Four-and-one-half years' experience in monitoring of reproducibility of an MR spectroscopy system--application of in vitro results to interpretation of in vivo data.

The primary purpose of this work was to assess long-term in vitro reproducibility of metabolite levels measured using 1H MRS (proton magnetic resonance spectroscopy). The secondary purpose was to use the in vitro results for interpretation of 1H MRS in vivo spectra acquired from patients diagnosed with Canavan disease. 1H MRS measurements were performed in the period from April 2006 to September 2010. 118 short and 116 long echo spectra were acquired from a stable phantom during this period. Change-point analysis of the in vitro N-acetylaspartate levels was exploited in the computation of fT factor (ratio of the actual to the reference N-acetylaspartate level normalized by the reciprocity principle). This coefficient was utilized in the interpretation of in vivo spectra analyzed using absolute reference technique. The monitored time period was divided into six time intervals based on short echo in vitro data (seven time intervals based on long echo in vitro data) characterized by fT coefficient ranging from 0.97 to 1.09 (based on short echo data) and from 1.0 to 1.11 (based on long echo data). Application of this coefficient to interpretation of in vivo spectra confirmed increased N-acetylaspartate level in Canavan disease. Long-term monitoring of an MRS system reproducibility, allowing for absolute referencing of metabolite levels, facilitates interpretation of metabolic changes in white matter disorders.

Magnetic resonance spectroscopy as a predictor of conversion of mild cognitive impairment to dementia.

BACKGROUND AND PURPOSE: Proton magnetic resonance spectroscopy ((1)H-MRS) is one of the imaging techniques that could be potentially useful for identification of patients with mild cognitive impairment (MCI) who are at increased risk of developing dementia. The aim of the study was to investigate if there is a difference in brain metabolism between stable MCI patients and converters to dementia and if a use of (1)H-MRS can predict the conversion from MCI to dementia. MATERIAL AND METHODS: Forty-one amnestic MCI patients and 35 cognitively unimpaired controls were examined by (1)H-MRS (TE - 35 ms) at baseline. Metabolite ratios (NAA/Cr, Cho/Cr, mI/Cr, Glx/Cr, NAA/Cho) were estimated in four different brain regions: posterior cingulate gyrus (PCG), left hippocampus (LH), cortical area of right (RPL) and left parietal lobe (LPL). Participants were followed up for a period of 12 months. RESULTS: Twelve subjects with MCI progressed to Alzheimer's disease (AD) after one year. Analysis showed that the NAA/Cr ratio in the LH was significantly lower in MCI patients than in controls (p=0.008), but there were no differences in metabolite ratios at baseline between MCI converters and stable subjects. mI/Cr ratio in RPL predicted the conversion to AD with sensitivity 70% and specificity 85% (p<0.0004). Coexistence of diabetes improved prediction, yielding 70% sensitivity and 96% specificity (p<0.0001). CONCLUSIONS: (1)H-MRS in MCI can be a predictor of cognitive decline and conversion to dementia, especially in MCI patients with coexisting diabetes. Further studies are needed to confirm this finding.

The bystander-effect: a meta-analytic review on bystander intervention in dangerous and non-dangerous emergencies.

Research on bystander intervention has produced a great number of studies showing that the presence of other people in a critical situation reduces the likelihood that an individual will help. As the last systematic review of bystander research was published in 1981 and was not a quantitative meta-analysis in the modern sense, the present meta-analysis updates the knowledge about the bystander effect and its potential moderators. The present work (a) integrates the bystander literature from the 1960s to 2010, (b) provides statistical tests of potential moderators, and (c) presents new theoretical and empirical perspectives on the novel finding of non-negative bystander effects in certain dangerous emergencies as well as situations where bystanders are a source of physical support for the potentially intervening individual. In a fixed effects model, data from over 7,700 participants and 105 independent effect sizes revealed an overall effect size of g = -0.35. The bystander effect was attenuated when situations were perceived as dangerous (compared with non-dangerous), perpetrators were present (compared with non-present), and the costs of intervention were physical (compared with non-physical). This pattern of findings is consistent with the arousal-cost-reward model, which proposes that dangerous emergencies are recognized faster and more clearly as real emergencies, thereby inducing higher levels of arousal and hence more helping. We also identified situations where bystanders provide welcome physical support for the potentially intervening individual and thus reduce the bystander effect, such as when the bystanders were exclusively male, when they were naive rather than passive confederates or only virtually present persons, and when the bystanders were not strangers.