Prospective Head Motion Compensation for MRI by Updating the Gradients and Radio Frequency During Data Acquisition

Abstract

Subject motion appears to be a limiting factor in numerous magnetic resonance imaging (MRI) 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. The most suitable for head imaging appears to be the orbital or spherical navigator methods. Navigators, however, not only lengthen the measurement because of the time required for acquisition of the position information, but also require additional excitation radio frequency (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 60Hz. The movement information on the object position (head) is used to compensate the motion in real time. This is done by updating the field of view (FOV) by recalculating the gradients and the RF-parameter of the MRI tomograph during the acquisition of k-space data based on the tracking data. Results of rotation phantom, in vivo experiments and the implementation in two different MRI sequences are presented.

Mapping Fetal Brain Development In Utero Using Magnetic Resonance Imaging: The Big Bang of Brain Mapping

“…In adult imaging, a range of motion correction schemes have been developed to allow imaging in the presence of motion. Prospective motion correction techniques make use of independent estimates of anatomical positioning to update the acquisition process as it proceeds, by modifying the phase or frequency encoding being used to define the scan geometry (59), or to exclude corrupted components of the signal acquired at known times of motion. A range of such techniques have been explored using optical (60, 61) or MRI marker (62) based tracking of patient anatomy.…”

Self-encoded Marker for Optical Prospective Head Motion Correction in MRI

“…In order to transfer the detected motion of these systems to motion, which actually occurred in the scanner image plane, a cross-calibration of both frame of references is required. External optical systems outside the scanner bore were used to track a marker attached to the patient's head [7]. Drawback of this system is, that it requires a line of sight on the marker inside the scanner.…”

Model-based attenuation of movement artifacts in fMRI

“…Other methods proposed in literature use optical tracking (Dold et al, , 2005, navigator pulses (Ward et al, 2000;Lee et al, 1996) or offline analysis of signal variance (Huang et al, 2008;Hickok, 2003) to estimate head movement and attenuate the artifacts, with online slice corrections (Ward et al, 2000;Lee et al, 1996), downweighting of corrupted images or replacing artifact-affected values by interpolation (Huang et al, 2008). However, all these methods estimate parameters only every repetition time (TR) (which has a resolution of a few seconds) and are insensitive to short-duration movements as involved in arm reaching and speech, which typically last less than a second.…”