摘要:

AbstractUsing a new method of xenon laser‐polarization that permits the generation of liter quantities of hyperpolarized129Xe gas, the first129Xe imaging results from the human chest and the first129Xe spectroscopy results from the human chest and head have been obtained. With polarization levels of approximately 2%, cross‐sectional images of the lung gas‐spaces with a voxel volume of 0.9 cm3(signal‐to‐noise ratio (SNR), 28) were acquired and three dissolved‐phase resonances in spectra from the chest were detected. In spectra from the head, one prominent dissolved‐phase resonance, presumably from brain parenchyma, was detected. With anticipated improvements in the129Xe polarization system, pulse sequences, RF coils, and breathing maneuvers, these results suggest the possibility for129Xe gas‐phase imaging of the lungs with a resolution approaching that of current conventional thoracic proton imaging. Moreover, the results suggest the feasibility of dissolved‐phase imaging of both the chest and brain with a resolution similar to that obtained with the

ISSN:0740-3194    

DOI:10.1002/mrm.1910370602

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

年代:1997

数据来源: WILEY

摘要:

AbstractA method for volume selective proton spectroscopy is presented based on a multiecho sequence with short refocusing interval tcp. It is demonstrated, that by appropriate choice of tcp on the order of 4–6 ms, signals from overlapping multiplets like the glutamine and glutamate (Glu/Gln) resonances in spectra of the human brain are considerably increased compared with a conventional PRESS volume selection scheme. Thus proton spectra fromJ‐coupled multiplet signals can be acquired withTEon the order of 20–30 ms avoiding the baseline problems arising at shorter echo times due to broad resonances. This allows to selectively acquire spectra from substances with longerT2without the confounding effects fromJ‐coupling occurring in conventional volume selection tec

ISSN:0740-3194    

DOI:10.1002/mrm.1910370603

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe accuracy of the measurement of total muscle glucose byin vivo13C NMR spectroscopy was tested in five normal volunteers during a euglycemic [1‐13C]glucose infusion. The NMR visible concentration calibrated using an external reference was compared with that calculated from plasma glucose concentration, assuming that glucose remained extracellular. The NMR measurement always provided higher values than the calculation from plasma glucose: 0.51 ± 0.035 (mean ± SE) versus 0.38 ± 0.005 mmol/liter of muscle on average. This systematic difference was interpreted as reflecting the presence of muscle glucose‐6‐phospnate, co‐resonating with free glucose. Thus, glucose appeared to be virtually 100% NMR visible in human skele

ISSN:0740-3194    

DOI:10.1002/mrm.1910370604

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

年代:1997

数据来源: WILEY

摘要:

AbstractDiffusion NMR spectroscopy was used to study intracellular volume and apparent water diffusion constants in different cell lines (DU145, human prostate cancer; AT3, rat prostate cancer; MCF‐7, human breast cancer; RIF‐1, mouse fibrosacroma). The cells were grown on various matrices (collagen sponge, collagen beads, polystyrene beads) which enabled continuous growth in perfused high density cell culture suitable for NMR studies. In perfused cell systems, the attenuation of the water signal versus the squared gradient strength was fitted by the sum of two decaying exponentials. For the slowly decaying component the apparent water diffusion constant at 37°C was 0.22 (±0.02) × 10−9s/m2for all cell lines at diffusion times>100 ms. It continuously increased up to 0.47(±0.05) × 10−9s/m2when the diffusion time was decreased to 8 ms, indicating restricted diffusion. No significant effect of the matrices was observed. The fractional volume of the slow component as determined from the biexponential diffusion curve correlated with the relative intracellular volume, as obtained from the cell density in the sample and the cell size as measured by light microsocopy. Therefore, this simple NMR approach can be used to determine intracellular volume in perfused cell cultures suitable for NMR studies. Using this information in combination with spectroscopic data, changes in intracellular metabolite concentration can be detected even when the cellular volume is changing during the experiment. The apparent diffusion constant for the fast diffusing component varied with growth matrix, cell density and cell type and also showed the typical characteristics of restricted diffusion (increase of apparent diffusion constan

ISSN:0740-3194    

DOI:10.1002/mrm.1910370605

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

年代:1997

数据来源: WILEY

摘要:

AbstractTo record brain temperature for comparison with rectal and temporalis muscle temperatures in preliminary studies before MR spectroscopy experiments, a thermistor was inserted into the basal ganglia in eight anesthetized, ventilated, and physiologically monitored rats. The rats were placed in an MR spectrometer and subjected to 60 min of global cerebral ischemia and 2 h of reperfusion without radiofrequency (RF) pulsing. Body temperature was maintained at 37.5–38.0°C (normothermia) or 36.5–37.0°C (mild hypothermia). Brain temperature during ischemia, which dropped to 31.9 ± 0.3 (hypothermia) and 33.6 ± 0.5±C (normothermia), correlated with temporalis muscle temperature (r2= 0.92) but not with body or magnet bore temperature measurements. Ischemia reduced brain temperature approximately 1.7°C in rats subjected to mild hypothermia (1° reduction of body temperature). Parallel MR spectroscopy experiments showed no significant difference in energy metabolites between normothermic and hypothermic rats during ischemia. However, the metabolic recovery was more extensive 20–60 min after the onset of reperfusion in hypothermia rats, although not thereafter (P<0.05). Mild hypothermia speeds metabolic recovery temporarily during reperfusion but does not retard energy failure during global isch

ISSN:0740-3194    

DOI:10.1002/mrm.1910370606

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

年代:1997

数据来源: WILEY

摘要:

AbstractQuantitative lactate imaging and spectroscopy were performed on phantoms and on electrically stimulated, excised frog skeletal muscle at macroscopic and microscopic resolutions. Lactate selectivity was achieved by use of a zero‐quantum/double‐quantum coherence (ZQC/DQC) lactate filter, which suppressed all signals besides lactate, including water and lipid, to below noise level. Three‐dimensional lactate data sets were acquired in 1–3 h; one of these spatial dimensions was frequency‐encoded and the other two were phase‐encoded. High‐resolution images were reconstructed using the spectral localization by imaging (SLIM) and generalized SLIM (GSLIM) techniques. Lactate quantitation was achieved by employing an external lactate concentration standard and was verified by comparison to quantitative STEAM‐localized and nonlocalized spectra that used total creatine as an internal concentration reference. Additionally, quantitatively accurate behavior of the SLIM and GSLIM techniques as applied to data sets of low signal‐to‐noise ratio and to macroscopically heterogeneous objects was verified using simulations and real muscle lactate data sets with

ISSN:0740-3194    

DOI:10.1002/mrm.1910370607

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

年代:1997

数据来源: WILEY

摘要:

AbstractN‐acetylaspartate (NAA) is found exclusively in neurons and their processes in the adult brain. Since the regional distribution of NAA may be imaged using magnetic resonance spectroscopic imaging (1H‐MRSI), a regional measure of neuronal density may be noninvasively obtained. The technique may be particularly useful in the diagnosis of diseases where neurons are selectively injured, since these diseases do not result in definitive changes on conventional imaging studies. The goal of this study was to determine whether1H‐MRSI measurement of NAA detects neuronal loss following global ischemia.1H‐MRSI was performed in rats 24 h after global ischemia was induced by bilateral carotid occlusion plus hypotension.1H‐MRSI showed that NAA was decreased by 29–74% in vulnerable regions, including the cortex, striatum, hippocampus, and, to a lesser extent, the thalamus. No change was observed in the brain stem or cerebellum. Regions where1H‐MRSI observed NAA was decreased also had histological evidence of selective neuronal necrosis and showed marked increase of lactate and alanine. These results show that1H‐MRSI detected loss of NAA in brain regions with selective neuronal loss, suggesting that1H‐MRSI measurements of NAA could detect neuronal loss in a variety of disease states where there is selective

ISSN:0740-3194    

DOI:10.1002/mrm.1910370608

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

年代:1997

数据来源: WILEY

摘要:

AbstractA new rapid spectroscopic imaging technique with improved sensitivity and lipid suppression, referred to as Proton Echo Planar Spectroscopic Imaging (PEPSI), has been developed to measure the 2‐dimensional distribution of brain lactate increases during hyperventilation on a conventional clincal scanner equipped with a head surface coil phased array. PEPSI images (nominal voxel size: 1.125 cm3) in five healthy subjects from an axial section approximately 20 mm inferior to the intercommissural line were obtained during an 8.5‐min baseline period of normocapnia and during the final 8.5 min of a 10‐min period of capnometry‐controlled hyperventilation (end‐tidal PCO2of 20 mmHg). The lactate/N‐acetyl aspartate signal increased significantly from baseline during hyperventilation for the insular cortex, temporal cortex, and occipital regions of both the right and left hemispheres, but not in the basal ganglia. Regional or hemispheric right‐to‐left differences were not found. The study extends previous work using single‐voxel MR spectroscopy to dynamically study hyperventilation effects on

ISSN:0740-3194    

DOI:10.1002/mrm.1910370609

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

年代:1997

数据来源: WILEY

摘要:

AbstractTo summarize and compare magnetization transfer data from biological tissues, a method was developed to extract the average absorption lineshape of the semi‐solid pool directly from magnetization transfer experimental data along with the four other parameters that characterize the two‐pool model of exchange. Magnetization transfer data for several biological tissues were analyzed using this method and the resulting “flexible” lineshapes were compared with super‐Lorentzian and “Kubo‐Tomita” lineshapes. The use of flexible lineshapes noticeably improves the fit of the two‐pool model to the data. The derived flexible lineshapes of all the tissues analyzed are physically realistic and show remarkably co

ISSN:0740-3194    

DOI:10.1002/mrm.1910370610

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

年代:1997

数据来源: WILEY

摘要:

AbstractA magnetic resonance imaging method for measuring theT2relaxation time constant is proposed. It is based on the assumption that, under very general conditions, the MR signal near a spin echo has a special symmetry arising from the refocusing nature of the 180° RF pulse. A gradient echo sampling of the spin echo (GESSE) sequence is implemented to evaluateT2by collecting multiple gradient echoes before and after the spin echo. This approach is a modification of the GESFIDE sequence proposed by Ma and Wehrli. However, our approach compares images that are not separated by any RF pulses and, as a result, is insensitive to slice profile imperfections. In addition, the calculatedT2value does not rely on any special assumptions about the MRI signal behavior in the presence of an inhomogeneous static magnetic field and, hence, is insensitive to the presence of static magnetic field inhomogeneities

ISSN:0740-3194    

DOI:10.1002/mrm.1910370611

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

年代:1997

数据来源: WILEY