Diffusion tensor imaging assessment of the epileptogenic zone in children with localization-related epilepsy

BACKGROUND AND PURPOSE

Patients with MR imaging-negative epilepsy could have subtle FCD. Our aim was to determine if structural changes could be identified by using DTI in children with intractable epilepsy, from MR imaging-visible FCD and MR imaging-negative localization-related epilepsy, that were concordant with the epileptogenic zone as defined by using the MEG dipole cluster.

MATERIALS AND METHODS

Eight children with MR imaging-visible FCD and 16 with MR imaging-negative epilepsy underwent DTI and MEG. Twenty-six age-matched healthy children underwent DTI. Analysis was performed on controls across individual patients. Agreement between the location of DTI abnormalities and FCD and MEG dipole clusters was assessed.

RESULTS

In patients with MR imaging-visible FCD, abnormal FA, MD, λ(1), λ(2), and λ(3) were lobar concordant with the MEG dipole cluster in 4/8 (50.0%), 5/8 (62.5%), 3/8 (37.5%), 6/8 (75.0%), and 5/8 (62.5%), respectively. In patients with MR imaging-visible FCD, abnormal FA, MD, λ(1), λ(2), and λ(3) overlapped the x-, y-, and z-axes of the MEG dipole cluster in 1/8 (12.5%), 4/8 (50%), 4/8 (50%), 6/8 (75%), and 4/8 (50%), respectively, and with FCD in 1/8 (12.5%), 3/8 (37.5%), 0/8 (0%), 3/8 (37.5%), and 1/8 (12.5%), respectively. In patients with MR imaging-negative epilepsy, abnormal FA, MD, λ(1), λ(2), and λ(3) were lobar-concordant with the MEG dipole cluster in 11/16 (68.8%), 11/16 (68.8%), 8/16 (50.0%), 10/16 (62.5%), and 10/16 (62.5%), respectively, and overlapped the x-, y-, and z-axes of the MEG dipole cluster in 9/16 (56.3%), 10/16 (62.5%), 8/16 (50%), 8/16 (50%), and 8/16 (50%), respectively. There was no significant difference between abnormal DTI lobar concordance with the MEG dipole cluster in patients with MR imaging-visible FCD and MR imaging-negative epilepsy.

CONCLUSIONS

White matter changes can be detected with DTI in children with MR imaging-visible FCD and MR imaging-negative epilepsy, which were concordant with the epileptogenic zone in more than half of the patients.

Alteration of human fetal subplate layer and intermediate zone during normal development on MR and diffusion tensor imaging

BACKGROUND AND PURPOSE

The subplate layer and intermediate zone are the precursors for neonatal white matter. The aims of this study were to evaluate 1) T1 and T2 signal intensity, and 2) FA of subplate and intermediate zone in postmortem fetuses and correlate with histology, and 3) T2 signal intensity of subplate and intermediate zone on antenatal MR imaging.

MATERIALS AND METHODS

Fourteen immersion-fixed normal brains from 18 to 25 gestational weeks underwent 1.5T MR imaging, including DTI and histologic examination. The subplate and intermediate zone were graded on a scale of 1-5 on T1 and T2, and FAs were evaluated and then correlated with age. Seventeen antenatal MR images from 20 to 26 gestational weeks with normal brain were evaluated by using the same grading.

RESULTS

On T1 postmortem MR imaging, subplate has lower signal intensity compared with intermediate zone; subplate signal intensity correlated positively (r = 0.66, P = .012) with age, and intermediate zone signal intensity correlated negatively (r = -0.78, P = .001) with age. On T2 postmortem MR imaging, subplate has higher signal intensity compared with intermediate zone and remained persistently high in signal intensity; intermediate zone signal intensity showed moderate correlation (r = 0.48, P = .086) with age. FA of subplate correlated positively (r = 0.55, P < .001) with age; FA of intermediate zone correlated negatively (r = -0.64, P < .0001) with age. On histology, extracellular matrix decreased and cellularity increased in subplate layer, tangentially organized cellularity decreased, and projecting fibers became thicker in intermediate zone with increasing gestation. The findings on T2-weighted antenatal MR imaging were similar to T2-weighted postmortem MR imaging.

CONCLUSIONS

The changes in signal intensity and FA of subplate and intermediate zone in the second trimester reflect microstructural changes on histology.

Effects of gradient encoding and number of signal averages on fractional anisotropy and fiber density index in vivo at 1.5 tesla

BACKGROUND

Tensor estimation can be improved by increasing the number of gradient directions (NGD) or increasing the number of signal averages (NSA), but at a cost of increased scan time.

PURPOSE

To evaluate the effects of NGD and NSA on fractional anisotropy (FA) and fiber density index (FDI) in vivo.

MATERIAL AND METHODS

Ten healthy adults were scanned on a 1.5T system using nine different diffusion tensor sequences. Combinations of 7 NGD, 15 NGD, and 25 NGD with 1 NSA, 2 NSA, and 3 NSA were used, with scan times varying from 2 to 18 min. Regions of interest (ROIs) were placed in the internal capsules, middle cerebellar peduncles, and splenium of the corpus callosum, and FA and FDI were calculated. Analysis of variance was used to assess whether there was a difference in FA and FDI of different combinations of NGD and NSA.

RESULTS

There was no significant difference in FA of different combinations of NGD and NSA of the ROIs (P>0.005). There was a significant difference in FDI between 7 NGD/1 NSA and 25 NGD/3 NSA in all three ROIs (P<0.005). There were no significant differences in FDI between 15 NGD/3 NSA, 25 NGD/1 NSA, and 25 NGD/2 NSA and 25 NGD/3 NSA in all ROIs (P>0.005).

CONCLUSION

We have not found any significant difference in FA with varying NGD and NSA in vivo in areas with relatively high anisotropy. However, lower NGD resulted in reduced FDI in vivo. With larger NGD, NSA has less influence on FDI. The optimal sequence among the nine sequences tested with the shortest scan time was 25 NGD/1 NSA.