Integrating and optimizing tonabersat in standard glioblastoma therapy: A preclinical study

Glioblastoma (GB), a highly aggressive primary brain tumor, presents a poor prognosis despite the current standard therapy, including radiotherapy and temozolomide (TMZ) chemotherapy. Tumor microtubes involving connexin 43 (Cx43) contribute to glioma progression and therapy resistance, suggesting Cx43 inhibition as a potential treatment strategy. This research aims to explore the adjuvant potential of tonabersat, a Cx43 gap junction modulator and blood-brain barrier-penetrating compound, in combination with the standard of care for GB. In addition, different administration schedules and timings to optimize tonabersat's therapeutic window are investigated. The F98 Fischer rat model will be utilized to investigate tonabersat's impact in a clinically relevant setting, by incorporating fractionated radiotherapy (three fractions of 9 Gy) and TMZ chemotherapy (29 mg/kg). This study will evaluate tonabersat's impact on tumor growth, survival, and treatment response through advanced imaging (CE T1-w MRI) and histological analysis. Results show extended survival in rats receiving tonabersat with standard care, highlighting its adjuvant potential. Daily tonabersat administration, both preceding and following radiotherapy, emerges as a promising approach for maximizing survival outcomes. The study suggests tonabersat's potential to reduce tumor invasiveness, providing a new avenue for GB treatment. In conclusion, this preclinical investigation highlights tonabersat's potential as an effective adjuvant treatment for GB, and its established safety profile from clinical trials in migraine treatment presents a promising foundation for further exploration.

An improved F98 glioblastoma rat model to evaluate novel treatment strategies incorporating the standard of care

Glioblastoma (GB) is the most common and malignant primary brain tumor in adults with a median survival of 12-15 months. The F98 Fischer rat model is one of the most frequently used animal models for GB studies. However, suboptimal inoculation leads to extra-axial and extracranial tumor formations, affecting its translational value. We aim to improve the F98 rat model by incorporating MRI-guided (hypo)fractionated radiotherapy (3 x 9 Gy) and concomitant temozolomide chemotherapy, mimicking the current standard of care. To minimize undesired tumor growth, we reduced the number of inoculated cells (starting from 20 000 to 500 F98 cells), slowed the withdrawal of the syringe post-inoculation, and irradiated the inoculation track separately. Our results reveal that reducing the number of F98 GB cells correlates with a diminished risk of extra-axial and extracranial tumor growth. However, this introduces higher variability in days until GB confirmation and uniformity in GB growth. To strike a balance, the model inoculated with 5000 F98 cells displayed the best results and was chosen as the most favorable. In conclusion, our improved model offers enhanced translational potential, paving the way for more accurate and reliable assessments of novel adjuvant therapeutic approaches for GB.

Assessment of the effect of therapy in a rat model of glioblastoma using [18F]FDG and [18F]FCho PET compared to contrast-enhanced MRI

Objective

We investigated the potential of [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) and [¹⁸F]Fluoromethylcholine ([¹⁸F]FCho) PET, compared to contrast-enhanced MRI, for the early detection of treatment response in F98 glioblastoma (GB) rats.

Methods

When GB was confirmed on T2- and contrast-enhanced T1-weighted MRI, animals were randomized into a treatment group (n = 5) receiving MRI-guided 3D conformal arc micro-irradiation (20 Gy) with concomitant temozolomide, and a sham group (n = 5). Effect of treatment was evaluated by MRI and [¹⁸F]FDG PET on day 2, 5, 9 and 12 post-treatment and [¹⁸F]FCho PET on day 1, 6, 8 and 13 post-treatment. The metabolic tumor volume (MTV) was calculated using a semi-automatic thresholding method and the average tracer uptake within the MTV was converted to a standard uptake value (SUV).

Results

To detect treatment response, we found that for [¹⁸F]FDG PET (SUV_mean x MTV) is superior to MTV only. Using (SUV_mean x MTV), [¹⁸F]FDG PET detects treatment effect starting as soon as day 5 post-therapy, comparable to contrast-enhanced MRI. Importantly, [¹⁸F]FDG PET at delayed time intervals (240 min p.i.) was able to detect the treatment effect earlier, starting at day 2 post-irradiation. No significant differences were found at any time point for both the MTV and (SUV_mean x MTV) of [¹⁸F]FCho PET.

Conclusions

Both MRI and particularly delayed [¹⁸F]FDG PET were able to detect early treatment responses in GB rats, whereas, in this study this was not possible using [¹⁸F]FCho PET. Further comparative studies should corroborate these results and should also include (different) amino acid PET tracers.

Automated MRI based pipeline for segmentation and prediction of grade, IDH mutation and 1p19q co-deletion in glioma

In the WHO glioma classification guidelines grade (glioblastoma versus lower-grade glioma), IDH mutation and 1p/19q co-deletion status play a central role as they are important markers for prognosis and optimal therapy planning. Currently, diagnosis requires invasive surgical procedures. Therefore, we propose an automatic segmentation and classification pipeline based on routinely acquired pre-operative MRI (T1, T1 postcontrast, T2 and/or FLAIR). A 3D U-Net was designed for segmentation and trained on the BraTS 2019 training dataset. After segmentation, the 3D tumor region of interest is extracted from the MRI and fed into a CNN to simultaneously predict grade, IDH mutation and 1p19q co-deletion. Multi-task learning allowed to handle missing labels and train one network on a large dataset of 628 patients, collected from The Cancer Imaging Archive and BraTS databases. Additionally, the network was validated on an independent dataset of 110 patients retrospectively acquired at the Ghent University Hospital (GUH). Segmentation performance calculated on the BraTS validation set shows an average whole tumor dice score of 90% and increased robustness to missing image modalities by randomly excluding input MRI during training. Classification area under the curve scores are 93%, 94% and 82% on the TCIA test data and 94%, 86% and 87% on the GUH data for grade, IDH and 1p19q status respectively. We developed a fast, automatic pipeline to segment glioma and accurately predict important (molecular) markers based on pre-therapy MRI.

Network diffusion modeling predicts neurodegeneration in traumatic brain injury

Objective

Traumatic brain injury (TBI) is a heterogeneous disease with multiple neurological deficits that evolve over time. It is also associated with an increased incidence of neurodegenerative diseases. Accordingly, clinicians need better tools to predict a patient’s long‐term prognosis.

Methods

Diffusion‐weighted and anatomical MRI data were collected from 17 adolescents (mean age = 15y8mo) with moderate‐to‐severe TBI and 19 healthy controls. Using a network diffusion model (NDM), we examined the effect of progressive deafferentation and gray matter thinning in young TBI patients. Moreover, using a novel automated inference method, we identified several injury epicenters in order to determine the neural degenerative patterns in each TBI patient.

Results

We were able to identify the subject‐specific patterns of degeneration in each patient. In particular, the hippocampus, temporal cortices, and striatum were frequently found to be the epicenters of degeneration across the TBI patients. Orthogonal transformation of the predicted degeneration, using principal component analysis, identified distinct spatial components in the temporal–hippocampal network and the cortico‐striatal network, confirming the vulnerability of these networks to injury. The NDM model, best predictive of the degeneration, was significantly correlated with time since injury, indicating that NDM can potentially capture the pathological progression in the chronic phase of TBI.

Interpretation

These findings suggest that network spread may help explain patterns of distant gray matter thinning, which would be consistent with Wallerian degeneration of the white matter connections (i.e., “diaschisis”) from diffuse axonal injuries and multifocal contusive injuries, and the neurodegenerative patterns of abnormal protein aggregation and transmission, which are hallmarks of brain changes in TBI. NDM approaches could provide highly subject‐specific biomarkers relevant for disease monitoring and personalized therapies in TBI.

Adjuvant therapeutic potential of tonabersat in the standard treatment of glioblastoma: A preclinical F98 glioblastoma rat model study

Purpose

Even with an optimal treatment protocol, the median survival of glioblastoma (GB) patients is only 12–15 months. Hence, there is need for novel effective therapies that improve survival outcomes. Recent evidence suggests an important role for connexin (Cx) proteins (especially Cx43) in the microenvironment of malignant glioma. Cx43-mediated gap junctional communication has been observed between tumor cells, between astrocytes and between tumor cells and astrocytes. Therefore, gap junction directed therapy using a pharmacological suppressor or modulator, such as tonabersat, could be a promising target in the treatment of GB. In this preclinical study, we evaluated the possible therapeutic potential of tonabersat in the F98 model.

Procedures

Female Fischer rats were inoculated with ± 25.000 F98 tumor cells in the right frontal lobe. Eight days post-inoculation contrast-enhanced T1-weighted (CE-T1w) magnetic resonance (MR) images were acquired to confirm tumor growth in the brain. After tumor confirmation, rats were randomized into a Control Group, a Connexin Modulation Group (CM), a Standard Medical Treatment Group (ST), and a Standard Medical Treatment with adjuvant Connexin Modulation Group (STCM). To evaluate therapy response, T2-weighted (T2w) and CE-T1w sequences were acquired at several time points. Tumor volume analysis was performed on CE-T1w images and statistical analysis was performed using a linear mixed model.

Results

Significant differences in estimated geometric mean tumor volumes were found between the ST Group and the Control Group and also between the STCM Group and the Control Group. In addition, significant differences in estimated geometric mean tumor volumes between the ST Group and the STCM Group were demonstrated. No significant differences in estimated geometric mean tumor volumes were found between the Control Group and the CM Group.

Conclusion

Our results demonstrate a therapeutic potential of tonabersat for the treatment of GB when used in combination with radiotherapy and temozolomide chemotherapy.

Prefrontal and temporal cortical thickness in adolescents with traumatic brain injury

AIM

To investigate the impact of traumatic injury on the developing prefrontal-temporal adolescent cortex, and correlated brain structural measures with neurocognitive functioning.

METHOD

Nineteen adolescents (12 males, 7 females, age range: 11-17y, mean 15y 8mo, standard deviation 1y 7mo, median 15y 11mo) with traumatic brain injury (TBI) were included. Cortical thickness of frontal and temporal lobes was assessed using magnetic resonance imaging. We correlated cortical thickness of prefrontal-temporal regions with age, time since injury, and neurocognitive functioning, and compared these results with a matched control cohort without TBI.

RESULTS

We found thinner prefrontal (p=0.039) and temporal cortices (p=0.002) in adolescents with TBI compared to typically developing children. Furthermore, significant age effect was observed on the prefrontal (r=-0.75, p=0.003) and temporal (r=-0.66, p=0.013) cortical thickness in typically developing adolescents, but not in adolescents with TBI. Executive function (measured using the Behaviour Rating Inventory of Executive Function questionnaire, with lower scores meaning higher functioning) was correlated with prefrontal cortical thickness in typically developing adolescents (r=0.72, p=0.009). Opposite trends were found for correlations between cortical thickness and executive function in the TBI and control cohort.

INTERPRETATION

Structural maturation in typically developing adolescents correlates with functional development: the older the adolescent, the thinner the prefrontal cortex, the better executive function. In adolescents with TBI we observed an opposite trend, that appeared significantly different from the control group: the thinner the prefrontal and temporal cortex, the worse executive functioning.

WHAT THIS PAPER ADDS

Cortical thickness is negatively correlated with age in typically developing adolescents. Prefrontal cortex thickness correlates negatively with executive function in typically developing adolescents. Correlations between cortical thickness and executive functioning rise for adolescents without traumatic brain injury (TBI). Correlations between cortical thickness and executive functioning fall for adolescents with TBI. Adolescents with TBI have a long-term impairment of adaptive functioning in daily living.

Technical feasibility of [18F]FET and [18F]FAZA PET guided radiotherapy in a F98 glioblastoma rat model

Background

Glioblastoma (GB) is the most common primary malignant brain tumor. Standard medical treatment consists of a maximal safe surgical resection, subsequently radiation therapy (RT) and chemotherapy with temozolomide (TMZ). An accurate definition of the tumor volume is of utmost importance for guiding RT. In this project we investigated the feasibility and treatment response of subvolume boosting to a PET-defined tumor part.

Method

F98 GB cells inoculated in the rat brain were imaged using T2- and contrast-enhanced T1-weighted (T1w) MRI. A dose of 20 Gy (5 × 5 mm²) was delivered to the target volume delineated based on T1w MRI for three treatment groups. Two of those treatment groups received an additional radiation boost of 5 Gy (1 × 1 mm²) delivered to the region either with maximum [¹⁸F]FET or [¹⁸F]FAZA PET tracer uptake, respectively. All therapy groups received intraperitoneal (IP) injections of TMZ. Finally, a control group received no RT and only control IP injections. The average, minimum and maximum dose, as well as the D₉₀-, D₅₀- and D₂- values were calculated for nine rats using both RT plans. To evaluate response to therapy, follow-up tumor volumes were delineated based on T1w MRI.

Results

When comparing the dose volume histograms, a significant difference was found exclusively between the D₂-values. A significant difference in tumor growth was only found between active therapy and sham therapy respectively, while no significant differences were found when comparing the three treatment groups.

Conclusion

In this study we showed the feasibility of PET guided subvolume boosting of F98 glioblastoma in rats. No evidence was found for a beneficial effect regarding tumor response. However, improvements for dose targeting in rodents and studies investigating new targeted drugs for GB treatment are mandatory.

Electronic supplementary material

The online version of this article (10.1186/s13014-019-1290-4) contains supplementary material, which is available to authorized users.

Is diffuse axonal injury on susceptibility weighted imaging a biomarker for executive functioning in adolescents with traumatic brain injury?

Traumatic brain injury (TBI) is a heterogeneous disorder in which diffuse axonal injury (DAI) is an important component contributing to executive dysfunction. During adolescence, developing brain networks are especially vulnerable to acceleration-deceleration forces. We aimed to examine the correlation between DAI (number and localization) and executive functioning in adolescents with TBI. We recruited 18 adolescents with a mean age of 15y8m (SD = 1y7m), averaging 2.5 years after sustaining a moderate-to-severe TBI with documented DAI. Susceptibility Weighted Imaging sequence was administered to localize the DAI lesions. The adolescents performed a neurocognitive test-battery, addressing different aspects of executive functioning (working memory, attention, processing speed, planning ability) and their parents completed the Behavior Rating Inventory of Executive Function (BRIEF) - questionnaire. Executive performance of the TBI-group was compared with an age and gender matched control group of typically developing peers. Based on these results we focused on the Stockings of Cambridge test and the BRIEF to correlate with the total number and location of DAI. Results revealed that the anatomical distribution of DAI, especially in the corpus callosum and the deep brain nuclei, may have more implications for executive functioning than the total amount of DAI in adolescents. Results of this study may help guide targeted rehabilitation to redirect the disturbed development of executive function in adolescents with TBI.

New fluoroethyl phenylalanine analogues as potential LAT1-targeting PET tracers for glioblastoma

The use of O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) as a positron emission tomography (PET) tracer for brain tumor imaging might have some limitations because of the relatively low affinity for the L-type amino acid transporter 1 (LAT1). To assess the stereospecificity and evaluate the influence of aromatic ring modification of phenylalanine LAT1 targeting tracers, six different fluoroalkylated phenylalanine analogues were synthesized. After in vitro Ki determination, the most promising compound, 2-[18F]-2-fluoroethyl-L-phenylalanine (2-[18F]FELP), was selected for further evaluation and in vitro comparison with [18F]FET. Subsequently, 2-[18F]FELP was assessed in vivo and compared with [18F]FET and [18F]FDG in a F98 glioblastoma rat model. 2-[18F]FELP showed improved in vitro characteristics over [18F]FET, especially when the affinity and specificity for system L is concerned. Based on our results, 2-[18F]FELP is a promising new PET tracer for brain tumor imaging.

The Path Toward PET-Guided Radiation Therapy for Glioblastoma in Laboratory Animals: A Mini Review

Glioblastoma is the most aggressive and malignant primary brain tumor in adults. Despite the current state-of-the-art treatment, which consists of maximal surgical resection followed by radiation therapy, concomitant, and adjuvant chemotherapy, progression remains rapid due to aggressive tumor characteristics. Several new therapeutic targets have been investigated using chemotherapeutics and targeted molecular drugs, however, the intrinsic resistance to induced cell death of brain cells impede the effectiveness of systemic therapies. Also, the unique immune environment of the central nervous system imposes challenges for immune-based therapeutics. Therefore, it is important to consider other approaches to treat these tumors. There is a well-known dose-response relationship for glioblastoma with increased survival with increasing doses, but this effect seems to cap around 60 Gy, due to increased toxicity to the normal brain. Currently, radiation treatment planning of glioblastoma patients relies on CT and MRI that does not visualize the heterogeneous nature of the tumor, and consequently, a homogenous dose is delivered to the entire tumor. Metabolic imaging, such as positron-emission tomography, allows to visualize the heterogeneous tumor environment. Using these metabolic imaging techniques, an approach called dose painting can be used to deliver a higher dose to the tumor regions with high malignancy and/or radiation resistance. Preclinical studies are required for evaluating the benefits of novel radiation treatment strategies, such as PET-based dose painting. The aim of this review is to give a brief overview of promising PET tracers that can be evaluated in laboratory animals to bridge the gap between PET-based dose painting in glioblastoma patients.

In Vivo DCE-MRI for the Discrimination Between Glioblastoma and Radiation Necrosis in Rats

PURPOSE

In this study, the potential of semiquantitative and quantitative analysis of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) was investigated to differentiate glioblastoma (GB) from radiation necrosis (RN) in rats.

PROCEDURES

F98 GB growth was seen on MRI 8-23 days post-inoculation (n = 15). RN lesions developed 6-8 months post-irradiation (n = 10). DCE-MRI was acquired using a fast low-angle shot (FLASH) sequence. Regions of interest (ROIs) encompassed peripheral contrast enhancement in GB (n = 15) and RN (n = 10) as well as central necrosis within these lesions (GB (n = 4), RN (n = 3)). Dynamic contrast-enhanced time series, obtained from the DCE-MRI data, were fitted to determine four function variables (amplitude A, offset from zero C, wash-in rate k, and wash-out rate D) as well as maximal intensity (Imax_F) and time to peak (TTP_F). Secondly, maps of semiquantitative and quantitative parameters (extended Tofts model) were created using Olea Sphere (_O). Semiquantitative DCE-MRI parameters included wash-in_O, wash-out_O, area under the curve (AUC_O), maximal intensity (Imax_O), and time to peak (TTP_O). Quantitative parameters included the rate constant plasma to extravascular-extracellular space (EES) (K _trans), the rate constant EES to plasma (K _ep), plasma volume (V _p), and EES volume (V _e). All (semi)quantitative parameters were compared between GB and RN using the Mann-Whitney U test. ROC analysis was performed.

RESULTS

Wash-in rate (k) and wash-out rate (D) were significantly higher in GB compared to RN using curve fitting (p = 0.016 and p = 0.014). TTP_F and TTP_O were significantly lower in GB compared to RN (p = 0.001 and p = 0.005, respectively). The highest sensitivity (87 %) and specificity (80 %) were obtained for TTP_F by applying a threshold of 581 s. K _trans, K _ep, and V _e were not significantly different between GB and RN. A trend towards higher V _p values was found in GB compared to RN, indicating angiogenesis in GB (p = 0.075).

CONCLUSIONS

Based on our results, in a rat model of GB and RN, wash-in rate, wash-out rate, and the time to peak extracted from DCE-MRI time series data may be useful to discriminate GB from RN.

"Unforgettable" - a pictorial essay on anatomy and pathology of the hippocampus

Abstract

The hippocampus is a small but complex anatomical structure that plays an important role in spatial and episodic memory. The hippocampus can be affected by a wide range of congenital variants and degenerative, inflammatory, vascular, tumoral and toxic-metabolic pathologies. Magnetic resonance imaging is the preferred imaging technique for evaluating the hippocampus. The main indications requiring tailored imaging sequences of the hippocampus are medically refractory epilepsy and dementia. The purpose of this pictorial review is threefold: (1) to review the normal anatomy of the hippocampus on MRI; (2) to discuss the optimal imaging strategy for the evaluation of the hippocampus; and (3) to present a pictorial overview of the most common anatomic variants and pathologic conditions affecting the hippocampus.

Teaching points

• Knowledge of normal hippocampal anatomy helps recognize anatomic variants and hippocampal pathology.

• Refractory epilepsy and dementia are the main indications requiring dedicated hippocampal imaging.

• Pathologic conditions centered in and around the hippocampus often have similar imaging features.

• Clinical information is often necessary to come to a correct diagnosis or an apt differential.

Kinetic Modeling and Graphical Analysis of 18F-Fluoromethylcholine (FCho), 18F-Fluoroethyltyrosine (FET) and 18F-Fluorodeoxyglucose (FDG) PET for the Fiscrimination between High-Grade Glioma and Radiation Necrosis in Rats

Background

Discrimination between glioblastoma (GB) and radiation necrosis (RN) post-irradiation remains challenging but has a large impact on further treatment and prognosis. In this study, the uptake mechanisms of 18F-fluorodeoxyglucose (18F-FDG), 18F-fluoroethyltyrosine (18F-FET) and 18F-fluoromethylcholine (18F-FCho) positron emission tomography (PET) tracers were investigated in a F98 GB and RN rat model applying kinetic modeling (KM) and graphical analysis (GA) to clarify our previous results.

Methods

Dynamic 18F-FDG (GB n = 6 and RN n = 5), 18F-FET (GB n = 5 and RN n = 5) and 18F-FCho PET (GB n = 5 and RN n = 5) were acquired with continuous arterial blood sampling. Arterial input function (AIF) corrections, KM and GA were performed.

Results

The influx rate (K_i) of 18F-FDG uptake described by a 2-compartmental model (CM) or using Patlak GA, showed more trapping (k₃) in GB (0.07 min^-1) compared to RN (0.04 min^-1) (p = 0.017). K₁ of 18F-FET was significantly higher in GB (0.06 ml/ccm/min) compared to RN (0.02 ml/ccm/min), quantified using a 1-CM and Logan GA (p = 0.036). 18F-FCho was rapidly oxidized complicating data interpretation. Using a 1-CM and Logan GA no clear differences were found to discriminate GB from RN.

Conclusions

Based on our results we concluded that using KM and GA both 18F-FDG and 18F-FET were able to discriminate GB from RN. Using a 2-CM model more trapping of 18F-FDG was found in GB compared to RN. Secondly, the influx of 18F-FET was higher in GB compared to RN using a 1-CM model. Important correlations were found between SUV and kinetic or graphical measures for 18F-FDG and 18F-FET. 18F-FCho PET did not allow discrimination between GB and RN.

Estimating blur at the brain gray-white matter boundary for FCD detection in MRI

Focal cortical dysplasia (FCD) is a frequent cause of epilepsy and can be detected using brain magnetic resonance imaging (MRI). One important MRI feature of FCD lesions is the blurring of the gray-white matter boundary (GWB), previously modelled by the gradient strength. However, in the absence of additional FCD descriptors, current gradient-based methods may yield false positives. Moreover, they do not explicitly quantify the level of blur which prevents from using them directly in the process of automated FCD detection. To improve the detection of FCD lesions displaying blur, we develop a novel algorithm called iterating local searches on neighborhood (ILSN). The novelty is that it measures the width of the blurry region rather than the gradient strength. The performance of our method is compared with the gradient magnitude method using precision and recall measures. The experimental results, tested on MRI data of 8 real FCD patients, indicate that our method has higher ability to correctly identify the FCD blurring than the gradient method.

(18)F-fluoromethylcholine (FCho), (18)F-fluoroethyltyrosine (FET), and (18)F-fluorodeoxyglucose (FDG) for the discrimination between high-grade glioma and radiation necrosis in rats: a PET study

INTRODUCTION

Discrimination between (high-grade) brain tumor recurrence and radiation necrosis (RN) remains a diagnostic challenge because both entities have similar imaging characteristics on conventional magnetic resonance imaging (MRI). Metabolic imaging, such as positron emission tomography (PET) could overcome this diagnostic dilemma. In this study, we investigated the potential of 2-[(18)F]-fluoro-2-deoxy-D-glucose ((18)F-FDG), O-(2-[(18)F]-fluoroethyl)-L-tyrosine ((18)F-FET), and [(18)F]-Fluoromethyl-dimethyl-2-hydroxyethylammonium ((18)F-fluoromethylcholine, (18)F-FCho) PET in discriminating high-grade tumor from RN.

METHODS

We developed a glioblastoma (GB) rat model by inoculating F98 GB cells into the right frontal region. Induction of RN was achieved by irradiating the right frontal region with 60 Gy using three arcs with a beam aperture of 3×3 mm (n=3). Dynamic PET imaging with (18)F-FDG, (18)F-FET, and (18)F-FCho, as well as (18)F-FDG PET at a delayed time interval (240 min postinjection), was acquired.

RESULTS

MRI revealed contrast-enhancing tumors at 15 days after inoculation (n=4) and contrast-enhancing RN lesions 5-6 months postirradiation (n=3). On (18)F-FDG PET, the mean lesion-to-normal ratio (LNRmean) was significantly higher in GB than in RN (p=0.034). The difference in the LNRmean between tumors and RN was higher on the late (18)F-FDG PET images than on the PET images reconstructed from the last time frame of the dynamic acquisition (this is at a conventional time interval). LNRs obtained from (18)F-FCho PET were not significantly different between GB and RN (p=1.000). On (18)F-FET PET, the LNRmean was significantly higher in GB compared to RN (p=0.034).

CONCLUSIONS

Unlike (18)F-FCho, (18)F-FDG and (18)F-FET PET were effective in discriminating GB from RN. Interestingly, in the case of (18)F-FDG, delayed PET seems particularly useful.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Our results suggest that (delayed) (18)F-FDG and (18)F-FET PET can be used to discriminate GB (recurrence) from RN. Confirmation of these results in clinical studies is needed.

Spontaneous delayed brain herniation through a subdural membrane after tumor surgery

BACKGROUND AND IMPORTANCE

We report on a rare case of spontaneous cerebral herniation through a subdural membrane in a 54-year-old patient. Brain herniation in adults as a complication of chronic subdural hematomas shortly after a neurosurgical intervention is rare. We are the first to report a case of delayed local herniation in an adult patient more than 1 year after a neurosurgical procedure.

CLINICAL PRESENTATION

The patient suffered from a low-grade oligodendroglioma since 1993. Radiotherapy was then applied, followed by resective surgery and chemotherapy in 2008 because of tumor progression. Subsequently, he developed a symptomatic subdural hygroma treated with a subduro-atrial cerebrospinal fluid shunt. In January 2010, the shunt was occluded. Follow-up brain imaging showed a stable situation after tumor resection, with a cyst in the temporal resection cavity and a stable subdural hygroma. In February 2011, the patient visited the emergency department because of an acute right hemiparesis and progressive motor aphasia. Urgent magnetic resonance imaging was suspicious of a herniation of brain parenchyma in the left middle cranial fossa. Explorative surgery showed a locally incarcerated brain herniation through a membrane with a ring-like aperture. Resection of this membrane led to normalization of the position of the brain tissue and to clinical improvement.

CONCLUSION

Brain herniation through a subdural membrane is an extremely rare complication, but must be a differential diagnosis in patients with a known chronic subdural hematoma or hygroma and clinical deterioration, even in the absence of recent surgery. Urgent surgical intervention of the herniated brain is recommended to reduce the risk of permanent neurological damage.

Automatic 3D graph cuts for brain cortex segmentation in patients with focal cortical dysplasia

In patients with intractable epilepsy, focal cortical dysplasia (FCD) is the most frequent malformation of cortical development. Identification of subtle FCD lesions using brain MRI scans is very often based on the cortical thickness measurement, where brain cortex segmentation is required as a preprocessing step. However, the accuracy of the selected segmentation method can highly affect the final FCD lesion detection. In this work, we propose an improved graph cuts algorithm integrating Markov random field-based energy function for more accurate brain cortex MRI segmentation. Our method uses three-label graph cuts and preforms automatic 3D MRI brain cortex segmentation integrating intensity and boundary information. The performance of the method is tested on both simulated MR brain images with different noise levels and real patients with FCD lesions. Experimental quantitative segmentation results showed that the proposed method is effective, robust to noise and achieves higher accuracy than other popular brain MRI segmentation methods. The qualitative validation, visually verified by a medical expert, showed that the FCD lesions were segmented well as a part of the cortex, indicating increased thickness and cortical deformation. The proposed technique can be successfully used in this, as well as in many other clinical applications.

Clinical added value of magnetic source imaging in the presurgical evaluation of refractory focal epilepsy

OBJECTIVE

This prospective, bicentre, blinded, intention to treat study assessed the clinical added value of magnetic source imaging (MSI) in the presurgical evaluation of patients with refractory focal epilepsy (RFE).

METHODS

70 consecutive patients with RFE (42 men; mean age 31.5 years, range 3-63) from two Belgian centres were prospectively included. All patients underwent conventional non-invasive presurgical evaluation (CNIPE) and a whole head magnetoencephalography recording (Elekta Neuromag). Equivalent current dipoles corresponding to interictal epileptiform discharges (IED) were fitted in the patients' spherical head model and coregistered on their MRI to produce MSI results. Results of CNIPE were first discussed blinded to the MSI results in respective multidisciplinary epilepsy surgery meetings to determine the presumed localisation of the epileptogenic zone and to set surgical or additional presurgical plans. MSI results were then discussed multidisciplinarily. MSI influence on the initial management plan was assessed.

RESULTS

Based on CNIPE, 21 patients had presumed extratemporal epilepsy, 38 had presumed temporal epilepsy and 11 had undetermined localisation epilepsy. MSI showed IED in 52 patients (74.5%) and changed the initial management in 15 patients (21%). MSI related changes were significantly more frequent in patients with presumed extratemporal or undetermined localisation epilepsy compared with patients with presumed temporal epilepsy (p≤0.001). These changes had a clear impact on clinical management in 13% of all patients.

CONCLUSION

MSI is a clinically relevant, non-invasive neuroimaging technique for the presurgical evaluation of patients with refractory focal epilepsy and, particularly, in patients with presumed extratemporal and undetermined localisation epilepsy.

Quantifying hemodynamic refractory bold effects in normal subjects at the single-subject level using an inverse logit fitting procedure

PURPOSE

To evaluate whether hemodynamic refractory effects provoked by repeated visual stimulation can be detected and quantified at the single-subject level using a recently described hemodynamic response function (HRF) fitting algorithm.

MATERIALS AND METHODS

Hemodynamic refractory effects were induced with an easily applicable functional MRI (fMRI) paradigm. A fitting method with inverse logit (IL) functions was applied to quantify net HRFs at the single-subject level with three interstimulus intervals (ISI; 1, 2, and 6 s). The model yielded amplitude, latencies, and width for each HRF.

RESULTS

HRF fitting was possible in 44 of 51 healthy volunteers, with excellent goodness-of-fit (R(2) = 0.9745 ± 0.0241). Refractory effects were most pronounced for the 1-s ISI (P < 0.001) and had nearly disappeared for the 6-s ISI.

CONCLUSION

Quantifying refractory effects in individuals was possible in 86.3% of normal subjects using the IL fitting algorithm. This setup may be suitable to explore such effects in individual patients.

Absence of haemodynamic refractory effects in patients with migraine without aura – an interictal fMRI study

Background: In healthy controls, haemodynamic refractory effects are observed with blood-oxygenation-level dependent (BOLD) functional MRI (fMRI): the haemodynamic response function (HRF) to the second stimulus in a pair of stimuli with short interstimulus interval (ISI) shows a decreased amplitude and an increased time-to-peak. We hypothesize that there may be interictal haemodynamic abnormalities in migraineurs.

Methods: An event-related fMRI design with paired face stimuli and varying ISIs was used to measure interictal HRFs in the face recognition area of patients with migraine without aura (MwoA) and controls. Net responses to the second stimulus in a pair were calculated and averaged per participant. Several characterizing parameters of the net responses were quantified and examined within each group.

Results: Refractory effects were not observed in our patient group. There are no changes in the net responses compared with the reference situation in patients, irrespective of the ISI, whereas in controls all HRF parameters are decreased or delayed for an ISI of 1 second.

Conclusion: This is the first fMRI study investigating the haemodynamic refractory effects in MwoA patients. Unlike in controls, these effects are not observed in migraineurs. Although currently unclear, it is tempting to speculate that this observation reflects the neurovascular correlate of lack of habituation measured with evoked potentials in migraineurs.

Palatal insufficiency as isolated sign of GQ1b antibody syndrome

Antiganglioside GQ1b antibodies mediate a continuum of disorders with overlapping features, fostering the concept of anti-GQ1b antibody syndrome. We present a patient whose palatal insufficiency was the only clinical sign of postinfectious GQ1b antibody syndrome. Cerebral magnetic resonance imaging confirmed involvement of the glossopharyngeal nerve and vagus nerve bilaterally, revealing gadolinium enhancement of both nerves bilaterally and thickening of the left nervus vagus. Magnetic resonance imaging may help in diagnosing postinfectious GQ1b antibody syndrome, especially at early stages and in monosymptomatic patients. Early diagnosis may lead to early therapy, resulting in a milder disease course by preventing further deterioration leading to the ataxia and ophthalmoplegia usually observed in patients with postinfectious GQ1b antibody syndrome.

Simulation and experimental verification of the diffusion in an anisotropic fiber phantom

Diffusion weighted magnetic resonance imaging enables the visualization of fibrous tissues such as brain white matter. The validation of this non-invasive technique requires phantoms with a well-known structure and diffusion behavior. This paper presents anisotropic diffusion phantoms consisting of parallel fibers. The diffusion properties of the fiber phantoms are measured using diffusion weighted magnetic resonance imaging and bulk NMR measurements. To enable quantitative evaluation of the measurements, the diffusion in the interstitial space between fibers is modeled using Monte Carlo simulations of random walkers. The time-dependent apparent diffusion coefficient and kurtosis, quantifying the deviation from a Gaussian diffusion profile, are simulated in 3D geometries of parallel fibers with varying packing geometries and packing densities. The simulated diffusion coefficients are compared to the theory of diffusion in porous media, showing a good agreement. Based on the correspondence between simulations and experimental measurements, the fiber phantoms are shown to be useful for the quantitative validation of diffusion imaging on clinical MRI-scanners.

Structural magnetic resonance imaging in epilepsy

Because of its sensitivity and high tissue contrast, magnetic resonance imaging (MRI) is the technique of choice for structural imaging in epilepsy. In this review the effect of using optimised scanning protocols and the use of high field MR systems on detection sensitivity is discussed. Also, the clinical relevance of adequate imaging in patients with focal epilepsy is highlighted. The most frequently encountered MRI findings in epilepsy are reported and their imaging characteristics depicted. Imaging focus will be on the diagnosis of hippocampal sclerosis and malformations of cortical development, two major causes of medically intractable focal epilepsy.

Comparison between functional magnetic resonance imaging at 1.5 and 3 Tesla: effect of increased field strength on 4 paradigms used during presurgical work-up

OBJECTIVES

We sought to evaluate the benefit of 3 T compared with 1.5 T during presurgical functional magnetic resonance imaging.

MATERIALS AND METHODS

Six participants performed a motor, a visual, and 2 language paradigms both at 1.5 and 3 T. The number of activated voxels, mean t-value, and assessment of language dominancy were compared between both field strengths. Group analysis was performed to evaluate the influence of field strength on the cortical language activation patterns.

RESULTS

The number of activated voxels and mean t-values were significantly higher at 3 T for all paradigms. Using the same statistical threshold, language activation was significantly less lateralized, and more activation zones were depicted at 3 T compared with 1.5 T.

CONCLUSIONS

Sensitivity associated with visual, motor and language functional magnetic resonance imaging increased significantly at 3 T. Additional cortical areas were depicted during language processing at 3 T. For assessment of language dominancy, usage of more stringent statistical thresholds at 3 T is suggested.

Language activation distributions revealed by fMRI in post-operative epilepsy patients: differences between left- and right-sided resections

OBJECTIVE

To reveal differences of cerebral activation related to language functions in post-operative temporal lobe epilepsy (TLE) patients.

METHODS

Right (RTL) and left temporal lobe (LTL) resected patients, and healthy controls were studied using functional magnetic resonance imaging (fMRI). Only patients with complete left-hemispheric language dominance according to the intracarotid amytal procedure (IAP) were included. Language-related activations were evoked by performing word generation and text reading language tasks. Activation lateralization and temporo-frontal distribution effects were analysed.

RESULTS

For word generation, only LTL patients showed reduced left lateralized activation compared to controls, due to a decrease in activation in the left prefrontal cortex and an increase in the right prefrontal cortex. For reading, the left-hemispheric lateralization in RTL patients increased because of enhanced activity in the left prefrontal cortex, whereas for LTL patients the activation became bilaterally distributed over the temporal lobes. Lateralization results between pre-operative IAP and post-operative fMRI were highly discordant. Significant temporo-frontal distribution changes manifested from the reading but not from the word generation task.

CONCLUSION

The cerebral language representation in post-operative LTL epilepsy patients is more bi-hemispherically lateralized than in controls and RTL patients. Post-operative temporo-frontal and interhemispheric redistribution effects, involving contralateral homologous brain areas, are suggested to contribute to the cerebral reorganisation of language function.

Lateralized Anterior Mesiotemporal Lobe Activation: Semirandom Functional MR Imaging Encoding Paradigm in Patients with Temporal Lobe Epilepsy—Initial Experience

PURPOSE

To prospectively demonstrate anterior mesiotemporal lobe (MTL) activation in healthy volunteers by using a semirandom memory-encoding paradigm and to prospectively compare lateralized functional magnetic resonance (MR) imaging activation with intracarotid amobarbital procedure (IAP) memory test results in patients with temporal lobe epilepsy (TLE) who were scheduled to undergo surgery.

MATERIALS AND METHODS

The study was approved by a local ethics committee, and written informed consent was obtained from all subjects. Eight healthy volunteers and 18 patients with TLE who were scheduled for surgery were included in the functional MR imaging study involving the use of a memory-encoding paradigm with variable epoch lengths. Subjects were instructed to memorize new pictures that were mixed among pictures that they had seen before. Data analysis entailed computations of the contrast between the MTL activation induced by the new pictures and the MTL activation induced by the old pictures and of the lateralization index, defined as the relative difference in the number of activated voxels between the left and right MTLs. Lateralization indexes were compared between the patients and the volunteers and statistically correlated with the patients' IAP memory test results. To study deviations from perfect correspondence between the functional MR imaging- and IAP-derived lateralization indexes, orthogonal regression analysis was applied. Proportional relations for the patients with left-sided TLE and for those with right-sided TLE were calculated separately.

RESULTS

The memory paradigm consistently activated the posterior and anterior MTL structures in both the healthy volunteers and the patients. Regression analysis revealed that functional MR imaging activation was stronger than the IAP results when it was lateralized to the contralateral MTL. This analysis also revealed a significant (P < .001) correlation between the functional MR imaging results and the IAP results in the patients with right-sided TLE but not in those with left-sided TLE (P > .1).

CONCLUSION

The functional MR imaging memory-encoding paradigm consistently yielded MTL activation in the volunteers and the patients with TLE, but lateralized functional MR imaging activation was in concordance with the IAP results in only those patients with right-sided TLE.

Trial pacing in mental rotation tasks

Functional imaging of mental rotation has revealed a wide variety of cortical activation patterns besides the consensus on parietal involvement. Some insight has been gained on the role of motor cortex, but the differential activation of other brain regions has received little attention. A previous fMRI study using a blocked substraction design [D'Esposito et al., NeuroImage 6 (1997) 113-121] has shown an effect of trial pacing on the observed activation pattern of a simple visuospatial task requiring mental rotation. In this study, we want to assess if trial pacing can help clarify some of the diversity in the observed cortical activation patterns associated with fMRI blocked designs of mental rotation so far, especially when comparing mental rotation of different stimuli. We used two different stimuli, i.e. hands and tools, that have been used in previous mental rotation studies. Our results revealed a bilateral involvement of lateral premotor and parietal cortex irrespective of trial pacing, but there was a marked influence of trial pacing on the observed activation of occipital and other frontal regions. Stimulus type specific activation patterns were entirely limited to the fixed-paced design. We conclude that trial pacing is a vital aspect when developing and interpreting the related imaging results of a blocked subtraction design. Fixed-paced designs may be more sensitive for duration effects. A self-paced trial schedule may be more appropriate to isolate the neural substrate of the cognitive component of interest or to exclude response time differences as a confounding factor.

Stimulus pacing affects the activation of the medial temporal lobe during a semantic classification task: an fMRI study

Our purpose was to explore the influence of stimulus pacing in blocked functional MRI studies on the activation pattern elicited by a semantic retrieval task. Twenty-two participants performed both a fixed-paced and a self-paced functional MR imaging experiment in which a semantic categorization (animal/object) task was contrasted with a perceptual (small/capital letter string) categorization task. Group and single-subject ROI analyses were computed. In both the fixed-paced and self-paced experiments, semantic categorization contrasted with perceptual categorization elicited a cerebral network generally accepted to be involved in semantic processing comprising left inferior prefrontal, left lateral temporal, paracingular and right cerebellar areas. Our main finding was that the self-paced stimulus modality additionally yielded significant activation in the medial temporal lobe (MTL) structures including the hippocampus and the parahippocampal gyrus. More elaborative single-subject ROI analyses revealed MTL activation in 86% of the subjects for the self-paced design, but only in 21% of subjects for the fixed-paced design. The discussion focuses on possible explanations for this finding. We conclude that a self-paced as opposed to a fixed-paced semantic retrieval paradigm is able to detect significant MTL activation in groups as well as in single-subjects. This offers opportunities for the application of such a design in clinical practice.

Visual extinction for motion

PURPOSE

To alert clinicians to the heretofore undescribed visual behavioral phenomenon of visual extinction limited to motion.

METHODS

Neuro-ophthalmological, neuropsychological and neuroimaging assessment of a 57-year-old man with vague visual complaints.

RESULTS

Extinction limited to visual motion perception in the left hemifield was demonstrated. The visual defect was attributed to a lesion involving the right occipito-temporo-parietal region in the presence of a left posterior infarction.

CONCLUSION

The importance of clinical examination for detection of this specific higher-order visual defect is stressed. The present observation may be helpful in understanding the effects of attention on visual perception and may have important implications for rehabilitation of patients with visual neglect.

MRI language dominance assessment in epilepsy patients at 1.0 T: region of interest analysis and comparison with intracarotid amytal testing

The primary goal of this study was to test the reliability of presurgical language lateralization in epilepsy patients with functional magnetic resonance imaging (fMRI) with a 1.0-T MR scanner using a simple word generation paradigm and conventional equipment. In addition, hemispherical fMRI language lateralization analysis and region of interest (ROI) analysis in the frontal and temporo-parietal regions were compared with the intracarotid amytal test (IAT). Twenty epilepsy patients under presurgical evaluation were prospectively examined by both fMRI and IAT. The fMRI experiment consisted of a word chain task (WCT) using the conventional headphone set and a sparse sequence. In 17 of the 20 patients, data were available for comparison between the two procedures. Fifteen of these 17 patients were categorized as left hemispheric dominant, and 2 patients demonstrated bilateral language representation by both fMRI and IAT. The highest reliability for lateralization was obtained using frontal ROI analysis. Hemispherical analysis was less powerful and reliable in all cases but one, while temporo-parietal ROI analysis was unreliable as a stand-alone analysis when compared with IAT. The effect of statistical threshold on language lateralization prompted for the use of t-value-dependent lateralization index plots. This study illustrates that fMRI-determined language lateralization can be performed reliably in a clinical MR setting operating at a low field strength of 1 T without expensive stimulus presentation systems.

Multilingualism: an fMRI study

To investigate the hypothesis that in multilingual speakers different languages are represented in distinct brain regions, 12 multilingual right-handed men performed a word fluency task, a picture naming task, a comprehension reading task, and their respective control tasks in three languages (Dutch, French, and English) while whole-head functional magnetic resonance imaging (fMRI) was applied. In general, all language tasks revealed predominantly overlapping regions of activation for the different languages. Cerebral activation during use of the foreign languages showed a tendency toward a more extensive recruitment of the areas activated in the native language and the activation of a greater number of regions. Word generation in the foreign languages elicited additional bilateral inferior frontal activation, including Broca's area and left middle temporal gyrus activation; in the native language, additional postcentral activation was found. Picture naming in the foreign languages recruited additional inferior-lateral and medial frontal regions predominantly on the left, and more posterior right hemispheric activation in the mother tongue. During comprehension reading there was more activation in medial posterior regions in the native language. Our results suggest that the performance of language tasks in different languages engages largely the same cerebral areas but that the brain, to perform at a comparable proficiency level, engages more neural substrates for later acquired languages. Our findings do not support the view that languages learned later in life entail more right hemispheric involvement. Finally, a consequent effect of language exposure was found for reading, where increased familiarity engages more occipital activation whereas decreased familiarity appears to be associated with increased left hemispheric inferior frontal activation.

Lessons for neuropsychology from functional MRI in patients with epilepsy

This contribution aims to review the major findings of pre- and postsurgical functional magnetic resonance imaging (fMRI) in patients with refractory epilepsy from a neuropsychological perspective. We compared the contribution of fMRI with the intracarotid amytal procedure (IAP) with respect to functional mapping of language and memory in patients with therapy-resistant epilepsy. We conclude that using comprehensive language paradigms, fMRI has been able (1) to provide estimates of the degree of language lateralization including the degree of involvement of the nondominant hemisphere, (2) to provide information on the location of its activated network during expressive and receptive language, and (3) to help delineate eloquent language regions in the vicinity of the surgical target, thus preventing postoperative complications. The contribution of the frequently observed nondominant hemisphere activation to language should be explored and its clinical relevance determined. Evidence from fMRI studies is accumulating that reorganization of cognitive and motor function favors the activation of contralateral homotopic areas, although this process is far from understood. The exact functional contribution of atypical areas of activation should be investigated critically. In the presurgical evaluation process, detailed and reliable localization of language and memory functions of the individual patient is mandatory and should be the ultimate goal in the development of comprehensive clinical fMRI protocols.

Neurostimulation for refractory epilepsy

Neurostimulation is an emerging treatment for refractory epilepsy. To date the precise mechanism of action remains to be elucidated. Better insight in the mechanism of action may identify seizure types or syndromes that respond to such a treatment and may guide the search for optimal stimulation parameters and finally improve clinical efficacy. In the past ten years some progress has been made through neurophysiological, neuroanatomical, neurochemical and cerebral blood flow studies in patients and animals undergoing vagus nerve stimulation (VNS). Interesting results have been found in VNS-treated patients that underwent evoked potential measurements, cerebrospinal fluid investigation, neuropsychological testing and PET, SPECT and fMRI testing. Desynchronisation of abnormal synchronous epileptic activity is one of the hypotheses on the mode of action that might primarily be responsible for an anti-seizure effect. There is however increasing evidence from research and clinical observation that VNS might establish a true and long-term anti-epileptic effect. It has been shown that VNS influences neurotransmission in the brain and provokes long-term changes in cerebral blood flow in areas crucial for epileptogenesis such as the thalamus and medial temporal lobe structures. Deep brain stimulation (DBS) for epilepsy has regained interest. Central nervous system structures known to play a key role in the epileptogenic network such as the thalamus and subthalamic nucleus have been targeted. Another approach is to target the ictal onset zone such as the medial temporal lobe. At Ghent University Hospital 10 patients have been treated with long-term amygdalohippocampal DBS. Several hypotheses have been raised for the mechanism of action of DBS for refractory seizures. Seizure reduction may be due to a microlesion caused by electrode insertion or by provoking a reversible functional lesion due to the effect of electrical current on hyperexcitable tissue. Neurophysiological techniques such as evoked potentials monitoring and intraoperative single unit potential recordings may guide correct electrode placement, individual DBS titration and elucidation of the mechanims of action of DBS for epilepsy.