Abstracts

Diffusion Tensor Imaging (DTI) has been recently used for detecting focal abnormalities in temporal lobe epilepsy (TLE). Tractography and directionally encoded color (DEC) mapping are derivatives of DTI and may allow 3-dimensional characterization of the structural changes of neuronal networks[italic]. [/italic]We conducted this study to evaluate the relative role of DEC mapping in lateralizing the seizure focus and mapping the structural changes in TLE. Sixteen patients with TLE being evaluated for epilepsy surgery were recruited for this study. All patients had unilateral TLE based on clinical history, routine EEG and unilateral ictal EEG recording. DTI was performed on a 1.5T Vision MR scanner using a single shot echo planar diffusion weighted imaging sequence. To determine the diffusion tensor fully, we collected diffusion-weighted images along six different directions with a b value of 1000 sec/mm² as well as an image acquired without diffusion weighting (b=0, B[sub]0[/sub] image). Seventeen coronal slices were acquired to cover the entire temporal lobes. The imaging parameters included: TR=6000ms, TE=100ms, FOV=240 mm, 98 x 128, and 4 acquisitions. The maps of mean diffusivity and fractional anisotropy (FA) were calculated from the diffusion-weighted images using software written in IDL (Interactive Data Language, USA). DEC FA-weighted images were calculated using statistical parametric mapping software (SPM[rsquo]99) and were assigned different colors (red, blue, [amp] green) along the three principle directions Left/Right, Superior /Inferior, Anterior/Posterior respectively. We performed visual inspection of the DEC FA-weighted images in both patient and control groups and identified any abnormal color patterns in the HF in the patient group. High-resolution brain MRI revealed unilateral HF abnormality in 12 of 16 patients while 4 of 16 had no abnormalities. DEC imaging mapping revealed unilateral defects in the color maps of the HF in 11 of 16 patients and the abnormal HF DEC maps lateralized to the temporal seizure focus in all patients. In addition, in 5 patients with either subtle HF signal abnormality or negative high-resolution MRI, a unilateral and widespread abnormal HF DEC pattern was detected and lateralized to the epileptogenic temporal lobe. DEC can detect the abnormal and/or epileptogenic HF in unilateral TLE. The loss of anisotropy and the HF color map defects ipsilateral to the seizure focus in TLE may reflect disruption of the structural organization, drop in neuronal count and gliosis in mesial temporal sclerosis. In addition, the DEC mapping may detect changes related to 3-dimensional structure of the neuronal networks connected with the seizure focus when such changes produce only subtle or no changes on high-resolution MRI.