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

Results

A total of 13 pediatric and 12 adult patients (mean age, 24 years; range, 10 months-70 years) were included in the review. The mean time between 1.5- and 3-T MRI was 1.3 years (range, 0.2-5 years). Diagnoses in the 19 cases of focal epilepsy were established histologically after surgical resection in nine cases and on the basis of characteristic clinical semiologic and imaging findings in the other 10 cases. The focal epilepsy syndromes diagnosed were cortical dysplasia in eight cases; two cases each of dysembryoplastic neuroepithelial tumor, mesial temporal sclerosis, hypothalamic hamartoma, cavernous malformation, and ganglio glioma; and one case of oligodendroglial hyperplasia (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8). Because they had generalized epilepsy syndromes without a structural lesion identified, the other six patients were included only in the image quality portion of the assessment (normal tissue contrast and technical or motion artifacts).

Figure 1.

17-year-old girl with intractable nocturnal seizures starting at age 2 years. Coronal FLAIR 1.5-T MR image shows questionable curvilinear focus of juxtacortical high signal intensity (arrows) in left occipital lobe. Abnormal signal intensity was missed at first review of images.

Figure 2.

17-year-old girl with intractable nocturnal seizures starting at age 2 years. Coronal FLAIR 3-T MR image shows curvilinear band of high signal intensity (arrows) in left occipital juxtacortical white matter without apparent mass effect. Focus was surgically resected, and histologic finding was focal cortical dysplasia with balloon cell features (Taylor's type).

Figure 3.

3-year-old boy with intractable left temporal lobe epilepsy. Coronal FLAIR 1.5-T MR image shows questionable area of subtly decreased signal intensity and size of anterior left hippocampus (arrow).

Figure 4.

3-year-old boy with intractable left temporal lobe epilepsy. Coronal FLAIR 3-T MR image shows left hippocampus smaller than in A with associated high signal intensity (arrow) and loss of internal architecture consistent with mesial temporal sclerosis. Surgical resection at age 6 years showed histologic findings confirming presence of mesial temporal sclerosis.

Figure 5.

3-year-old boy with intractable seizures. Coronal thin-slice T1-weighted spoiled gradient-recalled echo MR image suggests thickening (arrows) of right frontal cortex.

Figure 6.

3-year-old boy with intractable seizures. Companion 3-T coronal T1-weighted spoiled gradient-recalled echo MR image shows thickened indistinct cortex (arrows) in right frontal lobe. Gray-white matter contrast is better than in Figure 5.

Figure 7.

3-year-old boy with intractable seizures. Coronal 1.5-T STIR MR image suggests decreased arborization of normally T2-weighted hypointense white matter in right frontal lobe. Suggestion of thickened-appearing cortex (solid arrows) can easily be interpreted as volume averaging. Normal white-matter arborization (open arrow) is evident in left frontal lobe at site of thin cortical ribbon.

Figure 8.

3-year-old boy with intractable seizures. Companion 3-T STIR MR image shows thickening and indistinctness of right frontal gray-white matter junction (solid arrows) better than does Figure 7. Normal white-matter arborization (open arrow) is present where cortical ribbon shows normal thickness. After surgical resection of abnormal-appearing tissue at age 3 years, histologic finding was cortical glioneuronal dysplasia.

For each of the four quality parameters assessed, mean composite scores were higher for 3-T than for 1.5-T MRI ( Table 1 ). There were statistically significant differences in three of four parameters assessed: lesion characterization, tissue contrast, and imaging artifacts other than those related to patient motion. Motion artifacts were com parable at 3 T and 1.5 T without a statistically significant difference.

Correct lesion identification (separate from the quality analysis) was higher at 3 T than at 1.5 T with correct identification of the structural lesion in 65 of 74 (88%) compared with 55 of 74 (74%) individual interpretations ( Table 2 ). Two of the 76 interpretations in the cases of the 19 focal epilepsy patients were excluded because of missing data. Lesion characterization at 3 T and 1.5 T was compared only for the 19 of 26 patients with focal epilepsy ( Table 3 ). Lesion characterization (p = 0.0095) and tissue contrast (p = 0.0292) were consistently rated higher at 3 T than at 1.5 T. Odds ratios for correct lesion identification and characterization at 3 T and 1.5 T were 2.57 and 2.66, respectively ( Table 4 ). An interesting finding was that imaging artifacts were less troublesome at 3 T than at 1.5 T (p = 0.01). Although a trend toward greater motion artifacts was seen at 3 T, this difference was not statistically significant (p = 0.136). Intraclass correlation yielded moderate reliability among the four reviewers as a group (0.562) with a 95% CI of 0.466-0.643.

Twelve of the 19 patients with focal epilepsy underwent surgical resection of the epileptogenic focus. Seven of the 12 surgically treated patients had complete resolution of seizures, three had clinically moderate improvement, and two had no significant improvement in seizure frequency or severity during the early clinical follow-up period (mean, 571 days).

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