Epilepsy is a neurological disease characterized by seizures^[1]. One of the options to treat seizure is surgery. Accurate identification of epileptic lesion is therefore of great importance. T₁-weighted MR imaging is commonly used for surgical planning. When the epileptic lesions are small, however, it is difficult to identify them at lower field strength.

Ultra-high field (UHF) leads to sub-millimeter anatomic imaging in clinically reasonable scan time and has helped to correct misinterpretations of scans performed on lower fields^[2]. As the use of UHF expands, FDA approval of 7T MRI is upon us. Therefore, the importance of establishing protocols for 7T clinical MR application is increasing.

In this work, we 1) demonstrate the clinical superiority of in-vivo 7T imaging compared to lower field strength and 2) investigated tissue suppressed imaging techniques for identification of epileptic lesion.

Epilepsy patients who have received clinical diagnosis were scanned (IRB approved) at 7T MRI (Siemens) with a 32-receive channel head coil (Nova Medical). MP2RAGE^[3] sequence (Siemens), WM-suppressed and GM/WM boundary-suppressed^[4] images were collected. Scan parameters for MP2RAGE are as follows: TR/TE/TI₁/TI₂=6000/2.99/800/2600ms, flip angle=4°/5°, (0.75mm)³-isotropic voxels and GRAPPA factor=3. Inversion time (TI) of WM-suppressed and boundary-suppressed^[4] scans were optimized based on measured T₁ value using inversion recovery (IR) prepared EPI sequence^[5,6]. The optimized TIs for WM-/boundary-suppressed scans were 700 and 930ms respectively. Data were collected using MPRAGE^[7] sequence with same parameters as above except for TI(=700/930ms) and flip angle(=5°).

Figure 1 shows the strength of 7T in an epilepsy patient. At 7T, a lesion was seen at the depth of the parietal occipital fissure, superior to isthmus. The lesion was felt to be likely malformation of cortical development and possibly polymicrogyria. The patient’s seizure semiology could be explained by activation of the cortex around the lesion. This lesion was not clearly seen at 3T. In this patient, the 7T images make substantial differences in the clinical care^[8].

Figures 2 and 3 show the usefulness of WM-suppressed and boundary-suppressed technique, respectively. T₁ of epileptic lesions are larger than normal WM and similar with T₁ of GM/WM tissue border. In the WM-suppressed results(Fig. 2), the normal WM tissue was suppressed while the longer T₁ lesion was revealed with hyper-signal intensity (Fig. 2C,F). A patient with epileptic lesion at the parietal-operculum is shown in Fig.3. Because of the intermediate T₁ characteristics of the lesion the suppressed border line was blurred near at the lesion(Fig. 3D,H).

Figure 4 shows the challenge of 7T clinical imaging. In Figs. 4(A-C), the right hippocampus was slightly decreased in size(red arrows), with T₂*/FLAIR hyper-signal, suggestive of hippocampal sclerosis; the right amigdala also showed T₂*/FLAIR hyper-intensity(green arrows). The right hippocampus, amygdala, para-hippocampal gyrus, and temporal pole were resected and the patient became seizure-free. Surgical pathology confirmed the existence of hippocampal sclerosis and malformation of cortical development. Note that although the hippocampal sclerosis was clearly seen, the malformation of cortical development in the right para-hippocampal gyrus and temporal pole was not easily appreciable due to signal loss.

Figures 4D-F are 7T results from a patient with left temporal lobe seizures. Left mesial structure atrophy in the head of the hippocampus (red arrows) and left temporal-pole blurring were observed (yellow arrow). It was not clear whether the dimmer signal from the left temporal-pole was due to technical issue or real pathology. This patient underwent a standard left temporal lobectomy including the left hippocampus and became seizure-free. In surgical pathology, malformation of cortical development was found in the left temporal-pole.

In this work, we assessed the feasibility of 7T MR imaging as a clinical application for the epilepsy patients. Compared to lower field MRI, 7T MRI generates higher resolution and substantially improved anatomic image. These advantages can be helped correct misinterpretations at lower field. Tissue signal suppression using IR technique reveals the epileptic lesion with enhanced tissue contrast particularly lesions are surrounded by the other tissues which have different T₁.

However, low sensitivity and non-uniform tissue contrast, caused by non-uniform B₁ field, particularly in the temporal-pole presents a challenge and limit clinical application.

Recently, parallel transmission MRI (pTx), utilized with multiple-transmit coil elements, was proposed to address the aforementioned non-uniform B₁ issue particularly at UHF^[9]. pTx system may improve image quality and provide more accurate information for patient diagnoses. Future work will use pTx to address these issues.

This is an initial study of epilepsy patient scan using 7T. This study serves as a starting point toward 7T clinical scanning. In addition, it gives some insight as to current challenges and future work.