Using patient-specific hemodynamic response functions in combined EEG-fMRI studies in epilepsy

Kang, Joong Koo; Bénar, Christian; Al‐Asmi, Abdullah; Khani, Yahya Agha; Pike, G. Bruce; Dubeau, François; Gotman, Jean

doi:10.1016/s1053-8119(03)00290-8

Cited by 75 publications

(64 citation statements)

References 24 publications

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“…This method allows an evaluation of the HRF by assuming that it is the same for each event, but without constraining its shape. However, for the purpose of this study, the method was used to refine the calculation of the delay of the HRF in areas that showed BOLD effects in the primary statistical analysis, used as regions of interest (Kang et al, 2003). The use of a single canonical model HRF in the primary analysis would result in an estimated HRF that is relatively similar to the model.…”

Section: Methodological Issuesmentioning

confidence: 99%

“…The HRF was projected for a region of interest of 10 significantly activated voxels, centered on the voxel with the highest t value in the cluster. An HRF was projected over a 64-s time window (from 15 s prior to the EEG spike to 48 s after the spike) using a Fourier basis set of 20 sine-cosine waves (Josephs et al, 1997;Kang et al, 2003). Projected HRFs were sampled at one data point per second ( Fig.…”

Section: Calculation Of the Patient-specific Hrfmentioning

confidence: 99%

“…This low sensitivity could result from an HRF that differs significantly from the canonical or Glover response. Kang and coworkers demonstrated that the variability of the HRF to interictal discharges is quite high and that the use of a patient-specific HRF improves EEG-fMRI results (Kang et al, 2003). The use of four different HRFs further improved the detection of BOLD responses and can be implemented as a standard procedure for the analysis of EEG-fMRI studies (Bagshaw et al, 2004).…”

Section: Hrfs Used In Eeg-fmri For Epilepsy Patientsmentioning

confidence: 99%

“…There is evidence that the actual HRF varies depending on the brain region, individual and time of the recording (Aguirre et al, 1998). The use of multiple HRFs (Bagshaw et al, 2004) and patient-specific HRFs (Kang et al, 2003) in EEG-fMRI indeed is more sensitive to detect positive and negative BOLD responses that would be otherwise missed with the standard model. We improved the sensitivity of EEG-fMRI with the use of four different HRFs (peaking at 3, 5, 7 and 9 s) in a group of children with symptomatic epilepsy (Jacobs et al, 2006), and as in adults, the responses seem to be specific, as demonstrated by their concordance with the anatomical areas related to the generation of the spikes, as well as with the potentially epileptogenic lesion/region.…”

Section: Introductionmentioning

confidence: 99%

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Variability of the hemodynamic response as a function of age and frequency of epileptic discharge in children with epilepsy

et al. 2008

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EEG-fMRI is a non-invasive tool to investigate epileptogenic networks in patients with epilepsy. Different patterns of BOLD responses have been observed in children as compared to adults. A high intra-and intersubject variability of the hemodynamic response function (HRF) to epileptic discharges has been observed in adults. The actual HRF to epileptic discharges in children and its dependence on age are unknown. We analyzed 64 EEG-fMRI event types in 37 children (3 months to 18 years), 92% showing a significant BOLD response. HRFs were calculated for each BOLD cluster using a Fourier basis set. After excluding HRFs with a low signal-to-noise ratio, 126 positive and 98 negative HRFs were analyzed. We evaluated age-dependent changes as well as the effect of increasing numbers of spikes. Peak time, amplitude and signal-to-noise ratio of the HRF and the t-statistic score of the cluster were used as dependent variables. We observed significantly longer peak times of the HRF in the youngest children (0 to 2 years), suggesting that the use of multiple HRFs might be important in this group. A different coupling between neuronal activity and metabolism or blood flow in young children may cause this phenomenon. Even if the t-value increased with frequent spikes, the amplitude of the HRF decreased significantly with spike frequency. This reflects a violation of the assumptions of the General Linear Model and therefore the use of alternative analysis techniques may be more appropriate with high spiking rates, a common situation in children.

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Section: Methodological Issuesmentioning

confidence: 99%

Section: Calculation Of the Patient-specific Hrfmentioning

confidence: 99%

Section: Hrfs Used In Eeg-fmri For Epilepsy Patientsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Variability of the hemodynamic response as a function of age and frequency of epileptic discharge in children with epilepsy

et al. 2008

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“…The tests presented along the study reveal the influence of each parameter in the accuracy of BOLD activation maps, and also its contribution to false positives. To model the haemodynamic function a standard Gamma function with derivatives was used [2] (with a FWHM of 3 s [3] and a mean lag of 5 s [4]). Four and twenty-four spikes were analyzed, respectively, for patients 1 and 2.…”

Section: Methodsmentioning

confidence: 99%

Optimization of fMRI Processing Parameters for Simutaneous Acquisition of EEG/fMRI in Focal Epilepsy

et al. 2008

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-In the context of focal epilepsy, the simultaneous combination of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) holds a great promise as a technique by which the hemodynamic correlates of interictal spikes detected on scalp EEG can be identified.The fact that traditional EEG recordings have not been able to overcome the difficulty in correlating the ictal clinical symptoms to the onset in particular areas of the lobes, brings the need of mapping with more precision the epileptogenic cortical regions. On the other hand, fMRI suggested localizations more consistent with the ictal clinical manifestations detected.This study was developed in order to improve the knowledge about the way parameters involved in the physical and mathematical data, produced by the EEG/fMRI technique processing, would influence the final results. The evaluation of the accuracy was made by comparing the BOLD results with: the high resolution EEG maps; the malformative lesions detected in the T1 weighted MR images; and the anatomical localizations of the diagnosed symptomatology of each studied patient. The optimization of the set of parameters used, will provide an important contribution to the diagnosis of epileptogenic focuses, in patients included on an epilepsy surgery evaluation program.The results obtained allowed us to conclude that: by associating the BOLD effect with interictal spikes, the epileptogenic areas are mapped to localizations different from those obtained by the EEG maps representing the electrical potential distribution across the scalp (EEG); there is an important and solid bond between the variation of particular parameters (manipulated during the fMRI data processing) and the optimization of the final results, from which smoothing, deleted volumes, HRF (used to convolve with the activation design), and the shape of the Gamma function can be certainly emphasized.

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EEG‐fMRI of focal epileptic spikes: Analysis with multiple haemodynamic functions and comparison with gadolinium‐enhanced MR angiograms

Bagshaw

Aghakhani

Bénar

et al. 2004

Human Brain Mapping

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Combined EEG-fMRI has recently been used to explore the BOLD responses to interictal epileptiform discharges. This study examines whether misspecification of the form of the haemodynamic response function (HRF) results in significant fMRI responses being missed in the statistical analysis. EEG-fMRI data from 31 patients with focal epilepsy were analysed with four HRFs peaking from 3 to 9 sec after each interictal event, in addition to a standard HRF that peaked after 5.4 sec. In four patients, fMRI responses were correlated with gadolinium-enhanced MR angiograms and with EEG data from intracranial electrodes. In an attempt to understand the absence of BOLD responses in a significant group of patients, the degree of signal loss occurring as a result of magnetic field inhomogeneities was compared with the detected fMRI responses in ten patients with temporal lobe spikes. Using multiple HRFs resulted in an increased percentage of data sets with significant fMRI activations, from 45% when using the standard HRF alone, to 62.5%. The standard HRF was good at detecting positive BOLD responses, but less appropriate for negative BOLD responses, the majority of which were more accurately modelled by an HRF that peaked later than the standard. Co-registration of statistical maps with gadolinium-enhanced MRIs suggested that the detected fMRI responses were not in general related to large veins. Signal loss in the temporal lobes seemed to be an important factor in 7 of 12 patients who did not show fMRI activations with any of the HRFs.

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Using patient-specific hemodynamic response functions in combined EEG-fMRI studies in epilepsy

Cited by 75 publications

References 24 publications

Variability of the hemodynamic response as a function of age and frequency of epileptic discharge in children with epilepsy

Variability of the hemodynamic response as a function of age and frequency of epileptic discharge in children with epilepsy

Optimization of fMRI Processing Parameters for Simutaneous Acquisition of EEG/fMRI in Focal Epilepsy

EEG‐fMRI of focal epileptic spikes: Analysis with multiple haemodynamic functions and comparison with gadolinium‐enhanced MR angiograms

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