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. 2018 Jul;91(1087):20170593.
doi: 10.1259/bjr.20170593. Epub 2018 Mar 23.

Practical implications of motion correction with motion insensitive radial k-space acquisitions in MRI

Mustafa M Almuqbel  1   2   3 , Gareth Leeper  3 , David N Palmer  4   5 , Nadia L Mitchell  5   6 , Katharina N Russell  5   7 , Ross J Keenan  1   2   3 , Tracy R Melzer  1   2   8
Affiliations

Practical implications of motion correction with motion insensitive radial k-space acquisitions in MRI

Mustafa M Almuqbel et al. Br J Radiol. 2018 Jul.

Abstract

Objective: To highlight specific instances when radial k-space acquisitions in MRI result in image artifacts and how to ameliorate such artifacts.

Methods: We acquired axial T2 weighted MR images on (1) the American College of Radiology (ACR) phantom and (2) a sedated sheep with rectilinear and multiblade radial k-space filling acquisitions. Images were acquired on four (2 × 1.5T and 2 × 3T) different MRI scanners. For the radial k-space acquisitions, we acquired images with and without motion correction. All images were visually inspected for the presence of artifact.

Results: Images collected via the conventional rectilinear method were of diagnostic quality and free of artifact. Both ACR and sheep images acquired with radial k-space acquisitions and motion correction suffered significant artifact at different slice locations, scan sessions and across all the four scanners. Severity of the artifact was associated with echo train length. However, the artifact was eliminated when motion correction was not employed.

Conclusion: When little to no motion is present, the use of motion correction with radial k-space acquisitions can compromise image quality. However, image quality is quickly improved, and the artifact eliminated, by repeating the scan without motion correction or by using a conventional rectilinear alternative. Advances in Knowledge: By improving awareness and understanding of this artifact, MRI users will be able to adjust MRI protocols, resulting in more successful scanning sessions, better image quality, fewer call backs and increased diagnostic confidence.

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Figures

Figure 1.
Figure 1.
(Left) The standard rectilinear (line-by-line) method of filling k-space. (Right) the radial k-space sequence fills k-space in a rotational fashion. The black and red bands represent two of the blades used to fill k-space.
Figure 2.
Figure 2.
Axial brain images. (a) The effect of head motion on a conventional turbo spin echo T2 weighted image. (b) Significantly reduced motion artifact after using the motion insensitive sequence.
Figure 3.
Figure 3.
Axial T2 weighted images of the ACR phantom. (a) Conventional rectilinear turbo spin echo images are clear and show no artifact. (b–d) Motion insensitive radial k-space motion corrected “MoCo” images with different ETLs. (e) non-motion corrected (radial k-space acquisition) images show no artifact. This figure demonstrates how motion correction and motion insensitive radial k-space acquisition data can cause artifact in situations with little to no motion. Upon switching the motion correction algorithm off, the artifact disappears (e). It is also important to note that the signal-to-noise, as well as the contrast of the images, deteriorates as the ETL increases (b–d). ACR, American College of Radiology; ETL, echo train length.
Figure 4.
Figure 4.
Transverse brain images of a sedated sheep. (a) Axial motion corrected radial k-space T2 weighted image demonstrating the artifact. (b) Axial conventional rectilinear fast spin echo T2 weighted of the same sheep, in the same session, without the artifact.
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