| [Objective] Diffusion tensor imaging is a new imaging method that reflect pathohistologic appearance of lesions by measuring the diffusion change of water molecules. The purpose of this study was to assess average diffusion coefficient (DCavg) and anisotropy of hippocampi and white matter of temporal lobe and to investigate the role of DTI in lateralizing and locating the seizure focus in temporal lobe epilepsy (TLE). We also analyzed DTI abnormalities in several brain fibers and assessed the utility in revealing changes of structures beyond the temporal lobe, and used fiber tracking for virtual dissection of the fornix in patients with TLE and healthy subjects.[Materials and Methods] 55 TLE patients without brain tumor, vascular disease and congenital malformation were collected. The diagnosis of unilateral TLE was based on clinical examination, video-electroencephalogram, single photon emission computed tomography (SPECT) or position emission tomography (PET). Among these patients, MRI findings of 13 patients were consistent with unilateral hippocampal sclerosis. 55 patients were divided into 2 peroids according to interval between the time of the last seizure and the examination: postictal peroid (≤24 hours), interictal peroid (>24h). All patients and 32 healthy volunteers were examined with 1.5T Twin-Speed Infinity with Excite II (Signa;GE Medical System) and scaned with 8 channels head coil. The sequence included axial and sagittal Ti-FLAIR, axial and coronal T2WI, axial diffusion-weighted imaging, and axial diffusion tensor imaging with diffusion sensitive gradients applied in 13 directions.For hippocampal structures, T2WI, T2FLAIR and DTI were performed in an oblique coronal plane, orthogonal to the long axis of the hippocampus. On oblique coronal DTI images, the DCavg, fractional anisotropy (FA), 1-volume ratio (1-VR) and relative anisotropy (RA) of each hippocampus and temporal lobe were calculated through independent head, body and tail measurements of both left and right hippocampi. On axial DTI images, DCavg, FA, 1-VR and RA were calculated in anterior limb and posterior limb of internal capsule, external capsule, genu, body and splenium of corpus callosum. Every DTI parameter of every part was compared by ANOVA or t-test respectively and P value less than 0.05 was considered as statistical significance. Measurement of DTI parameters was compared with their difference, asymmetry index for the correct lateralization diagnosis of TLE by receiver operating characteristic(ROC) analysis.The DTI data was transferred into computer with DICOM format, and was reconstructed with the diffusion tensor software VolumeOnel .66. [Results]1. There were no statistically significant differences in DCavg, FA, 1-VR, RA between the right and left hippocampi. No significant differences among three parts of hippocampi for DCavg, FA, 1-VR and RA were found.2. Each parameter of DTI in the hippocampi and white mater of temporal lobe of postictal patients with TLE1) Parameter in the hippocampi: The DCavg in ipsilateral side and contralateral side was bigger than in control group (PO.05). The FA> 1-VR and RA had significant differences among the three groups (F value was 34.079> 30.538 ^ 27.166, P<0.0\), the values of the above parameters in ipsilateral side were smaller than that in contralateral side, the contralateral side smaller than control group.2)Parameter in the white matter of temporal lobe: The DCavg had no significant difference among ipsilateral side, contralateral side, and control group. The FA inipsilateral side was smaller than that in contralateral side and control group(.P<0.01). The 1-VR in ipsilateral side and contralateral side was smaller than that in control group^O.OS). The RA in ipsilateral side was smaller than that in contralateral side and control group(P<0.05).3. Each parameter of DTI in the hippocampi and white mater of temporal lobe of interictal patients with TLE1) Parameter in the hippocampi: The DCavg in ipsilateral side, contralateral side and control group had significant differences among the three groups (F value was 32.603, P<0.001), the value of the above parameter in ipsilateral side was bigger than that in contralateral side, the contralateral side bigger than control group.The FA> 1-VR> RA had significant differences among the three groups (F value was 69.941 n 59.21 K 42.537, PO.001), the values of the above parameters in ipsilateral side were smaller than that in contralateral side, the contralateral side smaller than control group.2) Parameter in the white matter of temporal lobe: The DCavg in ipsilateral side was bigger than that in contralateral side and control group(.P<0.001). The FA> 1-VR> RA had significant differences among the three groups(F value was 14.71 Ck 16.857n 21.597, P<0.0l), the values of the above parameters in ipsilateral side were smaller than that in contralateral side, the contralateral side smaller than control group.4. Comparison of each DTI parameter in the hippocampi and white mater of temporal lobe between postictal and interictal patients.1) Parameter in the ipsilateral hippocampi: There was statistically significant difference in DCavg between postictial and interictial patients (.P=0.004) . No significant differences for FA, 1-VR and RA were found.2) Parameter in the contralateral hippocampi and bilateral white matter of temporal lobe: No significant differences for DCavg, FA, 1-VR and RA betweenpostictial and interictial patients were found.5. Comparison of each DTI parameter among head, body and tail of hippocampi in interictal patients.1) Parameter in the ipsilateral hippocampi: The DCavg of head was bigger than in tail(P<0.05) and no significant differences between body and the other two parts were found(F>0.05). No significant differences for FA, 1-VR and RA were found (F value was 0.222, 0.928, 0.997, P>0.05) .2) Parameter in the contralateral hippocampi: The DCavg of tail was smaller than that of head and body(P<0.05) and ANOVA test showed no significant difference between head and body (P>0.05). No significant differences for FA, 1-VR and RA were found (F value was 0.113, 0.024, 0.151, P>0.05) .6. DTI of hippocampi for the lateralization diagnosis of interictal TLE1) Measurement of DTI parameters.The threshod of DCavg, FA , 1-VR and RA for lateralization diagnosis were 0.7575 (sensitivity 88.1%, specificity 87.5%), 0.2075 (sensitivity 92.9%, specificity 93.7%), 0.0489 (sensitivity 90.5%, specificity 93.7%) and0.173 (sensitivity 88.1%, specificity93.7%) .2) Difference of DTI parameters: The threshod of Docavg for lateralization diagnosis was 0.0205 (sensitivity 85.7%, specificity 87.5%) .3 )Asymmetry index of DTI parameters: The threshod of Alocavg- AIi-vr fO AIra were 2.6972 (sensitivity 85.7%, specificity 87.5%), 16.00535 (sensitivity 76.2%, specificity 59.4%) and 9.4229 (sensitivity 66.7%, specificity 62.5%) .7. DTI measurements of several brain white matter fibers in interictal patients1) DCavg of interictial patients and normal control: splenium, posterior limb of internal capsule, external capsule had significant differences (t value was 13.686, 1.655, 0.076, PO.01), the value of the above regions in interictial patients were bigger than that in normal control. No significant differences for other structures were found (t value was 0.234, 0.692 > 1.542, P>0.05) .2) FA of interictial patients and normal control: geniK spleniumk anterior limb of internal capsule external capsule had significant differences (t value was 2.723 % 13.686 > 1.487 n 7.183, PO.05), the value of the above regions in interictial patients were smaller than that in normal control. No significant differences for other structures were found (t value was 1.487 ^ 0.043, P>0.05) .8. In FT, the fornix in two patients and four healthy subjects was reconstructed clearly wih diffusion tensor tractography. Bilateral abnormalities of fractional anisotropy were observed in the fornix of patients with TLE, especially the ipsilateral side.[Conclusion]1. Diffusion changes in hippocampi of different periods of TLE were different, especially DCavg.2. Besides ipsilateral hippocampi, contralateral hippocampi demonstrated abnormalities of water diffusion and anisotropy, but these abnormalities mainly reflected long-term changes of TLE.3. Abnormal changes of water diffusion and anisotropy existed in white matter of temporal lobe, especially ipsilateral temporal lobe.4. The degree of increased water diffusion of hippocampi in interictial patients could vary along the their lengths, and the head and body of hippocampi showed the more abnormal DCavg.5. The lateralization diagnosis value of DTI parameter measurement was better than their difference and asymmetry index in interictal patients.6. Abnormal changes of water diffusion and anisotropy were not necessarily restricted to the the temporal lobe but might extend in other brain regions as well.7. The fiber tacking can display abnormalities of the limbic system in patients with TLE.[ Innovative point ] To study the changes of hippocampal diffusion andanisotropy in TLE patients of different periods. |
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