Improved data acquisition and processing strategies for blood oxygenatlon level-dependent (BOlO)-conlrast funcllona1 magnetie resonaneo imaging (fMRI), wllich enhance the functional eontrast-to-nolse ratio (CNR) by sampllng multiple echo limes In a single shot, are descrlbed. The dependence of Ihe CNR on Ti, Ihe image encoding time, and Ihe number of samplod oeho titnes are Investigated for exponentia1 fitting, echo summation, welghled echo summation, and averaglng of corrolalion maps oblainod at different echo limes. The mothod is validated In vlvo using visual stimulation and turbo proton echoplanar speelroseopie imaging (turbo-PEPSI), a new single-shot multi-slice MR spoclroscoplc Imaging teehnlque, whlch acqulres up 10 12 consocutive ochoplanar images wlth echo limes ranging from 1210213 msec. Quantitative Ti-mapplng slgnificanUy increasos Ihe measured extent of aetivatJon and the mean correlalion coefficient compared wilh convenlional echoplanar imaging. The sensltlvity gain with echo summation, wllicll is compulationally efficiet:'lt provides similar sensitivity as fitting. For all data processing methods sensltivlty is optimum wh on echo limes IIp 10 3.2 T 2 are sampled. This molhodology has implications for comparing functional sonsitivity at different magnetie field strengths and between braln regions with different magnetic field inhomogeneitics.

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Nighttime concentration profiles of the nitrate radical (NO3) together with NO2 and O3 were observed spectroscopically. Kinetic analysis of the NO3 formation, the early morning photolysis of NO3, and stoichiometric considerations allowed three independent estimates of the equilibrium constant Keq = [NO3] · [NO2]/[N2O5]. From those observations an average Keq of (2.0±l) × 1010 cm−3 (at 10°C) is derived. Maximum concentrations of NO3 were found to be highly variable. Lifetimes for NO3 shorter than l min in the presence of fog indicate a fast reaction of N2O5 with liquid water droplets. At relative humidities below 50% the maximum NO3 concentrations were still lower than expected from the NOx–O3 reaction sequences which must be due to unknown sinks for NO3 and/or N2O5 or to an inadequacy in the presently accepted reaction scheme.