18F-flumazenil: a γ-aminobutyric acid A-specific PET radiotracer for the localization of drug-resistant temporal lobe epilepsy

In vivo biomarkers of GABAergic function in epileptic rats treated with the GAT-1 inhibitor E2730

OBJECTIVE

E2730, an uncompetitive γ-aminobutyric acid (GABA) transporter-1 (GAT-1) inhibitor, has potent anti-seizure effects in a rodent model of chronic temporal lobe epilepsy, the kainic acid status epilepticus (KASE) rat model. In this study, we examined purported neuroimaging and physiological surrogate biomarkers of the effect of E2730 on brain GABAergic function.

METHODS

We conducted a randomized cross-over study, incorporating 1-week treatments with E2730 (100 mg/kg/day subcutaneous infusion) or vehicle in epileptic post-KASE rats. KASE rats underwent serial 9.4 T magnetic resonance spectroscopy (MRS) measuring GABA and other brain metabolites, [18F]Flumazenil positron emission tomography (PET) quantifying GABAA receptor availability, quantitative electroencephalography (qEEG) and transcranial magnetic stimulation (TMS)-mediated motor activity, as well as continuous video-EEG recording to measure spontaneous seizures during each treatment. Age-matched, healthy control animals treated with E2730 or vehicle were also studied.

RESULTS

E2730 treatment significantly reduced spontaneous seizures, with 8 of 11 animals becoming seizure-free. MRS revealed that E2730-treated animals had significantly reduced taurine levels. [18F]Flumazenil PET imaging revealed no changes in GABA receptor affinity or density during E2730 treatment. The power of gamma frequency oscillations in the EEG was decreased significantly in the auditory cortex and hippocampus of KASE and control rats during E2730 treatment. Auditory evoked gamma frequency power was enhanced by E2730 treatment in the auditory cortex of KASE and healthy controls, but only in the hippocampus of KASE rats. E2730 did not influence motor evoked potentials triggered by TMS.

SIGNIFICANCE

This study identified clinically relevant changes in multimodality imaging and functional purported biomarkers of GABAergic activity during E2730 treatment in epileptic and healthy control animals. These biomarkers could be utilized in clinical trials of E2730 and potentially other GABAergic drugs to provide surrogate endpoints, thereby reducing the cost of such trials.

EANM practice guidelines for an appropriate use of PET and SPECT for patients with epilepsy

Epilepsy is one of the most frequent neurological conditions with an estimated prevalence of more than 50 million people worldwide and an annual incidence of two million. Although pharmacotherapy with anti-seizure medication (ASM) is the treatment of choice, ~30% of patients with epilepsy do not respond to ASM and become drug resistant. Focal epilepsy is the most frequent form of epilepsy. In patients with drug-resistant focal epilepsy, epilepsy surgery is a treatment option depending on the localisation of the seizure focus for seizure relief or seizure freedom with consecutive improvement in quality of life. Beside examinations such as scalp video/electroencephalography (EEG) telemetry, structural, and functional magnetic resonance imaging (MRI), which are primary standard tools for the diagnostic work-up and therapy management of epilepsy patients, molecular neuroimaging using different radiopharmaceuticals with single-photon emission computed tomography (SPECT) and positron emission tomography (PET) influences and impacts on therapy decisions. To date, there are no literature-based praxis recommendations for the use of Nuclear Medicine (NM) imaging procedures in epilepsy. The aims of these guidelines are to assist in understanding the role and challenges of radiotracer imaging for epilepsy; to provide practical information for performing different molecular imaging procedures for epilepsy; and to provide an algorithm for selecting the most appropriate imaging procedures in specific clinical situations based on current literature. These guidelines are written and authorized by the European Association of Nuclear Medicine (EANM) to promote optimal epilepsy imaging, especially in the presurgical setting in children, adolescents, and adults with focal epilepsy. They will assist NM healthcare professionals and also specialists such as Neurologists, Neurophysiologists, Neurosurgeons, Psychiatrists, Psychologists, and others involved in epilepsy management in the detection and interpretation of epileptic seizure onset zone (SOZ) for further treatment decision. The information provided should be applied according to local laws and regulations as well as the availability of various radiopharmaceuticals and imaging modalities.

Assessment of a one-week ketogenic diet on brain glycolytic metabolism and on the status epilepticus stage of a lithium-pilocarpine rat model

The ketogenic diet (KD) has been shown to be effective in refractory epilepsy after long-term administration. However, its interference with short-term brain metabolism and its involvement in the early process leading to epilepsy remain poorly understood. This study aimed to assess the effect of a short-term ketogenic diet on cerebral glucose metabolic changes, before and after status epilepticus (SE) in rats, by using [18F]-FDG PET. Thirty-nine rats were subjected to a one-week KD (KD-rats, n = 24) or to a standard diet (SD-rats, n = 15) before the induction of a status epilepticus (SE) by lithium-pilocarpine administrations. Brain [18F]-FDG PET scans were performed before and 4 h after this induction. Morphological MRIs were acquired and used to spatially normalize the PET images which were then analyzed voxel-wisely using a statistical parametric-based method. Twenty-six rats were analyzed (KD-rats, n = 15; SD-rats, n = 11). The 7 days of the KD were associated with significant increases in the plasma β-hydroxybutyrate level, but with an unchanged glycemia. The PET images, recorded after the KD and before SE induction, showed an increased metabolism within sites involved in the appetitive behaviors: hypothalamic areas and periaqueductal gray, whereas no area of decreased metabolism was observed. At the 4th hour following the SE induction, large metabolism increases were observed in the KD- and SD-rats in areas known to be involved in the epileptogenesis process late-i.e., the hippocampus, parahippocampic, thalamic and hypothalamic areas, the periaqueductal gray, and the limbic structures (and in the motor cortex for the KD-rats only). However, no statistically significant difference was observed when comparing SD and KD groups at the 4th hour following the SE induction. A one-week ketogenic diet does not prevent the status epilepticus (SE) and associated metabolic brain abnormalities in the lithium-pilocarpine rat model. Further explorations are needed to determine whether a significant prevention could be achieved by more prolonged ketogenic diets and by testing this diet in less severe experimental models, and moreover, to analyze the diet effects on the later and chronic stages leading to epileptogenesis.

The Imageable Genome

Understanding human disease on a molecular level, and translating this understanding into targeted diagnostics and therapies are central tenets of molecular medicine1. Realizing this doctrine requires an efficient adaptation of molecular discoveries into the clinic. We present an approach to facilitate this process by describing the Imageable Genome, the part of the human genome whose expression can be assessed via molecular imaging. Using a deep learning-based hybrid human-AI pipeline, we bridge individual genes and their relevance in human diseases with specific molecular imaging methods. Cross-referencing the Imageable Genome with RNA-seq data from over 60,000 individuals reveals diagnostic, prognostic and predictive imageable genes for a wide variety of major human diseases. Having both the critical size and focus to be altered in its expression during the development and progression of any human disease, the Imageable Genome will generate new imaging tools that improve the understanding, diagnosis and management of human diseases.

Identification of the Hepatic Metabolites of Flumazenil and their Kinetic Application in Neuroimaging

Studies of the neurobiological causes of anxiety disorders have suggested that the γ-aminobutyric acid (GABA) system increases synaptic concentrations and enhances the affinity of GABA_A (type A) receptors for benzodiazepine ligands. Flumazenil antagonizes the benzodiazepine-binding site of the GABA/benzodiazepine receptor (BZR) complex in the central nervous system (CNS). The investigation of flumazenil metabolites using liquid chromatography (LC)-tandem mass spectrometry will provide a complete understanding of the in vivo metabolism of flumazenil and accelerate radiopharmaceutical inspection and registration. The main goal of this study was to investigate the use of reversed-phase high performance liquid chromatography (PR-HPLC), coupled with electrospray ionization triple-quadrupole tandem mass spectrometry (ESI-QqQ MS), to identify flumazenil and its metabolites in the hepatic matrix. Carrier-free nucleophilic fluorination with an automatic synthesizer for [¹⁸F]flumazenil, combined with nano-positron emission tomography (NanoPET)/computed tomography (CT) imaging, was used to predict the biodistribution in normal rats. The study showed that 50% of the flumazenil was biotransformed by the rat liver homogenate in 60 min, whereas one metabolite (M1) was a methyl transesterification product of flumazenil. In the rat liver microsomal system, two metabolites were identified (M2 and M3), as their carboxylic acid and hydroxylated ethyl ester forms between 10 and 120 min, respectively. A total of 10-30 min post-injection of [¹⁸F]flumazenil showed an immediate decreased in the distribution ratio observed in the plasma. Nevertheless, a higher ratio of the complete [¹⁸F]flumazenil compound could be used for subsequent animal studies. [¹⁸F] According to in vivo nanoPET/CT imaging and ex vivo biodistribution assays, flumazenil also showed significant effects on GABA_A receptor availability in the amygdala, prefrontal cortex, cortex, and hippocampus in the rat brain, indicating the formation of metabolites. We reported the completion of the biotransformation of flumazenil by the hepatic system, as well as [¹⁸F]flumazenil's potential as an ideal ligand and PET agent for the determination of the GABA_A/BZR complex for multiplex neurological syndromes at the clinical stage.

A Molecular Toolbox of Positron Emission Tomography Tracers for General Anesthesia Mechanism Research

With appropriate radiotracers, positron emission tomography (PET) allows direct or indirect monitoring of the spatial and temporal distribution of anesthetics, neurotransmitters, and biomarkers, making it an indispensable tool for studying the general anesthesia mechanism. In this Perspective, PET tracers that have been recruited in general anesthesia research are introduced in the following order: 1) ¹¹C/¹⁸F-labeled anesthetics, i.e., PET tracers made from inhaled and intravenous anesthetics; 2) PET tracers targeting anesthesia-related receptors, e.g., neurotransmitters and voltage-gated ion channels; and 3) PET tracers for studying anesthesia-related neurophysiological effects and neurotoxicity. The radiosynthesis, pharmacodynamics, and pharmacokinetics of the above PET tracers are mainly discussed to provide a practical molecular toolbox for radiochemists, anesthesiologists, and those who are interested in general anesthesia.

Automated Synthesis of [18F]Flumazenil Application in GABAA Receptor Neuroimaging Availability for Rat Model of Anxiety

Clinical studies have demonstrated that the γ-aminobutyric acid type A (GABAA) receptor complex plays a central role in the modulation of anxiety. Conditioned fear and anxiety-like behaviors have many similarities at the neuroanatomical and pharmacological levels. The radioactive GABA/BZR receptor antagonist, fluorine-18-labeled flumazenil, [18F]flumazenil, behaves as a potential PET imaging agent for the evaluation of cortical damage of the brain in stroke, alcoholism, and for Alzheimer disease investigation. The main goal of our study was to investigate a fully automated nucleophilic fluorination system, with solid extraction purification, developed to replace traditional preparation methods, and to detect underlying expressions of contextual fear and characterize the distribution of GABAA receptors in fear-conditioned rats by [18F]flumazenil. A carrier-free nucleophilic fluorination method using an automatic synthesizer with direct labeling of a nitro-flumazenil precursor was implemented. The semi-preparative high-performance liquid chromatography (HPLC) purification method (RCY = 15–20%) was applied to obtain high purity [18F]flumazenil. Nano-positron emission tomography (NanoPET)/computed tomography (CT) imaging and ex vivo autoradiography were used to analyze the fear conditioning of rats trained with 1–10 tone-foot-shock pairings. The anxiety rats had a significantly lower cerebral accumulation (in the amygdala, prefrontal cortex, cortex, and hippocampus) of fear conditioning. Our rat autoradiography results also supported the findings of PET imaging. Key findings were obtained by developing straightforward labeling and purification procedures that can be easily adapted to commercially available modules for the high radiochemical purity of [18F]flumazenil. The use of an automatic synthesizer with semi-preparative HPLC purification would be a suitable reference method for new drug studies of GABAA/BZR receptors in the future.

Nuclear imaging for localization and surgical outcome prediction in epilepsy: A review of latest discoveries and future perspectives

Background

Epilepsy is one of the most common neurological disorders. Approximately, one-third of patients with epilepsy have seizures refractory to antiepileptic drugs and further require surgical removal of the epileptogenic region. In the last decade, there have been many recent developments in radiopharmaceuticals, novel image analysis techniques, and new software for an epileptogenic zone (EZ) localization.

Objectives

Recently, we provided the latest discoveries, current challenges, and future perspectives in the field of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) in epilepsy.

Methods

We searched for relevant articles published in MEDLINE and CENTRAL from July 2012 to July 2022. A systematic literature review based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis was conducted using the keywords "Epilepsy" and "PET or SPECT." We included both prospective and retrospective studies. Studies with preclinical subjects or not focusing on EZ localization or surgical outcome prediction using recently developed PET radiopharmaceuticals, novel image analysis techniques, and new software were excluded from the review. The remaining 162 articles were reviewed.

Results

We first present recent findings and developments in PET radiopharmaceuticals. Second, we present novel image analysis techniques and new software in the last decade for EZ localization. Finally, we summarize the overall findings and discuss future perspectives in the field of PET and SPECT in epilepsy.

Conclusion

Combining new radiopharmaceutical development, new indications, new techniques, and software improves EZ localization and provides a better understanding of epilepsy. These have proven not to only predict prognosis but also to improve the outcome of epilepsy surgery.

Effective Preparation of [18F]Flumazenil Using Copper-Mediated Late-Stage Radiofluorination of a Stannyl Precursor

(1) Background: [18F]Flumazenil 1 ([18F]FMZ) is an established positron emission tomography (PET) radiotracer for the imaging of the gamma-aminobutyric acid (GABA) receptor subtype, GABAA in the brain. The production of [18F]FMZ 1 for its clinical use has proven to be challenging, requiring harsh radiochemical conditions, while affording low radiochemical yields. Fully characterized, new methods for the improved production of [18F]FMZ 1 are needed. (2) Methods: We investigate the use of late-stage copper-mediated radiofluorination of aryl stannanes to improve the production of [18F]FMZ 1 that is suitable for clinical use. Mass spectrometry was used to identify the chemical by-products that were produced under the reaction conditions. (3) Results: The radiosynthesis of [18F]FMZ 1 was fully automated using the iPhase FlexLab radiochemistry module, affording a 22.2 ± 2.7% (n = 5) decay-corrected yield after 80 min. [18F]FMZ 1 was obtained with a high radiochemical purity (>98%) and molar activity (247.9 ± 25.9 GBq/µmol). (4) Conclusions: The copper-mediated radiofluorination of the stannyl precursor is an effective strategy for the production of clinically suitable [18F]FMZ 1.

Cortical abnormalities of synaptic vesicle protein 2A in focal cortical dysplasia type II identified in vivo with 18F-SynVesT-1 positron emission tomography imaging

PURPOSE

The loss of synaptic vesicle glycoprotein 2A (SV2A) is well established as the major correlate of epileptogenesis in focal cortical dysplasia type II (FCD II), but this has not been directly tested in vivo. In this positron emission tomography (PET) study with the new tracer ¹⁸F-SynVesT-1, we evaluated SV2A abnormalities in patients with FCD II and compared the pattern to ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG).

METHODS

Sixteen patients with proven FCD II and 16 healthy controls were recruited. All FCD II patients underwent magnetic resonance imaging (MRI) and static PET imaging with both ¹⁸F-SynVesT-1 and ¹⁸F-FDG, while the controls underwent MRI and PET with only ¹⁸F-SynVesT-1. Visual assessment of PET images was undertaken. The standardized uptake values (SUVs) of ¹⁸F-SynVesT-1 were computed for regions of interest (ROIs), along with SUV ratio (SUVr) between ROI and centrum semiovale (white matter). Asymmetry indices (AIs) were analyzed between the lesion and the contralateral hemisphere for intersubject comparisons.

RESULTS

Lesions in the brains of FCD II patients had significantly reduced ¹⁸F-SynVesT-1 uptake compared with contralateral regions, and brains of the controls. ¹⁸F-SynVesT-1 PET indicated low lesion uptake in 14 patients (87.5%), corresponding to hypometabolism detected by ¹⁸F-FDG PET, with higher accuracy for lesion localization than MRI (43.8%) (P < 0.05). AI analyses demonstrated that in the lesions, SUVr for each of the radiotracers were not significantly different (P > 0.05), and ¹⁸F-SynVesT-1 SUVr correlated with that of ¹⁸F-FDG across subjects (R² = 0.41, P = 0.008). Subsequent visual ratings indicated that ¹⁸F-SynVesT-1 uptake had a more restricted pattern of reduction than ¹⁸F-FDG uptake in FCD II lesions (P < 0.05).

CONCLUSION

SV2A PET with ¹⁸F-SynVesT-1 shows a higher accuracy for the localization of FCD II lesions than MRI and a more restricted pattern of abnormality than ¹⁸F-FDG PET.

multi-patient dose synthesis of [18F]Flumazenil via a copper-mediated 18F-fluorination

Background

Flumazenil (FMZ) is a functionally silent imidazobenzodiazepine which binds to the benzodiazepine binding site of approximately 75% of the brain γ-aminobutyric acid-A receptors (GABA_ARs). Positron Emission Tomography (PET) imaging of the GABAARs with [¹¹C]FMZ has been used to evidence alterations in neuronal density, to assess target engagement of novel pharmacological agents, and to study disorders such as epilepsy and Huntington’s disease. Despite the potential of FMZ PET imaging the short half-life (t_1/2) of carbon-11 (20 min) has limited the more widespread clinical use of [¹¹C]FMZ. The fluorine-18 (¹⁸F) isotopologue with a longer t_1/2 (110 min) is ideally suited to address this drawback. However, the majority of current radiochemical methods for the synthesis of [¹⁸F]FMZ are non-trivial and low yielding. We report a robust, automated protocol that is good manufacturing practice (GMP) compatible, and yields multi-patient doses of [¹⁸F]FMZ.

Results

The fully automated synthesis was developed on the Trasis AllinOne (AIO) platform using a single-use cassette. [¹⁸F]FMZ was synthesized in a one-step procedure from [¹⁸F]fluoride, via a copper-mediated ¹⁸F-fluorination of a boronate ester precursor. Purification was performed by semi-preparative radio-HPLC and the collected fraction formulated directly into the final product vial. The overall process from start of synthesis to delivery of product is approximately 55 min. Starting with an initial activity of 23.6 ± 5.8 GBq (n = 3) activity yields of [¹⁸F]FMZ were 8.0 ± 1 GBq (n = 3). The synthesis was successfully reproduced at two independent sites, where the product passed quality control release criteria in line with the European Pharmacopoeia standards and ICH Q3D(R1) guidelines to be suitable for human use.

Conclusion

Reported is a fully automated cassette-based synthesis of [¹⁸F]FMZ that is Good Manufacturing Practice (GMP) compatible and produces multi-patient doses of [¹⁸F]FMZ.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41181-022-00158-z.

Longitudinal changes of focal cortical glucose hypometabolism in adults with chronic drug resistant temporal lobe epilepsy

A high proportion of patients with drug-resistant temporal lobe epilepsy (TLE) show focal relative hypometabolism in the region of the epileptogenic zone on [¹⁸F]-Fluorodeoxyglucose positron emission tomography (FDG PET). However, whether focal (hypo)metabolism changes over time has not been well studied. We analysed repeated [¹⁸F]-FDG PET scans of patients with TLE to determine longitudinal changes in glucose metabolism. Adults (n = 16; 9 female, 7 male) diagnosed with drug resistant chronic TLE were assessed. Each patient had two [¹⁸F]-FDG PET scans that were 2-95 months apart. Region-of-interest analysis was performed on MR images onto which PET scans were coregistered to determine the relative [¹⁸F]-FDG uptake (normalised to pons) in the bilateral hippocampi and temporal lobes. Statistical Parametric Mapping analysis investigated global voxel-wise changes in relative metabolism between timepoints. Normalised [¹⁸F]-FDG uptake did not change with time in the ipsilateral (baseline 1.14 ± 0.03, follow-up 1.19 ± -0.04) or contralateral hippocampus (baseline 1.18 ± 0.03, follow-up 1.19 ± 0.03). Uptake in the temporal neocortex also remained stable (ipsilateral baseline 1.35 ± 0.03, follow-up 1.30 ± 0.04; contralateral baseline 1.38 ± 0.04, follow-up 1.33 ± 0.03). The was no relationship between change in uptake on the repeated scans and the time between the scans. SPM analysis showed increases in metabolism in the ipsilateral temporal lobe in 2/16 patients. No areas of decreased metabolism concordant to the epileptogenic zone were identified. [¹⁸F]-FDG uptake showed no significant changes over time in patients with drug-resistant TLE. This suggests that repeating FDG-PET scans in patients with subtle or no hypometabolism is of low clinical yield.

GABAA Receptors in the Mongolian Gerbil: a PET Study Using [18F]Flumazenil to Determine Receptor Binding in Young and Old Animals

PURPOSE

Plastic changes in the central auditory system involving the GABAergic system accompany age-related hearing loss. Such processes can be investigated with positron emission tomography (PET) imaging using [¹⁸F]flumazenil ([¹⁸F]FMZ). Here, [¹⁸F]FMZ PET-based modeling approaches allow a simple and reliable quantification of GABA_A receptor binding capacity revealing regional differences and age-related changes.

PROCEDURES

Sixty-minute list-mode PET acquisitions were performed in 9 young (range 5-6 months) and 11 old (range 39-42 months) gerbils, starting simultaneously with the injection of [¹⁸F]FMZ via femoral vein. Non-displaceable binding potentials (BPnd) with pons as reference region were calculated for auditory cortex (AC), inferior colliculus (IC), medial geniculate body (MGB), somatosensory cortex (SC), and cerebellum (CB) using (i) a two-tissue compartment model (2TCM), (ii) the Logan plot with image-derived blood-input (Logan (BI)), (iii) a simplified reference tissue model (SRTM), and (iv) the Logan reference model (Logan (RT)). Statistical parametric mapping analysis (SPM) comparing young and old gerbils was performed using 3D parametric images for BPnd based on SRTM. Results were verified with in vitro autoradiography from five additional young gerbils. Model assessment included the Akaike information criterion (AIC). Hearing was evaluated using auditory brainstem responses.

RESULTS

BPnd differed significantly between models (p < 0.0005), showing the smallest mean difference between 2TCM as reference and SRTM as simplified procedure. SRTM revealed the lowest AIC values. Both volume of distribution (r² = 0.8793, p = 0.018) and BPnd (r² = 0.8216, p = 0.034) correlated with in vitro autoradiography data. A significant age-related decrease of receptor binding was observed in auditory (AC, IC, MGB) and other brain regions (SC and CB) (p < 0.0001, unpaired t test) being confirmed by SPM using pons as reference (p < 0.0001, uncorrected).

CONCLUSION

Imaging of GABA_A receptor binding capacity in gerbils using [¹⁸F]FMZ PET revealed SRTM as a simple and robust quantification method of GABA_A receptors. Comparison of BPnd in young and old gerbils demonstrated an age-related decrease of GABA_A receptor binding.

Performance of PET imaging for the localization of epileptogenic zone in patients with epilepsy: a meta-analysis

OBJECTIVES

The aim of this meta-analysis was to estimate the clinical use value of ¹¹C-FMZ and ¹⁸F-FDG in PET for the localization of epileptogenic zone and to provide evidence for practitioners' clinical decision-making.

METHODS

We searched PubMed and Embase in a time frame from inception to May 31, 2020. Studies utilizing FMZ or FDG-PET or FDG-PET/MRI used in patients with epilepsy, with EEG or surgical outcomes as the gold standard and corresponding outcomes such as concordance rates of PET or PET/MRI scan compared with reference standard, absolute numbers of participants with true-positive (TP), false-positive (FP), true-negative (TN), and false-negative (FN) results in FDG or FMZ PET. Pooled concordance rates, overall sensitivity, and specificity of ¹¹C-FMZ-PET and ¹⁸F-FDG-PET were calculated.

RESULTS

In total, 44 studies met the inclusion criteria. The pooled concordance rates of FDG-PET, FMZ-PET, and FDG-PET/MRI coregistration compared with reference standard were 0.67 (95% CI: 0.60-0.73), 0.75 (95% CI: 0.57-0.93), and 0.93 (95% CI: 0.89-0.97), respectively. The concordance rate of ¹⁸F-FDG-PET in patients with temporal lobe epilepsy (TLE) was 0.79 (0.63; 0.92). The overall sensitivity and specificity of ¹⁸F-FDG-PET were 0.66 (95% CI: 0.58-0.73) and 0.71 (95% CI: 0.63-0.78), respectively. ¹¹C-FMZ-PET displayed an overall sensitivity of 0.62 (95% CI: 0.49-0.73) and specificity of 0.73 (95% CI: 0.59-0.84).

CONCLUSIONS

Both ¹¹C-FMZ PET and ¹⁸F-FDG PET are the choice of modalities for the localization of epileptogenic zone, especially when coregistered with MRI.

KEY POINTS

• ¹¹C-FMZ-PET may be more helpful than ¹⁸F-FDG-PET in the localization of epilepsy foci. • Coregistration of FDG-PET and MRI is recommended in the localization of epileptogenic zone.

Innovative Molecular Imaging for Clinical Research, Therapeutic Stratification, and Nosography in Neuroscience

Over the past few decades, several radiotracers have been developed for neuroimaging applications, especially in PET. Because of their low steric hindrance, PET radionuclides can be used to label molecules that are small enough to cross the blood brain barrier, without modifying their biological properties. As the use of 11C is limited by its short physical half-life (20 min), there has been an increasing focus on developing tracers labeled with 18F for clinical use. The first such tracers allowed cerebral blood flow and glucose metabolism to be measured, and the development of molecular imaging has since enabled to focus more closely on specific targets such as receptors, neurotransmitter transporters, and other proteins. Hence, PET and SPECT biomarkers have become indispensable for innovative clinical research. Currently, the treatment options for a number of pathologies, notably neurodegenerative diseases, remain only supportive and symptomatic. Treatments that slow down or reverse disease progression are therefore the subject of numerous studies, in which molecular imaging is proving to be a powerful tool. PET and SPECT biomarkers already make it possible to diagnose several neurological diseases in vivo and at preclinical stages, yielding topographic, and quantitative data about the target. As a result, they can be used for assessing patients' eligibility for new treatments, or for treatment follow-up. The aim of the present review was to map major innovative radiotracers used in neuroscience, and explain their contribution to clinical research. We categorized them according to their target: dopaminergic, cholinergic or serotoninergic systems, β-amyloid plaques, tau protein, neuroinflammation, glutamate or GABA receptors, or α-synuclein. Most neurological disorders, and indeed mental disorders, involve the dysfunction of one or more of these targets. Combinations of molecular imaging biomarkers can afford us a better understanding of the mechanisms underlying disease development over time, and contribute to early detection/screening, diagnosis, therapy delivery/monitoring, and treatment follow-up in both research and clinical settings.

Construction of Pepstatin A-Conjugated ultrasmall SPIONs for targeted positive MR imaging of epilepsy-overexpressed P-glycoprotein

Surgical resection of the epileptogenic region is typically regarded to be practical and efficient for complete elimination of intractable seizures, which cannot be simply controlled by anti-epileptic drugs alone. To achieve a precision removal of the epileptogenic region and even a surgical cure, molecular imaging of epilepsy markers is highly essential for non-invasive accurate detection of the epileptogenic region. In this work, a peptide-targeted nanoprobe, based on ultrasmall superparamagnetic iron oxide nanoparticles (USPIONs), PA-USPIONs, was elaborately constructed to enable highly selective delivery and sensitive T₁-weighted positive magnetic resonance (MR) imaging of the epileptogenic region. Especially, Pepstatin A (PA), a small peptide which can specifically target to P-glycoprotein (P-gp) overexpressed at the epileptogenic region in a kainic acid (KA)-induced mice model of seizures, was conjugated onto the surface of PEGylated USPIONs. It has been demonstrated that the as-constructed PA-USPIONs nanoprobes have favorable T₁ contrast enhancement and high r₁ relaxivity compared with the clinically used T₁-MR contrast agent (Gd-DTPA) by systematic in vitro and vivo assessments. Importantly, the toxicity evaluation, especially to brains, was assessed by the histological as well as hematological examinations, demonstrating that the fabricated PA-USPIONs nanoprobes are featured with excellent biocompatibility, guaranteeing the further potential clinical application. This first report on the development of USPIONs as T₁-weighted MR contrast agents for active targeting of the epileptogenic region holds the high potential for precise resection of the according lesion in order to achieve therapeutic, often curative purposes.

Ex vivo characterization of neuroinflammatory and neuroreceptor changes during epileptogenesis using candidate positron emission tomography biomarkers

OBJECTIVE

Identification of patients at risk of developing epilepsy before the first spontaneous seizure may promote the development of preventive treatment providing opportunity to stop or slow down the disease.

METHODS

As development of novel radiotracers and on-site setup of existing radiotracers is highly time-consuming and expensive, we used dual-centre in vitro autoradiography as an approach to characterize the potential of innovative radiotracers in the context of epilepsy development. Using brain slices from the same group of rats, we aimed to characterise the evolution of neuroinflammation and expression of inhibitory and excitatory neuroreceptors during epileptogenesis using translational positron emission tomography (PET) tracers; ¹⁸ F-flumazenil (¹⁸ F-FMZ; GABA_A receptor), ¹⁸ F-FPEB (metabotropic glutamate receptor 5; mGluR5), ¹⁸ F-flutriciclamide (translocator protein; TSPO, microglia activation) and ¹⁸ F-deprenyl (monoamine oxidase B, astroglia activation). Autoradiography images from selected time points after pilocarpine-induced status epilepticus (SE; baseline, 24 and 48 hours, 5, 10 and 15 days and 6 and 12-14 weeks after SE) were normalized to a calibration curve, co-registered to an MRI-based 2D region-of-interest atlas, and activity concentration (Bq/mm² ) was calculated.

RESULTS

In epileptogenesis-associated brain regions, ¹⁸ F-FMZ and ¹⁸ F-FPEB showed an early decrease after SE. ¹⁸ F-FMZ decrease was maintained in the latent phase and further reduced in the chronic epileptic animals, while ¹⁸ F-FPEB signal recovered from day 10, reaching baseline levels in chronic epilepsy. ¹⁸ F-flutriciclamide showed an increase of activated microglia at 24 hours after SE, peaking at 5-15 days and decreasing during the chronic phase. On the other hand, ¹⁸ F-deprenyl autoradiography showed late astrogliosis, peaking in the chronic phase.

SIGNIFICANCE

Autoradiography revealed different evolution of the selected targets during epileptogenesis. Our results suggest an advantage of combined imaging of inter-related targets like glutamate and GABA_A receptors, or microglia and astrocyte activation, in order to identify important interactions, especially when using PET imaging for the evaluation of novel treatments.

Utility of MRI, PET, and ictal SPECT in presurgical evaluation of non-lesional pediatric epilepsy

Children with epilepsy and normal structural MRI pose a particular challenge in localization of epileptic foci for surgical resection. Many of these patients have subtle structural lesions such as mild cortical dysplasia that can be missed by conventional MRI but may become detectable by optimized and advanced MRI acquisitions and post-processing. Specificity of objective analytic techniques such as voxel-based morphometry remains an issue. Combination of MRI with functional imaging approaches can improve the accuracy of detecting epileptogenic brain regions. Analysis of glucose positron emission tomography (PET) combined with high-resolution MRI can optimize detection of hypometabolic cortex associated with subtle cortical malformations and can also enhance presurgical evaluation in children with epileptic spasms. Additional PET tracers may detect subtle epileptogenic lesions and cortex with enhanced specificity in carefully selected subgroups with various etiologies; e.g., increased tryptophan uptake can identify epileptogenic cortical dysplasia in the interictal state. Subtraction ictal SPECT can be also useful to delineate ictal foci in those with non-localizing PET or after failed surgical resection. Presurgical delineation of language and motor cortex and the corresponding white matter tracts is increasingly reliable by functional MRI and DTI techniques; with careful preparation, these can be useful even in young and sedated children. While evidence-based pediatric guidelines are still lacking, the data accumulated in the last decade strongly indicate that multimodal imaging with combined analysis of MRI, PET, and/or ictal SPECT data can optimize the detection of subtle epileptogenic lesions and facilitate seizure-free outcome while minimizing the postsurgical functional deficit in children with normal conventional MRI.

Characterization of Brain Dysfunction Induced by Bacterial Lipopeptides That Alter Neuronal Activity and Network in Rodent Brains

The immunopathological states of the brain induced by bacterial lipoproteins have been well characterized by using biochemical and histological assays. However, these studies have limitations in determining functional states of damaged brains involving aberrant synaptic activity and network, which makes it difficult to diagnose brain disorders during bacterial infection. To address this, we investigated the effect of Pam₃CSK₄ (PAM), a synthetic bacterial lipopeptide, on synaptic dysfunction of female mice brains and cultured neurons in parallel. Our functional brain imaging using PET with [¹⁸F]fluorodeoxyglucose and [¹⁸F] flumazenil revealed that the brain dysfunction induced by PAM is closely aligned to disruption of neurotransmitter-related neuronal activity and functional correlation in the region of the limbic system rather than to decrease of metabolic activity of neurons in the injection area. This finding was verified by in vivo tissue experiments that analyzed synaptic and dendritic alterations in the regions where PET imaging showed abnormal neuronal activity and network. Recording of synaptic activity also revealed that PAM reorganized synaptic distribution and decreased synaptic plasticity in hippocampus. Further study using in vitro neuron cultures demonstrated that PAM decreased the number of presynapses and the frequency of miniature EPSCs, which suggests PAM disrupts neuronal function by damaging presynapses exclusively. We also showed that PAM caused aggregation of synapses around dendrites, which may have caused no significant change in expression level of synaptic proteins, whereas synaptic number and function were impaired by PAM. Our findings could provide a useful guide for diagnosis and treatment of brain disorders specific to bacterial infection.SIGNIFICANCE STATEMENT It is challenging to diagnose brain disorders caused by bacterial infection because neural damage induced by bacterial products involves nonspecific neurological symptoms, which is rarely detected by laboratory tests with low spatiotemporal resolution. To better understand brain pathology, it is essential to detect functional abnormalities of brain over time. To this end, we investigated characteristic patterns of altered neuronal integrity and functional correlation between various regions in mice brains injected with bacterial lipopeptides using PET with a goal to apply new findings to diagnosis of brain disorder specific to bacterial infection. In addition, we analyzed altered synaptic density and function using both in vivo and in vitro experimental models to understand how bacterial lipopeptides impair brain function and network.

Small Molecule PET Tracers in Drug Discovery

The process of discovering and developing a new pharmaceutical is a long, difficult, and risky process that requires numerous resources. Molecular imaging techniques such as PET have recently become a useful tool for making decisions along a drug candidate's development timeline. PET is a translational, noninvasive imaging technique that provides quantitative information about a potential drug candidate and its target at the molecular level. Using this technique provides decisional information to ensure that the right drug candidate is being chosen, for the right target, at the right dose within the right patient population. This review will focus on small molecule PET tracers and how they are used within the drug discovery process. PET provides key information about a drug candidate's pharmacokinetic and pharmacodynamic properties in both preclinical and clinical studies. PET is being used in all phases of the drug discovery and development process, and the goal of these studies are to accelerate the process in which drugs are developed.

Imaging for Adults With Seizures and Epilepsy

PURPOSE OF REVIEW

This article discusses structural and functional neuroimaging findings in patients with seizures and epilepsy. The indications for neuroimaging in these patients and the potential diagnostic utility of these studies are presented.

RECENT FINDINGS

Patients presenting with new seizures typically require urgent imaging to rule out a critical underlying cause. MRI is the structural neuroimaging procedure of choice in individuals with epilepsy. Specific epilepsy protocols should be considered to increase the diagnostic yield of neuroimaging in patients with structural lesions associated with focal or generalized seizures. Common epileptogenic pathologic processes include mesial temporal sclerosis, malformations of cortical development, focal encephalomacia, primary brain tumors, vascular malformations, and neurocysticercosis. Functional neuroimaging studies are usually restricted to the evaluation of patients with drug-resistant focal epilepsy who are being considered for surgical treatment.

SUMMARY

The role of neuroimaging in epilepsy depends on the appropriate clinical indication. In patients without known epilepsy presenting with acute seizures, structural imaging is essential to rule out an underlying etiology (eg, subdural hematoma) that may require a specific therapeutic intervention. In individuals with new or previously uninvestigated epilepsy, MRI serves multiple purposes, including identifying a causative focal lesion and helping to diagnose the epilepsy type. In a significant number of patients with epilepsy, the MRI results are normal or reveal indeterminate findings. For patients with drug-resistant focal epilepsy, functional neuroimaging techniques, such as fludeoxyglucose-positron emission tomography (FDG-PET), ictal single-photon emission computed tomography (SPECT), or functional MRI (fMRI), may assist in surgical planning, especially in patients with MRI-negative epilepsy, whose prognosis for a seizure-free outcome after surgery is worse than for patients with an epileptogenic lesion on structural MRI.

Recent Advances in Radiotracer Imaging Hold Potential for Future Refined Evaluation of Epilepsy in Veterinary Neurology

Non-invasive nuclear imaging by positron emission tomography and single photon emission computed tomography has significantly contributed to epileptic focus localization in human neurology for several decades now. Offering functional insight into brain alterations, it is also of particular relevance for epilepsy research. Access to these techniques for veterinary medicine is becoming more and more relevant and has already resulted in first studies in canine patients. In view of the substantial proportion of drug-refractory epileptic dogs and cats, image-guided epileptic focus localization will be a prerequisite for selection of patients for surgical focus resection. Moreover, radiotracer imaging holds potential for a better understanding of the pathophysiology of underlying epilepsy syndromes as well as to forecast disease risk after epileptogenic brain insults. Importantly, recent advances in epilepsy research demonstrate the suitability and value of several novel radiotracers for non-invasive assessment of neuroinflammation, blood–brain barrier alterations, and neurotransmitter systems. It is desirable that veterinary epilepsy patients will also benefit from these promising developments in the medium term. This paper reviews the current use of radiotracer imaging in the veterinary epilepsy patient and suggests possible future directions for the technique.

Blood-Brain Barrier Driven Pharmacoresistance in Amyotrophic Lateral Sclerosis and Challenges for Effective Drug Therapies

The blood-brain barrier (BBB) is essential for proper neuronal function, homeostasis, and protection of the central nervous system (CNS) microenvironment from blood-borne pathogens and neurotoxins. The BBB is also an impediment for CNS penetration of drugs. In some neurologic conditions, such as epilepsy and brain tumors, overexpression of P-glycoprotein, an efflux transporter whose physiological function is to expel catabolites and xenobiotics from the CNS into the blood stream, has been reported. Recent studies reported that overexpression of P-glycoprotein and increase in its activity at the BBB drives a progressive resistance to CNS penetration and persistence of riluzole, the only drug approved thus far for treatment of amyotrophic lateral sclerosis (ALS), rapidly progressive and mostly fatal neurologic disease. This review will discuss the impact of transporter-mediated pharmacoresistance for ALS drug therapy and the potential therapeutic strategies to improve the outcome of ALS clinical trials and efficacy of current and future drug treatments.

Selected PET Radioligands for Ion Channel Linked Neuroreceptor Imaging: Focus on GABA, NMDA and nACh Receptors

Positron emission tomography (PET) neuroimaging of ion channel linked receptors is a developing area of preclinical and clinical research. The present review focuses on recent advances with radiochemistry, preclinical and clinical PET imaging studies of three receptors that are actively pursued in neuropsychiatric drug discovery: namely the γ-aminobutyric acid-benzodiazapine (GABA) receptor, nicotinic acetylcholine receptor (nAChR), and N-methyl-D-aspartate (NMDA) receptor. Recent efforts to develop new PET radioligands for these targets with improved brain uptake, selectivity, stability and pharmacokinetics are highlighted.

Synaptic and Neuronal Autoantibody-Associated Psychiatric Syndromes: Controversies and Hypotheses

Autoimmune encephalitis (AE) mediated by antibodies against synaptic and neuronal surface targets frequently presents with a psychiatric syndrome. In these patients, removal of autoantibodies treats the disease and outcomes are closely linked to early intervention. The discovery of these autoantibodies in isolated psychiatric syndromes has raised the possibility that these patients may derive similar benefits from immunotherapy, a potentially transformational approach to the treatment of mental illness. Although open-label case series suggest impressive therapeutic outcomes, the pathological relevance of these autoantibodies outside of canonical presentations is debated. The advent of diagnostic criteria for AE attempts to facilitate its prompt identification but risks prematurely neglecting the potential scientific and clinical significance of isolated syndromes that do not satisfy these criteria. Here, we propose using a syndrome-level taxonomy that has occasional, but not necessary, overlap with AE: synaptic and neuronal autoantibody-associated psychiatric syndromes or "SNAps". This will prevent confusion with AE and act heuristically to promote active investigation into this rare example of psychopathology defined on a molecular level. We suggest that this concept would have application in other autoantibody-associated syndromes including seizure, cognitive, and movement disorders, in which similar issues arise. We review putative direct and indirect mechanisms and outline experimentally testable hypotheses that would help to determine prospectively in whom autoantibody detection is relevant, and as important, in whom it is not. We summarize a pragmatic approach to autoantibody testing and management in severe mental illness in order to promptly diagnose AE and advocate a research-orientated experimental medicine paradigm for SNAps, where there is greater equipoise. We conclude that SNAps remains a nascent area of clinical neuroscience with great potential and in ongoing need of psychiatry-led basic and clinical research.

Advances of Molecular Imaging in Epilepsy

Positron emission tomography (PET) is a neuroimaging method that offers insights into the molecular functioning of a human brain. It has been widely used to study metabolic and neurotransmitter abnormalities in people with epilepsy. This article reviews the development of several PET radioligands and their application in studying the molecular mechanisms of epilepsy. Over the last decade, tracers binding to serotonin and γ-aminobutyric acid (GABA) receptors have been used to delineate the location of the epileptic focus. PET studies have examined the role of opioids, cannabinoids, acetylcholine, and dopamine in modulating neuronal hyperexcitability and seizure termination. In vivo analyses of drug transporters, e.g., P-glycoprotein, have increased our understanding of pharmacoresistance that could inform new therapeutic strategies. Finally, PET experiments targeting neuroinflammation and glutamate receptors might guide the development of novel biomarkers of epileptogenesis.

(18)F-fluorodeoxyglucose and (18)F-flumazenil positron emission tomography in patients with refractory epilepsy

BACKGROUND

Epilepsy is a neurological disorder characterized by epileptic seizures as a result of excessive neuronal activity in the brain. Approximately 65 million people worldwide suffer from epilepsy; 20-40% of them are refractory to medication therapy. Early detection of disease is crucial in the management of patients with epilepsy. Correct localization of the ictal onset zone is associated with a better surgical outcome. The modern non-invasive techniques used for structural-functional localization of the seizure focus includes electroencephalography (EEG) monitoring, magnetic resonance imaging (MRI), single photon emission tomography/computed tomography (SPECT/CT) and positron emission tomography/computed tomography (PET/CT). PET/CT can predict surgical outcome in patients with refractory epilepsy. The aim of the article is to review the current role of routinely used tracer 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) as well as non routinely used (18)F-Flumazenil ((18)F-FMZ) tracers PET/CT in patients with refractory epilepsy.

CONCLUSIONS

Functional information delivered by PET and the morphologic information delivered by CT or MRI are essential in presurgical evaluation of epilepsy. Nowadays (18)F-FDG PET/CT is a routinely performed imaging modality in localization of the ictal onset zone in patients with refractory epilepsy who are unresponsive to medication therapy. Unfortunately, (18)F-FDG is not an ideal PET tracer regarding the management of patients with epilepsy: areas of glucose hypometabolism do not correlate precisely with the proven degree of change within hippocampal sclerosis, as observed by histopathology or MRI. Benzodiazepine-receptor imaging is a promising alternative in nuclear medicine imaging of epileptogenic focus. The use of (11)C-FMZ in clinical practice has been limited by its short half-life and necessitating an on-site cyclotron for production. Therefore, (18)F-FMZ might be established as one of the tracers of choice for patients with refractory epilepsy because of better sensitivity and anatomical resolution.

Brain imaging in the assessment for epilepsy surgery

Brain imaging has a crucial role in the presurgical assessment of patients with epilepsy. Structural imaging reveals most cerebral lesions underlying focal epilepsy. Advances in MRI acquisitions including diffusion-weighted imaging, post-acquisition image processing techniques, and quantification of imaging data are increasing the accuracy of lesion detection. Functional MRI can be used to identify areas of the cortex that are essential for language, motor function, and memory, and tractography can reveal white matter tracts that are vital for these functions, thus reducing the risk of epilepsy surgery causing new morbidities. PET, SPECT, simultaneous EEG and functional MRI, and electrical and magnetic source imaging can be used to infer the localisation of epileptic foci and assist in the design of intracranial EEG recording strategies. Progress in semi-automated methods to register imaging data into a common space is enabling the creation of multimodal three-dimensional patient-specific datasets. These techniques show promise for the demonstration of the complex relations between normal and abnormal structural and functional data and could be used to direct precise intracranial navigation and surgery for individual patients.

Neuroimaging of epilepsy

Imaging is pivotal in the evaluation and management of patients with seizure disorders. Elegant structural neuroimaging with magnetic resonance imaging (MRI) may assist in determining the etiology of focal epilepsy and demonstrating the anatomical changes associated with seizure activity. The high diagnostic yield of MRI to identify the common pathological findings in individuals with focal seizures including mesial temporal sclerosis, vascular anomalies, low-grade glial neoplasms and malformations of cortical development has been demonstrated. Positron emission tomography (PET) is the most commonly performed interictal functional neuroimaging technique that may reveal a focal hypometabolic region concordant with seizure onset. Single photon emission computed tomography (SPECT) studies may assist performance of ictal neuroimaging in patients with pharmacoresistant focal epilepsy being considered for neurosurgical treatment. This chapter highlights neuroimaging developments and innovations, and provides a comprehensive overview of the imaging strategies used to improve the care and management of people with epilepsy.

Recent imaging advances in neurology

Over the recent years, the application of neuroimaging techniques such as magnetic resonance imaging (MRI) and positron emission tomography (PET) has considerably advanced the understanding of complex neurological disorders. PET is a powerful molecular imaging tool, which investigates the distribution and binding of radiochemicals attached to biologically relevant molecules; as such, this technique is able to give information on biochemistry and metabolism of the brain in health and disease. MRI uses high intensity magnetic fields and radiofrequency pulses to provide structural and functional information on tissues and organs in intact or diseased individuals, including the evaluation of white matter integrity, grey matter thickness and brain perfusion. The aim of this article is to review the most recent advances in neuroimaging research in common neurological disorders such as movement disorders, dementia, epilepsy, traumatic brain injury and multiple sclerosis, and to evaluate their contribution in the diagnosis and management of patients.

Neuroimaging of drug resistance in epilepsy

PURPOSE OF REVIEW

Drug resistance is an important clinical problem: it is associated with higher rates of somatic and psychiatric comorbidities and cognitive/memory decline, with seizures being just the 'tip of the iceberg'. This review summarizes recent developments in imaging research, focusing specifically on the functional consequence of chronic epilepsies and mechanisms of drug resistance, restricted to work published in 2013.

RECENT FINDINGS

Functional imaging approaches reliably identify underlying specific networks in patients with different epileptic syndromes, show specific responses to certain antiepileptic drugs and differentiate between responder and nonresponder. Functional MRI (fMRI) and the intracarotid amobarbital test (IAT) are generally congruent, but fMRI may be more sensitive than IAT to right hemisphere language processing. In addition, memory fMRI supports the functional adequacy of ipsilateral structures rather than functional reserve of the contralateral hemisphere. There is further evidence from group analysis of fMRI data for a node within the ipsilateral piriform cortex to be important for seizure modulation in focal refractory epilepsies of different cortical origin. Molecular imaging with verapamil-PET identifies P-glycprotein overexpression as a mechanism contributing to drug resistance in individual patients.

SUMMARY

Neuroimaging in epilepsy has progressed from correlations with demographic, semiologic, neuropsychological and other observational data primarily in patients undergoing presurgical investigations to imaging network connectivity changes in epilepsy syndromes, and testing specific mechanisms underlying drug-resistant epilepsy.

Advanced Imaging Techniques in the Diagnosis of Nonlesional Epilepsy: MRI, MRS, PET, and SPECT

Once patients have a diagnosis of localization related epilepsy (LRE), it is critical to further classify those patients into lesional or nonlesional for treatment and prognostic reasons. An individual with LRE may be classified as nonlesional for two reasons: 1) a lesion may not exist; that is, the structural abnormality that gives rise to seizures may be at the channel level or be spatially distributed in such a way that it would not be accurately termed a lesion, or 2) a lesion exists but is so subtle that standard clinical imaging is not sensitive enough to discriminate between the lesion and surrounding healthy brain tissue. As with any technology and disease process, this definition is dynamic, as we know that future imaging techniques will be developed and new disease mechanisms will be discovered, making detection of the epileptogenic underlying abnormality an ever-changing target.

Workshop on Neurobiology of Epilepsy appraisal: new systemic imaging technologies to study the brain in experimental models of epilepsy

Modern functional neuroimaging provides opportunities to visualize activity of the entire brain, making it an indispensable diagnostic tool for epilepsy. Various forms of noninvasive functional neuroimaging are now also being performed as research tools in animal models of epilepsy and provide opportunities for parallel animal/human investigations into fundamental mechanisms of epilepsy and identification of epilepsy biomarkers. Recent animal studies of epilepsy using positron emission tomography, tractography, and functional magnetic resonance imaging were reviewed. Epilepsy is an abnormal emergent property of disturbances in neuronal networks which, even for epilepsies characterized by focal seizures, involve widely distributed systems, often in both hemispheres. Functional neuroimaging in animal models now provides opportunities to examine neuronal disturbances in the whole brain that underlie generalized and focal seizure generation as well as various types of epileptogenesis. Tremendous advances in understanding the contribution of specific properties of widely distributed neuronal networks to both normal and abnormal human behavior have been provided by current functional neuroimaging methodologies. Successful application of functional neuroimaging of the whole brain in the animal laboratory now permits investigations during epileptogenesis and correlation with deep brain electroencephalography (EEG) activity. With the continuing development of these techniques and analytical methods, the potential for future translational research on epilepsy is enormous. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

Simulation-based optimisation of the PET data processing for partial saturation approach protocols

Positron emission tomography (PET) with [(11)C]Raclopride is an important tool for studying dopamine D2 receptor expression in vivo. [(11)C]Raclopride PET binding experiments conducted using the Partial Saturation Approach (PSA) allow the estimation of receptor density (B(avail)) and the in vivo affinity appK(D). The PSA is a simple, single injection, single scan experimental protocol that does not require blood sampling, making it ideal for use in longitudinal studies. In this work, we generated a complete Monte Carlo simulated PET study involving two groups of scans, in between which a biological phenomenon was inferred (a 30% decrease of B(avail)), and used it in order to design an optimal data processing chain for the parameter estimation from PSA data. The impact of spatial smoothing, noise removal and image resolution recovery technique on the statistical detection was investigated in depth. We found that image resolution recovery using iterative deconvolution of the image with the system point spread function associated with temporal data denoising greatly improves the accuracy and the statistical reliability of detecting the imposed phenomenon. Before optimisation, the inferred B(avail) variation between the two groups was underestimated by 42% and detected in 66% of cases, while a false decrease of appK(D) by 13% was detected in more than 11% of cases. After optimisation, the calculated B(avail) variation was underestimated by only 3.7% and detected in 89% of cases, while a false slight increase of appK(D) by 3.7% was detected in only 2% of cases. We found during this investigation that it was essential to adjust a factor that accounts for difference in magnitude between the non-displaceable ligand concentrations measured in the target and in the reference regions, for different data processing pathways as this ratio was affected by different image resolutions.

Combination of PET and Magnetoencephalography in the Presurgical Assessment of MRI-Negative Epilepsy

Despite major advances in neuroimaging, no lesion is visualized on MRI in up to a quarter of patients with drug-resistant focal epilepsy presenting for presurgical evaluation. These patients demonstrate poorer surgical outcomes than those with lesion seen on MRI. Accurate localization of the seizure onset zone (SOZ) is more difficult in MRI-negative patients and often requires invasive EEG recordings. Positron emission tomography (PET) and magnetoencephalography (MEG) have been proposed as clinically relevant tools to localize the SOZ prior to intracranial EEG recordings. However, there is no consensus regarding the optimal gold standard that should be used for assessing the performance of these presurgical investigations. Here, we review the current knowledge concerning the usefulness of PET and MEG for presurgical assessment of MRI-negative epilepsy. Beyond the individual diagnostic performance of MEG and of different PET tracers, including [(18)F]-fluorodeoxyglucose, [(11)C]flumazenil, and markers of 5-HT1A receptors, recent data suggest that the combination of PET and MEG might provide greater sensitivity and specificity than that of each of the two individual tests in patients with normal MRI.