摘要:

AbstractAn RF network and a dual‐tuned surface coil are described for obtaining proton‐decoupled, NOE enhanced19F spectra from a whole body clinical imager operating at 1.5 Tesla. The network removes19F frequency noise from the decoupler transmitter and prevents preamplifier saturation from high‐level decoupling signals. Proton decoupling of19F spectra was optimized using a sample of urine containing 5‐fluorouracil (5‐FU) and its catabolite fluoro‐β‐alanine (FBAL). Protondecoupled19F spectroscopyin vivois demonstrated by obtaining both nonlocalized spectra and spectra localized with three‐dimensional chemical shift imaging from the liver of patients undergoing 5

ISSN:0740-3194    

DOI:10.1002/mrm.1910370302

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

年代:1997

数据来源: WILEY

摘要:

AbstractA recently developed adiabatic coherent polarization transfer enhancement technique [H. Merkle, H. Wei, M. Garwood, K. Uǧurbil.J. Magn. Reson.99, 480–494 (1992)] was employed to perform13C spectroscopy in the intact canine heartin vivoduring [2‐13C]‐acetate infusion into the left descending coronary artery; the results were compared with13C spectra obtained with conventionally employed nuclear Overhauser enhancement. The results demonstrate that both methods can be performed by using surface coils to obtainin vivo13C spectra and that coherent polarization transfer provides better enhancement than NOE for [2‐13C]‐acetate but not for shortT

ISSN:0740-3194    

DOI:10.1002/mrm.1910370303

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

年代:1997

数据来源: WILEY

摘要:

AbstractShort image acquisition times and sensitivity to magnetic susceptibility favor the use of gradient echo imaging methods in functional MRI (fMRI). However, magnetic susceptibility effects attributed to air‐tissue interfaces also lead to severe signal loss in images of the large inferior frontal and lateral temporal cortices of the human brain, which renders these regions inaccessible tofMRI. The signal loss is caused by the local field gradients in the slice selection direction. A multigradient echo with magnetic susceptibility inhomogeneity compensation method (MGESIC) is proposed to overcome this problem. The MGESIC method effectively corrects the susceptibility artifacts and maintains the advantages of gradient echo methods to both BOLD sensitivity and fast image acquisition. The effectiveness of the MGESIC method is demonstrated byfMRI experimental results within the olfactory corte

ISSN:0740-3194    

DOI:10.1002/mrm.1910370304

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

年代:1997

数据来源: WILEY

摘要:

AbstractIt is shown that a repetitive pulse sequence consisting of two 90° pulses and gradients in a 1:2 ratio around the second 90° pulse generates interscan shifted stimulated echoes (SSTEs) and intrascan multiple spin echoes (MSEs). Separation of these two types of signals is accomplished using specific gradient crusher schemes. The intensity of the SSTEs is an order of magnitude larger than that of the MSEs and determines the signal contrast if both effects are selected simultaneously. The SSTE sequence generates improved contrast between gray and white matter, even at high field, which is explained in terms of increased inverseT1‐weighting for the interscan echo. The MSE image has low signal to noise and no detectable contrast. The effect of interscan diffusion weighting is also discus

ISSN:0740-3194    

DOI:10.1002/mrm.1910370305

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

年代:1997

数据来源: WILEY

摘要:

AbstractA method for MR angiography after bolus injection of a normal dose (0.1 mmol/kg) of contrast agent is presented. Projection angiograms are acquired with a non‐slice selective Snapshot FLASH sequence with a time resolution of 1 s per image or better. Typically 40 to 60 images are acquired consecutively after bolus injection of a contrast agent. The signal from vessels can be separated from background by postprocessing based on the observed temporal evolution of the signal intensities during bolus passage. The subsecond projection MR‐DSA is a reliable and robust technique to produce high resolution anatomical images of the vascular system avoiding the necessity of exact timing of the contrast agent bolus. It also supplies functional information about the hemodynamics in the observed region including perfus

ISSN:0740-3194    

DOI:10.1002/mrm.1910370306

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

年代:1997

数据来源: WILEY

摘要:

Abstract31P,1H and lactate spectroscopic imaging was used to evaluate the effects of hypothermia on focal cerebral ischemia produced by middle cerebral artery occlusion. The effects on high energy phosphate metabolism, pH, lactate and NAA were investigated in 24 spontaneously hypertensive rats subjected to either permanent or transient ischemia. Under either normothermic (37.5°C) or hypothermic (32°C) conditions, with permanent 6‐h occlusion, there was little difference between groups in either the NMR measurements or the volume of infarction. In animals that underwent 3 h of ischemia followed by 12 h of reperfusion, the ischemic changes in lactate, pH, NAA, and high‐energy phosphate returned toward control values, and there was a protective effect of hypothermia (infarct volume of 211 ± 26 and 40 ± 14 mm3in normothermic and hypothermic groups, respectively). Thus, hypothermia did not ameliorate the changes in lactate, pH, NAA, or high energy phosphate levels occurring during ischemia, however, during reperfusion there was an improvement in both the recovery of these metabolites and pathological outcome in hypothermic compared with normothermic

ISSN:0740-3194    

DOI:10.1002/mrm.1910370307

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe method of single quantum13C editing is analyzed and implemented with water suppressedJ‐refocused coherence transfer spectroscopy. Analysis of the13C inversion pulse demonstrates that it is optimally placed into the second echo of theJ‐refocused sequence. We have used this method to acquire13C‐edited spectra of glutamate from phantoms andin vivo.The turnover of13C4‐labeled glutamate in human brainin vivowas observed in parasagittal gray matter using a volume head coil at 4.1 T with a time resolution of

ISSN:0740-3194    

DOI:10.1002/mrm.1910370308

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

年代:1997

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910370309

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe role of water of hydration in proton relaxation in tissues as exemplified by hydrated collagen in beef tendon was studied as a function of temperature from −40° to 37°C by using cross‐relaxation spectroscopy. Experimental data were fitted to a simple binary spin‐bath model. The outcome of this procedure allows the construction of a semi‐quantitative depiction of proton relaxation in a heterogeneous system and its change as one of the water fractions freezes at about −10 to −20°C, a transition observed by NMR and confirmed independently by differential scanning calorimetry. Such physical depiction provides a crude but insightful interpretation of the role “bound” water plays in proton relaxation. This may be important in shedding light on the mechanism of tissue relaxation and its role in MRI diagnosis, particularly for those diseases such as liver cirrhosis where the water‐macromolecular interaction pl

ISSN:0740-3194    

DOI:10.1002/mrm.1910370310

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

年代:1997

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910370311

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

年代:1997

数据来源: WILEY