(1)H MR spectroscopy in epilepsy

[Neurophysiological and functional neuroimaging methods in the assessment of migraines and epilepsy with vertigo]

A review of the current literature shows that the combined use of neurophysiological and structural-functional neuroimaging methods has significantly expanded the understanding of the mechanisms of migraine with vestibular dysfunction: functional and structural disorders were found in brain regions involved in multisensory vestibular control and Central vestibular processing. Analysis of numerous studies shows that epilepsy can also cause vestibular symptoms, they can occur both without epileptic markers, and in combination with epileptic paroxysms. In isolated epileptic vertigo, according to studies widely presented in the literature, epileptic activity was most often detected by EEG data in the temporal regions, to a lesser extent in the parietal regions. In these studies, neuroimaging findings of foci of reduced substance density were found, which could be a consequence of deafferentation, as well as violations of connections with the focus of neuronal activity. In the absence of structural abnormalities, numerous studies have shown using magnetic resonance spectroscopy, diffusion MRI, and PET that the physiological basis for impaired neuronal metabolism was a decrease in synaptic activity, a violation of maintaining the difference in membrane potentials on the surface of the hippocampus, or changes in neighboring tracts of the white matter of the brain.

Fast, regional three-dimensional hybrid (1D-Hadamard 2D-rosette) proton MR spectroscopic imaging in the human temporal lobes

1 H-MRSI is commonly performed with gradient phase encoding, due to its simplicity and minimal radio frequency (RF) heating (specific absorption rate). Its two well-known main problems-(i) "voxel bleed" due to the intrinsic point-spread function, and (ii) chemical shift displacement error (CSDE) when slice-selective RF pulses are used, which worsens with increasing volume of interest (VOI) size-have long become accepted as unavoidable. Both problems can be mitigated with Hadamard multislice RF encoding. This is demonstrated and quantified with numerical simulations, in a multislice phantom and in five healthy young adult volunteers at 3 T, targeting a 2-cm thick temporal lobe VOI through the bilateral hippocampus. This frequently targeted region (e.g. in epilepsy and Alzheimer's disease) is subject to strong, 1-2 ppm.cm-1 regional B0, susceptibility gradients that can dramatically reduce the signal-to-noise ratio (SNR) and water suppression effectiveness. The chemical shift imaging (CSI) sequence used a 3-ms Shinnar-Le Roux (SLR) 90° RF pulse, acquiring eight steps in the slice direction. The Hadamard sequence acquired two overlapping slices using the same SLR 90° pulses, under twofold stronger gradients that proportionally halved the CSDE. Both sequences used 2D 20 × 20 rosette spectroscopic imaging (RSI) for in-plane spatial localization and both used RF and gradient performance characteristics that are easily met by all modern MRI instruments. The results show that Hadamard spectroscopic imaging (HSI) suffered dramatically less signal bleed within the VOI compared with CSI (<1% vs. approximately 26% in simulations; and 5%-8% vs. >50%) in a phantom specifically designed to test these effects. The voxels' SNR per unit volume per unit time was also 40% higher for HSI. In a group of five healthy volunteers, we show that HSI with in-plane 2D-RSI facilitates fast, 3D multivoxel encoding at submilliliter spatial resolution, over the bilateral human hippocampus, in under 10 min, with negligible CSDE, spectral and spatial contamination and more than 6% improved SNR per unit time per unit volume.

Alterations in Brain Metabolites in Patients with Epilepsy with Impaired Consciousness: A Case-Control Study of Interictal Multivoxel 1H-MRS Findings

BACKGROUND AND PURPOSE

Previous studies have shown perfusion abnormalities in the thalamus and upper brain stem in patients with epilepsy with impaired consciousness. We hypothesized that these areas associated with consciousness will also show metabolic abnormalities. However, metabolic abnormalities in those areas correlated with consciousness has not been characterized with multiple-voxel ¹H-MRS. In this study, we investigated the metabolic alterations in these brain regions and assessed the correlation between seizure features and metabolic alterations.

MATERIALS AND METHODS

Fifty-seven patients with epilepsy and 24 control subjects underwent routine MR imaging and 3D multiple-voxel ¹H-MRS. Patients were divided into 3 subgroups: focal impaired awareness seizures (n = 18), primary generalized tonic-clonic seizures (n = 19), and secondary generalized tonic-clonic seizures (n = 20). The measured metabolite alterations in NAA/Cr, NAA/(Cr + Cho), and Cho/Cr ratios in brain regions associated with the consciousness network were compared between the patient and control groups. ROIs were placed in the bilateral inferior frontal gyrus, supramarginal gyrus, cingulate gyrus, precuneus, thalamus, and upper brain stem. Correlations between clinical parameters (epilepsy duration and seizure frequency) and metabolite alterations were analyzed.

RESULTS

Significantly lower NAA/Cr and NAA/(Cho + Cr) ratios (P < .05 and < .01, respectively) were observed in the bilateral thalamus and upper brain stem in all experimental groups, and significantly high Cho/Cr ratios (P < .05) were observed in the right thalamus in the focal impaired awareness seizures group. There were no significant differences in metabolite ratios among the 3 patient groups (P > .05). The secondary generalized tonic-clonic seizures group showed a negative correlation between the duration of epilepsy and the NAA/(Cr + Cho) ratio in the bilateral thalamus (P < .05).

CONCLUSIONS

Metabolic alterations were observed in the brain stem and thalamus in patients with epilepsy with impaired consciousness.

Neuroimaging methods in Epilepsy of Temporal Origin

Background:

Temporal Lobe Epilepsy (TLE) comprises the most common form of symptomatic refractory focal epilepsy in adults. Accurate lateralization and localization of the epileptogenic focus are a significant prerequisite for determining surgical candidacy once the patient has been deemed medically intractable. Structural MR imaging, clinical, electrophysiological, and neurophysiological data have an established role in the localization of the epileptogenic foci. Nevertheless, hippocampal sclerosis cannot be detected on MR images in more than 30% of patients with TLE, and the presurgical assessment remains controversial. </P><P> Discussion: In the last years, advanced MR imaging techniques, such as 1H-MRS, DWI, DTI, DSCI, and fMRI, may provide valuable additional information regarding the physiological and metabolic characterization of brain tissue. MR imaging has shifted towards functional and molecular imaging, thus, promising to improve the accuracy regarding the lateralization and the localization of the epileptogenic focus. Additionally, nuclear medicine studies, such as SPECT and PET imaging modalities, have become an asset for the decoding of brain function and activity, and can be diagnostically helpful as well, since they provide valuable data regarding the altered metabolic activity of the seizure foci.

Conclusion:

Overall, advanced MRI, SPECT, and PET imaging techniques are increasingly becoming an essential part of TLE diagnostics, when the epileptogenic area is not identified on structural MRI or when structural MRI, clinical, and electrophysiological findings are not in concordance.

1H-MRS metabolite's ratios show temporal alternation in temporal lobe seizure: Comparison between interictal and postictal phases

PURPOSES

To determine ¹H-MRSI metabolites changes in interictal and postictal phases of patients suffering from mesial temporal lobe epilepsy with hippocampal sclerosis and lateralization of seizure foci.

MATERIALS AND METHODS

MR spectroscopic imaging was performed in 5 adult patients with refractory temporal lobe epilepsy interictally and immediately after the seizure and in 4 adult control subjects. All patients underwent MR imaging and VideoEEG Monitoring.

RESULTS

The results showed statistically significant decreases in N-acetylaspartate/Creatine, N-acetylaspartate/Choline and N-acetylaspartate/(creatine+choline) immediately after ictus in ipsilateral hippocampus as compared with control data and contralateral hippocampus of patients while no statistically significant difference was presented in interictal phase.

CONCLUSION

The present study clearly indicates ¹H-MRS abnormalities following an ictus of temporal lobe epilepsy with metabolite recovery in interictal phase. This finding suggests postictal ¹H-MRS as a possible useful tool to assist in lateralizing and localizing of seizure foci in epileptic patients with structural lesions.

The Relationships Between Quantitative MR Parameters in Hippocampus in Healthy Subjects and Patients With Temporal Lobe Epilepsy

We introduce a new magnetic resonance (MR) method based on a pixel-by-pixel image processing to examine relationships between metabolic and structural processes in the pathologic hippocampus. The method was tested for lateralization of the epileptogenic zone in patients with temporal lobe epilepsy (TLE). Twenty patients with drug-resistant TLE and fifteen healthy controls were examined at 3T. The measurement protocol contained T2-weighted MR images, spectroscopic imaging, diffusion tensor imaging and T2 relaxometry. Correlations between quantitative MR parameters were calculated on a pixel-by-pixel basis using the CORIMA program which enables automated pixel identification in the normal tissue according to control data. All MR parameters changed in the anteroposterior direction in the hippocampus and correlation patterns and their slopes differed between patients and controls. Combinations of T2 relaxation times with metabolite values represent the best biomarkers of the epileptogenic zone. Correlations with mean diffusivity did not provide sufficiently accurate results due to diffusion image distortions. Quantitative MR analysis non-invasively provides a detailed description of hippocampal pathology and may represent complementary tool to the standard clinical protocol. However, the automated processing should be carefully monitored in order to avoid possible errors caused by MR artifacts.

Value of Proton-MR-Spectroscopy in the Diagnosis of Temporal Lobe Epilepsy; Correlation of Metabolite Alterations With Electroencephalography

Background

Epilepsy, a well-known mostly idiopathic neurologic disorder, has to be correctly diagnosed and properly treated. Up to now, several diagnostic approaches have been processed to determine the epileptic focus.

Objectives

The aim of this study was to discover whether proton-MR-spectroscopic imaging (MRSI) aids in the diagnosis of temporal lobe epilepsy in conjunction with classical electroencephalography (EEG) findings.

Patients and Methods

Totally, 70 mesial temporal zones consisting of 39 right hippocampi and 31 left hippocampi of 46 patients (25 male, 21 female) were analyzed by proton MRSI. All patients underwent a clinical neurologic examination, scalp EEG recording and prolonged video EEG monitoring. Partial seizures on the right, left or both sides were recorded in all patients. All patients were under medical treatment and none of the patients underwent amygdalohippocampectomy and similar surgical procedures.

Results

The normal average lactate (Lac), phosphocreatine, N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), myo-inositol, glutamate and glutamine (Glx) peaks and Nacetyl aspartate/Cr, NAA/ Cho + Cr, Cho/Cr ratios were measured from the healthy opposite hippocampi or from the control subjects. The Lac, glutamate and glutamine (Glx), myo-inositol, phosphocreatine and NAA metabolites plus Cho/Cr ratio showed statistical difference between the normal and the epileptic hippocampi. Cho, Cr metabolites plus NAA/Cr, NAA/ Cho + Cr ratios were almost the same between the groups. The sensitivity of Proton-MR-Spectroscopy for lateralization of the epileptic foci in all patients was 96% and the specificity was 50%.

Conclusions

Proton-MRSI can easily be considered as an alternative modality of choice in the diagnosis of temporal lobe epilepsy and in the future; Proton-MR-Spectroscopy may become the most important technique used in epilepsy centers.