Neuroimaging In Epilepsy Research Articles

Neuroimaging of epilepsy

It can sometimes be difficult, when examining surgical specimens, to detect underlying pathological abnormalities that may account for disordered electrical activity. For accurate diagnosis, neuropathologists and clinicians need to share common preoperative information about resected brain tissue. Our group has been able to use structural, functional, and electrophysiological neuroimaging techniques to visualize epileptogenic areas preoperatively. MRI is the most sensitive and useful examination to demonstrate structural abnormalities in patients with partial or localization-related epilepsy. Temporal lobe epilepsy, neoplastic lesions, vascular lesions, and developmental anomaly can all be surgically corrected under favorable circumstances. Functional neuroimaging by positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are useful tools for detecting epileptic foci. PET and SPECT demonstrate subtle functional changes related to epilepsy that ultimately may enable the detection of epileptogenic areas invisible to MRI. PET/SPECT images coregistered to MRI and statistical parametric mappings are of more value for detecting than PET/SPECT images alone. Electrophysiological neuroimaging with analytical software is very useful for visually understanding epileptogenic phenomena. Computerized voltage topographic mappings overlapped on three-dimensional MRI with multichannel electrodes visually demonstrate ictal onset areas and seizure propagation. A new method of multimodal image-guided intervention enables the detection of epileptogenic areas by electrocorticography, PET images, and MRI during epilepsy surgery. Neuropathologists using this method can collect precise structural, functional, and electrophysiological findings on surgical specimens. Neuroimaging of epilepsy is useful for visually clarifying structural, functional, and electrophysiological information on epilepsy patients. This approach is key for diagnosing the background pathological abnormalities of resected tissue.

Prächirurgische Epilepsiediagnostik - Rolle der Bildgebung

Im Rahmen der prächirurgischen Epilepsiediagnostik kommt den bildgebenden Verfahren, vor allem der Kernspintomografie (MRT), eine besondere Bedeutung zu, da der Nachweis einer Läsion die Chancen des Patienten auf einen erfolgreichen Eingriff deutlich erhöht. Die Computertomografie (CCT) spielt bei dieser speziellen Fragestellung so gut wie keine Rolle und wird nur in Einzelfällen bei der Frage nach Verkalkungen eingesetzt. Neuere MRT-Verfahren erlauben die Darstellung des Verlaufs von Bahnen (Diffusions-Tensor-Imaging - DTI) oder die nichtinvasive Analyse von spezifischen Metaboliten (Kernspinspektroskopie - MRS). Neben diesen Verfahren zur Erfassung struktureller Auffälligkeiten werden Verfahren der funktionellen Bildgebung eingesetzt, um interiktale und z.T. auch iktale Veränderungen von Hirnmetabolismus, -durchblutung oder Rezeptorbelegung zu erfassen. Hierbei spielen vor allem die Positronenemissions-Tomografie (PET), die entweder mit Fluoro-Deoxy-Glucose (FDG) oder spezifischen Liganden wie Flumazenil durchgeführt wird, und die Single-Photonen-Emissions-Computertomografie (SPECT) eine Rolle. Spezielle Verfahren ermöglichen die Überlagerung von funktionellen Bildern mit MRT-Aufnahmen und damit eine exakte anatomische Lokalisation von Veränderungen (image fusion). Durch Einsatz funktioneller MRT-Verfahren (fMRT) ist die Identifizierung primärer senso-motorischer Areale sowie der Repräsentation von Sprachfunktion und Gedächtnis möglich.

Book Review

Book Review

Localizing Value of Ictal–Interictal SPECT Analyzed by SPM (ISAS)

The goal of neuroimaging in epilepsy is to localize the region of seizure onset. Single-photon emission computed tomography with tracer injection during seizures (ictal SPECT) is a promising tool for localizing seizures. However, much uncertainty exists about how to interpret late injections, or injections done after seizure end (postictal SPECT). A widely available and objective method is needed to interpret ambiguous ictal and postictal scans, with changes in multiple brain regions. Ictal or postictal SPECT scans were performed by using [99mTc]-labeled hexamethyl-propylene-amine-oxime (HMPAO), and images were analyzed by comparison with interictal scans for each patient. Forty-seven cases of localized epilepsy were studied. We used methods that can be implemented anywhere, based on freely downloadable software and normal SPECT databases (http://spect.yale.edu). Statistical parametric mapping (SPM) was used to localize a single region of seizure onset based on ictal (or postictal) versus interictal difference images for each patient. We refer to this method as ictal-interictal SPECT analyzed by SPM (ISAS). With this approach, ictal SPECT identified a single unambiguous region of seizure onset in 71% of mesial temporal and 83% of neocortical epilepsy cases, even with late injections, and the localization was correct in all (100%) cases. Postictal SPECT, conversely, with injections performed soon after seizures, was very poor at localizing a single region based on either perfusion increases or decreases, often because changes were similar in multiple brain regions. However, measuring which hemisphere overall had more decreased perfusion with postictal SPECT, lateralized seizure onset to the correct side in approximately 80% of cases. ISAS provides a validated and readily available method for epilepsy SPECT analysis and interpretation. The results also emphasize the need to obtain SPECT injections during seizures to achieve unambiguous localization.

IS005 Neuroimaging of epilepsy

IS005 Neuroimaging of epilepsy

Clinical application of neuroimaging in epilepsy

Objective: To evaluate the use of neuroimaging in clinical practice and to assess the prevalence of detected structural abnormalities in epilepsy patients in a clinical set up. Methods: 919 outpatients...

Neuroimaging of epilepsy.

Neuroimaging has an important role in the investigation and treatment of patients with epilepsy. Diagnosis of the underlying substrate in a given patient with epilepsy determines prognosis with higher accuracy than electroencephalography. Neuroimaging techniques include computed tomography (CT) and magnetic resonance imaging (MRI), although CT has a diminished role for diagnosis. MRI is the most appropriate imaging technique in the initial investigation of patients with epilepsy. MRI is the most sensitive technique for the diagnosis of hippocampal sclerosis, tumors, and malformations of cortical development. MRI is also critical for neurosurgical planning. Other imaging techniques such as positron emission tomography (PET) and single photon emission computed tomography are reserved for patients with intractable epilepsy when surgery is contemplated. New developments such as MR spectroscopy, receptor PET, and magnetic source imaging are becoming clinical tools and have the promise of improving diagnosis.

Sailing into the 21st Century: Magnetic Resonance Techniques in Epilepsy

The objective of the IIIrd International MagneticResonance and Epilepsy symposium was to discuss ourpresent knowledge of magnetic resonance (MR) tech-niques and their application to the study of human epi-lepsy. This symposium focused on three essential topics:the enhancement of imaging methods to improve lesiondetection in patients with epilepsy, the application ofmetabolic imaging using MR spectroscopy, and finally,investigation of functional techniques such as functionalMRI (fMRI) combined with EEG and MR diffusion-weighted imaging (DWI) and perfusion-weighted imag-ing techniques to examine functional changes for thedetection of abnormalities in patients with epilepsy.As in any other medical field, knowledge of epilepsy,its diagnosis, and its treatment has developed in succes-sive stages based on clinical observation and intuitioncoupled with technologic advances (1). The preeminenceof EEG as the essential laboratory investigation in thestudy of epilepsy has now been diminished by the intro-duction of modern neuroimaging techniques, particularlyMRI (2–4). This has become even more apparent in thelast few years with the addition of further noninvasiveneuroimaging techniques, such as positron emission to-mography (PET), magnetic resonance spectroscopy(MRS), and magnetic source imaging (MSI), which havepermitted the detection of previously unsuspected pathol-ogy in a large number of patients with epilepsy (2,5–9).Furthermore, these modern neuroimaging techniques havefundamentally influenced the surgical treatment of epilepsybecause the need for invasive electrophysiologic techniqueshas decreased. The role of the lesion in epileptogenesis hasnow been reevaluated and is now well recognized.The importance of MRI is well known to all thosetreating patients with epilepsy. In 1997, the InternationalLeague Against Epilepsy Neuroimaging Commissionpublished the recommendations for neuroimaging of pa-tients with epilepsy (10). Among the recommendationsof the Commission is the one that all patients in whomepilepsy develops should have, in the ideal situation, ahigh-quality MRI. Application of this principle to allpatients with epilepsy, except for those with clear-cutidiopathic generalized epileptic syndromes, should never becompromised. It is clear that the rationale for neuroimagingin epilepsy is identification of pathology that can then dic-tate specific treatment strategies and also identification ofspecific etiologic substrates that can aid in the identificationand classification of specific epileptic syndromes (11,12).MRI can also predict the nature of structural pathology andmay be able to detect the presence of abnormalities distantfrom the putative epileptogenic region (13). This has led toelaboration of the concept of pseudolocalization, and therealization that seizures may appear to originate in oneregion while a structural abnormality may be present inanother region. Finally, there is sufficient evidence thatMRI is the most important predictor for successful surgicaltreatment of temporal lobe epilepsy (14,15).Although current MR techniques are able to detectpathology in many more patients with epilepsy than waspossible a few years ago, a large number of patients withepilepsy have normal MR studies. How can we improvethe detection capability of MR in epilepsy? Enhancedimaging can be achieved with techniques for improvingspatial resolution, image contrast, or both. These goalscan be achieved using phased-array surface coils, imageaveraging, or high-field-strength MRI (16). For example,surface coil imaging can add value to the examination inl50% of patients with normal MRIs in selected patientswith well-localized electroclinical syndromes. Similarly,image averaging can be used to improve the signal-to-noise ratio (SNR) of an MRI by performing several MRIstudies and spatially co-registering and then combiningthe images into a single study (17). Finally, high-fieldMR (3–8 T) can provide high SNR with the potential forimproved imaging. Experimental results show an ap-proximately linear increase in SNR with increasing fieldstrength. The expected increase in SNR with small voxelsize can provide improved imaging details. These tech-niques and examples of their potential applications aredescribed under high-resolution imaging.More than a decade ago, Jack et al. (18,19) introducedto the epilepsy community the use of hippocampal volu-metry for the quantitative determination of hippocampalatrophy in temporal lobe epilepsy. It is now clear thatalthough quantitative volumetric analysis of medial tem-

The value of neuroimaging in diagnosis of epilepsy

Neuroimaging examines the relationship between abnormalities of brain function in epilepsy patients (seizures, impaired cognitive function, psychiatric co-morbidity etc.) and focal or more widespread brain pathology. Since the mid-1980s, the introduction of magnetic resonance imaging (MRI) into clinical neurology has had an impact on the diagnosis, treatment, and research of epilepsy only comparable with the advent of the electroencephalography (EEG) fifty years ago. MRI plays the important role of identifying single or multiple structural lesions responsible for the epileptic seizures. Thus, visual assessment of MRI plays an important role in the differentiation between symptomatic, cryptogenic, and idiopathic epilepsies. This diagnostic step leads to therapeutic decisions (medical treatment vs. surgery) and prognostic evaluations. If a structural lesion identified with MRI correlates with seizure-type, EEG and other clinical data, the likelihood of rendering the patient seizure free with epilepsy surgery is increased. Clinical research into epilepsy uses quantitative MRI (volumetry, T2-relaxometry, magnetic resonance spectroscopy [MRS], voxel-based morphometry) to reduce those cases initially labeled as cryptogenic. Quantitative MRI questions the belief that there is epilepsy without structural brain abnormality at all. Functional MRI (fMRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT) demonstrate changes associated with epileptic seizures and pathology, and changes associated with EEG abnormalities and their cessation. Functional neuroimaging is also used for the identification of functional brain tissue before surgery. Physiologically or pathologically active neuronal tissue is believed to be identified by glucose or oxygen consumption (PET), cerebral blood flow (PET, SPECT, perfusion MRI), and cerebral blood oxygenation (blood oxygenation level dependent [BOLD] fMRI). PET also offers the opportunity to visualize the in-vivo distribution of neuronal receptors which are implicated in the generation, the spread, and the cessation of seizures.

Functional neuroimaging in epilepsy: FDG PET and ictal SPECT.

Epileptogenic zones can be localized by F-18 fluorodeoxyglucose positron emission tomography (FDG PET) and ictal single-photon emission computed tomography(SPECT). In medial temporal lobe epilepsy, the diagnostic sensitivity of FDG PET or ictal SPECT is excellent, however, the sensitivity of MRI is so high that the incremental sensitivity by FDG PET or ictal SPECT has yet to be proven. When MRI findings are ambiguous or normal, or discordant with those of ictal EEG, FDG PET and ictal SPECT are helpful for localization without the need for invasive ictal EEG. In neocortical epilepsy, the sensitivities of FDG PET or ictal SPECT are fair. However, because almost a half of the patients are normal on MRI, FDG PET and ictal SPECT are helpful for localization or at least for lateralization in these non-lesional epilepsies in order to guide the subdural insertion of electrodes. Interpretation of FDG PET has been recently advanced by voxel-based analysis and automatic volume of interest analysis based on a population template. Both analytical methods confirmed the performance of previous visual interpretation results. Ictal SPECT was analyzed using subtraction methods(coregistered to MRI) and voxel-based analysis. Rapidity of injection of tracers, HMPAO versus ECD, and repeated ictal SPECT, which remain the technical issues of ictal SPECT, are detailed.

Magnetic Resonance in Epilepsy.

Part 1 Principles: introduction to epilepsy principles of MR principles of neuroimaging in epilepsy. Part 2 Structural neuroimaging in epilepsy: anatomy of the Hippocamons temporal and frontal lobe epilepsy occipito-parietal epilepsy disorders of the cerebral hemispheres disorders of neuronal migration and organization neurosurgical applications of MRI in epilepsy miscellaneous use of MRI in epilepsy. Part 3 New MR techniques and applications in epilepsy: MR spectroscopy in epilepsy high resolution MR imaging functional MR imaging overview of the role of MR in epilepsy.

Imaging in epilepsy.

Neuroimaging in epilepsy now includes magnetic resonance imaging, positron emission tomography (PET), single-photon emission tomography (SPECT), magnetoencephalography, and magnetic resonance spectroscopy. Recent advances in neuroimaging include improved rates of detection of lesions on structural imaging using quantitative methods, identification of metabolic patterns on functional imaging with PET, and recognition of the value of ictal SPECT in seizure localization.

Neuroimaging of epilepsy, movement disorders, and degenerative diseases

Neuroimaging has improved the understanding, diagnosis, and management of several neurologic diseases and syndromes. Recent advances in the neuroimaging of epilepsy, movement disorders, and degenerative diseases of the nervous system are reviewed. Current research confirms that structural and functional neuroimages each provide unique, clinically useful information in these disorders. Quantification of images improves their diagnostic sensitivity and specificity. Presymptomatic or early neurochemical changes have been identified and followed longitudinally in several neurodegenerative diseases, providing a method for monitoring response to therapeutic intervention and pathophysiologic hypothesis testing. Functional activation studies and receptor-specific radioligands continue to advance our understanding of these disorders. Future methods will take increasing advantage of both the ability to measure neuropharmacological and neurochemical changes in vivo, and the ability to combine images and information obtained with distinct structural and functional neuroimaging modalities.