Magnetic resonance imaging of epilepsy at 3 Tesla

Decision-making in stereotactic epilepsy surgery

Surgery can cure or significantly improve both the frequency and the intensity of seizures in patients with medication-refractory epilepsy. The set of diagnostic and therapeutic interventions involved in the path from initial consultation to definitive surgery is complex and includes a multidisciplinary team of neurologists, neurosurgeons, neuroradiologists, and neuropsychologists, supported by a very large epilepsy-dedicated clinical architecture. In recent years, new practices and technologies have emerged that dramatically expand the scope of interventions performed. Stereoelectroencephalography has become widely adopted for seizure localization; stereotactic laser ablation has enabled more focal, less invasive, and less destructive interventions; and new brain stimulation devices have unlocked treatment of eloquent foci and multifocal onset etiologies. This article articulates and illustrates the full framework for how epilepsy patients are considered for surgical intervention, with particular attention given to stereotactic approaches.

Recommendations for the use of structural magnetic resonance imaging in the care of patients with epilepsy: A consensus report from the International League Against Epilepsy Neuroimaging Task Force

Structural magnetic resonance imaging (MRI) is of fundamental importance to the diagnosis and treatment of epilepsy, particularly when surgery is being considered. Despite previous recommendations and guidelines, practices for the use of MRI are variable worldwide and may not harness the full potential of recent technological advances for the benefit of people with epilepsy. The International League Against Epilepsy Diagnostic Methods Commission has thus charged the 2013-2017 Neuroimaging Task Force to develop a set of recommendations addressing the following questions: (1) Who should have an MRI? (2) What are the minimum requirements for an MRI epilepsy protocol? (3) How should magnetic resonance (MR) images be evaluated? (4) How to optimize lesion detection? These recommendations target clinicians in established epilepsy centers and neurologists in general/district hospitals. They endorse routine structural imaging in new onset generalized and focal epilepsy alike and describe the range of situations when detailed assessment is indicated. The Neuroimaging Task Force identified a set of sequences, with three-dimensional acquisitions at its core, the harmonized neuroimaging of epilepsy structural sequences-HARNESS-MRI protocol. As these sequences are available on most MR scanners, the HARNESS-MRI protocol is generalizable, regardless of the clinical setting and country. The Neuroimaging Task Force also endorses the use of computer-aided image postprocessing methods to provide an objective account of an individual's brain anatomy and pathology. By discussing the breadth and depth of scope of MRI, this report emphasizes the unique role of this noninvasive investigation in the care of people with epilepsy.

Lennox-Gastaut syndrome: a comprehensive review

Lennox-Gastaut syndrome (LGS) is considered an epileptic encephalopathy and is defined by a triad of multiple drug-resistant seizure types, a specific EEG pattern showing bursts of slow spike-wave complexes or generalized paroxysmal fast activity, and intellectual disability. The prevalence of LGS is estimated between 1 and 2% of all patients with epilepsy. The etiology of LGS is often divided into two groups: identifiable (genetic-structural-metabolic) in 65 to 75% of the patients and LGS of unknown cause in others. Lennox-Gastaut syndrome may be considered as secondary network epilepsy. The seizures in LGS are usually drug-resistant, and complete seizure control with resolution of intellectual and psychosocial dysfunction is often not achievable. Reduction in frequency of the most incapacitating seizures (e.g., drop attacks and tonic-clonic seizures) should be the major objective. Valproate, lamotrigine, and topiramate are considered to be the first-line drugs by many experts. Other effective antiepileptic drugs include levetiracetam, clobazam, rufinamide, and zonisamide. The ketogenic diet is an effective and well-tolerated treatment option. For patients with drug resistance, a further therapeutic option is surgical intervention. Corpus callosotomy is a palliative surgical procedure that aims at controlling the most injurious seizures. Finally, vagus nerve stimulation offers reasonable seizure improvement. The long-term outcome for patients with LGS is generally poor. This syndrome is often associated with long-term adverse effects on intellectual development, social functioning, and independent living.

In Vitro Longitudinal Relaxivity Profile of Gd(ABE-DTTA), an Investigational Magnetic Resonance Imaging Contrast Agent

Purpose

MRI contrast agents (CA) whose contrast enhancement remains relatively high even at the higher end of the magnetic field strength range would be desirable. The purpose of this work was to demonstrate such a desired magnetic field dependency of the longitudinal relaxivity for an experimental MRI CA, Gd(ABE-DTTA).

Materials and Methods

The relaxivity of 0.5mM and 1mM Gd(ABE-DTTA) was measured by Nuclear Magnetic Relaxation Dispersion (NMRD) in the range of 0.0002 to 1T. Two MRI and five NMR instruments were used to cover the range between 1.5 to 20T. Parallel measurement of a Gd-DTPA sample was performed throughout as reference. All measurements were carried out at 37°C and pH 7.4.

Results

The relaxivity values of 0.5mM and 1mM Gd(ABE-DTTA) measured at 1.5, 3, and 7T, within the presently clinically relevant magnetic field range, were 15.3, 11.8, 12.4 s^-1mM^-1 and 18.1, 16.7, and 13.5 s^-1mM^-1, respectively. The control 4 mM Gd-DTPA relaxivities at the same magnetic fields were 3.6, 3.3, and 3.0 s^-1mM^-1, respectively.

Conclusions

The longitudinal relaxivity of Gd(ABE-DTTA) measured within the presently clinically relevant field range is three to five times higher than that of most commercially available agents. Thus, Gd(ABE-DTTA) could be a practical choice at any field strength currently used in clinical imaging including those at the higher end.

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.

Three-dimensional balanced steady state free precession myocardial perfusion cardiovascular magnetic resonance at 3T using dual-source parallel RF transmission: initial experience

BACKGROUND

The purpose of this study was to establish the feasibility of three-dimensional (3D) balanced steady-state-free-precession (bSSFP) myocardial perfusion cardiovascular magnetic resonance (CMR) at 3T using local RF shimming with dual-source RF transmission, and to compare it with spoiled gradient echo (TGRE) acquisition.

METHODS

Dynamic contrast-enhanced 3D bSSFP perfusion imaging was performed on a 3T MRI scanner equipped with dual-source RF transmission technology. Images were reconstructed using k-space and time broad-use linear acquisition speed-up technique (k-t BLAST) and compartment based principle component analysis (k-t PCA).

RESULTS

In phantoms and volunteers, local RF shimming with dual source RF transmission significantly improved B1 field homogeneity compared with single source transmission (P=0.01). 3D bSSFP showed improved signal-to-noise, contrast-to-noise and signal homogeneity compared with 3D TGRE (29.8 vs 26.9, P=0.045; 23.2 vs 21.6, P=0.049; 14.9% vs 12.4%, p=0.002, respectively). Image quality was similar between bSSFP and TGRE but there were more dark rim artefacts with bSSFP. k-t PCA reconstruction reduced artefacts for both sequences compared with k-t BLAST. In a subset of five patients, both methods correctly identified those with coronary artery disease.

CONCLUSION

Three-dimensional bSSFP myocardial perfusion CMR using local RF shimming with dual source parallel RF transmission at 3T is feasible and improves signal characteristics compared with TGRE. Image artefact remains an important limitation of bSSFP imaging at 3T but can be reduced with k-t PCA.

The fornix and limbic system

The limbic system is predominantly involved in memory and emotional output. Its 2 principle components are the hippocampus (involved in memory as part of the Papez circuit) and the amygdala (involved in emotional responses, memories and drives). The principle clinical manifestations of limbic disease are epilepsy, confusional states, and cognitive impairment. The connections of the limbic system are widespread and are now becoming visible on diffusion tensor imaging. Many different diseases may affect the limbic system. An appreciation of its functional anatomy along with its white matter tract connections improves assessment of infiltrative disease in particular. Small lesions in the Papez circuit may have devastating neuropsychological consequences. An active search strategy based on the knowledge presented in this paper will increase the likelihood of making an accurate diagnosis for patients affected by these conditions.

3T MRI improves the detection of transmantle sign in type 2 focal cortical dysplasia

PURPOSE

Type 2 focal cortical dysplasia (FCD2) is one of the main causes of refractory partial epilepsy, but often remains overlooked by MRI. This study aimed to elucidate whether 3T MRI offers better detection and characterization of FCD2 than 1.5T, using similar coils and acquisition time.

METHODS

Two independent readers reviewed the 1.5T and 3T MR images of 25 patients with histologically proven FCD2. For both magnetic fields, the ability to detect a lesion was analyzed. We compared the identification of each of the five criteria typical of FCD2 (cortical thickening, blurring, cortical signal changes, subcortical signal changes, and "transmantle" sign) and artifacts, using a four-point scale (0-3). Interobserver reliability for lesion detection was calculated.

KEY FINDINGS

Seventeen lesions (68%) were detected at 3T, two of which were overlooked at 1.5T. Interobserver reliability was better at 3T (κ = 1) than at 1.5T (κ = 0.83). The transmantle sign was more clearly identified at 3T than 1.5T (mean visualization score: 1.72 vs. 0.56; p = 0.002).

SIGNIFICANCE

The use of 3T MRI in patients suspected of type 2 FCD improves the detection rate and the lesion characterization owing to the transmantle sign being more clearly seen at 3T. This point is of interest, since this feature is considered as an MR signature of FCD2.

3 TESLA MR imaging in adults with focal onset epilepsy

OBJECTIVE

The finding of cerebral epileptogenic lesions in magnetic resonance (MR) has demonstrated to be a relevant prognostic factor for potential surgical candidates. In a series of consecutive adults with focal onset epilepsy, we investigated the yield of 3T MR imaging for detecting epileptogenic cerebral lesions.

MATERIALS AND METHODS

We prospectively recruited 161 adult patients with a diagnosis of focal epilepsy, all of whom underwent standardized MR imaging study performed with a 3T magnet.

RESULTS

Lesion-related epilepsy was observed in 48% of patients, and 12% of cryptogenic patients showed subtle or non-specific lesions related to the epileptogenic source. The most common findings were focal cortical dysplasia and vascular lesions, followed by mesial temporal sclerosis, tumors, and scars from previous cerebral injuries. Patients older than 72 years were more likely to have vascular epilepsy.

CONCLUSIONS

Diagnostic assessment using a standardized 3T MR imaging protocol for focal-onset epilepsy detects lesions in nearly half the patients. Our results indicate that elders with focal epilepsy should be searched for vascular lesions.

Clinical features of late-onset partial cryptogenic epilepsy: toward an idiopathic temporal epilepsy?

Adult-onset epilepsy is commonly thought to be secondary to a brain lesion. However, the etiology of adult-onset epilepsy remains unknown in approximately 25% of patients, despite progress in medical and diagnostic tools. In the present study, we investigated whether late-onset partial cryptogenic epilepsies could be subgrouped based on seizure semiology and clinical characteristics. A total of 41 patients with late-onset cryptogenic epilepsy were included, and the corresponding clinical and electrophysiological data were analyzed. The following three clinical subgroups were identified: 1) a group that fulfilled the diagnostic criteria of transient epileptic amnesia (TEA); 2) a group with late-onset cryptogenic epilepsies with a temporal seizure semiology; and 3) a cryptogenic extratemporal group, which was consistent with the categorization of cryptogenic epilepsies, i.e., epilepsies involving unknown lesions. The temporal group showed homogeneous clinical characteristics, especially a rapid evolution and a greater tendency toward generalization and pharmacoresistance compared with the other two groups. Transient epileptic amnesia was associated with a higher frequency of sleep disorders than either of the other groups. Our findings argue for the clinical identification of a subgroup of late-onset temporal epilepsy that might constitute an idiopathic form. The association between TEA and sleep disorders would suggest a possible pathophysiological role of sleep apnea syndromes in TEA.

Magnetic field interactions of copper-containing intrauterine devices in 3.0-Tesla magnetic resonance imaging: in vivo study

Objective

An ex vivo study found a copper-containing intrauterine device (IUD) to be safe for women undergoing an MRI examination at a 3.0-T field. No significant artifacts caused by the metallic implant were detected. However, there are still no in vivo data about these concerns. The aim of this study was to evaluate 3.0-T magnetic field interactions of copper-containing IUDs in vivo.

Materials and Methods

Magnetic field interactions and potential adverse events were evaluated in 33 women using a questionnaire-based telephone survey. Two experienced radiologists performed artifact evaluation on MR images of the pelvis.

Results

Eighteen patients were eligible for the survey. One patient reported a dislocation of the IUD after the MR examination. All other patients had no signs of field interactions. No IUD-related artifacts were found.

Conclusion

MRI at 3.0-T is possible for women with copper-containing IUDs. However, consulting a gynecologist to check the correct position of the IUD and exclude complications after an MR examination is highly recommended. High-quality clinical imaging of the female pelvis can be performed without a loss in image quality.

The value of repeat neuroimaging for epilepsy at a tertiary referral centre: 16 years of experience

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20–30% of patients with refractory focal epilepsy have normal MRI scans.

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We evaluated the role of repeated MRI with better technology in detecting pathology.

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804 patients underwent MRI at 1.5T and subsequently at 3T with superior head coils.

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Relevant new diagnoses were made in 37 (5%) and affected patient management.

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Rescanning patients with focal epilepsy and previously normal MRI is beneficial.

Purpose

Magnetic resonance imaging (MRI) is the investigation of choice for detecting structural lesions that underlie and may accompany epilepsy. Despite advances in imaging technology, 20–30% of patients with refractory focal epilepsy have normal MRI scans. We evaluated the role of repeated imaging with improved MRI technology – an increase in field strength from 1.5 T to 3 T and superior head coils – in detecting pathology not previously seen.

Methods

Retrospective review of a large cohort of patients attending a tertiary epilepsy referral centre who underwent MRI at 1.5 T (1995–2004) and subsequently 3 T (2004–2011) with improved head coils. Scan reports were reviewed for the diagnoses and medical notes for the epilepsy classification.

Results

804 patients underwent imaging on both scanners, the majority with focal epilepsy (87%). On repeat scanning at 3 T, 37% of scans were normal and 20% showed incidental findings. Positive findings included hippocampal sclerosis (13%), malformations of cortical development (8%), other abnormalities (4%) and previous surgery (18%). A total of 37 (5%) relevant new diagnoses were made on the 3 T scans not previously seen at 1.5 T. The most common new findings were hippocampal sclerosis, focal cortical dysplasia and dysembryoplastic neuroepithelial tumour. These findings affected patient management with several patients undergoing neurosurgery.

Conclusions

The higher field strength and improved head coils were associated with a clinically relevant increased diagnostic yield from MRI. This highlights the importance of technological advances and suggests that rescanning patients with focal epilepsy and previously negative scans is clinically beneficial.