摘要:

AbstractInin vivophosphorus magnetic resonance spectroscopy (MRS), spectroscopic imaging (SI) can be used as a flexible localization technique, producing spectra from multiple volumes in a single examination. Presented here are phosphorus SI studies of human organs in which a selective‐volume SI reconstruction was used rather than the usual array‐format SI reconstruction. A linear predictor technique was used to estimate the initial points of the free induction decay missing because of the delay needed for phase‐encoding gradients, significantly reducing the baseline artifacts which commonly complicate interpretation of SI spectra. In studies of heart, brain, liver, and kidney, the performance of SI was found to compare favorably with that of ISIS. SI phosphorus metabolite intensity images from a brain tumor patient were obtained at 2 X 2‐cm in‐plane resolution (with “slice” thickness of roughly 16 cm, determined by coil sensitivity) in 34 min, demonstrating the feasibility of obtaining clinically useful metabolite images in clinically reasonable examination times. © 1989 Acade

ISSN:0740-3194    

DOI:10.1002/mrm.1910120302

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

年代:1989

数据来源: WILEY

摘要:

AbstractMany methods of chemical shift imaging have been described recently. In most cases, these methods couple resolution and imaging time. The most flexible methods use time‐varying gradients to cover a large region ofkspace on each excitation. We present here a new time‐varying gradient method that offers a decrease in scan time (when SNR is sufficient), simplifies the reconstruction problem by retaining an essentially rectilinear sampling grid, and makes efficient use of scan time by minimizing gradient reversals. Implementation on a standard high‐field imaging system (GE Signa) is discussed, and experimental results are shown. An application of the method to the generation of water reference data sets is described. © 1989 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910120303

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

年代:1989

数据来源: WILEY

摘要:

AbstractA technique for the very rapid measurement of blood flow with high spatial resolution is described. The method combines the previously validated technique of phase velocity mapping and echo‐planar principles. The relatively small diameter of blood vessels enables a high‐resolution echo‐planar flow measurement to be made with as few as 16 echoes such that the method can be incorporated into a near standard NMR scanner. Two sequence variations are tested and validatedin vitroand one is used to demonstratein vivoblood flow measurement. The results are shown to compare well with a previously validated less rapid method. The technique should enhance the potential of NMR flow imaging by enabling sudden changes in flow to be studied. It should also simplify the measurement of blood flow in small mobile vessels such as the coronary arteries. © 1989 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910120304

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

年代:1989

数据来源: WILEY

摘要:

AbstractAlterations in cytosolic metabolites and [Mg2+], were monitored using31P magnetic resonance spectroscopy during inotropic stimulation of isolated rat heart [10 nMisoproterenol, 0.6 μMisobutyl‐1‐methylxanthine (IBMX), 5 μMouabain]. All drugs significantly elevated contractile function (rate‐pressure product) andMVO2by approximately 100‐150% (P0.001), decreased cytosolic [creatine phosphate] ([CrP]) and [ATP] (approximately 65 and 80% of control values, respectively) (P0.001), increased [Pi] to more than 180% of pretreatment values, and decreased [ H+] by less than 15% (P0.05). A significant relative shift in the α‐P and β‐P resonances of ATP (P0.01) occurred with inotropic stimulation. [Mg2+], calculated on the basis of these shifts was found to be 0.78 ± 0.1 mMin control hearts, and increased to maxima of 1.9 ± 0.2,2.0 ±0.2, and 2.9 ± 0.2 mMduring infusion of isoproterenol, IBMX, and ouabain, respectively. Changes in [Mg2+], correlate with cytosolic [ATP]+ [CrP] in all hearts (r= 0.89, 0.91, and 0.88 in isoproterenol‐, IBMX‐, and ouabain‐treated hearts, respectively). The significantly higher [Mg2+], with ouabain infusion (P0.01) at similar workloads and [ATP] + [CrP]supports the proposal that a ouabain‐inhibited Mg2+pump exists in the plasma membrane. The data support acute changes in [ Mg2+]iduring alterations in inotropic state that may be important in modulating metabolic and contractile function.

ISSN:0740-3194    

DOI:10.1002/mrm.1910120305

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

年代:1989

数据来源: WILEY

摘要:

AbstractIsolated kidney cortical tubules require a very rapid oxygen supply and mechanical agitation to be optimally functional. A sample chamber in which a tubule suspension is oxygenated by recirculating oxygen gas inside a coil of dialysis fibers to avoid cell loss through bubbling and in which the tubules are agitated by a gas‐driven turbine has been designed. In such a system, dog cortical tubules (35‐45 mg/ml) were found to be metabolically stable for more than 3 h as indicated by linear lactate consumption and glucose production. Small pH variations resulting from carbon dioxide and bicarbonate productions were measured. Good‐quality23Na NMR spectra of dog kidney cortical tubules were recorded with such a system, allowing a I‐min time resolution.The authors are particularly grateful to Mr. Michel Brunette, Groupe de Recherche en Transport Membranaire, for the construction of the NMR chamber. The technical assistance of Mrs. Pierrette Fournel, Mr. Jacques Sénécal, and Mrs. Josette Noël is gratefully acknowledged. This project was supported by the Kidney Foundation of Canada and the Medical Research Council of Canada. H.A. is the recipient of a Medical Research Council studentship. Y.B. is chercheur‐boursier of the Fonds de la Recherche en Santé du Québec. © 1989 Acad

ISSN:0740-3194    

DOI:10.1002/mrm.1910120306

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

年代:1989

数据来源: WILEY

摘要:

AbstractSpatially localized, natural abundance, carbon (13C) NMR spectroscopy has been combined with proton (1H) decoupling and nuclear Overhauser enhancement to improveI3C sensitivity up to five‐fold in the human leg, liver, and heart. Broadband‐decoupled13C spectra were acquired in 1 s to 17 min with a conventional 1.5‐T imaging/ spectroscopy system, an auxiliary1H decoupler, an air‐cooled dual‐coil coplanar surface probe, and both depth‐resolved surface coil spectroscopy (DRESS) and one‐dimensional phase‐encoding gradient NMR pulse sequences. The surface coil probe comprised circular and figure‐eight‐shaped coils to eliminate problems with mutual coupling of coils at high decoupling power levels applied duringI3C reception. Peak decoupler RF power deposition in tissue was computed numerically from electromagnetic theory assuming a semi‐infinite plane of uniform biological conductor. Peak values at the surface were calculated at 4 to 6 W/kg in any gram of tissue for each watt of decoupler power input excluding all coil and cable losses, warning of potential local RF heating problems in these and related experiments. The average power deposition was about 9 mW/kg per watt input, which should present no systemic hazard. At 3 W input, human13C spectra were decoupled to a depth of about 5 cm while some Overhauser enhancement was sustained up to about 3 cm depth, without ill effect. The observation of glycogen in localized natural abundance13C spectra of heart and muscle suggests that metabolites in the citric acid cycle should be observable noninvasively using13C‐labeled substrates. ©

ISSN:0740-3194    

DOI:10.1002/mrm.1910120307

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

年代:1989

数据来源: WILEY

摘要:

AbstractA method for obtaining nuclear magnetic resonance (NMR) spectroscopic signals confined to the cerebral cortex in rat using a cortical coil constructed based on the principles of the zig‐zag coil is described. We obtained31P NMR spectra of normal cerebral cortex and cold‐induced injured cortex using this cortical coil. The cortical coil clearly demonstrated an increase in inorganic phosphate (Pi) confined to cerebral cortex which, by contrast, the conventional planar surface coil failed to detect. There are significant metabolic differences between cortex and subcortical tissues. The technique described here, capable of assessing cortical metabolismin vivowithout contamination by the underlying tissue, has substantial application to studies of cerebral metabolism. © 1989 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910120308

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

年代:1989

数据来源: WILEY

摘要:

AbstractA one‐dimensional phase‐encoded spectroscopy sequence was implemented on a GE 1.5‐T Signa imager and the feasibility of its application to monitor the31P metabolities of superficial tumors was demonstrated. Serial31P spectra of I‐cm slices with adequate signal‐to‐noise ratio and insignificantT2weighting can be obtained in 28 min. The degree of “bleeding” effect was reduced with increased phase‐encoding steps. © 1989 A

ISSN:0740-3194    

DOI:10.1002/mrm.1910120309

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

年代:1989

数据来源: WILEY

摘要:

AbstractA 1‐17 water suppression pulse sequence for phase‐distortion‐free surface coil NMR spectroscopy was constructed and testedin vivoon cat brain. The sequence produces brain spectra free of phase distortions, but some degradation of water suppression quality compared to closely related sequences which produce phase distortions was observed. © 1989 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910120310

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

年代:1989

数据来源: WILEY

摘要:

AbstractThree rf coil designs of equal volume (approximately 15 ml) were compared using conductive samples. Magnetic loss into the sample was the dominant noise source. At physiological conductivity the sensitivity of the horizontally aligned solenoid and loop‐gap resonator was only 1.3 ± 0.2 times that of the vertically aligned slotted tube resonator. © 1989 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910120311

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

年代:1989

数据来源: WILEY