Reduction of motion artifact in cine MRI using variable-density spiral trajectories

Stanford Medicine, Stanford, California, United States
Magnetic Resonance in Medicine (Impact Factor: 3.57). 04/1997; 37(4):569-75. DOI: 10.1002/mrm.1910370416
Source: PubMed


Dynamic cardiac imaging in MRI is a very challenging task. To obtain high spatial resolution, temporal resolution, and signal-to-noise ratio (SNR), single-shot imaging is not sufficient. Use of multishot techniques resolves this problem but can cause motion artifacts because of data inconsistencies between views. Motion artifacts can be reduced by signal averaging at some cost in increased scan time. However, for the same increase in scan time, other techniques can be more effective than simple averaging in reducing the artifacts. If most of the energy of the inconsistencies is limited to a certain region of kappa-space, increased sampling density (oversampling) in this region can be especially effective in reducing motion artifacts. In this work, several variable-density spiral trajectories are designed and tested. Their efficiencies for artifact reduction are evaluated in computer simulations and in scans of normal volunteers. The SNR compromise of these trajectories is also investigated. The authors conclude that variable-density spiral trajectories can effectively reduce motion artifacts with a small loss in SNR as compared with a uniform density counterpart.

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    • "The method proposed by Liao et al. [22] uses a variable-density stack of spiral trajectories which varies the sampling density both along the kx-ky plane and the kz direction. The method is shown to preserve reasonable image quality while reducing the acquisition time by approximately half compared to a fullysampled stack of spirals. "

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    • "For spiral sequences, motion artefacts tend to take the form of swirls and depending on the imaging region of interest these can be less of a problem than phase-encode ghosts. Variable-density spirals that oversample the centre of k-space, at a cost of undersampling the edges, have also been shown to reduce respiratory artefacts in segmented cine images [83]. "
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    • "In both tSNR and sSNR measures, a trend was observed showing slightly higher SNR values for the spiral readout. The shorter TE of the spiral readout and some of its intrinsic advantages, such as its relative insensitivity to movement and flow artifacts (Ahn et al., 1986; Delattre et al., 2010; King, 2004; Liao et al., 1997), may be contributing to achieve higher SNR values, but this could also be due to the in-plane blurring observed in the spiral images. "
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