An NMR method is presented for measuring compartment-specific water diffusion coefficient (D) values. It uses relaxography, employing an extracellular contrast reagent (CR) to distinguish intracellular (IC) and extracellular (EC) (1)H(2)O signals by differences in their respective longitudinal (T(1)) relaxation times. A diffusion-weighted inversion-recovery spin-echo (DW-IRSE) pulse sequence was used to acquire IR data sets with systematically and independently varying inversion time (TI) and diffusion-attenuation gradient amplitude (g) values.
The water apparent diffusion coefficient (ADC) in rabbit Achilles tendon is anisotropic, diffusion-time dependent, and changes as a function of tensile load. Water ADC changes of tendon under mechanical load are thought to be due to the extrusion of water from the more restricted tendon core to a relatively unrestricted bulk phase at the periphery (rim) of the tendon. Tensile loading may influence water ADC values by changing the spatial separation of restricting barriers (e.g., increasing the tendon fibril packing density).
In vivo 19fluorine nuclear magnetic resonance spectroscopy was used to measure the brain concentration of fluoxetine and norfluoxetine in five patients with obsessive-compulsive disorder and three with major depression. The mean brain:plasma ratio of the parent drug plus the metabolite was significantly elevated to 2.6 (SD = 1.0) (95% confidence interval = 1.9-3.3). This accumulation may have implications for understanding both the therapeutic and the toxic effects of fluoxetine.
PURPOSE: To quantify lithium in the human brain.
METHODS: A 7Li MR spectroscopy method was developed with special features for high precision including: a) sampling a large cerebral volume to maximize the signal-to-noise ratio; b) adiabatic excitation pulses to ensure uniform spin mutation; c) morphometric analysis of the MR images of the sampled cerebrum; d) a mathematical model derived from empirical data to correct for receiver inhomogeneity effects; and e) a long interpulse delay, to eliminate errors arising from uncertain T1 values.
In vivo magnetic resonance spectroscopy (MRS) was used to determine the relationship between serum and brain lithium levels in bipolar patients (n=25). Over the broad range of serum lithium levels observed, the correlation (r=.68) with brain lithium levels was high. This correlation was much weaker (r=.39) when limited to only those patients with serum lithium levels in the range of 0.6-1.0 mmol/l. This variability may account for failure of lithium prophylaxis in some patients who have serum lithium levels in the therapeutic range.
Lithium specifically and potentially inhibits membrane transport of choline. However, the effect of lithium on human neuronal choline content is unknown. This study was performed to determine if lithium alters the human brain choline concentration in vivo. In vivo proton magnetic resonance spectroscopy was used to compare the relative brain concentration of choline-containing compounds in seven lithium-treated patients and six lithium-free controls. No significant difference was observed in the mean relative choline resonance between the patient and control groups.
A novel method of chemical shift imaging utilizing echoplanar imaging (EPI) has been developed for the purpose of improving the spatial resolution of metabolite images for the specific goal of high spatial resolution mapping of neuronal content. An EPI sequence was modified to allow temporal offsets of the 180 degree refocusing pulse that encode the chemical shift information into the phase of the signal.
A proton dynamic nuclear polarization (DNP) NMR signal enhancement (epsilon) close to thermal equilibrium, epsilon = 0.89, has been obtained at high field (B(0) = 5 T, nu(epr) = 139.5 GHz) using 15 mM trityl radical in a 40:60 water/glycerol frozen solution at 11 K. The electron-nuclear polarization transfer is performed in the nuclear rotating frame with microwave irradiation during a nuclear spin-lock pulse.
In this communication, we report enhancements of nuclear spin polarization by dynamic nuclear polarization (DNP) in static and spinning solids at a magnetic field strength of 9T (250 GHz for g=2 electrons, 380 MHz for 1H). In these experiments, 1H enhancements of up to 170+/-50 have been observed in 1-13C-glycine dispersed in a 60:40 glycerol/water matrix at temperatures of 20K; in addition, we have observed significant enhancements in 15N spectra of unoriented pf1-bacteriophage.
Electron paramagnetic resonance spectroscopy at 139.5 GHz has been used to study p21 ras complexed with Mn(II) and guanosine 5'-(beta, gamma-imidotriphosphate), an analog of GTP. The p21 sample studied was selectively labeled with [17O gamma]threonine to a final enrichment of 30%. A Mn(II)-17O hyperfine interaction was observed, but the value of the coupling constant, 0.11 +/- 0.04 mT, is the smallest such value yet reported.
