NAA/Cho is an excellent marker for localizing the epileptogenic zone in TLE.

There is in vivo 1H-MRSI evidence of neuronal degeneration or loss and excess Glu + Gln in the medulla of patients with ALS. Although this cross-sectional study cannot identify which change occurred first, the higher Glx signal in the medulla of patients with more dysarthria and dysphagia is consistent with the hypothesis of Glu excitotoxicity in ALS pathogenesis. Longitudinal 1H-MRSI studies of the medulla (and other brain regions) in more patients with ALS are required to confirm these findings and to determine whether such metabolite changes will be useful in monitoring disease progression, in clinical diagnosis, and in understanding the pathogenesis of ALS.

The increase in MR visible sodium, associated with the decrease in ADC is consistent with the hypothesis that sequential seizures caused an increase in sodium influx and perturbation of membrane ion homeostasis, which eventually evolved into an irreversible phase of cellular edema, with increased MR visible intracellular sodium and decreased ADC. Return of ADC to near-control level and persistent high sodium level at 7 days may be explained by the increase in extracellular space and tissue necrosis.

Background and Purpose-Many patients with acute stroke are excluded from receiving thrombolysis agents within the necessary time limit (3 or 6 hours from stroke onset) because they or their family members are unable provide the time of stroke onset. Brain tissue sodium concentration ([Na ϩ ]) increases gradually and incessantly during the initial hours of experimental focal cerebral ischemia but only in severely damaged brain regions. We propose that this steady increase in [Na ϩ ] can be used to estimate the time after arterial occlusion in the rat middle cerebral artery occlusion model of ischemic stroke. Methods-Sixteen anesthetized Sprague-Dawley rats underwent permanent middle cerebral artery occlusion combined with bilateral common artery occlusion. After 100 to 450 minutes, diffusion-weighted MRI was used to generate apparent diffusion coefficient (ADC) maps, cerebral blood flow (CBF) was determined with 14 C-iodoantipyrine (in a subset of 7 animals), and the brain was frozen. Autoradiographic CBF sections and punch samples for Na ϩ analysis were obtained from the brain at the same level of the MR image. Severely at risk regions were identified with an ADC of Ͻ520 m 2 /s and, in the subset, with both ADC of Ͻ520 m 2 /s and CBF of Ͻ40 mL ⅐ 100 g Ϫ1 ⅐ min