Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Quantitative measurements of regional and tissue specific concentrations of brain metabolites were measured in elderly subjects using multislice proton magnetic resonance spectroscopic imaging ((1)H MRSI). Selective k-space extrapolation and an inversion-recovery sequence were used to minimize lipid contamination and linear regression was used to account for partial volume problems. The technique was applied to measure the concentrations of N-acetyl aspartate (NAA), and creatine (Cr)- and choline (Cho)-containing compounds in cortical gray and white matter, and white matter lesions of the frontal and the parietal lobe in 40 normal elderly subjects (22 females and 18 males, 56-89 years old, mean age 74 +/- 8). ⋯ Cho was 28% lower in cortical gray matter than in white matter. Furthermore, NAA and Cr changes correlated with age. In conclusion, regional and tissue differences of brain metabolites must be considered in addition to age-related changes when interpreting (1)H MRSI data.
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Ischemic tissues generate nitric oxide (NO) by direct reduction of tissue nitrite under the acidic conditions that occur during ischemia. In view of the important implications of this enzyme-independent mechanism of NO generation on the pathogenesis and treatment of tissue injury, the NO formation in mice subjected to cardiopulmonary arrest was measured and imaged. Real-time measurement of NO generation was performed by detection of naturally generated NO-heme complexes in tissues using L-band electron paramagnetic resonance (EPR) spectroscopy. ⋯ The observed signal was largely due to heme-bound NO, which accounted for the high concentrations found in these organs. This increased NO formation during cardiopulmonary arrest could contribute to the difficulty of resuscitation after long periods of arrest. Magn Reson Med 45:700-707, 2001.
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Comparative Study
Broadband proton decoupling for in vivo brain spectroscopy in humans.
A new decoupling sequence, PBAR, is described for broadband heteronuclear decoupling in vivo in humans at 1.5T. The sequence uses non-adiabatic, frequency- and amplitude-modulated inversion pulses designed to minimize decoupling sidebands at low applied gammaB(2) RF field levels and to cover only the narrow range of resonance offsets encountered in practice. The offset dependence of the decoupling efficiency of PBAR is demonstrated and compared to the conventional WALTZ-4 sequence. ⋯ Applications of PBAR are shown in vivo in the human brain both for (31)P and natural abundance (13)C spectroscopy using volume decoupling coils. The PBAR sequence allows whole brain [(1)H]-[13]C decoupling to be performed at 1.5T with a standard head coil within FDA guidelines for RF power deposition. Magn Reson Med 45:226-232, 2001.
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Image selected in vivo spectroscopy (ISIS) is a volume selection method often used for in vivo (31)P MRS, since it is suitable for measurements of substances with short T(2). However, ISIS can suffer from significant signal contributions caused by T(1) smearing from regions outside the VOI. A computer model was developed to simulate this contamination. ⋯ The simulation results show that contamination due to T(1) smearing is, effectively, eliminated with E-ISIS and is significantly lower than for ISIS-0 and ISIS-1. E-ISIS offers increased accuracy for quantitative and qualitative determination of substances studied using in vivo MRS. Hence, E-ISIS can be valuable for both clinical and research applications.
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Comparative Study Clinical Trial
H(2)(15)O PET validation of steady-state arterial spin tagging cerebral blood flow measurements in humans.
Steady-state arterial spin tagging approaches can provide quantitative images of CBF, but have not been validated in humans. The work presented here compared CBF values measured using steady-state arterial spin tagging with CBF values measured in the same group of human subjects using the H(2)(15)O IV bolus PET method. ⋯ However, for a central white matter ROI, blood flow values determined using arterial spin tagging were significantly underestimated compared to corrected blood flow values determined using H(2)(15)O PET. This underestimation could be caused by an underestimation of the arterial transit time for white matter regions.