NMR in biomedicine
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Proton MR spectroscopy ((1)H MRS)-visible total choline-containing compounds (tCho-compounds) are derivatives of membrane phospholipids and, in part, may act as a long-term second-messenger system for cellular proliferation. Experimental evidence suggests increasing concentrations of tCho-compounds during cellular proliferation. The present study was conducted in order to test the hypothesis that in vivo measurements of tCho-concentrations using (1)H MRS allow assessment of the proliferative activity of neuroepithelial brain tumors presurgically. ⋯ A highly significant positive correlation (p < 0.0001, r(2) = 0.81) was found between the tCho-concentration and the labeling index. It was concluded that the determination of tCho-concentrations using in vivo (1)H MRS could provide a novel and noninvasive assessment of the proliferative activity of neuroepithelial brain tumors, pointing at (1)H MRS as a useful method for differentiating proliferating from non-proliferating tissues. Hence, potential indications for the clinical application of (1)H MRS are grading tumors presurgically, early detection of anaplastic transformation, and monitoring treatment.
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Comparative Study Clinical Trial
Relaxation times of choline, creatine and N-acetyl aspartate in human cerebral white matter at 1.5 T.
Several studies have investigated the T1 and T2 relaxation time of choline, creatine and N-acetyl aspartate in cerebral white matter in normal human subjects. However, these studies demonstrate a large variation in T1 and T2 values. In the present study, relaxation times of choline, creatine and N-acetyl aspartate were determined in cerebral white matter in 15 control subjects (age 21 +/- 2 y, mean +/- SD) at 1.5 T. ⋯ The mean voxel size was 14 cm3. The T1 relaxation times of choline, creatine and N-acetyl aspartate were 1091 +/- 132 (mean +/- SD), 1363 +/- 137 and 1276 +/- 132 ms. The T2 relaxation times were 352 +/- 52, 219 +/- 29 and 336 +/- 46 ms, respectively.
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The physiological effects of various hyperpolarized helium and xenon MRI-compatible breathing protocols were investigated in 17 Sprague-Dawley rats, by continuous monitoring of blood oxygen saturation, heart rate, EKG, temperature and endotracheal pressure. The protocols included alternating breaths of pure noble gas and oxygen, continuous breaths of pure noble gas, breath-holds of pure noble gas for varying durations, and helium breath-holds preceded by two helium rinses. Alternate-breath protocols up to 128 breaths caused a decrease in oxygen saturation level of less than 5% for either helium or xenon, whereas 16 continuous-breaths caused a 31.5% +/- 2.3% decrease in oxygen saturation for helium and a 30.7% +/- 1. 3% decrease for xenon. ⋯ Breath-holds longer than 10 s preceded by pre-rinses caused oxygen saturation to drop below 90%. These findings demonstrate the need for standardized noble gas inhalation procedures that have been carefully tested, and for continuous physiological monitoring to ensure the safety of the subject. We find short breath-hold and alternate-breath protocols to be safe procedures for use in hyperpolarized noble gas MRI experiments.
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Comparative Study
Reproducibility of human cardiac 31P-NMR spectroscopy.
The reproducibility of the phosphocreatine to adenosine triphosphate ratio (PCr/ATP) was assessed from cardiac phosphorus-31 (31P) NMR spectra of the human left ventricle acquired with three different localization techniques. Cardiac 31P-NMR spectra (n = 68) were obtained at rest from 16 healthy subjects with three-dimensional (3D) image selected in vivo spectroscopy (ISIS), 1D spectroscopic imaging (SI), or with a combination of 2D ISIS and the 1D SI technique (ISIS + SI). The average PCr/ATP ratios were 1.41 +/- 0.20 for ISIS + SI and 1.31 +/- 0.19 for ISIS and were in the lower range of values obtained in previous studies, mainly because of a lower saturation correction factor for the cardiac PCr/ATP ratio. ⋯ Intersubject standard deviations of the PCr/ATP ratio were comparable to values reported previously. For all three localization techniques the absolute intra-examination differences in PCr/ATP (0.06 for ISIS to 0.15 for ISIS + SI) were significantly smaller (p approximately 0.03) than inter-examination differences (0.24 for ISIS to 0.29 for ISIS + SI). Therefore, consecutive acquisition of cardiac 31P-NMR spectra from the same patient during a single examination, e.g. under various cardiac loading conditions, appears to be a reliable approach for metabolic evaluation of heart disease.
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A technique for remotely controlling the degree of carotid artery occlusion in the gerbil model of cerebral ischaemia has been developed. The technique relies on manually adjustable nylon snares around the carotid arteries, in conjunction with a computer-based monitoring system, to control the degree of occlusion. ⋯ The model was used to determine the sensitivity of cerebral energy metabolism to reduced cerebral blood flow under normothermic conditions and in mild hypothermia (30 degrees C). Hypothermia had a protective effect in that energy metabolites were maintained at flows significantly below the normothermic threshold.