil arrays in MRSI has some effect on the requirements for both water and lipid suppression. These techniques and a MRSl pulse sequence that provides a high spectroscopic resolution are described and discussed. Experimental results at 1.5 T show that metabolite maps of N‐acetylaspartate (NAA), choline (Cho), phosphocreatine (PCr)/creatine (Cr) can be obtained within a 5‐min a

ISSN:0740-3194    

DOI:10.1002/mrm.1910400204

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

年代:1998

数据来源: WILEY

摘要:

AbstractIn a recent contribution [MRM 38:269–274 (1997)], it was reported that an excitation by a series of sinc‐shaped slice‐selective RF pulses with binomial amplitude ratios and complete spin refocusing between consecutive pulses leads to water‐ or fat‐selective images of high quality. A method for simultaneous water and fat imaging in multislice operation is presented based on the principle of alternated line scanning and linear superposition of several excitations. For example, a 1‐3‐3‐1 pulse train with suitable interpulse delays results in a water‐selective excitation, whereas a 1 ‐3‐ 3 ‐1train leads to a selective excitation of fat (transmitter frequency corresponds with the Larmor frequency of water protons). Phase cycling of the excitation (1 ‐3‐ 3 ‐1for the even line numbers ink‐space, but1‐ 3 ‐3‐1 for the odd line numbers) causes a shift ofn/2 lines in phase‐encode direction for the fat signals in ann×mmatrix. The principle of linear superposition explains why an excitation of 2 ‐ 0 ‐ 6 ‐ 0 for the even lines and 0 ‐ 6 ‐ 0 ‐ 2 for the odd lines results in a final image with unshifted water signals and shifted fat signals. Both water and fat portions are simultaneously exhibited and separated without any signal loss. Examples recorded by a gradient‐echo sequence demonstrate the potential of the new technique that allows a reduction of up to 50% of measuring time co

ISSN:0740-3194    

DOI:10.1002/mrm.1910400205

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

年代:1998

数据来源: WILEY

摘要:

AbstractDetailed measurement of the neural response to flicker frequency using functional MRI (fMRI) were made. The fMRl signal peaks at a flicker frequency of 8 Hz in human V1, in agreement with previous positron emission tomography (PET) and fMRl experiments. The modulation amplitude of the hemodynamic response to varying continuous periods of flicker stimulation was measured. The hemodynamic response was not observed to be modulated by neural modulation for periods shorter than 6.7 s. The resemblance between the BOLD response to the stimulus presentation frequency and the base‐line power spectra at the same frequencies suggests that the same underlying mechanism could be responsible for both curves and that the base‐line fMRl power spectrum is probably due to base‐line electrical activity in the brain. The integrals of the resting base‐line power spectrum, the background power spectrum, the respiration component, and the cardiac component were found to be linearly dependen

ISSN:0740-3194    

DOI:10.1002/mrm.1910400206

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

年代:1998

数据来源: WILEY

摘要:

AbstractA customized computer program (MRIView) is described for visualizing and quantifying complex blood flow patterns in major vessels, using nongated and cardiac‐gated three‐dimensional (3D) velocity data obtained with MR velocity‐encoded phase pulse sequences. Streamlines, arrows, and particle paths (collectively referred to as “paths”) can be computed interactively, using both forward and backward time integration of the velocity field. The program provides interactive cross‐sectional and 3D perspective visualization of the paths, with quantification and statistical analysis of average speed, through‐plane velocity, cross‐sectional area, and flow. Normal flow patterns in the carotid artery, basilar artery tip, ascending aorta, coronary arteries, descending aorta, and renal arteries, as well as abnormal flow patterns in basilar tip aneurysms, have been investigated. The program revealed flow patterns in these regions with features that are well known from Doppler ultrasound and other features that have not been reported previously. The association between specific abnormal flow patterns and development of atherosclerosis suggests that particle paths can be used to assess risk of plaque formation and progression, as well as to evaluate flow dynamics and vascular patency before and after vascula

ISSN:0740-3194    

DOI:10.1002/mrm.1910400207

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

年代:1998

数据来源: WILEY

摘要:

AbstractBy combining nuclear magnetic relaxometry on 39 ferritin samples with different iron loading with magnetometry, results were obtained that suggest a new interpretation of the core structure and magnetic properties of ferritin. These studies provide evidence that, contrary to most earlier reports, the ferritin core is antiferromagnetic (AFM)even at body temperatureand possesses a superparamagnetic (SPM) moment due to incomplete cancellation of antiparallel sublattices, as predicted by Néel's theory. This moment also provides a likely explanation for the anomalousT2shortening in ferritin solution. However, the number of SPM moments derived from this model is less than the number of ferritin molecules determined chemically, and a similar discrepancy was found by retrospectively fitting previously published magnetometry data. In other words, only a fraction of the ferritin molecules seem to be SPM. The studies also provide evidence for paramagnetic (PM) Curie‐Weiss iron ions at the core surface, where the local Néel temperature is lower; these ions are apparently responsible for the weakerT1shortening. In fact, the conversion of uncompensatedAFMlattice ions toPM ions could explain the small number ofSPMparticles. The apparent Curie Law behavior of ferritin thus appears to be a coincidental result of different temperature dependences of thePMandSPMcompone

ISSN:0740-3194    

DOI:10.1002/mrm.1910400208

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

年代:1998

数据来源: WILEY

摘要:

AbstractHuman transferrin was covalently coupled to ultrasmall superparamagnetic iron oxide (USPIO) particles, and the trans‐ferrin‐USPIO obtained was investigatedin vivoin experimental SMT/2A tumor‐bearing rats (rat mammary carcinoma). Physicochemical characterization showed an overall size of 36 nm (DLS) with a core size of 5 nm (TEM). Relaxivities wereR,1= 23.6 andR2= 52.1 liter/mmol · s (0.47 T). Bound transferrin was 280 μg/mgof iron. Pharmacokinetic investigations revealed a half‐life of 17 min in normal rats. The MR evaluation of tumor signal intensity over time showed a 40% (range 25–55%) signal reduction 150 min after injection with the reduction persisting for at least 8 h. Control experiments using the parent USPIO compound or USPIO labeled with a nonspecific human serum albumin (HSA‐USPIO) showed a change of only 10% (range 5–15%) in tumor signal intensity over time. The results demonstrate that a combination of the USPIO relaxivity properties with the specificity of transferrin‐medi‐ated endocytosis allowsin vivodetection of t

ISSN:0740-3194    

DOI:10.1002/mrm.1910400209

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

年代:1998

数据来源: WILEY

摘要:

AbstractA new functional imaging method has been developed and used to measureT2*‐ and initial intensity (I0)‐parameter maps of multiple slices during activation of the cortex with high temporal resolution. Multiple echo‐planar images (EPls) are read out after a single excitation of the spin system, leading to several images with increasing effective echo times. Changes induced by primary visual stimulation inT2* and I0were measured in eight subjects. Although stimulation‐induced increases in I0only occurred at short repetition times,T2* increased from 57.3 to 60.9 ms on average. The method combines the high stability of a single shot EPI experiment with the high information content of a multiecho acquisition. In addition, stimulation‐induced changes in inflow can be easily separated from true blood oxygenation level dependent (BOLD) signa

ISSN:0740-3194    

DOI:10.1002/mrm.1910400210

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

年代:1998

数据来源: WILEY

摘要:

AbstractFuzzy logic clustering algorithms are a new class of processing strategies for functional MRI (fMRI). In this study, the ability of such methods to detect brain activation on application of a stimulus task is demonstrated. An optimization of the selected algorithm with regard to dtfferent parameters is proposed. These parameters include (a) those defining the preprocessing procedure of the data set; (b) the definition of the distance between two time courses, considered asp‐dimensional vectors, wherepis the number of sequential images in the fMRl data set; and (c) the number of clusters to be considered. Based on the assumption that such a clustering algorithm should cluster the pixel time courses according to their similarity and not their proximity (in terms of distance), cross‐correlation‐based distances are defined. A clear mathematical description of the algorithm is proposed, and its convergence is proven when similarity measures are used instead of conventional Euclidean distance. The differences between the membership function given by the algorithm and the probability are clearly exposed. The algorithm was tested on artificial data sets, as well as on data sets from six volunteers undergoing stimulation of the primary visual cortex. The fMRl maps provided by the fuzzy logic algorithm are compared to those achieved by the well established cross‐correlation te

ISSN:0740-3194    

DOI:10.1002/mrm.1910400211

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

年代:1998

数据来源: WILEY