Usefulness of pulsed arterial spin labeling MR imaging in mesial temporal lobe epilepsy

Associations of Cerebral Blood Flow Patterns With Gray and White Matter Structure in Patients With Temporal Lobe Epilepsy

BACKGROUND AND OBJECTIVES

Neuroimaging studies in patients with temporal lobe epilepsy (TLE) show widespread brain network alterations beyond the mesiotemporal lobe. Despite the critical role of the cerebrovascular system in maintaining whole-brain structure and function, changes in cerebral blood flow (CBF) remain incompletely understood in the disease. Here, we studied whole-brain perfusion and vascular network alterations in TLE and assessed its associations with gray and white matter compromises and various clinical variables.

METHODS

We included individuals with and without pharmaco-resistant TLE who underwent multimodal 3T MRI, including arterial spin labelling, structural, and diffusion-weighted imaging. Using surface-based MRI mapping, we generated individualized cortico-subcortical profiles of perfusion, morphology, and microstructure. Linear models compared regional CBF in patients with controls and related alterations to morphological and microstructural metrics. We further probed interregional vascular networks in TLE, using graph theoretical CBF covariance analysis. The effects of disease duration were explored to better understand the progressive changes in perfusion. We assessed the utility of perfusion in separating patients with TLE from controls using supervised machine learning.

RESULTS

Compared with control participants (n = 38; mean ± SD age 34.8 ± 9.3 years; 20 females), patients with TLE (n = 24; mean ± SD age 35.8 ± 10.6 years; 12 females) showed widespread CBF reductions predominantly in fronto-temporal regions (Cohen d -0.69, 95% CI -1.21 to -0.16), consistent in a subgroup of patients who remained seizure-free after surgical resection of the seizure focus. Parallel structural profiling and network-based models showed that cerebral hypoperfusion may be partially constrained by gray and white matter changes (8.11% reduction in Cohen d) and topologically segregated from whole-brain perfusion networks (area under the curve -0.17, p < 0.05). Negative effects of progressive disease duration further targeted regional CBF profiles in patients (r = -0.54, 95% CI -0.77 to -0.16). Perfusion-derived classifiers discriminated patients from controls with high accuracy (71% [70%-82%]). Findings were robust when controlling for several methodological confounds.

DISCUSSION

Our multimodal findings provide insights into vascular contributions to TLE pathophysiology affecting and extending beyond mesiotemporal structures and highlight their clinical potential in epilepsy diagnosis. As our work was cross-sectional and based on a single site, it motivates future longitudinal studies to confirm progressive effects, ideally in a multicentric setting.

Breath-Hold-Triggered BOLD fMRI in Drug-Resistant Nonlesional Focal Epilepsy-A Pilot Study

PURPOSE

Individuals with drug-resistant epilepsy may benefit from epilepsy surgery. In nonlesional cases, where no epileptogenic lesion can be detected on structural magnetic resonance imaging, multimodal neuroimaging studies are required. Breath-hold-triggered BOLD fMRI (bh-fMRI) was developed to measure cerebrovascular reactivity in stroke or angiopathy and highlights regional network dysfunction by visualizing focal impaired flow increase after vasodilatory stimulus. This regional dysfunction may correlate with the epileptogenic zone. In this prospective single-center single-blind pilot study, we aimed to establish the feasibility and safety of bh-fMRI in individuals with drug-resistant non-lesional focal epilepsy undergoing presurgical evaluation.

METHODS

In this prospective study, 10 consecutive individuals undergoing presurgical evaluation for drug-resistant focal epilepsy were recruited after case review at a multidisciplinary patient management conference. Electroclinical findings and results of other neuroimaging were used to establish the epileptogenic zone hypothesis. To calculate significant differences in cerebrovascular reactivity in comparison to the normal population, bh-fMRIs of 16 healthy volunteers were analyzed. The relative flow change of each volume of interest (VOI) of the atlas was then calculated compared to the flow change of the whole brain resulting in an atlas of normal cerebral reactivity. Consequently, the mean flow change of every VOI of each patient was tested against the healthy volunteers group. Areas with significant impairment of cerebrovascular reactivity had decreased flow change and were compared to the epileptogenic zone localization hypothesis in a single-blind design.

RESULTS

Acquisition of bh-fMRI was feasible in 9/10 cases, with one patient excluded due to noncompliance with breathing maneuvers. No adverse events were observed, and breath-hold for intermittent hypercapnia was well tolerated. On blinded review, we observed full or partial concordance of the local network dysfunction seen on bh-fMRI with the electroclinical hypothesis in 6/9 cases, including cases with extratemporal lobe epilepsy and those with nonlocalizing 18F-fluorodeoxyglucose positron emission tomography (FDG-PET).

CONCLUSION

This represents the first report of bh-fMRI in individuals with epilepsy undergoing presurgical evaluation. We found bh-fMRI to be feasible and safe, with a promising agreement to electroclinical findings. Thus, bh-fMRI may represent a potential modality in the presurgical evaluation of epilepsy. Further studies are needed to establish clinical utility.

Exploring ASL perfusion MRI as a substitutive modality for 18F-FDG PET in determining the laterality of mesial temporal lobe epilepsy

OBJECTIVE

The aim of this investigation was to determine whether a correlation could be discerned between perfusion acquired through ASL MRI and metabolic data acquired via 18F-fluorodeoxyglucose (18F-FDG) PET in mesial temporal lobe epilepsy (mTLE).

METHODS

ASL MRI and 18F-FDG PET data were gathered from 22 mTLE patients. Relative cerebral blood flow (rCBF) asymmetry index (AIs) were measured using ASL MRI, and standardized uptake value ratio (SUVr) maps were obtained from 18F-FDG PET, focusing on bilateral vascular territories and key bitemporal lobe structures (amygdala, hippocampus, and parahippocampus). Intra-group comparisons were carried out to detect hypoperfusion and hypometabolism between the left and right brain hemispheres for both rCBF and SUVr in right and left mTLE. Correlations between the two AIs computed for each modality were examined.

RESULTS

Significant correlations were observed between rCBF and SUVr AIs in the middle temporal gyrus, superior temporal gyrus, and hippocampus. Significant correlations were also found in vascular territories of the distal posterior, intermediate anterior, intermediate middle, proximal anterior, and proximal middle cerebral arteries. Intra-group comparisons unveiled significant differences in rCBF and SUVr between the left and right brain hemispheres for right mTLE, while hypoperfusion and hypometabolism were infrequently observed in any intracranial region for left mTLE.

CONCLUSION

The study's findings suggest promising concordance between hypometabolism estimated by 18F-FDG PET and hypoperfusion determined by ASL perfusion MRI. This raises the possibility that, with prospective technical enhancements, ASL perfusion MRI could be considered an alternative modality to 18F-FDG PET in the future.

Subclinical epileptiform discharges in Alzheimer's disease are associated with increased hippocampal blood flow

BACKGROUND

In epilepsy, the ictal phase leads to cerebral hyperperfusion while hypoperfusion is present in the interictal phases. Patients with Alzheimer's disease (AD) have an increased prevalence of epileptiform discharges and a study using intracranial electrodes have shown that these are very frequent in the hippocampus. However, it is not known whether there is an association between hippocampal hyperexcitability and regional cerebral blood flow (rCBF). The objective of the study was to investigate the association between rCBF in hippocampus and epileptiform discharges as measured with ear-EEG in patients with Alzheimer's disease. Our hypothesis was that increased spike frequency may be associated with increased rCBF in hippocampus.

METHODS

A total of 24 patients with AD, and 15 HC were included in the analysis. Using linear regression, we investigated the association between rCBF as measured with arterial spin-labelling MRI (ASL-MRI) in the hippocampus and the number of spikes/sharp waves per 24 h as assessed by ear-EEG.

RESULTS

No significant difference in hippocampal rCBF was found between AD and HC (p-value = 0.367). A significant linear association between spike frequency and normalized rCBF in the hippocampus was found for patients with AD (estimate: 0.109, t-value = 4.03, p-value < 0.001). Changes in areas that typically show group differences (temporal-parietal cortex) were found in patients with AD, compared to HC.

CONCLUSIONS

Increased spike frequency was accompanied by a hemodynamic response of increased blood flow in the hippocampus in patients with AD. This phenomenon has also been shown in patients with epilepsy and supports the hypothesis of hyperexcitability in patients with AD. The lack of a significant difference in hippocampal rCBF may be due to an increased frequency of epileptiform discharges in patients with AD.

TRIAL REGISTRATION

The study is registered at clinicaltrials.gov (NCT04436341).

Lateralization of interictal temporal lobe hypoperfusion in lesional and non-lesional temporal lobe epilepsy using arterial spin labeling MRI

PURPOSE

Non-invasive imaging studies play a critical role in the presurgical evaluation of patients with drug-resistant temporal lobe epilepsy (TLE), particularly in helping to lateralize the seizure focus. Arterial Spin Labeling (ASL) MRI has been widely used to non-invasively study cerebral blood flow (CBF), with somewhat variable interictal alterations reported in TLE. Here, we compare temporal lobe subregional interictal perfusion and symmetry in lesional (MRI+) and non-lesional (MRI-) TLE compared to healthy volunteers (HVs).

METHODS

Twenty TLE patients (9 MRI+, 11 MRI-) and 14 HVs under went 3 T Pseudo-Continuous ASL MRI through an epilepsy imaging research protocol at the NIH Clinical Center. We compared normalized CBF and absolute asymmetry indices in multiple temporal lobe subregions.

RESULTS

Compared to HVs, both MRI+ and MRI- TLE groups demonstrated significant ipsilateral mesial and lateral temporal hypoperfusion, specifically in the hippocampal and anterior temporal neocortical subregions, with additional hypoperfusion in the ipsilateral parahippocampal gyrus in the MRI+ and contralateral hippocampus in the MRI- TLE groups. Contralateral to the seizure focus, there was significant relative hypoperfusion in multiple subregions in the MRI- compared to the MRI+ TLE groups. The MRI+ group therefore had significantly greater asymmetry across multiple temporal subregions compared to the MRI- TLE and HV groups. No significant differences in asymmetry were found between the MRI- TLE and HV groups.

CONCLUSION

We found a similar extent of interictal ipsilateral temporal hypoperfusion in MRI+ and MRI- TLE. However, significantly increased asymmetries were found only in the MRI+ group due to differences in perfusion contralateral to the seizure focus between the patient groups. The lack of asymmetry in the MRI- group may negatively impact the utility of interictal ASL for seizure focus lateralization in this patient population.

Alteration of intracranial blood perfusion in temporal lobe epilepsy, an arterial spin labeling study

Background

A critical necessity before surgical resection in mesial temporal lobe epilepsy (mTLE) is lateralizing the seizure focus in the temporal lobe. This study aimed to investigate the differences in perfusion pattern changes in right and left mTLE.

Methods

42 mTLE patients (22 left and 20 right mTLE) and 14 controls were surveyed with pulsed arterial spin labeling at 3.0 T. The mean cerebral blood flow (CBF) and asymmetry index (AI) were calculated in the bilateral temporal lobe, amygdala, hippocampus, parahippocampus, and nine bilateral vascular territories ROIs. The alterations in whole-brain CBF were identified using statistical parametric mapping (SPM).

Results

CBF decreased in ipsilateral sides in both epilepsy subcohorts, with right mTLE showing a significant difference in most ROIs while left mTLE exhibiting no significant change. CBF comparison of left mTLE and controls showed a significant drop in ROI analysis in left middle temporal and left intermediate posterior cerebral artery and in AI analysis in parahippocampus, distal anterior cerebral artery, distal middle cerebral artery, and intermediate anterior cerebral artery. CBF hypoperfusion was seen in ROI analysis in the left intermediate anterior cerebral artery, left middle temporal, right middle temporal, left superior temporal in the right mTLE compared to controls. Left mTLE CBF differed significantly from right mTLE CBF in right distal middle cerebral artery ROI and AI of proximal middle cerebral artery.

Conclusion

Our result revealed that mTLE affects extratemporal regions and both mTLE subcohorts with different perfusion patterns, which may enhance the performance of preoperative MRI assessment in lateralization procedures.

Multimodal combination of neuroimaging methods for localizing the epileptogenic zone in MR-negative epilepsy

The objective was to determine the optimal combination of multimodal imaging methods (IMs) for localizing the epileptogenic zone (EZ) in patients with MR-negative drug-resistant epilepsy. Data from 25 patients with MR-negative focal epilepsy (age 30 ± 10 years, 16M/9F) who underwent surgical resection of the EZ and from 110 healthy controls (age 31 ± 9 years; 56M/54F) were used to evaluate IMs based on 3T MRI, FDG-PET, HD-EEG, and SPECT. Patients with successful outcomes and/or positive histological findings were evaluated. From 38 IMs calculated per patient, 13 methods were selected by evaluating the mutual similarity of the methods and the accuracy of the EZ localization. The best results in postsurgical patients for EZ localization were found for ictal/ interictal SPECT (SISCOM), FDG-PET, arterial spin labeling (ASL), functional regional homogeneity (ReHo), gray matter volume (GMV), cortical thickness, HD electrical source imaging (ESI-HD), amplitude of low-frequency fluctuation (ALFF), diffusion tensor imaging, and kurtosis imaging. Combining IMs provides the method with the most accurate EZ identification in MR-negative epilepsy. The PET, SISCOM, and selected MRI-post-processing techniques are useful for EZ localization for surgical tailoring.

Role of Interictal Arterial Spin Labeling Magnetic Resonance Perfusion in Mesial Temporal Lobe Epilepsy

Context:

Electrophysiological and hemodynamic data can be integrated to accurately identify the generators of abnormal electrical activity in drug-resistant focal epilepsy. Arterial Spin Labeling (ASL), a magnetic resonance imaging (MRI) technique for quantitative noninvasive measurement of cerebral blood flow (CBF), can provide a direct measure of variations in cerebral perfusion associated with the epileptogenic zone.

Aims:

1. To evaluate usefulness of ASL for detecting interictal temporal hypoperfusion to localize the epileptogenic zone in patients of drug resistant mesial temporal lobe epilepsy (MTLE). 2. Correlation of localization of epileptogenic zone on ASL MR perfusion with structural MRI and EEG.

Methods and Materials:

30 patients with MTLE and10 age and gender matched normal controls were studied. All patients underwent ictal video EEG monitoring non-invasively, MR imaging with epilepsy protocol and pseudocontinuous ASL (PCASL) perfusion study. Relative CBF (rCBF) values in bilateral mesial temporal lobes were measured utilizing quantitative analysis of perfusion images. A perfusion asymmetry index (AI) was calculated for each region.

Results:

In patients, ipsilateral mesial temporal rCBF was significantly decreased compared with contralateral mesial temporal rCBF (p = 0.021). Mesial temporal blood flow was more asymmetric in patients than in normal control participants (p = 0.000). Clear perfusion asymmetry on PCASL-MRI was identified despite normal structural-MRI in 5 cases, agreeing with EEG laterality.

Conclusions:

Pseudo-continuous ASL offers a promising approach to detect interictal hypoperfusion in TLE and as a clinical alternative to SPECT and PET due to non-invasiveness and easy accessibility. Incorporation of ASL into routine pre-surgical evaluation protocols can help to localize epileptogenic zone in surgical candidates.

Arterial spin labeling for presurgical localization of refractory frontal lobe epilepsy in children

Background

Epilepsy is one of the most common chronic neurological diseases. Despite the great variety and prevalence of antiepileptic drug treatments, one-third of epilepsies remain drug resistant. The frontal lobe is extensive, and frontal lobe seizures are difficult to locate, which increases the difficulty of the preoperative localization of the epileptogenic zone.

Case presentation

Two previously healthy girls with refractory frontal lobe epilepsy showed significant perfusion abnormalities in the right frontal lobe using the cerebral blood perfusion (CBF) quantitative analysis system. They became seizure-free after lesionectomy of the frontal lobe by ASL combined with electroencephalography (EEG) rapid localization. The histopathological diagnosis was focal cortical dysplasia (FCD) type IIa and IIb.

Conclusions

The positive outcome suggests that the combined use of ASL with EEG could be a beneficial option for the presurgical evaluation of pediatric epilepsy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40001-021-00564-0.

Diagnostic Accuracy of Arterial Spin-Labeling MR Imaging in Detecting the Epileptogenic Zone: Systematic Review and Meta-analysis

BACKGROUND

A noninvasive, safe, and economic imaging technique is required to identify epileptogenic lesions in the brain.

PURPOSE

Our aim was to perform a meta-analysis evaluating the accuracy of arterial spin-labeling in localizing the epileptic focus in the brain and the changes in the blood perfusion in these regions.

DATA SOURCES

Our sources were the PubMed and EMBASE data bases.

STUDY SELECTION

English language studies that assessed the diagnostic accuracy of arterial spin-labeling for detecting the epileptogenic zone up to July 2019 were included.

DATA ANALYSIS

The symptomatogenic foci of seizures in the brain were determined and used as the references. The relevant studies were evaluated using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. The outcomes were evaluated using the pooled sensitivity, pooled specificity, pooled accuracy, diagnostic odds ratio, area under the summary receiver operating characteristic curve, and likelihood ratio.

DATA SYNTHESIS

Six studies that included 174 patients qualified for this meta-analysis. The pooled sensitivity, pooled specificity, and area under the summary receiver operating characteristic curve were 0.74 (95% CI, 0.65-0.82), 0.35 (95% CI, 0.03-0.90), and 0.73 (95% CI, 0.69-0.76), respectively. The accuracy of arterial spin-labeling for localizing the epileptic focus was 0.88 (accuracy in arterial spin-labeling/all perfusion changes in arterial spin-labeling) in cases of a positive arterial spin-labeling result. The epileptogenic zone exhibited hyperperfusion or hypoperfusion.

LIMITATIONS

Only a few studies were enrolled due to the strict inclusion criteria.

CONCLUSIONS

Arterial spin-labeling can be used for assessing, monitoring, and reviewing, postoperatively, patients with epilepsy. Blood perfusion changes in the brain may be closely related to the seizure time and pattern.

Epileptogenic zone detection in MRI negative epilepsy using adaptive thresholding of arterial spin labeling data

Drug-resistant epilepsy is a diagnostic and therapeutic challenge, mainly in patients with negative MRI findings. State-of-the-art imaging methods complement standard epilepsy protocols with new information and help epileptologists to increase the reliability of their decisions. In this study, we investigate whether arterial spin labeling (ASL) perfusion MRI can help localize the epileptogenic zone (EZ). To that end, we developed an image processing method to detect the EZ as an area with hypoperfusion relative to the contralateral unaffected side, using subject-specific thresholding of the asymmetry index in ASL images. We demonstrated three thresholding criteria (termed minimal product criterion, minimal distance criterion, and elbow criterion) on 29 patients with MRI-negative epilepsy (age 32.98 ± 10.4 years). The minimal product criterion showed optimal results in terms of positive predictive value (mean 0.12 in postoperative group and 0.22 in preoperative group) and true positive rate (mean 0.71 in postoperative group and 1.82 in preoperative group). Additionally, we found high accuracy in determining the EZ side (mean 0.86 in postoperative group and 0.73 in preoperative group out of 1.00). ASL can be easily incorporated into the standard presurgical MR protocol, and it provides an additional benefit in EZ localization.

Differential contribution of excitatory and inhibitory neurons in shaping neurovascular coupling in different epileptic neural states

Understanding the neurovascular coupling (NVC) underlying hemodynamic changes in epilepsy is crucial to properly interpreting functional brain imaging signals associated with epileptic events. However, how excitatory and inhibitory neurons affect vascular responses in different epileptic states remains unknown. We conducted real-time in vivo measurements of cerebral blood flow (CBF), vessel diameter, and excitatory and inhibitory neuronal calcium signals during recurrent focal seizures. During preictal states, decreases in CBF and arteriole diameter were closely related to decreased γ-band local field potential (LFP) power, which was linked to relatively elevated excitatory and reduced inhibitory neuronal activity levels. Notably, this preictal condition was followed by a strengthened ictal event. In particular, the preictal inhibitory activity level was positively correlated with coherent oscillating activity specific to inhibitory neurons. In contrast, ictal states were characterized by elevated synchrony in excitatory neurons. Given these findings, we suggest that excitatory and inhibitory neurons differentially contribute to shaping the ictal and preictal neural states, respectively. Moreover, the preictal vascular activity, alongside with the γ-band, may reflect the relative levels of excitatory and inhibitory neuronal activity, and upcoming ictal activity. Our findings provide useful insights into how perfusion signals of different epileptic states are related in terms of NVC.

Simultaneously acquired PET and ASL imaging biomarkers may be helpful in differentiating progression from pseudo-progression in treated gliomas

OBJECTIVES

The aim of this work was investigating the methods based on coupling cerebral perfusion (ASL) and amino acid metabolism ([¹⁸F]DOPA-PET) measurements to evaluate the diagnostic performance of PET/MRI in glioma follow-up.

METHODS

Images were acquired using a 3-T PET/MR system, on a prospective cohort of patients addressed for possible glioma progression. Data were preprocessed with statistical parametric mapping (SPM), including registration on T1-weighted images, spatial and intensity normalization, and tumor segmentation. As index tests, tumor isocontour maps of [¹⁸F]DOPA-PET and ASL T-maps were created and metabolic/perfusion abnormalities were evaluated with the asymmetry index z-score. SPM map analysis of significant size clusters and semi-quantitative PET and ASL map evaluation were performed and compared to the gold standard diagnosis. Lastly, ASL and PET topography of significant clusters was compared to that of the initial tumor.

RESULTS

Fifty-eight patients with unilateral treated glioma were included (34 progressions and 24 pseudo-progressions). The tumor isocontour maps and T-maps showed the highest specificity (100%) and sensitivity (94.1%) for ASL and [¹⁸F]DOPA analysis, respectively. The sensitivity of qualitative SPM maps and semi-quantitative rCBF and rSUV analyses were the highest for glioblastoma.

CONCLUSION

Tumor isocontour T-maps and combined analysis of CBF and [¹⁸F]DOPA-PET uptake allow achieving high diagnostic performance in differentiating between progression and pseudo-progression in treated gliomas. The sensitivity is particularly high for glioblastomas.

KEY POINTS

• Applied separately, MRI and PET imaging modalities may be insufficient to characterize the brain glioma post-therapeutic profile. • Combined ASL and [¹⁸F]DOPA-PET map analysis allows differentiating between tumor progression and pseudo-progression.

Arterial Spin Labeling is a Useful MRI Method for Presurgical Evaluation in MRI-Negative Focal Epilepsy

Arterial spin labeling (ASL) is an MRI technique measuring brain perfusion using magnetically labeled blood as a tracer. The clinical utility of ASL for presurgical evaluation in non-lesional epilepsy as compared with the quantitative analysis of interictal [¹⁸F] fluorodeoxyglucose PET (FDG-PET) was studied. In 10 patients (4 female; median age 29 years) who underwent a complete presurgical evaluation followed by surgical resection, the presurgical FDG-PET and ASL scans were compared with the resection masks using asymmetry index (AI) maps. The positive predictive value (PPV) and sensitivity (SEN), were calculated from the number of voxels inside the mask (true positive), and outside the mask (false positive). The comparison of the PPVs showed better PPV in 6 patients using ASL and in 2 patients with PET. SEN was better in 4 patients using ASL and in 5 patients with PET. According to the Wilcoxon signed rank test for PPV (p = 0.74) and for SEN (p = 0.43), these methods have similar predictive power. ASL is a useful method for presurgical evaluation in non-lesional epilepsy. The main benefits of ASL over PET are that it avoids radiation exposure for patients, and it offers lower costs, higher availability, and better time efficiency.

The utility of arterial spin labeling in the presurgical evaluation of poorly defined focal epilepsy in children

OBJECTIVE

The authors sought to assess the utility of arterial spin labeling (ASL) perfusion 3T-MRI for the presurgical evaluation of poorly defined focal epilepsy in pediatric patients.

METHODS

Pseudocontinuous ASL perfusion 3T-MRI was performed in 25 consecutive children with poorly defined focal epilepsy. ASL perfusion abnormalities were detected qualitatively by visual inspection and quantitatively by calculating asymmetry index (AI) maps and significant z-score cluster maps based on successfully operated cases. ASL results were prospectively compared to scalp EEG, structural 3T-MRI, FDG-PET, ictal/interictal SPECT, magnetoencephalography (MEG), and intracranial recording results, as well as the final surgically proven epileptogenic zone (EZ) in operated patients who had at least 1 year of good (Engel class I/II) seizure outcome and positive histopathology results.

RESULTS

Qualitative ASL perfusion abnormalities were found in 17/25 cases (68%), specifically in 17/20 MRI-positive cases (85.0%) and in none of the 5 MRI-negative cases. ASL was concordant with localizing scalp EEG findings in 66.7%, structural 3T-MRI in 90%, FDG-PET in 75%, ictal/interictal SPECT in 62.5%, and MEG in 75% of cases, and with intracranial recording results in 40% of cases. Eleven patients underwent surgery; in all 11 cases the EZ was surgically proven by positive histopathology results and the patient having at least 1 year of good seizure outcome. ASL results were concordant with this final surgically proven EZ in 10/11 cases (sensitivity 91%, specificity 50%). All 10 ASL-positive patients who underwent surgery had positive surgical pathology results and good long-term postsurgical seizure outcome at a mean follow-up of 39 months. Retrospective quantitative analysis based on significant z-score clusters found 1 true-positive result that was missed by qualitative analysis and 3 additional false-positive results (sensitivity 100%, specificity 23%).

CONCLUSIONS

ASL supports the hypothesis regarding the EZ in poorly defined focal epilepsy cases in children. Due to its convenience and noninvasive nature, the authors recommend that ASL be added routinely to the presurgical MRI evaluation of epilepsy. Future optimized quantitative methods may improve the diagnostic yield of this technique.

Brain volume and perfusion asymmetry in temporal lobe epilepsy with and without hippocampal sclerosis

Objectives: To detect and compare the features of interictal perfusion and volume asymmetry between temporal lobe epilepsy (TLE) patients with and without hippocampal sclerosis (HS).Methods: Sixty-one TLE patients (mean age 28.4 ± 9.3 years; 28 female/33 male) with unilateral signs of HS (TLE-HS+) and 25 TLE patients (mean age 29.8 ± 8.0 years; 17 female/8 male) without HS (TLE-HS-) were included. Thirty healthy volunteers served as controls (mean age 26.0 ± 8.7 years; 22 female/8 male). Brain segmentation and volume calculation were performed. Quantitative cerebral blood flow (CBF) values were measured based on arterial spin labeling (ASL). The asymmetry indices (AIs) of volume and perfusion were calculated.Results: TLE-HS+ (adjusted P = 0.001) and TLE-HS- patients (adjusted P = 0.006) had significantly higher hippocampal perfusion AIs than controls. TLE-HS+ and TLE-HS- had similar hippocampal perfusion AIs (adjusted P = 1.00). TLE-HS+ had higher hippocampal volume AIs than TLE-HS- and controls (adjusted P < 0.001). TLE-HS- and controls had similar hippocampal volume AIs (adjusted P = 1.00). All (100%) TLE-HS+ patients had positive hippocampal perfusion or volume AIs. No significant correlation between the AIs of hippocampal perfusion and volume was found in both TLE-HS+(P = 0.894) and TLE-HS- (P = 0.106) patients. TLE-HS+ patients demonstrated more extensive whole-brain asymmetry of both perfusion and volume than TLE-HS- patients.Conclusion: TLE-HS+ and TLE-HS- patients have different patterns of whole-brain perfusion and volume asymmetry. Hippocampal perfusion asymmetry was revealed in both TLE-HS+ and TLE-HS- patients.

Localizing the seizure onset zone by comparing patient postictal hypoperfusion to healthy controls

Arterial spin labeling (ASL) MRI can provide seizure onset zone (SOZ) localizing information in up to 80% of patients. Clinical implementation of this technique is limited by the need to obtain two scans per patient: a postictal scan that is subtracted from an interictal scan. We aimed to determine whether it is possible to limit the number of ASL scans to one per patient by comparing patient postictal ASL scans to baseline scans of 100 healthy controls. Eighteen patients aged 20-55 years underwent ASL MRI <90 min after a seizure and during the interictal period. Each postictal cerebral blood flow (CBF) map was statistically compared to average baseline CBF maps from 100 healthy controls (pvcASL; patient postictal CBF vs. control baseline CBF). The pvcASL maps were compared to subtraction ASL maps (sASL; patient baseline CBF minus patient postictal CBF). Postictal CBF reductions from pvcASL and sASL maps were seen in 17 of 18 (94.4%) and 14 of 18 (77.8%) patients, respectively. Maximal postictal hypoperfusion seen in pvcASL and sASL maps was concordant with the SOZ in 10 of 17 (59%) and 12 of 14 (86%) patients, respectively. In seven patients, both pvcASL and sASL maps showed similar results. In two patients, sASL showed no significant hypoperfusion, while pvcASL showed significant hypoperfusion concordant with the SOZ. We conclude that pvcASL is clinically useful and although it may have a lower overall concordance rate than sASL, pvcASL does provide localizing or lateralizing information for specific cases that would be otherwise missed through sASL.

Cerebral Blood Flow Alterations in High Myopia: An Arterial Spin Labeling Study

Objective

The aim of this study was to explore cerebral blood flow (CBF) alterations in subjects with high myopia (HM) using three-dimensional pseudocontinuous arterial spin labeling (3D-pcASL).

Methods

A total of sixteen patients with bilateral HM and sixteen age- and sex-matched healthy controls (HCs) were recruited. All subjects were right-handed. Image data preprocessing was performed using SPM8 and the DPABI toolbox. Clinical parameters were acquired in the HM group. Two-sample t-tests and Pearson correlation analysis were applied in this study.

Results

Compared to HCs, patients with HM exhibited significantly increased CBF in the bilateral cerebellum, and no decreases in CBF were detected in the brain. However, no relationship was found between the mean CBF values in the different brain areas and the disease duration (P > 0.05).

Conclusions

Using ASL analysis, we detected aberrant blood perfusion in the cerebellum in HM patients, contributing to a better understanding of brain abnormalities and brain plasticity through a different perspective.

CT perfusion measurement of postictal hypoperfusion: localization of the seizure onset zone and patterns of spread

PURPOSE

Seizures are often followed by a period of transient neurological dysfunction and postictal alterations in cerebral blood flow may underlie these symptoms. Recent animal studies have shown reduced local cerebral blood flow at the seizure onset zone (SOZ) lasting approximately 1 h following seizures. Using arterial spin labelling (ASL) MRI, we observed postictal hypoperfusion at the SOZ in 75% of patients. The clinical implementation of ASL as a tool to identify the SOZ is hampered by the limited availability of MRI on short notice. Computed tomography perfusion (CTP) also measures blood flow and may circumvent the logistical limitations of MRI. Thus, we aimed to measure the extent of postictal hypoperfusion using CTP.

METHODS

Fourteen adult patients with refractory focal epilepsy admitted for presurgical evaluation were prospectively recruited and underwent CTP scanning within 80 min of a habitual seizure. Patients also underwent a baseline scan after they were seizure-free for > 24 h. The acquired scans were qualitatively assessed by two reviewers by visual inspection and quantitatively assessed through a subtraction pipeline to identify areas of significant postictal hypoperfusion.

RESULTS

Postictal blood flow reductions of > 15 ml/100 g^-1/min^-1 were seen in 12/13 patients using the quantitative method of analysis. In 10/12 patients, the location of the hypoperfusion was partially or fully concordant with the presumed SOZ. In all patients, additional areas of scattered hypoperfusion were seen in areas corresponding to seizure spread.

CONCLUSION

CTP can reliably measure postictal hypoperfusion which is maximal at the presumed SOZ.

Similar and Differing Distributions Between 18F-FDG-PET and Arterial Spin Labeling Imaging in Temporal Lobe Epilepsy

Background: Despite the increasing use of arterial spin labeling (ASL) in patients with epilepsy, little is known about its brain regional distribution pattern, including diaschisis, and its correspondence with FDG-PET. Here, we investigated the regional match and mismatch between FDG-PET and ASL in temporal lobe epilepsy (TLE). Methods: We recruited 27 patients with unilateral TLE, who underwent inter-ictal ASL and FDG-PET scans. These images were spatially normalized using Statistical Parametric Mapping 12, and the regional values in both ASL and FDG-PET were calculated using PMOD software within 20 volumes of interest (VOIs), including the temporal lobe, adjacent cortices, subcortical structures, and cerebellum. ASL images of 37 healthy controls were also analyzed and compared. Results: Whereas, ASL showed significant side differences, mainly in the temporal and frontal lobes, the significant abnormalities in FDG-PET were more widespread and included the insula and supramarginal gyrus. Ipsilateral thalamic reduction was found in FDG-PET only. The detectability of the focus side compared with the contralateral side was generally higher in FDG-PET. The discriminative values in ASL compared with healthy controls were higher in temporal neocortex and amygdala VOIs. Conclusions: There are similar and differing regional distributions between FDG-PET and ASL in TLE, possibly reflecting regional match and mismatch of cerebral blood flow and metabolism. At this stage, it seems that ASL couldn't present comparable clinical usefulness with FDG-PET. These findings deepen our knowledge of ASL imaging and are potentially useful for its further application.

Clinical Value of Hybrid TOF-PET/MR Imaging-Based Multiparametric Imaging in Localizing Seizure Focus in Patients with MRI-Negative Temporal Lobe Epilepsy

BACKGROUND AND PURPOSE

Temporal lobe epilepsy is the most common type of epilepsy. Early surgical treatment is superior to prolonged medical therapy in refractory temporal lobe epilepsy. Successful surgical operations depend on the correct localization of the epileptogenic zone. This study aimed to evaluate the clinical value of hybrid TOF-PET/MR imaging-based multiparametric imaging in localizing the epileptogenic zone in patients with MR imaging-negative for temporal lobe epilepsy.

MATERIALS AND METHODS

Twenty patients with MR imaging-negative temporal lobe epilepsy who underwent preoperative evaluation and 10 healthy controls were scanned using PET/MR imaging with simultaneous acquisition of PET and arterial spin-labeling. On the basis of the standardized uptake value and cerebral blood flow, receiver operating characteristic analysis and a logistic regression model were used to evaluate the predictive value for the localization. Statistical analyses were performed using statistical parametric mapping. The values of the standardized uptake value and cerebral blood flow, as well as the asymmetries of metabolism and perfusion, were compared between the 2 groups. Histopathologic findings were used as the criterion standard.

RESULTS

Complete concordance was noted in lateralization and localization among the PET, arterial spin-labeling, and histopathologic findings in 12/20 patients based on visual assessment. Concordance with histopathologic findings was also obtained for the remaining 8 patients based on the complementary PET and arterial spin-labeling information. Receiver operating characteristic analysis showed that the sensitivity and specificity of PET, arterial spin-labeling, and combined PET and arterial spin-labeling were 100% and 81.8%, 83.3% and 54.5%, and 100% and 90.9%, respectively. When we compared the metabolic abnormalities in patients with those in healthy controls, hypometabolism was detected in the middle temporal gyrus (P < .001). Metabolism and perfusion asymmetries were also located in the temporal lobe (P < .001).

CONCLUSIONS

PET/MR imaging-based multiparametric imaging involving arterial spin-labeling may increase the clinical value of localizing the epileptogenic zone by providing concordant and complementary information in patients with MR imaging-negative temporal lobe epilepsy.

Role of contrast-free MR-perfusion in the diagnosis of potential epileptogenic foci in children with focal epilepsia

ASL (Arterial Spin Labeling) – a novel modality of MR angiography – is based on radio-frequency labeling of aqueous protons in the arterial blood; the method is used to monitor blood supply to  organs, including the brain. So far there has been little information on the use of ASL in children with focal epilepsy, especially in the pre-surgery period.

Aim:to evaluate the perfusion patterns in seizure-free children with drug resistant focal epilepsy (FE) using the ASL mode of MRI.

Materials and methods.We studied the ASL data of 54 (23-boys/31 girls) patients with FE  treated in the Dpt. of Neurology at the Russian State Children Hospital from 2015 to 2018. The  patients’ age varied from 4 months to 17 years. All images were produced with a 3T GE Discovery  750W system.

Results. We found several brain perfusion patterns in children with FE; among other factors, those patterns depended on the clinical status of the patient, i. e. the interictal period or the early post- seizure period. The main pattern of the interictal period was characterized by a focal decrease in  perfusion located around a structural focus identified on MRI scans. In the early post-seizure  period, there was an increase in the arterial perfusion in the area of a structural epileptogenic lesion.

Conclusion.ASL-MRI is an effective diagnostic method providing more information on children  with FE during their pre-surgery phase. The ASL modality needs further research to rationalize its wider use as a preferred diagnostic tool or as a combination with the more complex PET and SPECT.

The Imaging of Localization Related Symptomatic Epilepsies: The Value of Arterial Spin Labelling Based Magnetic Resonance Perfusion

Accurate identification of the epileptogenic zone is an important prerequisite in presurgical evaluation of refractory epilepsy since it affects seizure-free outcomes. Apart from structural magnetic resonance imaging (sMRI), delineation has been traditionally done with electroencephalography and nuclear imaging modalities. Arterial spin labelling (ASL) sequence is a non-contrast magnetic resonance perfusion technique capable of providing similar information. Similar to single-photon emission computed tomography, its utility in epilepsy is based on alterations in perfusion linked to seizure activity by neurovascular coupling. In this article, we discuss complementary value that ASL can provide in the evaluation and characterization of some basic substrates underlying epilepsy. We also discuss the role that ASL may play in sMRI negative epilepsy and acute scenarios such as status epilepticus.

Comparison between simultaneously acquired arterial spin labeling and 18F-FDG PET in mesial temporal lobe epilepsy assisted by a PET/MR system and SEEG

Objective

In the detection of seizure onset zones, arterial spin labeling (ASL) can overcome the limitations of positron emission tomography (PET) with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG), which is invasive, expensive, and radioactive. PET/magnetic resonance (MR) systems have been introduced that allow simultaneous performance of ASL and PET, but comparisons of these techniques with stereoelectroencephalography (SEEG) and comparisons among the treatment outcomes of these techniques are still lacking. Here, we investigate the effectiveness of ASL compared with that of SEEG and their outcomes in localizing mesial temporal lobe epilepsy (MTLE) and assess the correlation between simultaneously acquired PET and ASL.

Methods

Between October 2016 and August 2017, we retrospectively studied 12 patients diagnosed with pure unilateral MTLE. We extracted and quantitatively computed values for ASL and PET in the bilateral hippocampus. SEEG findings and outcome were considered the gold standard of lateralization. Finally, the bilateral asymmetry index (AI) was calculated to assess the correlation between PET and ASL.

Results

Our results showed that hypoperfusion in the hippocampus detected using ASL matched the SEEG-defined epileptogenic zone in this series of patients. The mean normalized voxel value of ASL in the contralateral hippocampus was 0.97 ± 0.19, while in the ipsilateral hippocampus, it was 0.84 ± 0.14. Meanwhile, significantly decreased perfusion and metabolism were observed in these patients (Wilcoxon, p < 0.05), with a significant positive correlation between the AI values derived from PET and ASL (Pearson's correlation, r = 0.74, p < 0.05).

Significance

In our SEEG- and outcome-defined patients with MTLE, ASL could provide significant information during presurgical evaluation, with the hypoperfusion detected with ASL reliably lateralizing MTLE. This non-invasive technique may be used as an alternative diagnostic tool for MTLE lateralization.

•

ASL has been increasingly used in presurgical evaluations in epilepsy recent years.

•

Comparisons of ASL and PET with a PET/MR system using SEEG and treatment outcomes as gold-standard are still lacking.

•

Decreased perfusion consistent with hypometabolism and SEEG was observed with ASL.

•

ASL offers an effective non-invasive alternative to PET in evaluation of MTLE.

Usefulness of Pulsed Arterial Spin Labeling Magnetic Resonance Imaging in New-onset Seizure Patients and Its Comparison with Dynamic Susceptibility Contrast Magnetic Resonance Imaging

Introduction

Dynamic susceptibility contrast (DSC) perfusion and pulsed arterial spin labeling (PASL) imaging are newer advanced magnetic resonance sequences which are capable of detecting vascular changes in patients with new-onset seizure disorder even when no significant abnormalities are visualized on conventional sequences. The purpose of our study is to establish utility of arterial spin labeling (ASL) in new-onset seizure patients and compare ASL with DSC perfusion sequence.

Materials and Methods

Twenty-six patients coming to emergency department with new-onset seizure disorder were evaluated using DSC and ASL sequence. Perfusion asymmetry was assessed using region of interests taken at places where signal asymmetry was maximal.

Results

PASL sequence showed focal vascular changes in form of hyperperfusion in four patients, hypoperfusion in nine patients, and normal perfusion in 13 patients. Altered perfusion whether hypo/hyperperfusion was detected in five out of 16 patients even when conventional sequences were normal. There was strong positive linear correlation between ASL and DSC with P = 0.001.

Conclusion

Noninvasive PASL is capable of detecting vascular changes induced by seizure and is comparable to DSC sequence. Thus, it is recommended when there is a need for repeated evaluations; in follow-up/therapy response assessment and when contrast administration is contraindicated.

Seizure onset zone localization using postictal hypoperfusion detected by arterial spin labelling MRI

Neurological dysfunction following epileptic seizures is a well-recognized phenomenon. Several potential mechanisms have been suggested to explain postictal dysfunction, with alteration in cerebral blood flow being one possibility. These vascular disturbances may be long lasting and localized to brain areas involved in seizure generation and propagation, as supported by both animal and human studies. Therefore, measuring perfusion changes in the postictal period may help localize the seizure onset zone. Arterial spin labelling is a non-invasive, rapid and reproducible magnetic resonance imaging technique that measures cerebral perfusion. To this end, we measured postictal perfusion in patients with drug resistant focal epilepsy who were admitted to our seizure-monitoring unit for presurgical evaluation. Twenty-one patients were prospectively recruited and underwent arterial spin labelling scanning within 90 min of a habitual seizure. Patients also underwent a similar scan in the interictal period, after they were seizure-free for at least 24 h. The acquired scans were subtracted to identify the areas of significant postictal hypoperfusion. The location of the maximal hypoperfusion was compared to the presumed seizure onset zone to assess for concordance. Also, the localizing value of this technique was compared to other structural and functional imaging modalities. Postictal perfusion reductions of >15 units (ml/100 g/l) were seen in 15/21 patients (71.4%). In 12/15 (80%) of these patients, the location of the hypoperfusion was partially or fully concordant with the location of the presumed seizure onset zone. This technique compared favourably to other neuroimaging modalities, being similar or superior to structural magnetic resonance imaging in 52% of cases, ictal single-photon emission computed tomography in 60% of cases and interictal positron emission tomography in 71% of cases. Better arterial spin labelling results were obtained in patients in whom the seizure onset zone was discernible based on non-invasive data. Thus, this technique is a safe, non-invasive and relatively inexpensive tool to detect postictal hypoperfusion that may provide useful data to localize the seizure onset zone. This technique may be incorporated into the battery of conventional investigations for presurgical evaluation of patients with drug resistant focal epilepsy.

Combining arterial-spin labeling with functional magnetic resonance imaging measurement for characterizing patients with minimal hepatic encephalopathy

AIM

Our objective is to explore key changes in brain functions in relation to minimal hepatic encephalopathy (MHE). We incorporated both resting-state functional magnetic resonance imaging (fMRI) and arterial spin labeling (ASL) to enhance the detection of MHE.

METHODS

We undertook fMRI scanning for 56 MHE patients and 66 healthy controls. Region functional connectivity was carried out to assess the connectivity status between pairs of regions among 90 brain regions. Additionally, blood flow (BF) status was measured by ASL for all subjects. Spearman's correlation test was implemented to identify any correlation among z-values, results from number connection test type A, and digit symbol tests. Finally, the receiver operating characteristic curve was generated for assessing the accuracy of BF in MHE diagnosis.

RESULTS

The corresponding functional connectivity was significantly different between MHE and control groups in 15 regions. For MHE patients, BF showed an increasing pattern in regions of interest. Blood flood in the putamen was positively correlated with number connection test type A neuropsychological performance, whereas it was negatively correlated with the digit symbol test. Blood flood in the right putamen showed the highest value of area under the curve with a sensitivity of 85.7% and specificity of 89.4%.

CONCLUSION

Connectivity impairment resulting from ganglia-thalamo-cortical circuits may play important roles in mediating the development of MHE patients. An increase in the BF, particularly in the right putamen, may be considered as evidence for the presence of MHE.

Arterial Spin Labeling Perfusion of the Brain: Emerging Clinical Applications

Arterial spin labeling (ASL) is a magnetic resonance (MR) imaging technique used to assess cerebral blood flow noninvasively by magnetically labeling inflowing blood. In this article, the main labeling techniques, notably pulsed and pseudocontinuous ASL, as well as emerging clinical applications will be reviewed. In dementia, the pattern of hypoperfusion on ASL images closely matches the established patterns of hypometabolism on fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) images due to the close coupling of perfusion and metabolism in the brain. This suggests that ASL might be considered as an alternative for FDG, reserving PET to be used for the molecular disease-specific amyloid and tau tracers. In stroke, ASL can be used to assess perfusion alterations both in the acute and the chronic phase. In arteriovenous malformations and dural arteriovenous fistulas, ASL is very sensitive to detect even small degrees of shunting. In epilepsy, ASL can be used to assess the epileptogenic focus, both in peri- and interictal period. In neoplasms, ASL is of particular interest in cases in which gadolinium-based perfusion is contraindicated (eg, allergy, renal impairment) and holds promise in differentiating tumor progression from benign causes of enhancement. Finally, various neurologic and psychiatric diseases including mild traumatic brain injury or posttraumatic stress disorder display alterations on ASL images in the absence of visualized structural changes. In the final part, current limitations and future developments of ASL techniques to improve clinical applicability, such as multiple inversion time ASL sequences to assess alterations of transit time, reproducibility and quantification of cerebral blood flow, and to measure cerebrovascular reserve, will be reviewed. ^© RSNA, 2016 Online supplemental material is available for this article.

Identification of cerebral perfusion using arterial spin labeling in patients with seizures in acute settings

This study aimed to explore the utility of arterial spin labeling perfusion-weighted imaging (ASL-PWI) in patients with suspected seizures in acute settings. A total of 164 patients who underwent ASL-PWI for suspected seizures in acute settings (with final diagnoses of seizure [n = 129], poststroke seizure [n = 18], and seizure mimickers [n = 17]), were included in this retrospective study. Perfusion abnormality was analyzed for: (1) pattern, (2) multifocality, and (3) atypical distribution against vascular territories. Perfusion abnormality was detected in 39% (50/129) of the seizure patients, most (94%, 47/50) being the hyperperfusion pattern. Of the patients with perfusion abnormality, multifocality or hemispheric involvement and atypical distribution against vascular territory were revealed in 46% (23/50) and 98% (49/50), respectively. In addition, seizures showed characteristic features including hyperperfusion (with or without non-territorial distribution) on ASL-PWI, thus differentiating them from poststroke seizures or seizure mimickers. In patients in whom seizure focus could be localized on both EEG and ASL-PWI, the concordance rate was 77%. The present study demonstrates that ASL-PWI can provide information regarding cerebral perfusion status in patients with seizures in acute settings and has the potential to be used as a non-invasive imaging tool to identify the cerebral perfusion in patients with seizures.

Impaired cerebral blood flow networks in temporal lobe epilepsy with hippocampal sclerosis: A graph theoretical approach

Graph theory is an emerging method to investigate brain networks. Altered cerebral blood flow (CBF) has frequently been reported in temporal lobe epilepsy (TLE), but graph theoretical findings of CBF are poorly understood. Here, we explored graph theoretical networks of CBF in TLE using arterial spin labeling imaging. We recruited patients with TLE and unilateral hippocampal sclerosis (HS) (19 patients with left TLE, and 21 with right TLE) and 20 gender- and age-matched healthy control subjects. We obtained all participants' CBF maps using pseudo-continuous arterial spin labeling and analyzed them using the Graph Analysis Toolbox (GAT) software program. As a result, compared to the controls, the patients with left TLE showed a significantly low clustering coefficient (p=0.024), local efficiency (p=0.001), global efficiency (p=0.010), and high transitivity (p=0.015), whereas the patients with right TLE showed significantly high assortativity (p=0.046) and transitivity (p=0.011). The group with right TLE also had high characteristic path length values (p=0.085), low global efficiency (p=0.078), and low resilience to targeted attack (p=0.101) at a trend level. Lower normalized clustering coefficient (p=0.081) in the left TLE and higher normalized characteristic path length (p=0.089) in the right TLE were found also at a trend level. Both the patients with left and right TLE showed significantly decreased clustering in similar areas, i.e., the cingulate gyri, precuneus, and occipital lobe. Our findings revealed differing left-right network metrics in which an inefficient CBF network in left TLE and vulnerability to irritation in right TLE are suggested. The left-right common finding of regional decreased clustering might reflect impaired default-mode networks in TLE.

Capability of arterial spin labeling MR imaging in localizing seizure focus in clinical seizure activity

PURPOSE

The purpose of this study was to evaluate cerebral blood flow using arterial spin labeling (ASL) perfusion magnetic resonance (MR) imaging in patients with clinical seizure activity and determine its diagnostic performance in identifying seizure focus.

MATERIALS AND METHODS

Institutional Review Board of our hospital approved this retrospective study. Informed consent was waived. Clinical seizure focus was determined by a neurologist based on seizure semiology, electroencephalography, and conventional imaging modalities. The diagnostic performance of ASL perfusion MR imaging to identifying seizure focus compared to clinical seizure focus was analyzed.

RESULTS

Clinical seizure focus was localized in 95% (42/44) of patients. The sensitivity and specificity of ASL perfusion MR imaging for identifying seizure focus were 74% (95% CI: 58%, 86%) (clinical seizure focus was localizable in 31 of 42 patients, including complete concordance in 10 patients and partial concordance in 21 patients) and 0% (95% CI: 0%, 84%) (for the two patients whose clinical seizure foci were not localizable, they were identified by ASL perfusion MR imaging), respectively. Thus, the overall accuracy of ASL perfusion MR imaging for localizing seizure focus was 70% (33/44). For 4 patients who had abnormal perfusion on ASL, their seizure foci based on ASL perfusion MR imaging were discordant with clinical seizure foci.

CONCLUSION

ASL perfusion MR imaging can provide information about perfusion status and important diagnostic clue in localizing seizure focus in patients with clinical seizure activity. It has the potential as a non-invasive complementary diagnostic tool for patients with clinical seizure activity.

Cerebral metabolism and perfusion in MR-negative individuals with refractory focal epilepsy assessed by simultaneous acquisition of (18)F-FDG PET and arterial spin labeling

The major challenge in pre-surgical epileptic patient evaluation is the correct identification of the seizure onset area, especially in MR-negative patients. In this study, we aimed to: (1) assess the concordance between perfusion, from ASL, and metabolism, from ¹⁸F-FDG, acquired simultaneously on PET/MR; (2) verify the utility of a statistical approach as supportive diagnostic tool for clinical readers. Secondarily, we compared ¹⁸F-FDG PET data from the hybrid PET/MR system with those acquired with PET/CT, with the purpose of validate the reliability of ¹⁸F-FDG PET/MR data.

Twenty patients with refractory focal epilepsy, negative MR and a defined electro-clinical diagnosis underwent PET/MR, immediately followed by PET/CT. Standardized uptake value ratio (SUVr) and cerebral blood flow (CBF) maps were calculated for PET/CT-PET/MR and ASL, respectively. For all techniques, z-score of the asymmetry index (z_AI) was applied for depicting significant Right/Left differences. SUVr and CBF images were firstly visually assessed by two neuroimaging readers, who then re-assessed them considering z_AI for reaching a final diagnosis.

High agreement between ¹⁸F-FDG PET/MR and ASL was found, showing hypometabolism and hypoperfusion in the same hemisphere in 18/20 patients, while the remaining were normal. They were completely concordant in 14/18, concordant in at least one lobe in the remaining. z_AI maps improved readers' confidence in 12/20 and 15/20 patients for ¹⁸F-FDG PET/MR and ASL, respectively. ¹⁸F-FDG PET/CT-PET/MR showed high agreement, especially when z_AI was considered.

The simultaneous metabolism-perfusion acquisition provides excellent concordance on focus lateralisation and good concordance on localisation, determining useful complementary information.

•

Simultaneous PET/MR to evaluate cerebral perfusion and glucose metabolism in MR-negative refractory focal epilepsy patients.

•

ASL and ¹⁸F-FDG PET/MR showed excellent concordance on lateralisation and good concordance on localisation of focus.

•

ASL and ¹⁸F-FDG PET/MR can provide complementary information for focus localisation.

•

An individually-tailored z-score approach can allow a better identification of the epileptic focus.

Application of Arterial Spin Labelling in the Assessment of Ocular Tissues

Arterial spin labelling (ASL) is a noninvasive magnetic resonance imaging (MRI) modality, capable of measuring blood perfusion without the use of a contrast agent. While ASL implementation for imaging the brain and monitoring cerebral blood flow has been reviewed in depth, the technique is yet to be widely used for ocular tissue imaging. The human retina is a very thin but highly stratified structure and it is also situated close to the surface of the body which is not ideal for MR imaging. Hence, the application of MR imaging and ASL in particular has been very challenging for ocular tissues and retina. That is despite the fact that almost all of retinal pathologies are accompanied by blood perfusion irregularities. In this review article, we have focused on the technical aspects of the ASL and their implications for its optimum adaptation for retinal blood perfusion monitoring. Retinal blood perfusion has been assessed through qualitative or invasive quantitative methods but the prospect of imaging flow using ASL would increase monitoring and assessment of retinal pathologies. The review provides details of ASL application in human ocular blood flow assessment.

A neuroradiologist's guide to arterial spin labeling MRI in clinical practice

Arterial spin labeling (ASL) is a non-invasive MRI technique to measure cerebral blood flow (CBF). This review provides a practical guide and overview of the clinical applications of ASL of the brain, as well its potential pitfalls. The technical and physiological background is also addressed. At present, main areas of interest are cerebrovascular disease, dementia and neuro-oncology. In cerebrovascular disease, ASL is of particular interest owing to its quantitative nature and its capability to determine cerebral arterial territories. In acute stroke, the source of the collateral blood supply in the penumbra may be visualised. In chronic cerebrovascular disease, the extent and severity of compromised cerebral perfusion can be visualised, which may be used to guide therapeutic or preventative intervention. ASL has potential for the detection and follow-up of arteriovenous malformations. In the workup of dementia patients, ASL is proposed as a diagnostic alternative to PET. It can easily be added to the routinely performed structural MRI examination. In patients with established Alzheimer’s disease and frontotemporal dementia, hypoperfusion patterns are seen that are similar to hypometabolism patterns seen with PET. Studies on ASL in brain tumour imaging indicate a high correlation between areas of increased CBF as measured with ASL and increased cerebral blood volume as measured with dynamic susceptibility contrast-enhanced perfusion imaging. Major advantages of ASL for brain tumour imaging are the fact that CBF measurements are not influenced by breakdown of the blood–brain barrier, as well as its quantitative nature, facilitating multicentre and longitudinal studies.

International Veterinary Epilepsy Task Force recommendations for a veterinary epilepsy-specific MRI protocol

Epilepsy is one of the most common chronic neurological diseases in veterinary practice. Magnetic resonance imaging (MRI) is regarded as an important diagnostic test to reach the diagnosis of idiopathic epilepsy. However, given that the diagnosis requires the exclusion of other differentials for seizures, the parameters for MRI examination should allow the detection of subtle lesions which may not be obvious with existing techniques. In addition, there are several differentials for idiopathic epilepsy in humans, for example some focal cortical dysplasias, which may only apparent with special sequences, imaging planes and/or particular techniques used in performing the MRI scan. As a result, there is a need to standardize MRI examination in veterinary patients with techniques that reliably diagnose subtle lesions, identify post-seizure changes, and which will allow for future identification of underlying causes of seizures not yet apparent in the veterinary literature.

There is a need for a standardized veterinary epilepsy-specific MRI protocol which will facilitate more detailed examination of areas susceptible to generating and perpetuating seizures, is cost efficient, simple to perform and can be adapted for both low and high field scanners. Standardisation of imaging will improve clinical communication and uniformity of case definition between research studies. A 6–7 sequence epilepsy-specific MRI protocol for veterinary patients is proposed and further advanced MR and functional imaging is reviewed.

Presurgical evaluation of mesial temporal lobe epilepsy with multiple advanced MR techniques at 3T

BACKGROUND AND PURPOSE

Accurate localization of the epileptogenic zone is essential for successful surgical treatment of mesial temporal lobe epilepsy (MTLE). The aim of this study was to analyze and compare the hippocampal volumetry (HV), MR spectroscopy (MRS), Dynamic susceptibility contrast (DSC) and pulsed arterial spin labeling (pASL) perfusion techniques in a large sample size of refractory MTLE patients.

MATERIALS AND METHODS

Forty-two patients with medically refractory MTLE who underwent preoperative evaluation and eleven normal controls were studied. Pathologic and control hippocampi were compared in terms of hippocampal volume, metabolite ratios and relative hippocampal perfusion values. By using cut-off points and asymmetry indexes, percentages of performance indicators for each technique were calculated in groups of MR (+), MR (-) and bilateral MTLE.

RESULTS

For all techniques, a statistically significant difference was found between the pathologic and control hippocampus groups (P<0.001). Also, all of them except HV had diagnostic value in groups of MR (-) and bilateral MTLE.

CONCLUSION

HV, MRS, DSC and pASL have achieved comparable performance and each of them provides important information about the lateralization of epileptogenic focus. Among those, pASL and MRS may easily be used as an adjunct to conventional MR.

Patient-specific detection of cerebral blood flow alterations as assessed by arterial spin labeling in drug-resistant epileptic patients

Electrophysiological and hemodynamic data can be integrated to accurately and precisely identify the generators of abnormal electrical activity in drug-resistant focal epilepsy. Arterial Spin Labeling (ASL), a magnetic resonance imaging (MRI) technique for quantitative noninvasive measurement of cerebral blood flow (CBF), can provide a direct measure of variations in cerebral perfusion associated with the epileptic focus. In this study, we aimed to confirm the ASL diagnostic value in the identification of the epileptogenic zone, as compared to electrical source imaging (ESI) results, and to apply a template-based approach to depict statistically significant CBF alterations. Standard video-electroencephalography (EEG), high-density EEG, and ASL were performed to identify clinical seizure semiology and noninvasively localize the epileptic focus in 12 drug-resistant focal epilepsy patients. The same ASL protocol was applied to a control group of 17 healthy volunteers from which a normal perfusion template was constructed using a mixed-effect approach. CBF maps of each patient were then statistically compared to the reference template to identify perfusion alterations. Significant hypo- and hyperperfused areas were identified in all cases, showing good agreement between ASL and ESI results. Interictal hypoperfusion was observed at the site of the seizure in 10/12 patients and early postictal hyperperfusion in 2/12. The epileptic focus was correctly identified within the surgical resection margins in the 5 patients who underwent lobectomy, all of which had good postsurgical outcomes. The combined use of ESI and ASL can aid in the noninvasive evaluation of drug-resistant epileptic patients.

pASL versus DSC perfusion MRI in lateralizing temporal lobe epilepsy

BACKGROUND

Accurate lateralization of the epileptogenic focus in temporal lobe epilepsy (TLE) is crucial. Pulsed arterial spin labeling (pASL) has the capability of quantifying local relative cerebral blood flow (rCBF) by measuring the inflow of electromagnetically labeled arterial blood into the target area, and can be used in the presurgical workup of refractory TLE.

PURPOSE

To evaluate pASL in detecting mesial temporal lobe (mTL) perfusion asymmetry for the lateralization of the epileptogenic focus in patients with refractory TLE and to compare it with dynamic susceptibility contrast enhanced (DSC) magnetic resonance imaging (MRI) technique.

MATERIAL AND METHODS

This study was approved by the local ethical committee, and written informed consent was obtained in each patient. Thirty-six patients with medically refractory TLE and 11 healthy volunteer was enrolled in this study. Following brain MRI, pASL and DSC perfusion were performed in all subjects at 3T. rCBF measurements with two different perfusion MRI technique were compared between the patient and healthy volunteers. Lateralization based on perfusion asymmetry index (AI) were also evaluated and compared with clinical lateralization.

RESULTS

rCBF ratios measured in healthy volunteers by two different perfusion technique did not show any statistically significant difference. In TLE patients rCBF ratio of the ipsilateral (affected) side was found to be significantly lower than the contralateral (unaffected) side with both technique. The AI in the patient group was 8.86 ± 3.88 with pASL and 8.39 ± 4.06 with DSC. Correlation coefficient between clinical laterality and perfusion AI were 0.86 for pASL and 0.83 for DSC.

CONCLUSION

pASL can successfully detect interictal asymmetry in patients with TLE and can readily be combined with routine structural assessment for lateralization, providing an alternative to DSC perfusion.

Neuroimaging in refractory epilepsy. Current practice and evolving trends

Identification of the epileptogenic zone is of paramount importance in refractory epilepsy as the success of surgical treatment depends on complete resection of the epileptogenic zone. Imaging plays an important role in the locating and defining anatomic epileptogenic abnormalities in patients with medically refractory epilepsy. The aim of this article is to present an overview of the current MRI sequences used in epilepsy imaging with special emphasis of lesion seen in our practices. Optimisation of epilepsy imaging protocols are addressed and current trends in functional MRI sequences including MR spectroscopy, diffusion tensor imaging and fusion MR with PET and SPECT are discussed.

Functional neuro-imaging as a pre-surgical tool in epilepsy

Functional neuro-imaging techniques are helpful in the pre-surgical evaluation of epilepsy for localization of the epileptogenic zone as ancillary tools to electroencephalography (EEG) and magnetic resonance imaging (MRI) or when other localization techniques are normal, non-concordant or discordant. Positron emission tomography (PET) and ictal single photon emission computed tomography (ictal SPECT) imaging are traditional tests that have been reported to have good sensitivity and specificity although the results are better with more expertise as is true for any technique. More recently magnetoencephalogram/magnetic source imaging (MEG/MSI), diffusion tensor imaging and functional magnetic resonance imaging (fMRI) have been used in localization and functional mapping during the pre-surgical work-up of epilepsy. Newer techniques such as fMRI-EEG, functional connectivity magnetic resonance imaging and near infra-red spectroscopy, magnetic resonance spectroscopy and magneto nanoparticles hold promise for further development that could then be applied in the work-up of epilepsy surgery. In this manuscript, we review these techniques and their current position in the pre-surgical evaluation of epilepsy.

Clinical evaluation of an arterial-spin-labeling product sequence in steno-occlusive disease of the brain

Introduction

In brain perfusion imaging, arterial spin labeling (ASL) is a noninvasive alternative to dynamic susceptibility contrast-magnetic resonance imaging (DSC-MRI). For clinical imaging, only product sequences can be used. We therefore analyzed the performance of a product sequence (PICORE-PASL) included in an MRI software-package compared with DSC-MRI in patients with steno-occlusion of the MCA or ICA >70%.

Methods

Images were acquired on a 3T MRI system and qualitatively analyzed by 3 raters. For a quantitative analysis, cortical ROIs were placed in co-registered ASL and DSC images. Pooled data for ASL-cerebral blood flow (CBF) and DSC-CBF were analyzed by Spearman’s correlation and the Bland-Altman (BA)-plot.

Results

In 28 patients, 11 ASL studies were uninterpretable due to patient motion. Of the remaining patients, 71% showed signs of delayed tracer arrival. A weak correlation for DSC-relCBF vs ASL-relCBF (r = 0.24) and a large spread of values in the BA-plot owing to unreliable CBF-measurement was found.

Conclusion

The PICORE ASL product sequence is sensitive for estimation of delayed tracer arrival, but cannot be recommended to measure CBF in steno-occlusive disease. ASL-sequences that are less sensitive to patient motion and correcting for delayed blood flow should be available in the clinical setting.

Regional correlation between resting state FDG PET and pCASL perfusion MRI

To determine how arterial spin labeling (ASL) measured perfusion relates to baseline metabolism, we compared resting state cerebral perfusion using pseudo-continuous ASL and cerebral glucose metabolism using (18)F-FDG PET in 20 normal volunteers. Greater regional metabolism relative to perfusion was observed in the putamen, orbitofrontal and temporal lobes, whereas perfusion was relatively higher in the hippocampus and insula. In a region of interest analysis limited to gray matter, the overall mean correlation between perfusion and metabolism across voxels was r=0.43 with considerable regional variability. Cross-voxel correlations between relative perfusion and metabolism in mean ASL and PET images of all 20 subjects were the highest in the striatum (caudate: r=0.78; putamen: r=0.81), and the lowest in medial temporal structures (amygdala: r=0.087; hippocampus: r=-0.26). Correlations between mean relative perfusion and metabolism across 20 subjects were the highest in the striatum (caudate: r=0.76; putamen: r=0.58), temporal lobe (r=0.59), and frontal lobe (r=0.52), but very poor in all other structures (r<0.3), particularly in caudal structures such as the hippocampus (r=-0.0026), amygdala (r=0.18), and insula (r=0.14). Although there was good overall correlation between perfusion and glucose metabolism, regional variability should be considered when using either ASL or (18)F-FDG PET as surrogate markers for neural activity.