Many studies have shown that Pc3-4 pulsations (~0.014-0.1 Hz) observed in Earth's magnetosphere during daytime hours originate in the ion foreshock region of the solar wind, just upstream from Earth's bow shock. They occur when the interplanetary magnetic field (IMF) is primarily radial-when the IMF cone angle θ xB ≤ 45°. However, our knowledge of ion foreshock conditions is often incomplete because of the very limited number of spacecraft providing upstream data. In this study we compared 13 months of wave observations at two widely separated ground stations (Hornsund, Svalbard and Halley, Antarctica) to IMF values in the OMNI database in order to test this relation. Values of θ xB and the empirically predicted wave frequency (f calc = 0.06 B IMF ) were compared to daily Fourier spectrograms displaying pulsation power and frequency. Although there was often good temporal agreement between low θ xB and increased Pc3-4 wave power, numerous counterexamples were also evident. A statistical study of wave activity in quarter hour increments showed that Pc3-4 pulsations were associated with low θ xB values, 81% of the time at Hornsund and 83% at Halley. IMF cone angle data from all available upstream monitors were compared to wave observations for a more limited number of days; many of these showed inconsistent IMF orientations. This study indicates some of the limitations of the existing upstream monitors and provides a quantitative estimate (~80%) of the accuracy of the OMNI data set in characterizing conditions near the nose of Earth's bow shock under predominantly radial IMF conditions.

Numerous human diseases involve abnormal metabolism, and proton exchange is an effective source of magnetic resonance imaging (MRI) contrast for assessing metabolism. One MRI technique that capitalizes on proton exchange is R 1 relaxation in the rotating frame (R 1ρ ). Here we investigated the sensitivity of R 1ρ to various proton-exchange mechanisms at spin-lock pulses within FDA safety guidelines for radiofrequency-induced heating. We systematically varied pH known to change the rate of proton exchange as well as the glucose and lysine concentrations, thus changing the number of amide, hydroxyl, and amine exchangeable sites in a series of egg-white albumin phantoms. The resulting effects on quantitative relaxation time measurements of R 1ρ , R 1 , and R 2 were observed at 3T. Using spin-lock amplitudes available for human imaging (less than 23.5μT) at near physiologic temperatures, we found R 1ρ was more sensitive to physiologic changes in pH than to changes in glucose and lysine concentrations. In addition, R 1ρ was more sensitive to pH changes than R 1 and R 2 . Models of proton exchange fit to the relaxation measurements suggest that amide groups were the primary source of pH sensitivity. Together, these experiments suggest an optimal spin-lock amplitude for measuring pH changes while not exceeding FDA subject heating limitations.

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Spin-lattice relaxation in the rotating frame (T1ρ) is a relaxation parameter measured in nuclear magnetic resonance studies. This parameter has been found to be sensitive to chemical exchange processes occurring in diseased tissue associated with abnormal metabolism when measured in magnetic resonance imaging (MRI). Metabolic changes in tissue affected by abnormal metabolism can be quantified with good spatial and temporal resolution using T1ρ, better than a similar method of assessment known as CEST and current methods such as spectroscopic (1 Hand 31 P-MRS) and nuclear medicine (PET) methods used in clinical settings. Though T1ρ has these advantages, there is no consensus as to which metabolic changes T1ρ is most sensitive. The metabolic changes may be pH related, or due to changes in concentration of metabolites like glucose and glycogen. This work is tries to identify which metabolite evokes the greatest change in T1ρ by studying the response of three spin relaxation measures (T1ρ, T2 and T1) at different temperatures. It was found that T1ρ is more sensitive to pH changes than glucose and lysine at 3T. Also at body temperature, the pH results showed a non-linear trend for T1ρ signifying the limited range of sensitivity in the pH range of 6.9 to 7.5. The T2 results can be used to explain this trend. v