To evaluate metabolite concentrations in cortical gray matter, hippocampus, and thalamus of healthy adults, and to investigate precision and reproducibility of quantitative proton magnetic resonance ...spectroscopy ( super(1)H-MRS) in these gray matter regions. Quantitative single-voxel short echo-time spectra were obtained from healthy human cortex, hippocampus, and thalamus. Subjects were examined twice. Metabolite concentrations, quantification precision, and reproducibility were determined. There were no significant differences between test and retest measurements. Regional differences were observed with respect to metabolite concentrations, quantification precision, and reproducibility. Quantification precision and reproducibility of N-acetylaspartate and N-acetyl aspartylglutamate (tNAA), creatine and phosphocreatine (tCr), choline-containing compounds (Cho), and myo-inositol (myo-Ins), were better than those of glutamate (Glu) and glutamine (Gln). Generally, precision and reproducibility were better in cortex than in hippocampus or thalamus. The quantification precision was shown to correlate both with reproducibility and spectral linewidth. The reliability of quantitative MRS depends on the metabolite concerned, its concentration, and on the brain area studied. Moreover, the quantification precision of a metabolite in a single spectrum appears to be a reliable measure for its reproducibility in a longitudinal study.
Serial MRI studies are used to analyse change in multiple sclerosis (MS) lesion volume in clinical trials. As such an evaluation is very time consuming and subject to quantification errors, one might ...assess only the change in number or size of lesions using subtracted images. The advantage of subtracted images is that both new and/or enlarging and resolving and/or shrinking lesions can be evaluated, resulting in a more precise volume change than a net volume change. We studied the interobserver agreement in the detection of active MS lesions using paired dual-echo T sub(2)-weighted spin-echo studies (3-mm slices) of 30 MS patients with a range of MS disease activity on MRI from treatment trials. Using an automatic matching algorithm based on mutual information, the follow-up scan was registered to baseline, after which subtracted images were obtained. After a training session with formulation of guidelines, six observers identified new, enlarging, resolving and shrinking lesions on subtracted images. Weighted kappa ( Kappa ) values were calculated to assess interobserver agreement. Good agreement was found for new lesions ( Kappa 0.69 plus or minus 0.08), while moderate agreement was found for enlarging lesions ( Kappa 0.52 plus or minus 0.06). When new and enlarging lesions were combined, good agreement was found for "positive" activity ( Kappa 0.71 plus or minus 0.06). The interobserver agreement was poor for resolving lesions ( Kappa 0.31 plus or minus 0.07), and moderate for shrinking lesions ( Kappa 0.53 plus or minus 0.08). In conclusion, the use of subtracted images in the visual detection of new T sub(2) lesions resulted in a good level of interobserver agreement for "positive" disease activity. Subtraction of registered images is a reliable, time efficient method to assess disease progression in MS.
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