Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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The clinical usefulness of the application of spin-echo diffusion-weighted imaging in the evaluation of extraaxial cysts and epidermoid tumors is demonstrated in a series of 15 patients. Apparent diffusion coefficient (ADC) images based on intravoxel incoherent motion (IVIM) were obtained with a maximum gradient b value = 100 s/mm2. Lesion ADC was qualitatively compared to external phantoms. ⋯ On the other hand, all cysts had ADC similar to the stationary water phantom. Lesion delineation was improved due to the replacement of normal pulsatile (very high ADC) cisternal CSF. Direct quantitative measurements of ADC using this technique may not be possible due to unavoidable motion artifact.
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This contribution reports the first direct and noninvasive observation of cerebral glucose in normal anesthetized rats (n = 16) using short-echo-time localized proton NMR spectroscopy (2.35 T, STEAM, TR = 6000 ms, TE = 20 ms, 125 microliters). In addition to resonances from N-acetyl aspartate (NAA), glutamate, total creatine, cholines, taurine, and myoinositol, all spectra exhibit strongly coupled resonances from glucose (3.43, 3.80 ppm) that are readily identifiable using model solutions. The observed level of cerebral glucose in fasted rats covered a range of 15-40% of that of NAA giving absolute concentrations of 1.1-2.8 mM when NAA is taken to be 7 mM. The arterial blood glucose concentration was 7.7 +/- 0.8 mM in the same group of animals.
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Two-dimensional shift-correlated (COSY) and J-resolved NMR spectroscopy was used to identify and assign resonance in the aliphatic region (0.8 to 4.5 ppm) of the 1H spectrum of acid extracts and tissue of rat brain. The chemical shift and spin-spin coupling constants of several resonances, which could not be resolved in one-dimensional spectra of tissue, were determined. These properties, together with the appropriate multiplet structure and scalar coupling patterns observed in 2D J-resolved and COSY spectra, were used to assign the resonances of lactate, threonine, alanine gamma-amino butyrate, N-acetyl aspartate, aspartate, glutamate, glutamine, taurine, and myo-inositol. ⋯ The nonmetabolite resonances were assigned to macromolecules. Analysis of 2D COSY contour plots in conjunction with 1D spectra revealed that the total creatinine (creatinine + phosphocreatine) resonance at 3.0 ppm was overlapped by both GABA and macromolecules. This macromolecule resonance was present in a 2D COSY spectrum of the rat brain obtained in situ with a surface coil following cardiac arrest, indicating that its presence in the 2D spectrum of excised brain tissue did not arise from tissue disruption.
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Comparative Study
Hemodynamic and hepatic pH responses to sodium bicarbonate and Carbicarb during systemic acidosis.
Rats subjected to ammonium chloride-induced metabolic acidosis were given alkalinization therapy with either sodium bicarbonate or Carbicarb. Ammonium chloride-induced severe metabolic acidosis had minimal effect on mean arterial blood pressure and cardiac output. This acidosis resulted in a small but statistically significant fall in intracellular liver pH (pHi) as measured with 31P magnetic resonance spectroscopy (7.01 +/- 0.05 vs 7.08 +/- 0.04, p less than 0.05). ⋯ Carbicarb therapy resulted in systemic alkalinization without major changes in arterial pCO2, cardiac output, or mean arterial blood pressure. Moreover, Carbicarb effected a sustained intracellular alkalinization of the liver (phi = 7.12 +/- 0.07 at 5 min, p less than 0.05, pHi = 7.19 +/- 0.07 at 10 min, p less than 0.01, pHi = 7.16 +/- 0.06 at 15 min, p less than 0.01, vs baseline pHi = 7.05 +/- 0.06). These data suggest that Carbicarb may be a more effective buffer than sodium bicarbonate during conditions where ventilation is limited and hemodynamic instability is present.
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We describe the first in vivo imaging determination of normal lung tissue's multiexponential transverse magnetization decay. Normal spontaneously breathing rats were used for the measurements. To obtain motion-insensitive images, we used a modified line scan imaging technique which we call the interleaved line scan (ILS). ⋯ From a series of 16 Hahn spin-echo images with echo times ranging from 16 to 90 ms, we obtained a two-component T2 decay for normal peripheral lung tissue. The measured fast and slow T2 components were 9.5 +/- 1.0 and 34 +/- 5.0 ms for the right lung and 9.0 +/- 1.5 and 32 +/- 4.5 for the left lung. The relative magnetization for the slow T2 component was 7.0 +/- 4.5% for the right lung and 10 +/- 3.0% for the left lung.