摘要:

AbstractThis study describes a new single spin‐echo spatial localization sequence, BASSALE or BAnd‐Selective Spin echo Acquisition for Localized Editing, that overcomes a number of the limitations of the STEAM and PRESS volume selection pulse sequences. It achievesconformalvolume localization in a single shot by spatially tailored suppression of all magnetization outside a 2D region of interest followed by selection of a single orthogonal slice. This separation of spatial localization from the echo formation process has permitted use of a spectrally selective cosine‐modulated sinc refocusing pulse to acquire localized1H spectra with the water suppression efficiency of STEAM and the sensitivity of PRESS. Echoes formed by such spectrally selective pulses have been termedbandselectivespin echoes. The BASSALE sequence attains shorter echo times than PRESS, inhibits scalar spin‐spin interactions to permit localized editing andT2relaxometry of metabolites with J‐coupled spins (e.g., lactate), is insensitive to homonuclear multiple‐quantum and polarization transfer effects, and can be made sensitive or insensitive to spin displacement effects. Applications are shown both with phantoms andin situin th

ISSN:0740-3194    

DOI:10.1002/mrm.1910320302

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

年代:1994

数据来源: WILEY

摘要:

AbstractMagnetization transfer imaging (MT) and localized proton spectroscopy (1H‐MRS) were utilized in the evaluation of lesioins (high signal abnormalities onT2‐weighted images) and normal‐appearing white matter (NAWM) in multiple sclerosis (MI). Eleven patients with a clinical diagnosis of MS were independently evaluated with both1H‐MRS and MT. The magnetization transfer ratio (MTR) of lesions was compared with the relative concentration of Kacetyl‐aspartate (NAA) and a composite peak at 2.1 to 2.6 ppm termed “marker peaks”. The MTR of white matter lesions in the MS patients was markedly decreased (6–34%; normal ≈︁42%), and correlated well with increase in the marker peaks region (0.94–3.89). There was no correlation between the relative concentration of NAA and MTR. Increased resonance peaks in the 2.1 to 2.6 ppm range and marked decreases in MTR may be a relatively specific indica

ISSN:0740-3194    

DOI:10.1002/mrm.1910320303

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

年代:1994

数据来源: WILEY

摘要:

AbstractMacromolecule resonances underlying metabolites in1H NMR spectra were investigated in temporal lobe biopsy tissue from epilepsy patients and from localized1H spectra of the brains of healthy volunteers. The1H NMR spectrum of brain tissue was cornpared with that of cytosol and dialyzed cytosol after removal of low molecular weight molecules (4500 daltons) at 8.4 and 2.1 Tesla. The assignment of specific resonances to macromolecules in 2.1 Tesla, short‐TE, localized human brain1H NMR spectrain vivowas made on the basis of a J‐editing method using the spectral parameters (δ,J) and connectivities determined from 2D experimentsin vitro. Two prominent corinectivities associated with macromoleculesin vitro(0.93–2.05 δ and 1.6–3.00 δ) were also detectedin vivoby theJ‐editing method. Advantage was taken of the large difference in measuredT1relaxation times between macromolecule and metabolite resonances in the brain spectrum to acquire ‘metabolite‐nulled’ macromolecule spectra. These spectra appear identical to the spectra of macromolecule

ISSN:0740-3194    

DOI:10.1002/mrm.1910320304

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

年代:1994

数据来源: WILEY

摘要:

AbstractLow pH appears to enhance the effectiveness of therapeutic hyperthermia.13C and31P NMR spectroscopy have been employed to examine the possibility that elevating glucose in a solid tumor while simultaneously reducing tumor blood flow would induce a more profound acidosis than either treatment alone. When blood flow in RIF‐1 tumors was acutely reduced by administration of hydralazine and additional glucose was delivered locally by intratumoral injection, tumor acidosis (as determined by31P NMR spectroscopy) during the period of reduced blood flow was not enhanced, relative to administration of hydralarine alone. Tumor NTP/P1ratios decreased significantly within 20 min of hydralazine administration, whether or not glucose was injected, although NTP/P1ratios were slightly higher in tumors that received extra glucose. Tumor lactate concentrations were not significantly different in glucose‐supplemented tumors, despite glucose concentratlons that were 4 to 5 times higher. When the added glucose was labeled with13C, no correlation was detected between the pH in an individual tumor and the intensity of the 3‐[13C]‐lactate resonance in the sam

ISSN:0740-3194    

DOI:10.1002/mrm.1910320305

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn ivivomagnetic resonance spectroscopy (MRS) has revealed that phsophomonoesters (PME) such as phosphocholine (PCho) and phosphoethanolamine (PEth) are elevated in tumalrs and rapidly proliferating tissues. The regulation of PME levels and their relationship to proliferation are not well known. In the present study, we investigated the regulation of PCho and PEth levels in rat glioma cells grownin vivoandin vitrousing31P and13C MRS. However, the ability of cells to produce choline endogenously is variable. To fully understand regulation of PCho levels, it is necessary to characterize the activity of the endogenous pathway, if it exists. This was first investigated by following the metabolic fate of13C‐labeled methionine of 9L glioma tumorsin vivo.Our results indicate that there is a significant amount ofde novocholine synthesisin ivivo.However, similar experiments performedin virrousing cells cultured in bioreactors indicated that glioma cells themselves are unable to synthesize cholinede novo, suggesting that thein vivoresults were due to the involvement of extra‐tunnoral organs, e.g., liver. Furtherin vitroexperiments demonstrated that the uptake and phosphorylation of physiologically relevant concentrations of exogenous choline is very active in these systems. Thus, it appears that the exogenous pathway for PCho biosynthesis predominates and regulates PCho levels in glioma cells. Our results also demonstrate that PCho levels are lowest, and PEth levels are highest, in non‐proliferating cells. These observations indicate that there is a decrease in the biosynthesis of PCho concomitant with a redulction in culture growth. The source of the increased PEth is, as yet, unde

ISSN:0740-3194    

DOI:10.1002/mrm.1910320306

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

年代:1994

数据来源: WILEY

摘要:

AbstractInversion recovery gradient recalled echo planar imaging (TI/TR/TE= 700/2000/10 ms) was used to dynamically monitor the first pass of an intravascular (GdDOTA‐polylysine) and an extravascular (GdDTPA‐BMA) contrast agent through normal rat myocardium. It was found that myocardial enhancement increased with dose of the intravascutar agent to a limiting value of ∼50% of fully relaxed intensity, consistent with enhancement of 40% of myocardial water content during the first pass. Larger doses produced no further increase in peak response. On the other hand, the extravascular agent caused incrementally increased enhancement throughout the dose range examined to a final value of 68 ± 2% of fully relaxed intensity. The profile of dose dependence for both agents was inconsistent with monoexponentialT1relaxation. It was concluded that (a) compartmentalization of myocardial water combined with restricted myocardial water diffusion limits the peak response during bolus transit; (b) extraction of the extravascular agent during transit elevates the peak response over that obtained from agent confined to the vascular volume; and (c) models that assume simple monoexponential r, relaxation to derive timedensity curves do not adequately describe the relationship between changes in signal intensity,R1and contrast concent

ISSN:0740-3194    

DOI:10.1002/mrm.1910320307

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe present a reconstruction method for phased array multicoil data that is compatible with phase contrast MR angiography. The proposed algorithm can produce either complex difference or phase difference angiograms. Directional flow and quantitative information are preserved with the phase difference reconstruction. The proposed method is computationally efficient and avoids intercoil cancellation errors near the velocity aliasing boundary. Feasibility of the method is demonstrated on human scans.

ISSN:0740-3194    

DOI:10.1002/mrm.1910320308

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn this paper a new method is presented for the relative assessment of brain iron concentrations based on the evaluation of T2and T2* ‐weighted images. A multiecho sequence is employed for rapid measurement of T2and T2*, enabling calculation of the line broadening effect ( T2′). Several groups have failed to show a correlation between T2and brain iron content. However, quantification of T2′, and the associated relaxation rate R2′, may provide a more specific relative measure of brain iron concentration. This may find application in the study of brain diseases, which cause associated changes in brain iron levels. A new method of field inhomogeneity correction is presented that allows the separation of global and local field inhomogeneities, leading to more accurate T2* measurements and hence, T2′ values. The combination of T2*, and T2‐weighted MRI methods enables the differentiation of Parlkinson's disease patients from normal age‐matched controls based on differences in iron content within the sub

ISSN:0740-3194    

DOI:10.1002/mrm.1910320309

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe combined a vector decomposition technique with Gaussian probability thresholding in feature space to segment normal brain tissues, tumors, or other abnormalities on dual‐echo MR images. The vector decomposition technique assigns to each voxel a fractional volume for each of two tissues. A probability threshold, based on an assumed Gaussian probability density function describing random noise, isolates a region in feature space for fractional volume calculation that minimizes contamination from other tissues. The calculated fractional volumes are unbiased estimates of the true fractional volumes. The contrast‐to‐noise ratio (CNR) between tissues on the segmented images is the same as the Euclidean norm of CNRs in the original images. The method is capable of segmenting more than two tissues from a set ot dual‐echo images by sequentially analyzing different pairs of tissues. The model is analyzed mathematically and in experiments with a phantom. Two clinical examples are pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910320310

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

年代:1994

数据来源: WILEY

摘要:

AbstractModels have been developed for the signal changes occurring in human peripheral muscle after thermal stress for some methods of measuring temperaturein vivo. These include the dependency ofT1, on temperature, observed by both direct, and magnetization transfer, experiments, and the temperature sensitivity of the diffusion coefficient and the chemical shift of the water proton line. Results show the relative complexity of theT1‐dependent models when there are significant variations in, possibly amongst other things, tissue perfusion, and how the predictions made using them match the behavior of the practical values quite well. Using changes in the diffusion coefficient appears less problematic, although there can still be significant errors in temperature calibrations. The problems with this approach are likely to be due to the consequences of anisotropy in tissu

ISSN:0740-3194    

DOI:10.1002/mrm.1910320311

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

年代:1994

数据来源: WILEY