Motion correction in MRI of the brain

Abstract

Subject motion in MRI is a relevant problem in the daily clinical routine as well as in scientific studies. Since the beginning of clinical use of MRI, many research groups have developed methods to suppress or correct motion artefacts. This review focuses on rigid body motion correction of head and brain MRI and its application in diagnosis and research. It explains the sources and types of motion and related artefacts, classifies and describes existing techniques for motion detection, compensation and correction and lists established and experimental approaches. Retrospective motion correction modifies the MR image data during the reconstruction, while prospective motion correction performs an adaptive update of the data acquisition. Differences, benefits and drawbacks of different motion correction methods are discussed.

Figure 1

Categories of motion correction.

Figure 2

In Cartesian MRI, motion artefacts mainly occur in phase direction. Eye movement with (a) horizontal and (b) vertical phase direction.

Figure 3

Motion artefacts depending on motion pattern and direction with (a) periodic respiratory motion, (b) peristaltic motion, and random motion patterns with (c) in-plane head motion, and (d) through-plane flow motion.

Figure 4

K-space trajectories used in the different self-navigation techniques.

Figure 5

Spin-echo sequence with additional linear NAV echo acquisition (between dotted lines) as proposed in (Ehman and Felmlee 1989).

Figure 6

Motion tracking using image registration. Acquiring multi-slice axial MRI data sets, the motion can be measured as (a) slice-to-volume, (b) stack-to-volume, and (c) group-wise approach. The slice intersection technique can be applied, when multi-slice multi-view (coronal, transversal, sagittal) acquisition is used.

Figure 7

Effect of rotation around the z-axis in image space on a 2D Cartesian k-space.

Figure 8

Prospective motion correction pipeline: motion data has to be delivered in scanner coordinates, or at least the sequence needs the means, to convert the pose to scanner coordinates, e.g. via a transformation matrix. Therefore, cross calibration is necessary for external tracking devices. During the scan, the motion data is acquired and the latest motion pose is used to apply the required translation and rotation by adjusting the gradients and frequencies. In contrast to retrospective motion, the correction is performed during the scan which results in an instant delivery of a consistent k-space data and thus a corrected image with standard reconstruction. Optionally, an additional retrospective correction of residual artefacts can be performed after the scan.

Figure 9

Motion-corrupted and motion-corrected brain images. In high resolution images even small motion (a) can cause blurring and introduce artificial edges (see arrows) that are removed in the corrected image (b). With stronger motion (c) the image becomes largely ‘non-diagnostic’ with unrecognizable details that are also recovered in the corrected image (d). The images have a resolution of 0.25 mm × 0.25 mm × 2.00 mm (a), (b) and 0.28 mm × 0.28 mm × 1.00 mm (c), (d) with very similar motion within each pair.

Figure 10

The 3D SPGR images from 7T MRI show the residual artefacts after applying prospective Mo–Co under three different types of motion. The artefacts in the frontal lobes (red ovals) and temporal lobes (red circles) appear more visible with increasing motion amplitudes. Below the images are their corresponding motion patterns including 3 parameters of translation (x, y, z) and 3 parameters of rotation (R_x, R_y, R_z).