Optimization of Simultaneous Multi Slice EPI for clinical fMRI

Abstract: Functional MRI is a method used to map brain functionality, where the blood oxygen level (BOLD) imaging method is frequently used. Stimulation of neurons leads to an increase in energy and oxygen consumption and signal can be detected since oxygen changes the magnetic properties of the blood. In order to measure the signal variation, a fast pulse sequence is required. The purpose of this master thesis was to examine multiband EPI, which compared to the standard EPI, excite several slices simultaneously. Even though this technique leads to an improvement in the temporal resolution, it also gives a decrease in the temporal signal to noise ratio and more pronounced artifacts which increases with the acceleration factor. Hence, it can be assumed that an optimal acceleration factor exists, where temporal resolution gains and decreased temporal resolution are balanced out. Phantom measurements were first performed using three head coils (20, 32 and 64 channels). From the phantom measurements a volunteer protocol was set up. Based on ten volunteers, the area of activation and activation strength were determined. A comparison with the standard technique was made for the 20 and 64 channel coils. Based on the volunteer results, a complementary study with an incomplete paradigm was set up in order to examine the gain when using multiband clinically if the patients are non-compliant. An increase in BOLD-sensitivity was seen in moderately accelerated images when using the 64 channel head coil, which can be beneficial to use in a clinical setting. No advantage with multiband EPI could be seen when using the 20 channel head coil. Because only one volunteer was examined, no conclusions could be drawn from the study with an incomplete paradigm. However, the results indicate that it can be beneficial with multiband in a clinical case of a non-compliant patient.