Imaging of freely moving objects by means of real-time image coordinates update using an external optical motion tracking system
Subject motion appears to be a limiting factor in numerous magnetic resonance imaging applications. For head imaging the subject's ability to maintain the same head position for a considerable period of time places restrictions on the total acquisition time. For healthy individuals this time typically does not exceed 10 minutes and may be considerably reduced in case of pathology. In particular, head tremor, which often accompanies stroke, may render certain high-resolution 2D and 3D techniques inapplicable. Several navigator techniques have been proposed to circumvent the subject motion problem. Navigators, however, not only lengthen the measurement because of the time required for acquisition of the position information, but also require additional excitation RF pulses to be incorporated into the sequence timing, which disturbs the steady state. Here we demonstrate the possibility of interfacing the MR scanner with an external optical motion tracking system, capable of determining the object's position with sub-millimeter accuracy and an update rate of 25Hz. The information on the object position is used without time penalty to update the position of the imaging volume during the acquisition of k-space data. Results of rotation phantom and in vivo experiments and the implementation in two different MRI sequences are shown.