ISSN:0740-3194    

DOI:10.1002/mrm.1910340102

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

年代:1995

数据来源: WILEY

摘要:

AbstractUnderstanding the relationship between fMRI signal changes and activated cortex is paramount to successful mapping of neuronal activity. To this end, the relative extravascular and intravascular contribution to fMRI signal change from capillaries (localized), venules (less localized) and macrovessels (remote, draining veins) must be determined. In this work, the authors assessed both the extravascular and intravascular contribution to blood oxygenation level‐dependent gradient echo signal change at 1.5 T by using a Monte Carlo model for susceptibility‐based contrast in conjunction with a physiological model for neuronal activation‐induced changes in oxygenation and vascular volume fraction. The authors compared our Model results with experimental fMRI signal changes with and without velocity sensitization via bipolar gradients to null the intravascular signal. The model and experimental results are in agreement and suggest that the intravascular spins account for the majority of fMRI signal change onT2*‐weighted images a

ISSN:0740-3194    

DOI:10.1002/mrm.1910340103

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

年代:1995

数据来源: WILEY

摘要:

AbstractTo reduce respiratory blur and ghosts in 3D coronary imaging, a data acquisition scheme using consistent multiple breath‐holds was implemented. A navigator echo was acquired and processed in real time to dynamically measure diaphragm position. This information was provided as a visual prompt to the patient to maintain consistency in breath‐hold levels such that the variation range of diastolic heart position was less than 2 mm. Preliminary results indicate that this multiple breath‐hold acquisition scheme, compared with acquisition under respiration, can significantly reduce blur and ghost artifacts in 3D coronary im

ISSN:0740-3194    

DOI:10.1002/mrm.1910340104

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn vivo1H MR spectra of the prefrontal cortex acquired with the stimulated echo acquisition mode (STEAM)TE= 20 ms sequence were quantified to determine relative levels of cerebral metabolites.A prioriknowledge of spectra from individual metabolites in aqueous solution was incorporated into a frequency domain quantification technique. The accuracy and precision of modeling these metabolites were investigated with simulated spectra of varying signal‐to‐noise ratios (SNRs) and relative metabolite levels. The efficacy of modelingin vivodata was tested by quantifying 10 repeated measures of two consecutively acquiredin vivospectra (an 8−cm3volume of interest (VOI) and a 4−cm3VOI positioned within the 8−cm3VOI) on the same normal subject. The differences in levels of glutamate (Glu), phosphocreatine plus creatine (PCr+Cr) and choline‐containing compounds (Cho1between spectra from the 8− and 4−cm3VOIs corresponded with the expected differences observed in the proportions of gray matter within the VOIs (estimated from1H images). Correcting for theT1andT2relaxation, the estimated concentrations ofN‐acetylaspartate, PCr+Cr, Cho1, Glu, and glutamine were consistent with previousin vivoa

ISSN:0740-3194    

DOI:10.1002/mrm.1910340105

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

年代:1995

数据来源: WILEY

摘要:

AbstractSince transmembrane sodium gradient is essential to many cell functions, there is continuing interest in methods that differentiate intracellular and extracellular Na+. In the kidney, shift reagent (SR) aided23Na magnetic resonance spectros‐copy (MRS) has been successfully used only in isolated cells, tubules, and the perfused organ. In this report, we demonstrate for the first time that TmDOTP5−can be used to distinguish Na+compartments in kidneysin vivo.Infusion of 80 mMTmDOTP5−withoutadded Ca2+produced three resolved23Na resonances, which we have assigned to intracellular Na+, vascular Na+, and intraluminal Na+. In comparison, infusion of 400 mMDyTTHA3−produced two broad and unresolved resonances. The31P spectra of the cellular high energy phosphate metabolites indicate that TmDOTP5−is safe forin vivoapplications. Washout studies suggest that this SR displays renal clearance similar to that of MR imaging contrast agents. However, the glomerular filtration rate (GFR) in animals infused with TmDOTP5−was reduced by 49% compared with the GFR in control animals, perhaps due to the hypotensive effects of the SR. We conclude that TmDOTP5−is effectively cleared from the blood of live animals but that a different formulation will be required for clinica

ISSN:0740-3194    

DOI:10.1002/mrm.1910340106

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

年代:1995

数据来源: WILEY

摘要:

AbstractElevated brain lactate has been observed byin vivoproton MRS in different pathological situations. The origin of this lactate remains controversial. The possibility that it was produced by the metabolism of phagocytic cells has been proposed. To investigate this hypothesis, the authors have employed high‐resolution proton MRS to monitor changes in glucose, lactate, and other metabolites in the medium used to culture human monocyte‐derived macrophagesin vitro.Results show that the differentiation of human monocytes/macrophages in the presence of physiological stimulating factors (M‐CSF or GM‐CSF) was associated with an increase in lactate production and glucose utilization. The present results are consistent with the hypothesis that lactate detected by proton MRSin vivomay be produced by the metabolism of macrophages when infiltrates of these cells are present. The possible extrapolation of the authors' finding to thein vivosituation and its relevance are di

ISSN:0740-3194    

DOI:10.1002/mrm.1910340107

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

年代:1995

数据来源: WILEY

摘要:

AbstractA technique is demonstrated for the acquisition and processing of multislice, first‐pass contrast‐enhanced pelfusion images in the myocardium. The acquisition is a modification of “keyhole” imaging in which time series images are acquired by sampling a limited segment ofk‐space, corresponding to the low spatial frequencies. In the modification demonstrated here, keyhole samples are divided into two groups that are sampled on alternate cardiac cycles. The alternate “missing”k‐space portions are synthesized by Fourier interpolation. Visualization of contrast agent accumulation by image subtraction is demonstrated. A motion artifact reduction process using time domain Fourier filtering is used to reduce artifacts from respiration. Studies were performed on 46 patients at 1.5 T using gadoteridol (0.05–0.1 mmol/kg) injected into the right antecubital vein in conjunction with radionuclide imaging. Fully concordant studies were noted in 27 of these patients. Remaining studies were either partially or completely discordant for reasons relating to the differing natures of radionuclide versus MR contrast agen

ISSN:0740-3194    

DOI:10.1002/mrm.1910340108

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

年代:1995

数据来源: WILEY

摘要:

AbstractA 3D projection reconstruction (3DPR) method was used to obtainin vivo11B images in a large canine brain tumor model and in a human infused with borocaptate sodium (BSH). Studies were performed in dogs with and without gliosarcomas implanted and grown to a size of 2–3 cm. The 3DPR method demonstrates a signal‐to‐noise ratio (SNR) that allows qualitative kinetic studies of the boron compound in normal and tumor tissue of the head. The measurements indicate initial uptake of the BSH compound in tumor to be less than that in muscle with no uptake in normal brain tissue. Moreover, uptake of BSH in tissue was found to lag the boron concentration in blood with delays that depend on tissue type. In addition, the first human boron images were obtained on a patient who underwent surgical resection and volumetric debulking of a large (7 cm) glioblastoma multiforme. BSH was readily taken up in residual tumor tissue, while diffusion into the resection volume was s

ISSN:0740-3194    

DOI:10.1002/mrm.1910340109

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

年代:1995

数据来源: WILEY

摘要:

AbstractA method that can be used to evaluate the performance of MRI methods for detecting discrete regional activations using functional MRI is presented. Computer derived receiver‐operator‐characteristic (ROC) curves have been used to evaluate quantitatively a range of conditions encountered in functional MRI studies. ROC analysis allows multiple acquisition strategies and multiple postprocessing strategies to be quantitatively and objectively compared. The authors first present this analysis technique and then illustrate its use for assessing the relative performances of different functional MRI data acquisition strategies using different gradient echo, echo‐planar imaging protocols. In addition, the authors have used the ROC analysis to evaluate and compare several methods for analyzing functional MRI data to extract regions of activation. This approach to assessing the performance of different methods is of general use and can be applied to evaluate other data acquisition protocols and postprocessing me

ISSN:0740-3194    

DOI:10.1002/mrm.1910340110

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

年代:1995

数据来源: WILEY

摘要:

AbstractA method is described for the correction of geometric distortions occurring in echo planar images. The geometric distortions are caused in large part by static magnetic field inho‐mogeneities, leading to pixel shifts, particularly in the phase encode direction. By characterizing the field inhomogeneities from a field map, the image can be unwarped so that accurate alignment to conventionally collected images can be made. The algorithm to perform the unwarping is described, and results from echo planar images collected at 1.5 and 4 Tesla are show

ISSN:0740-3194    

DOI:10.1002/mrm.1910340111

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

年代:1995

数据来源: WILEY