MR SPECTROSCOPY IN THE EVALUATION OF EPILEPSY

Ictal asystole during long-term video-EEG; semiology, localization, and intervention

Ictal arrhythmias are disturbances of cardiac conduction that occur during clinical or electrographic seizures. Ictal asystole (IA) is rare, and its incidence can range from 0.3–0.4% in patients with epilepsy who were monitored by video-EEG (van der Lende et al., 2015).

We report on ten patients (six males and four females) with an age ranging from 31 to 70 years old) who were monitored in our video-EEG (VEEG) unit over the last eight years. These patients were selected based on the history of documented ictal asystole during inpatient VEEG monitoring). In our series the mean latency from the seizure onset to the onset of ictal asystole was 22 seconds and the mean duration of the IA was 15.8 seconds. During the asystolic phase the seizures may clinically continue or syncopal signs may supervene.

In our case series all the patients had either left or right temporal lobe epilepsy, six of which were lesional. We found two patterns of ictal semiology in our series. The first group of patients included five patients who experienced a rapid onset of IA in their seizure and the second group where the latency of ictal asystole was relatively late. All our cohort had a permanent pacemaker following the diagnosis, six of these patients have been event free since placement.

Improvements in high-field localized MRS of the medial temporal lobe in humans using new deformable high-dielectric materials

The intrinsic nonuniformities in the transmit radiofrequency field from standard quadrature volume resonators at high field are particularly problematic for localized MRS in areas such as the temporal lobe, where a low signal-to-noise ratio and poor metabolite quantification result from destructive B₁⁺ field interference, in addition to line broadening and signal loss from strong susceptibility gradients. MRS of the temporal lobe has been performed in a number of neurodegenerative diseases at clinical fields, but a relatively low signal-to-noise ratio has prevented the reliable quantification of, for example, glutamate and glutamine, which are thought to play a key role in disease progression. Using a recently developed high-dielectric-constant material placed around the head, localized MRS of the medial temporal lobe using the stimulated echo acquisition mode sequence was acquired at 7 T. The presence of the material increased the signal-to-noise ratio of MRS by a factor of two without significantly reducing the sensitivity in other areas of the brain, as shown by the measured B₁⁺ maps. An increase in the receive sensitivity B₁⁻ was also measured close to the pads. The spectral linewidth of the unsuppressed water peak within the voxel of interest was reduced slightly by the introduction of the dielectric pads (although not to a statistically significant degree), a result confirmed by using a pad composed of lipid. Using LCmodel for quantitative analysis of metabolite concentrations, the increase in signal-to-noise ratio and the slight decrease in spectral linewidth contributed to statistically significant reductions in the Cramer-Rao lower bounds (CRLBs), also allowing the levels of glutamate and glutamine to be quantified with CRLBs below 20%.