P154 Probing the sensitivity of a novel MR head coil array for TMS/fMRI studies of the motor cortex

Abstract

Question The typical setup used in online TMS/fMRI experiments presents some limitations, most importantly the poor sensitivity of the MR coil (Fig. 1a) Download : Download high-res image (262KB) Download : Download full-size image . In addition, new imaging techniques like parallel imaging and multiband excitation are not available. To get over these limitations, a dedicated MR coil array (Fig. 1b) for combining TMS with fMRI was developed (Navarro de et al., 2015) . We present results of an online TMS/fMRI experiment over the motor cortex to show the advantages of the new setup. Methods The experiment was performed at 3T (Siemens, Germany). The TMS system included a MagProX100 stimulator and an MRi-B91 MR-compatible TMS coil (MagVenture, Denmark). Six healthy subjects participated in the study. Functional images were acquired using a multiband EPI sequence (TR/TE = 1000/33 ms), 14 slices, 1.5 × 1.5 × 3 mm3. Slices were aligned parallel to the TMS coil and covered primary motor cortex. The stimulation protocol comprised 20 stimulation blocks, with five blocks of each of the following stimulation intensities: 80, 90, 100 and 110% of the individual’s motor threshold distributed randomly over the experiment. A finger tapping task was also conducted. Data analysis was performed using SPM12. The design matrix comprised four task regressors representing the 4 stimulation amplitudes. For each subject, two regions were defined based on fMRI activation maps: (i) the global maximum, and (ii) the maximum within M1. Results Fig. 2a,b Download : Download high-res image (632KB) Download : Download full-size image shows group results as the mean of the BOLD signal intensity change in percent for the two voxels defined above with indicator of statistical significance. In addition, averaged time courses were calculated for global maximum (2c) and the M1 maximum (2d). Conclusions In both regions, a monotonic ascending relationship of signal change amplitude with TMS intensity was observed. While activations at the global maxima were statistically significant for all intensities, results on the M1 maximum are only significant for the 100% and 110% intensities. These results on M1 are consistent with results obtained before (Bestmann et al., 2004) . Contrary to the standard setup, the new one didn’t suffer of any artefacts under the TMS coil, where the global maximal activation was always found. The obtained time courses demonstrated the efficiency of the new setup to acquire the signal with high accuracy.