Serial magnetic resonance (MR) studies that included proton MR spectroscopic imaging (MRSI), contrast-enhanced MR imaging (MRI), and lesion volumetric studies were performed on 25 multiple sclerosis (MS) patients with mild to modest clinical deficits. Each patient was scanned at varying intervals for up to 2 years, resulting in a total of 124 usable MR sessions. In these longitudinal studies, metabolic changes were observed on MRSI for some subjects before the appearance of lesions on MRI scanning. Regional changes in metabolite levels were observed to be dynamic and reversible in some patients. Transient changes in N-acetylaspartate (NAA) levels were sometimes found in acute plaques and indicate that a reduced NAA level does not necessarily imply axonal loss. An inverse correlation between the average NAA within the spectroscopic volume and the total lesion volume in the whole brain was observed. This negative correlation implies that NAA can serve as an objective marker of the disease burden. Strong lipid peaks in the absence of gadolinium enhancement and MRI-defined lesions were observed in 4 patients. This observation suggests that demyelination can occur independent of perivenous inflammatory changes and supports the presence of more than one pathophysiological process leading to demyelination in MS.

The relative distributions of N-acetylaspartate (NAA) + N-acetylaspartylglutamate (NAAG), creatine + phosphocreatine (Cr/PCr), and choline (Cho) in the gray and white matter of human brain were determined by utilizing proton magnetic resonance spectroscopic imaging (SI). The SI data was processed using an automated spectroscopic image processing algorithm, and image segmentation was performed using a supervised technique. Linear regression analysis indicated that the NAA + NAAG (2.01 ppm) and Cr/PCr (3.02 ppm) peaks are greater in gray matter compared with white matter. The large intersubject variation observed in the Cho (3.20 ppm) resonance prevented the assessment of its regional distribution with confidence.

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Fourier transform infrared isotopic study of the ν4 and ν5 stretching modes of linear C6 in Ar at 10 K J. Chem. Phys. 98, 71 (1993); 10.1063/1.464618Ab initio study of the geometry, stretching, vibrations, and assignment of the observed frequencies of the ground state C6H (hexatriynyl) radical A study of the Fourier transfonn infrared (FfIR) spectrum of the products of the vacuum ultraviolet (VUV) photolysis of acetylene and 1,3-butadiene trapped in solid Ar has resulted in the identification of a vibration of the C 6 H (hexatriynyl) radical at 1953.4 cm -I. The spectra of various D and \3C isotopomers of C 6 H produced from isotopically substituted precursors have been observed. The complex, overlapping spectra resulting from partial 13 C substitution have been fitted using a force constant adjustment calculation and support the assignment of the 1953.4 cm -1 absorption to a C=C stretching fundamental of linear C 6 H. The results of an ROHF/6-31G* ab initio calculation of the vibrational frequencies for the fundamentals of linear C 6 H are also reported.

Studies have been performed to evaluate the reproducibility of longitudinal acquisitions with short TE spectroscopic magnetic resonance (MR) imaging of human brain. In healthy volunteers, the ratios of N-acetyl-aspartate (NAA) and choline (Cho) with respect to total creatine (Cr) (creatine and phosphocreatine) have been examined in terms of voxel-to-voxel, acquisition-to-acquisition, and subject-to-subject variation. Overall coefficients of variation for NAA/Cr ratios and Cho/Cr ratios were 18% and 16%, respectively. The interacquisition variation was not statistically significant (P = .05) for either ratio. In terms of F ratios, the dominant source of variation in the NAA/Cr ratio was intersubject variability, whereas for the Cho/Cr ratio the dominant source of variation was intervoxel variability. Consequences of spectroscopic processing with spatial apodization and postacquisition water suppression and resolution enhancement were also examined. Such reproducibility studies are crucial if longitudinal spectroscopic evaluations are to be performed in a clinical setting to follow the natural course of disease states or the effects of therapy.

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A Fourier transform infrared (FTIR) isotopic study of the C4H (butadiynyl) radical produced by trapping the products from the vacuum ultraviolet photolysis of diacetylene (C4H2) and 1,3-butadiene (C4H6) in solid argon at 10 K has been carried out in the midinfrared from 400–3900 cm−1. A variety of carbon-13 and deuterium substituted C4H2 and C4H6 parent molecules were used to produce various isotopomers of C4H. On the basis of their isotopic behavior two absorptions at 3307.4 and 2083.9 cm−1 have been assigned to the ν1, C–H stretching and ν2, C 3/4 C stretching modes. The previous identification of the other C 3/4 C stretching mode, ν3=2060.6 cm−1, which was based on the effects of deuteration, has been confirmed and the corresponding frequencies for various 13C-substituted isotopomers have been measured. The following frequencies have been obtained for ν1, ν2, and ν3 for C4H isotopomers: 3307.2, 2078.9, and 2023.8 cm−1 for H–C 3/4 C–C 3/4 13C; 3307.2, 2069.9, and 2032.5 cm−1 for H–C 3/4 C–13C 3/4 C; 3307.2, 2066.8, and 2054.0 cm−1 for H–C 3/4 13C–C 3/4 C; 3293.3, 2048.9, and 2057.4 cm−1 for H–13C 3/4 C–C 3/4 C; 3292.5, 2050.6, and 2024.6 cm−1 for H–13C 3/4 C–C 3/4 13C; 3292.5, 2050.6, and 2030.0 cm−1 for H–13C 3/4 C–13C 3/4 C; 3306.3, 2063.3, and 2019.5 cm−1 for H–C 3/4 13C–C 3/4 13C; 3306.3, 2050.6, and 2018.0 cm−1 for H–C 3/4 13C–13C 3/4 C; 3290.1, 2007.9, and 1981.6 cm−1 for H–13C 3/4 13C–13C 3/4 13C; and 2579.3, 2056.5, and 2049.7 cm−1 for D–C 3/4 C–C 3/4 C.

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