RESUMO
The selection of a suitable low dielectric constant liquid for radiofrequency coil nonuniformity measurements is described. Measurements of dielectric constant (relative permittivity) were made on a range of candidate liquids. After excluding liquids that were too inflammable or too viscous, Esso Bayol 82 oil (dielectric constant epsilon' = 2.37) was chosen. At 1.5 T, a 27 cm diameter cylindrical phantom (test object) filled with Bayol 82 has a maximum nonuniformity of 1.9% arising from radiofrequency standing waves. The maximum diameter cylinder that can be used without the nonuniformity exceeding 2% is given for a range of liquids and field strengths. The construction of customized containers that fit closely inside a radiofrequency head coil from glass fiber reinforced resin ("fiberglass") is described. Thermal expansion of the liquid takes place without a rise in the internal pressure in the container.
Assuntos
Imageamento por Ressonância Magnética/instrumentação , Imagens de Fantasmas , Dimetilpolisiloxanos/química , Condutividade Elétrica , Desenho de Equipamento , Incêndios , Vidro/química , Humanos , Hidrocarbonetos/química , Óleos Industriais , Querosene , Espectroscopia de Ressonância Magnética , Óleos/química , Óleos de Plantas/química , Poliésteres , Pressão , Silicones/química , Soluções/química , Propriedades de Superfície , Termodinâmica , ViscosidadeRESUMO
T1 and T2 values were calculated from guinea pig brain in vivo at 0.5 T. T1 values showed significant dependence on body temperature, but the effect varied significantly from animal to animal and from one tissue type to another. Mean dependencies were 8.2 ms/degrees C for corpus callosum, 14.7 ms/degrees C for gray matter, and 21.5 ms/degrees C for hemispheric white matter (1.7, 2.6, and 4.5%/degrees C, respectively), all with respect to core temperature. These findings suggest that body temperature monitoring and control may be needed when sensitive measurements of T1 are being made. There was evidence for regulation of brain temperature within the hyperthermic range of body temperature.
Assuntos
Temperatura Corporal/fisiologia , Encéfalo/anatomia & histologia , Encéfalo/fisiologia , Imageamento por Ressonância Magnética , Animais , Regulação da Temperatura Corporal/fisiologia , Corpo Caloso/anatomia & histologia , Corpo Caloso/fisiologia , Cobaias , Hipertermia Induzida , Hipotermia InduzidaRESUMO
The measurement of absolute concentration of 31P metabolites is described, using water 1H as an internal concentration standard. An analysis of the effect of variations in coil Q on flip angle and sensitivity is presented and verified experimentally. Concentrations of nucleoside triphosphate in rat brain and muscle have been measured.
Assuntos
Espectroscopia de Ressonância Magnética/métodos , Fósforo/metabolismo , Animais , Fenômenos Químicos , Físico-Química , Fósforo/análise , Ratos , TrítioRESUMO
Whilst in vivo NMR spectroscopy provides much useful biochemical information, a limitation to such studies has been the difficulty in quantitating the results to obtain absolute metabolite concentrations. We report here a simple direct method to obtain absolute metabolite concentrations when using in vivo NMR with radiofrequency surface coils. The method has been validated for nucleoside triphosphates in two tissues; rat brain and skeletal muscle. The results obtained are in close agreement with nucleoside triphosphate concentrations obtained using other methods. Precautions for the accurate application of the method are discussed. This method can be applied to other metabolites, coils and NMR nuclei.
Assuntos
Química Encefálica , Espectroscopia de Ressonância Magnética , Músculos/análise , Concentração Osmolar , Fósforo/análise , Animais , Espectroscopia de Ressonância Magnética/métodos , Radioisótopos de Fósforo , Ratos , Ratos EndogâmicosRESUMO
Phosphorus (31P) nuclear magnetic resonance spectroscopy was used to study intracellular metabolism in the brains of 6 normal newborn infants and 10 infants who had been asphyxiated during delivery. In the normal infants spectral peaks mainly attributable to adenosine triphosphate, phosphocreatine (PCr), phosphodiesters plus phospholipids, and inorganic orthophosphate (Pi) were always detected, together with an additional large peak in the phosphomonoester region indicating the presence of a metabolite or metabolites (probably largely phosphoethanolamine) which may be involved in rapid growth of the brain. In the asphyxiated infants, data obtained on the first day of life showed no differences from those in normal infants, but by the second to ninth days inverse changes in the concentrations of PCr and Pi had caused a significant reduction in PCr/Pi. This latency suggest the possibility of effective early treatment before irreversible metabolic damage sets in. Mean intracellular pH when PCr/Pi was minimal was 7.17 +/- 0.10. Values for PCr/Pi below 0.80 were associated with a very bad prognosis for survival and early neuro-developmental outcome.
Assuntos
Asfixia Neonatal/metabolismo , Encéfalo/metabolismo , Metabolismo Energético , Espectroscopia de Ressonância Magnética , Difosfato de Adenosina/metabolismo , Trifosfato de Adenosina/metabolismo , Feminino , Humanos , Concentração de Íons de Hidrogênio , Recém-Nascido , Masculino , NAD/metabolismo , Fosfatos/metabolismo , Fosfocreatina/metabolismo , Fósforo , Análise EspectralRESUMO
Intracellular metabolism in the brains of seven infants, born at 33-40 weeks' gestation and aged 44 h to 17 days, was studied on fourteen occasions by phosphorus nuclear magnetic resonance spectroscopy (31P NMRS). The characteristic spectral peaks of ATP, phosphocreatine (PCr), phosphodiesters, and inorganic orthophosphate (Pi) were always detected, together with a large peak attributed mainly to ribose-5-phosphate. The ratio of PCr to Pi NMRS signals (which are related to concentration) in one infant thought to have a normal brain was 1.7. In three infants who had severe birth asphyxia the PCr/Pi ratio ranged from 0.2 to 1.0 but increased as their clinical condition improved: infusions of mannitol solution caused a rapid increase in the ratio on four occasions in two of these infants. The PCr/Pi ratio was 1.4 in an infant with congenital cerebral atrophy and 0.7 in an infant with meningitis. Grossly abnormal 31P spectra antedated the detection by ultrasound of large porencephalic cysts in two infants. No systematic changes in intracellular pH (calculated from the chemical shift of the Pi resonance) were observed: the mean value for all observations was 7.2 +/- SD 0.1 (n = 14).