Different aspects of hyperacute cerebral ischemia are depicted at DW and HW imaging before infarction is depicted at conventional MR or CT. These techniques may improve stroke diagnosis and may contribute to advances in treatment.

The purpose of this study was to develop a method for obtaining simultaneous electrophysiological and functional magnetic resonance imaging data. Using phantom experiments and tests on several of the investigators, a method for obtaining simultaneous electrophysiological and fMRI data was developed and then tested in three volunteers including two task activation experiments. It was then applied in a sleep experiment (n = 12). Current limiting resistance and low-pass filtering were added to the electrophysiological circuit. Potential high frequency current loops were avoided in the electrical layout near the subject. MRI was performed at 1.5 T using conventional and echo planar imaging sequences. There was no evidence of subject injury. Expected correlations were observed between the electrophysiological and fMIU data in the task activation experiments. The fMRI data were not sigruficantly degraded by the electrophysiological apparatus. Alpha waves were detected from within the magnet in seven of the 15 experimental sessions. There was degradation of the electrophysiological data due to ballistocardiographic artifacts (pulsatile whole body motion time-locked to cardiac activity) which vaned between subjects from being minimal to becoming large enough to make detection of alpha waves difficult. We concluded that simultaneous fMRI and electrophysiological recording is possible with minor modifications of standard electrophysiological equipment. Our initial results suggest this can be done safely and without compromise of the fMRI data. The usefulness of this technique for studies of such things as sleep and epilepsy is promising. Applications requiring higher precision electrophysiological data, such as evoked response measurements, may require modifications based on ballistocardiographic effects. Address reprint requests to Bruce R. Rosen, M.D., Ph.D., Department of Radiology, Massachusetts General Hospital, MGH-NMR Within the last few years, several magnetic resowhich are sensitive to local changes in cerebral hemo-nance imaging (MRI) techniques have been developed Center,

The biexponential relaxation behavior of the sodium nucleus affects the accuracy of quantitative measurement of in vivo tissue sodium concentration (TSC). Theoretical analysis and in vivo experimental results are used to demonstrate the extent of the large bias in the measured TSC that arises when the relaxation behavior in vivo differs significantly from that of the calibration standards which is when a significant fraction of the total sodium signal decays with a relaxation time much shorter than the echo time (TE) used for imaging. This bias can be as large as 20% for measurements of TSC in a normal rat brain with TE = 2 ms. Our findings indicate that shortening the echo time (TE < 0.5 ms) by projection imaging is a reliable means of obtaining accurate in vivo estimates for TSC using MR.

Summary: Purpose: To study in humans the hemodynamic and metabolic consequences of both photic stimulationtriggered and spontaneous generalized epileptiform discharges.Methods: Simultaneous EEG, functional magnetic resonance imaging (fMRI) and MR spectroscopy were performed in a 1.5-T scanner in 16 patients with generalized epilepsy, including nine with photosensitive epilepsy, and 12 normal subjects.Results: With a flash stimulation duration of 2 s, prominent visual cortex activation was seen in all normals and patients. There were no fMRI-registered hemodynamic abnormalities found in relation to the brief photoparoxysmal spike-wave activity evoked in the photosensitive patients. However, irrespective of the presence of a spike-wave response to the photic stimulation, the photosensitive patients showed four unique findings compared with normals: (a) slightly, but significantly, increased lactate levels in the occipital cortex in the resting state, (b) an increased area of visual cortical activation with photic stimulation, (c) simultaneous with the occipital cortex stimulus-induced increased fMRI signal there were noncontiguous areas of signal attenuation most prominent in perirolandic regions, and (d) a marked decrement (undershoot) of fMRI signal intensity immediately after the photic stimulation in the occipital cortex and in the region of the posterior cingulate gyms.Conclusions: These findings suggest abnormal interictal metabolism and increased vascular reactivity in the photosensitive patients. Key Words: Functional MRI-MR spectroscopyGeneralized epilepsy-Photosensitive-EEG.Most studies of the pathophysiology of the generalized epilepsies in humans have used positron emission tomography (PET) and fluorodeoxyglucose (FDG). In the interictal periods, these investigations showed a normal cerebral metabolic rate for glucose (CMRGlc) (1-3), and during ictal episodes of various types showed both increased and decreased CMRGlc and cerebral blood flow (CBF) (1-7). Thus these data suggest that further investigations in the human generalized epilepsies might advance the understanding of their pathophysiologies.Functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy (MRS) are noninvasive and require no isotopes or contrast agents. fMRI has a spatial resolution of a few millimeters or less and a

Summary:Purpose: To study metabolic and hemodynamic correlates of photic stimulation-triggered discharges.Methods: Simultaneous EEG, functional MRI (fMRI) and magnetic resonance spectroscopy (MRS) were performed in nine patients with photosensitive epilepsy and in 12 normal subjects.Results: Prominent visual cortex activation was seen in all normal subjects and patients, and no fMRI-registered hemodynamic abnormalities were correlated with the brief photoparoxysmal spike-wave activity evoked in the photosensitive patients. However, irrespective of the presence of a spike-wave response to the photic stimulation, the photosensitive patients showed four findings not seen in the normal subjects: (a) slightly, but significantly, elevated lactate levels in the occipital cortex in the resting state; (b) an increased area of visual cortical activation with photic stimulation; (c) simultaneous with the occipital cortex stimulus-induced increased M R I signal, there were noncontiguous areas of signal attenuation most prominent in perirolandic regions; and (d) a marked decrement (undershoot) of fMRI signal intensity immediately after the photic stimulation in the occipital cortex and in the region of the posterior cingulate gyrus.Conclusions: These findings suggest abnormal interictal metabolism and increased vascular reactivity in the photosensitive patients. Key Words: Functional MRI-MR spectroscopyGeneralized epilepsy-Photosensitive-EEG.Functional magnetic resonance imaging (fMRI) during focal seizures has revealed localized changes in CBF (1,2). Warach et al. (3) used fMRI to study blood-flow changes related to epileptic discharges in two patients, one with generalized spike-wave discharges, both of whom showed focal increases in signal intensity indicative of focal increased blood flow. 'H Magnetic resonance spectroscopy (MRS) showed an increase in lactate during physiologic photic stimulation in normal subjects (4), but Cendes et al. (5) found no lactate changes in five patients during or soon after absence seizures associated with generalized epilepsy. We performed fMRI and 'H MRS in patients with a photoparoxysmal response (PPR) by using EEG recordings during MR data acquisition to verify the presence of a PPR. METHODSNine patients, eight women, with a mean age of 28 years (range, 18-46 years), with primary generalized epiDr. Hill is currently at