Project Title: Motion Amelioration (ESR L)
Supervisor: Prof. Oliver Speck
Centre: Otto-von-Guericke University, Magdeburg
There are a range of methods available to correct motion in MRI. Most simply, MR acquisition protocols can be optimized to establish strategies that minimise the movement-generated artefacts, by simulating the effect of different MR sequences. However the required changes to the sequences will require balancing optimum contrast or spatial resolution against effects of motion. Another strategy is to monitor motion and then correct for it. Motion can be monitored using MR signals from the object being scanned (navigator techniques) and these can be very successful, although they can perturb the imaging sequence. Alternatively motion can be monitored by external pose tracking methods such as optical or electromagnetic sensors attached to the head via the scalp or a dental cast. The movement parameters from the sensor system can be used to correct the data in post-processing or prospectively by continuous adjustment of the imaging parameters in real-time so that the scan volume follows the motion. This is most straightforward for brain imaging since the head can be treated as a rigid body whose movement is characterized by six parameters. A variety of methods for tracking movement have been envisaged, including optical or NMR based measurements. However, the accuracy requirements for ultra-high resolution imaging are extremely high. While many of the basic principles and methods have been developed, in practical use of such methods, a number of effects have to be considered and integrated into the correction. For very small motion in cooperative subjects, the newest methods (as described above) can be very efficient. However, for larger motion as found in patients, effects other than the mere displacement have to be considered: motion of the object within the receiver coil causes significant alterations in coil sensitivities relative to the object, magnetic field homogeneity within the object and imaging properties of the scanner, caused by the non-linear gradient field. These effects must be addressed to overcome the severe limitations of current motion correction techniques, requiring significant refinements of both retrospective and prospective motion correction techniques.
Meetings Attended: Joint Annual Meeting ISMRM/ESMRMB 2014 (Milan)