Diagnosis of mesial temporal sclerosis with conventional versus fast spin-echo MR imaging

Quantitative multi-compartmental SPECT image analysis for lateralization of temporal lobe epilepsy

This study assesses the utility of compartmental analysis of SPECT data in lateralizing ictal onset in cases of a putative mesial temporal lobe epilepsy (mTLE). An institutional archival review provided 46 patients (18M, 28F) operated for a putative mTLE who achieved an Engel class Ia postoperative outcome. This established the standard to assure a true ictal origin. Ictal and interictal SPECT images were separately coregistered to T1-weighted (T1W) magnetic resonance (MR) image using a rigid transformation and the intensities matched with an l(1) norm minimization technique. The T1W MR image was segmented into separate structures using an atlas-based automatic segmentation technique with the hippocampi manually segmented to improve accuracy. Mean ictal-interictal intensity difference values were calculated for select subcortical structures and the accuracy of lateralization evaluated using a linear classifier. Hippocampal SPECT analysis yielded the highest lateralization accuracy (91%) followed by the amygdala (87%), putamen (67%) and thalamus (61%). Comparative FLAIR and volumetric analyses yielded 89% and 78% accuracies, respectively. A multi-modality analysis did not generate a higher accuracy (89%). A quantitative anatomically compartmented approach to SPECT analysis yields a particularly high lateralization accuracy in the case of mTLE comparable to that of quantitative FLAIR MR imaging. Hippocampal segmentation in this regard correlates well with ictal origin and shows good reliability in the preoperative analysis.

FLAIR signal and texture analysis for lateralizing mesial temporal lobe epilepsy

Standard magnetic resonance (MR) imaging analysis in several cases of mesial temporal lobe epilepsy (mTLE) either fail to show an identifiable hippocampal asymmetry or provide only subtle distinguishing features that remain inconclusive. A retrospective analysis of hippocampal fluid-attenuated inversion recovery (FLAIR) MR images was performed in cases of mTLE addressing, particularly, the mean and standard deviation of the signal and its texture. Preoperative T1-weighted and FLAIR MR images of 25 nonepileptic control subjects and 36 mTLE patients with Engel class Ia outcomes were analyzed. Patients requiring extraoperative electrocorticography (ECoG) with intracranial electrodes and thus judged to be more challenging were studied as a separate cohort. Hippocampi were manually segmented on T1-weighted images and their outlines were transposed onto FLAIR studies using an affine registration. Image intensity features including mean and standard deviation and wavelet-based texture features were determined for the hippocampal body. The right/left ratios of these features were used with a linear classifier to establish laterality. Whole hippocampal within-subject volume ratios were assessed for comparison. Mean and standard deviation of FLAIR signal intensities lateralized the site of epileptogenicity in 98% of all cases, whereas analysis of wavelet texture features and hippocampal volumetry each yielded correct lateralization in 94% and 83% of cases, respectively. Of patients requiring more intensive study with extraoperative ECoG, 17/18 were lateralized effectively by the combination of mean and standard deviation ratios despite a ratio of mean signal intensity near one in some. The analysis of mean and standard deviation of FLAIR signal intensities provides a highly sensitive method for lateralizing the epileptic focus in mTLE over that of volumetry or texture analysis of the hippocampal body.

Mesial temporal sclerosis after posterior reversible encephalopathy syndrome

Neither intrathecal methotrexate nor posterior reversible encephalopathy syndrome has previously been reported to result in mesial temporal sclerosis. Described here is the case of a boy with no risk factors for mesial temporal sclerosis who presented with posterior reversible encephalopathy syndrome and partial complex seizures 8 days after initiation of intrathecal methotrexate for treatment of Burkitt lymphoma, and who ultimately progressed to intractable temporal lobe epilepsy due to left mesial temporal sclerosis.

Magnetic resonance imaging of patients with epilepsy

Magnetic resonance imaging (MRI) is the radiological investigation of choice for the evaluation of patients with epilepsy. It is able to detect and characterize the structural origin of seizures, and significantly influences treatment planning and prognosis. The indications for MRI, protocols used for MRI in epilepsy and the relevant imaging anatomy are discussed. The major categories of epileptogenic lesions which result in chronic seizures are reviewed and illustrated. Mesial temporal sclerosis is emphasized, reflecting its major importance as a cause of medically intractable epilepsy. The role of MRI in the planning and assessment of epilepsy surgery is considered.

Fast fluid-attenuated inversion recovery (FLAIR) compared with T2-weighted spin-echo in the magnetic resonance diagnosis of mesial temporal sclerosis

RATIONALE AND OBJECTIVES

The authors compare coronal fast fluid-attenuated inversion recovery (FLAIR) with coronal T2-weighted spin-echo (SE) magnetic resonance (MR) techniques in the diagnosis of mesial temporal sclerosis (MTS).

METHODS

In this prospective study, the authors assessed MR scans of 30 patients with drug-resistant temporal lobe epilepsy (based on clinical symptomatology and electroencephalographic registrations) with MR features suggestive of MTS. MR scans of age-, sex-, and scanner-matched patients, referred for MR assessment of white matter disease, without a history of epilepsy and with no visible abnormalities on MR, were used as controls. In 16 patients the MR diagnosis was confirmed by histologic abnormalities consistent with MTS. Coronal T2 SE and FLAIR images of patients and controls were presented to two experienced radiologists in random order for independent blinded review. Hippocampal and associated extrahippocampal temporal lobe abnormalities were used for the diagnosis of MTS.

RESULTS

The sensitivity of observer A was 97% for the T2 SE sequence and 100% for the FLAIR; the specificity of observer A for both techniques was 100%. The sensitivity of observer B was 53% for T2 SE and 83% for FLAIR; the specificity for observer B was 93% for the T2 SE and 100% for FLAIR.

CONCLUSION

Coronal FLAIR images provide a similar or increased yield in the detection of MTS compared with T2-weighted SE images.

Neuroimaging in epilepsy

Neuroimaging techniques have improved the understanding, diagnosis, and management of epilepsy. By providing excellent structural information, MRI is the technique of choice in evaluating patients with epilepsy. Functional imaging techniques, including MR spectroscopy, functional MRI, positron emission tomography, and single photon emission CT, permit noninvasive assessment of the epileptic substrate, its functional status, and neuroreceptors. The MRI-based techniques will potentially assume a greater role in the cost-effective workup of the patient. Currently, newer techniques such as magnetoencephalography, magnetic source imaging, and optical imaging are research tools.

Assessment of the preferred plane and sequence in the depiction of mesial temporal sclerosis using magnetic resonance imaging

RATIONALE AND OBJECTIVES

Definition of optimal magnetic resonance (MR) scanning plane and conventional MR sequence for the detection of mesial temporal sclerosis (MTS).

METHODS

Coronal and axial T2-weighted images and axial T2-weighted images parallel to the long axis of the hippocampus (APLAH) and coronal inversion recovery (IR) images were obtained in patients with medically intractable temporal lobe epilepsy in their phase 1 preoperative evaluation. Thirty-three consecutive MR scans were reviewed by a panel of three radiologists. Twenty-three patients had MR abnormalities consistent with MTS, and ten scans were normal. To assess the best single scanning technique, another group of three radiologists, who were masked to all patient data, individually assessed the different planes and sequences of the 33 studies presented separately in a random fashion. For each plane and sequence, the likelihood (L) ratio for the correct diagnosis was determined separately.

RESULTS

For all planes considered separately, a likelihood ratio of 4.4 was optimal for the coronal T2-weighted images. The likelihood ratio of APLAH T2 was 2.2; of axial T2, 3.9; of coronal IR, indefinite because of 100% specificity.

CONCLUSIONS

For the assessment of MTS, coronal T2-weighted images were considered the best single scanning technique.

Fast spin-echo MR imaging of the eye

Magnetic resonance imaging of the eye usually includes T2-weighted images both for screening purposes and for characterization of melanoma. Conventional T2-weighted spin-echo (SE) imaging suffers both from long acquisition times and incomplete recovery of the vitreous' signal. A fast SE sequence was therefore compared prospectively with conventional sequences in 29 consecutive patients with lesions of the eye. Fast SE images delineated melanoma and other lesions of the eye from vitreous better than conventional T2-weighted images. Image quality and lesion conspicuity were improved on the fast sequence. Whereas melanoma appeared hypointense to vitreous on both types of images, subretinal effusion was hypointense on fast images and hyperintense on conventional T2-weighted images. Ghosting of the globe, which, however, did not decrease diagnostic value, was more pronounced on fast images. Conventional T2-weighted images may be replaced by fast SE images in MR studies of the eye with a gain in lesion conspicuity and significant time saving.

Long-term follow-up of patients treated surgically for medically intractable epilepsy: results in 291 patients treated at Mayo Clinic Rochester between July 1972 and March 1985

To assess the long-term outcome in patients who underwent surgical treatment of intractable epilepsy, we retrospectively reviewed the medical records of 291 consecutive Mayo patients treated between July 1972 and March 1985. We also evaluated the responses to a follow-up mailed questionnaire or telephone interview completed in 1992. Of the 291 patients, 245 (94% of the 261 patients known to be alive at the time of the survey) responded to the follow-up questioning. Information on the patients' neurologic status (including frequency of seizures, use of antiepileptic drugs, and self-reported assessment of functional capacity) and their overall satisfaction with the operative procedure and postoperative outcome were evaluated. Two hundred ninety patients survived the operation and were dismissed from the hospital. Of the 245 patients who responded to the follow-up survey, 41% and 58% had been free of seizures since surgical treatment and for 3 years preceding the follow-up survey, respectively. In addition, of the respondent cohort, 36% were successfully weaned off all antiepileptic drugs. Patients reported improvement in their daily functional capacity and quality of life after surgical treatment. For example, in comparison with the preoperative assessment, the patients' ability to obtain a driver's license was significantly increased, and seizure-related driving accidents, falls, and bodily injury significantly decreased. Furthermore, on the basis of current knowledge of the operation and its outcome, 85% reported that they would repeat the operative procedure. Thus, surgical treatment of intractable epilepsy is an effective option that is met with patient satisfaction.

The future technical development of MRI

In this essay the author makes predictions on how the future of MRI will develop for the short term, the intermediate term, and the long term; these periods of time are defined as the present to the next 3 years, 3 to 5 years, and beyond 5 years, respectively. For each time period, general scientific trends and specific applications are presented. Despite about 15 years of extensive scientific research and significant application to clinical imaging, there continue to be many opportunities for additional technical development in MRI as its role in clinical use and the extent of its scientific significance expand.

Contrast optimization of fluid-attenuated inversion recovery (FLAIR) imaging

The optimization of contrast is considered for the fluid-attenuated inversion recovery (FLAIR) MRI pulse sequence, specifically the contrast of multiple sclerosis (MS) to white matter (WM). A performance bound is identified at 1.5 Tesla as that provided using an inversion time (TI) of 2900 ms. It is shown that TR/TI times exceeding 11000/2600 ms provide about 90% of the MS-WM contrast possible theoretically. The commonly reported TR/TI combination of 6000/2000 provides only about 60%. For TR times exceeding 8000 ms, an echo time (TE) of 140 ms is at or near optimum. Use of TR/TI times less than 9000/2400 lacks efficiency in multisection imaging. Predicted relative contrast performance of TR/TI 11000/2600 versus 6000/2000 was evaluated in seven patients with known MS lesions, and measurements closely matched theoretical predictions. It is strongly recommended that for near optimum contrast and high multisection efficiency, FLAIR should be performed with TR/TI times exceeding 10000/2500 ms.

MRI-based hippocampal volumetrics: data acquisition, normal ranges, and optimal protocol

The process of producing magnetic resonance (MR) volume measurements can be divided into considerations of acquisition and postprocessing of the MR data. With careful attention to both of these, precise and reproducible measurements can be achieved. A statistical description of hippocampal measurements in normal volunteers must be available for comparison if volumetrics are employed either for clinical or research purposes. A wide range in "normal" hippocampal volume is present in the studies of normal young adults that have been reported to date. This variability is most probably due to interinstitutional differences in hippocampal boundary criteria, and in the software employed for counting pixels in a defined region of interest (ROI). Because the numeric output from the volume measurement procedure is highly technique-dependent, the statistical description of "normal" should be determined or calibrated at each institution wishing to use these techniques.