摘要:

AbstractThe use of a current‐generated, inhomogeneous, surface‐spoiling magnetic field gradient for enhancing magnetic resonance spatial localization, by rapidly inducing spin phase incoherence in surface lying regions of a sample is examined theoretically. A geometrically simple surface‐spoiling magnetic field gradient coil design is presented and its gradient field characterized via computer simulations. Mathematical expressions describing the time dependence of net sample spin phase coherence under influence of the spoiling gradient are developed for application with homogeneous (B1) volume coils. The dependence of spoiling efficiency on the magnetogyric ratio of the nuclide under investigation and on the current driving the gradient field is described. Spoiling periods of ca 1–2 ms with driving currents of ca 0.5–1.0 A are predicted to be adequate for surface‐spoiling experiments with rat, e.g., for noninvasive monitoring of liver. A companion article W. Chen and J. J. H. Ackerman,NMR Biomed., 3, 158–165 (1990)) describes implementation of the surface‐spoiling technique with multicompartment models (phantoms) and

ISSN:0952-3480    

DOI:10.1002/nbm.1940030402

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe use of inhomogeneous surface‐spoiling magnetic field gradients for elimination of signal from surface lying regions of a sample was theoretically examined in the companion article (W. Chen and J. J. H. Ackerman,NMR Biomed.3, 147–157 (1990)). Using the spoiling gradient coil design described therein, this article presents experimental verification of the feasibility of such an approach to enhanced spatial localization. Single coil mode31P NMR surface coil interrogation of both a two compartment phantom and ratin vivoare shown to provide excellent suppression of surface lying regions with minimal degradation of signal from the deep lying region of interest. Both pulse‐and‐collect and spin echo sequences were highly efficient in concert with spoiling gradient periods of 0.5–2 ms and driving currents of 0.5–2 A. The use of a current‐generated surface spoiling gradient offers a robust means to remove surface tissue signal contributions and can be implemented with a wide range of localizing pulse sequences and imag

ISSN:0952-3480    

DOI:10.1002/nbm.1940030403

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractA computer‐based pattern recognition (PR) approach has been applied to the interpretation of1H NMR generated urinalysis data in a variety of experimental toxicity states in the rat.1H NMR signal intensities for each endogenous metabolite in urine were regarded as coordinates in multi‐dimensional space and analysed using computer pattern recognition methods through which the dimensionality was reduced for display and categorization purposes. Initially 17 metabolic dimensions were used which were defined by the scored relative concentrations of a variety of urinary metabolites detected in1H NMR spectra. By employing the unsupervised learning methods of 2‐ and 3‐dimensional nonlinear mapping (NLM) different types of toxin (hepatotoxins, cortical and papillary nephrotoxins) could be classified according to NMR‐detectable biochemical effects in the urine. The robustness of the classification methods, and the influence of the addition of new scored biochemical data reflecting dose response situations, nutritional effects on toxicity, sex differences in biochemical response to toxins and addition of a new toxin class (testicular toxin) to the pattern recognition analysis were also evaluated. We find that the initial training set maps are fundamentally stable to the addition of all data types and that the PR methods correctly ‘predicted’ the toxicological effects of the test compounds. These results confirm the power and wide applicability of linked PR and1H NMR urinalysis as an approach to the generation and classification of acute toxic

ISSN:0952-3480    

DOI:10.1002/nbm.1940030404

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractTrimethylamines are required as substrates in the biosynthesis of a number of important molecules in the cell. Herein, we describe the use of choline, deuterated in its 9 methyl positions, as an NMR label for following the distribution and metabolism of methyl groups after intravenous choline infusion. Deuterium (2H) NMR spectroscopy of the rabbit kidneyin vivorevealed a linear uptake of infused choline that was directly proportional to the rate of infusion. The sensitivity limit for the spectroscopic studiesin vivowas in the order of 100 μMfor a 2 min data collection. After the infusion,2H NMR imaging of the kidneyin vivodemonstrated high trimethylamine concentrations in both the cortex and inner medulla but not in the outer medulla. The inner medullary fraction, however, was more labile to diuresis induced by furosemide. Companion high resolution2H NMR studies of extracts revealed a cortex betaine/choline concentration ratio of 0.69 ± 0.05 (mean ± SEM,n= 3) before furosemide administration. Following furosemide infusion, the cortex betaine/choline concentration ratio was 3 ± 1 (n= 6). Thus,2H renal images following furosemide treatment can be interpreted as metabolic maps of betaine distribution. In addition, extraction studies revealed high concentrations of labelled choline and betaine in the liver. These data demonstrate that2H‐labelled choline is an effective marker of choline methyl metabolismin vivoand should provide a unique tool for the investigation of this important subs

ISSN:0952-3480    

DOI:10.1002/nbm.1940030405

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractBlood flow and phosphorus metabolites have been measured simultaneously in the murine RIF‐1 tumourin vivo. Blood flow was measured using the H2washout technique and31P NMR spectroscopy was used to measure high energy phosphates, inorganic phosphate and intracellular pH within the tumour. Following NMR and flow measurements, hydralazine was administered and the measurements repeated. There was always a decrease in blood flow, and a fall in nucleoside triphosphate detected by NMR, after administration of hydralazine. At blood flows in excess of 15 mL 100 g−1min−1the nucleoside triphosphate/inorganic phosphate ratio was 1.0 or greater, whereas at flows in the range of 5–12 mL 100 g−1min−1the ratio fell to below 0.5, and at flows below 5 mL 100 g−1min−1there was no detectable resonance from nucleosi

ISSN:0952-3480    

DOI:10.1002/nbm.1940030406

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractWe have obtained localized, water‐suppressed proton magnetic resonance spectra from eleven astrocytomasin vivo. Localized phosphorus spectra were also obtained from three of these tumors. All tumors were examined prior to surgery, radiotherapy or chemotherapy. Examinations were performed with a commercially available 1.5 Tesla combined imaging and spectroscopy system using a stimulated echo pulse sequence for protons and an ISIS pulse sequence for phosphorus. A relatively high lactate resonance intensity correlated with a more malignant histological tumor grade and more aggressive behaviour. The resonance intensity ofN‐acetylaspartate/creatine was decreased and choline/creatine was increased, but these did not reliably discriminate between tumor grades. Other unidentified resonances not present in spectra of normal brain were sometimes seen. Proton magnetic resonance spectroscopy provides a new method for determining the metabolic behaviour of astrocytomas that may be useful in the clinical assessment of patients with these tum

ISSN:0952-3480    

DOI:10.1002/nbm.1940030407

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe application of one‐dimensional31P chemical shift imaging to the study of the isolated perfused rat heart is described. Its applicability for the examination of regional ischemia in the isolated perfused rat heart is demonstrated. The data sets show clearly the localization to the ischemic and nonischemic regions of the heart. Such studies will permit the correlation of cardiac metabolism and function in a controlled manner that is not possible in the application of these techniques to the intact animal. In particular, the time resolution of the experiments will enable spatially localized metabolic studies to be performedduringthe onset of ischemia andduring reperfusio

ISSN:0952-3480    

DOI:10.1002/nbm.1940030408

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

ISSN:0952-3480    

DOI:10.1002/nbm.1940030401

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY