Further steps toward direct magnetic resonance (MR) imaging detection of neural action currents: optimization of MR sensitivity to transient and weak currents in a conductor.

The characteristics of an MRI technique that could be used for direct detection of neuronal activity are investigated. It was shown that magnitude imaging using echo planar imaging can detect transient local currents. The sensitivity of this method was thoroughly investigated. A partial k-space EPI acquisition with homodyne reconstruction was found to increase the signal change. A unique sensitivity to the position of the current pulse within the imaging sequence was demonstrated with the greatest signal change occurring when the current pulse coincides with the acquisition of the center lines of k-space. The signal change was shown to be highly sensitive to the spatial position of the current conductor relative to the voxel. Furthermore, with the use of optimization of spatial and temporal placement of the current pulse, the level of signal change obtained at this lower limit of current detectability was considerably magnified. It was possible to detect a current of 1.7 microA applied for 20 ms with an imaging time of 1.8 min. The level of sensitivity observed in our study brings us closer to that theoretically required for the detection of action currents in nerves.

Myoinositol abnormalities in temporal lobe epilepsy.

PURPOSE: This study used magnetic resonance spectroscopy (MRS) to examine metabolite abnormalities in the temporal and frontal lobe of patients with temporal lobe epilepsy (TLE) of differing severity. METHODS: We investigated myoinositol in TLE by using short-echo MRS in 34 TLE patients [26 late onset (LO-TLE), eight hippocampal sclerosis (HS-TLE)], and 16 controls. Single-voxel short-echo (35 ms) MR spectra of temporal and frontal lobes were acquired at 1.5 T and analyzed by using LCModel. RESULTS: The temporal lobe ipsilateral to seizure origin in HS-TLE, but not LO-TLE, had reduced N-acetylaspartate (NA) and elevated myoinositol (MI; HS-TLE NA, 7.8 +/- 1.9 mM, control NA, 9.2 +/- 1.3 mM; p < 0.05; HS-TLE MI, 6.1 +/- 1.6 mM, control mI 4.9 +/- 0.8 mM, p< 0.05). Frontal lobe MI was low in both patient groups (LO-TLE, 4.3 +/- 0.8 mM; p < 0.05; HS-TLE, 3.6 +/-.05 mM; p < 0.001; controls, 4.8 +/- 0.5 mM). Ipsilateral frontal lobes had lower MI (3.8 +/- 0.7 mM; p < 0.01) than contralateral frontal lobes (4.3 +/- 0.8 mM; p < 0.05). CONCLUSIONS: MI changes may distinguish between the seizure focus, where MI is increased, and areas of seizure spread where MI is decreased.