HALO: A software tool for real-time head alignment in the MR scanner

Magnetic resonance imaging (MRI) studies in human subjects often require multiple scanning sessions/visits. Changes in a subjects head position across sessions result in different alignment between brain tissues and the magnetic field which leads to changes in magnetic susceptibility. These changes can have considerable impacts on acquired signals. Therefore, we developed the Head Alignment Optimization (HALO) tool. HALO provides real-time visual feedback of a subjects current head position relative to the position in a previous session. We verified that HALO enabled subjects to actively align their head positions to the desired position of their initial sessions. Our pilot sample of healthy subjects were able to improve their head alignment significantly using HALO and achieved good alignment with their first session meeting stringent criteria similar to that used for within-run head motion (less than 2mm translation or 2 degrees rotation in any direction from the desired position). Utilization of HALO in longitudinal studies will reduce the noise across sessions related to changes in magnetic susceptibility. HALO has been made publicly available.