RESUMEN
133Cs NMR chemical shifts and relaxation times have been measured for tissue samples in vitro and in vivo from rats which have been fed on a high cesium, low potassium diet, which leads to a predominantly intracellular distribution of this ion, similar to that of K+. The high sensitivity, large chemical shift range, and narrow linewidths of 133Cs, compared with 39K, allow chemical shift differences to be observed between tissues, and in subcellular organelles such as mitochondria. For example, in vitro tissue chemical shifts, relative to 150 mM CsCl, are 1.06 +/- 0.11 ppm for liver, 0.02 +/- 0.05 ppm for brain, 1.76 +/- 0.20 ppm for erythrocytes, and -0.13 +/- 0.02 ppm for plasma. T1 and spin-echo T2 values range from 1.26 +/- 0.05 s (T1), and 0.028 +/- 0.006 s (T2) for liver, to 6.49 +/- 0.19 s and 1.12 +/- 0.03 s for plasma. 133Cs relaxation times show the same relative trends between tissues as are observed in 39K tissue studies.
Asunto(s)
Isótopos de Cesio , Dieta , Espectroscopía de Resonancia Magnética/métodos , Potasio en la Dieta/administración & dosificación , Animales , Cesio/farmacocinética , Eritrocitos/química , Hígado/química , Ratas , Ratas Sprague-Dawley , Distribución TisularRESUMEN
133Cs relaxation-time studies of tissues from rats into which cesium has been incorporated by dietary loading have been carried out in vivo and in vitro. Whereas tissue T1 values are on the order of seconds, T2 values are as low as a few tens of milliseconds. 133Cs tissue relaxation times are analogous to those of 39K in the same tissues, but are more readily measured because of the greater sensitivity of 133Cs compared with 39K. T1 and T2 data of excised tissue at two resonance frequencies (65.60 and 39.37 MHz) and temperatures (302 and 278K) have been analyzed in terms of a general description of spin-7/2 relaxation. The results are consistent with most of the cesium ions being in a free state, undergoing fast exchange with bound ions having long correlation times located in one or more intracellular compartments.
Asunto(s)
Cesio/química , Imagen por Resonancia Magnética/métodos , Animales , Sitios de Unión , Cesio/administración & dosificación , Femenino , Espectroscopía de Resonancia Magnética , Modelos Estructurales , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
Differences in the NMR detectability of 39K in various excised rat tissues (liver, brain, kidney, muscle, and testes) have been observed. The lowest NMR detectability occurs for liver (61 +/- 3% of potassium as measured by flame photometry) and highest for erythrocytes (100 +/- 7%). These differences in detectability correlate with differences in the measured 39K NMR relaxation constants in the same tissues. 39K detectabilities were also found to correlate inversely with the mitochondrial content of the tissues. Mitochondria prepared from liver showed greatly reduced 39K NMR detectability when compared with the tissue from which it was derived, 31.6 +/- 9% of potassium measured by flame photometry compared to 61 +/- 3%. The detectability of potassium in mitochondria was too low to enable the measurement of relaxation constants. This study indicates that differences in tissue structure, particularly mitochondrial content are important in determining 39K detectability and measured relaxation rates.
Asunto(s)
Espectroscopía de Resonancia Magnética , Potasio/análisis , Animales , Encéfalo/ultraestructura , Química Encefálica , Eritrocitos/química , Eritrocitos/ultraestructura , Riñón/química , Riñón/ultraestructura , Hígado/química , Hígado/ultraestructura , Masculino , Mitocondrias/ultraestructura , Músculos/química , Músculos/ultraestructura , Ratas , Ratas Sprague-Dawley , Testículo/química , Testículo/ultraestructuraRESUMEN
In this study we have found that NMR detectability of 39K in rat thigh muscle may be substantially higher (up to 100% of total tissue potassium) than values previously reported of around 40%. The signal was found to consist of two superimposed components, one broad and one narrow, of approximately equal area. Investigations involving improvements in spectral parameters such as signal-to-noise ratio and baseline roll, together with computer simulations of spectra, show that the quality of the spectra has a major effect on the amount of signal detected, which is largely due to the loss of detectability of the broad signal component. In particular, lower-field spectrometers using conventional probes and detection methods generally have poorer signal-to-noise and worse baseline roll artifacts, which make detection of a broad component of the muscle signal difficult.
Asunto(s)
Espectroscopía de Resonancia Magnética , Músculos/química , Potasio/análisis , Animales , Simulación por Computador , Diseño de Equipo , Espectroscopía de Resonancia Magnética/instrumentación , Espectroscopía de Resonancia Magnética/métodos , Modelos Biológicos , Fotometría/métodos , Potasio/química , Ratas , Factores de TiempoRESUMEN
PURPOSE: To use magnetic resonance (MR) spectroscopy to characterize clinical isolates of Cryptococcus neoformans and a glioma cell line in culture and in experimental rats. MATERIALS AND METHODS: One- and two-dimensional hydrogen 1 MR spectra were acquired from fungi cultured in vitro (16 isolates of C neoformans, three of Candida albicans, three of Aspergillus fumigatus, three of Saccharomyces cerevisiae) and a C6 glioma cell line. Cerebral biopsy specimens were obtained from healthy rats and animals with experimental infections or gliomas (19 healthy brains, 20 cryptococcomas, and 19 gliomas). Unequivocal signal assignment was performed for cell suspensions and tissue samples by using homo- and heteronuclear two-dimensional correlation spectra. RESULTS: MR spectra of C neoformans and cerebral cryptococcomas--but not of other fungi, healthy brains, or gliomas--were dominated by resonances from the cytosolic disaccharide alpha,alpha-trehalose. This spectral pattern was different from that of gliomas, which was dominated by lipids and an increased choline-creatine ratio, and that of healthy brain. CONCLUSION: A remarkably high concentration of alpha,alpha-trehalose in relation to other metabolites that are visible with MR spectroscopy is diagnostic of C neoformans. Cerebral cryptococcomas are an uncommon but serious manifestation of cryptococcosis in humans. Application of these results to the noninvasive diagnosis of cerebral cryptococcomas would help reduce the risk and expense of unnecessary surgery or biopsy and expedite patient treatment.