Qualitative Comparison of 3-T and 1.5-T MRI in the Evaluation of Epilepsy

Pramit M. Phal; Alexander Usmanov; Gary M. Nesbit; James C. Anderson; David Spencer; Paul Wang; Jonathan A. Helwig; Colin Roberts; Bronwyn E. Hamilton

Disclosures

Am J Roentgenol. 2008;191(3):890-895. 

In This Article

Abstract and Introduction

Objective: MRI at 3 T, which has a higher signal-to-noise ratio than 1.5-T MRI, is potentially more sensitive and specific at delineating epileptogenic lesions and may influence management of refractory epilepsy. The purposes of the current study were to compare image quality of 3-T MRI with that of 1.5-T MRI in the evaluation of epilepsy and, in cases of focal epilepsy, to compare the two field strengths in terms of lesion detection and characterization.
Materials and Methods: Retrospective review was performed on 50 sets of MR images of 25 patients who underwent both 3-T and 1.5-T brain imaging with a dedicated epilepsy protocol, including fast spin-echo T2-weighted, coronal FLAIR, coronal fast multiplanar inversion recovery, and 3D spoiled gradient-recalled echo pulse sequences. Parameters assessed were distortion and artifact, lesion conspicuity, gray-white matter differentiation, and motion. Each pulse sequence was graded on a 4-point scale. Reviewers performed qualitative assessments of the site of abnormality and the most likely diagnosis.
Results: MRI at 3 T outperformed MRI at 1.5 T in all four parameters and was statistically superior (p < 0.05) to 1.5-T MRI in all categories except motion. On 3-T MRI, lesions were detected in 65 of 74 cases compared with 55 of 74 cases at 1.5 T (p = 0.0364), and lesions were accurately characterized in 63 of 74 cases compared with 51 of 74 cases at 1.5 T (p = 0.0194). The odds ratios showed identification of a focal epileptogenic lesion with 3-T MRI 2.57 times as likely as identification with 1.5-T MRI and accurate characterization of lesions 2.66 times as likely as characterization with 1.5-T MRI.
Conclusion: In evaluation of epilepsy, MRI at 3 T performed better than 1.5-T MRI in image quality, detection of structural lesions, and characterization of lesions. High-field-strength imaging should be considered for patients with intractable epilepsy and normal or equivocal findings on 1.5-T MRI.

Epilepsy is a disease with serious consequences for patients and society.[1,2,3] For patients with partial complex epilepsy, identifying a focal structural brain abnormality offers the best potential for surgical cure and improvement in quality of life. For patients with medically refractory focal epilepsy, surgery not only is the single remaining treatment option but also offers the best chance for a permanent cure and is the most cost-effective approach in the long term.[4,5]

The current barrier to surgery for many patients with medically refractory partial complex epilepsy is lack of identification of an abnormality on images. MRI is key to surgical success because it enables accurate anatomic identification of the epileptogenic focus, which is critical for preoperative planning and localization.[6,7] Assessment is ideally performed at dedicated epilepsy centers with close collaboration among neurologists, neurosurgeons, and radiolo gists. Safe surgery requires careful analysis of structural brain lesions with alignment of the clinical and imaging evidence. MRI plays a key role in diagnosis and localiza tion. Many patients presenting to our epi lepsy center have localized syndromes that raise clinical suspicion of the presence of a focal structural abnormality, yet in many instances, a lesion has not been localized at previous imaging evaluation. High-field-strength MRI has potential for improving epilepsy evaluation because of the greater signal-to-noise ratio of 3-T MRI compared with 1.5-T MRI.

The goal of our study was to assess the diagnostic value of 3-T compared with 1.5-T whole-brain MRI in the evaluation of epilepsy. We selected for review all patients who underwent both 3-T and 1.5-T whole-brain MRI for epilepsy regardless of the reason for repeated imaging. We evaluated the pro portions of correct detection of structural lesions, observer-assessed lesion conspicuity, normal gray-white matter tissue contrast, and imaging artifacts in a group of epilepsy patients who had undergone consecutive 1.5- and 3-T MRI examinations at our institution.

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