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Correction of vibration artifacts in DTI using phase-encoding reversal (COVIPER).

Mohammadi S, Nagy Z, Hutton C, Josephs O, Weiskopf N - Magn Reson Med (2011)

Bottom Line: We refined the model of vibration-induced echo shifts, showing that asymmetric k-space coverage in widely used Partial Fourier acquisitions results in locally differing signal loss in images acquired with reversed phase encoding direction (blip-up/blip-down).COVIPER was validated against low vibration reference data, resulting in an error reduction of about 72% in fractional anisotropy maps.COVIPER can be combined with other corrections based on phase encoding reversal, providing a comprehensive correction for eddy currents, susceptibility-related distortions and vibration artifact reduction.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, United Kingdom. siawoosh.mohammadi@ucl.ac.uk

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a: Example of signal-dropout due to vibration on an axial slice of a diffusion-weighted image (top row) as well as the corresponding shift in k-space (middle row, amplitude of complex raw data) and the projection of the k-space signal along the dashed line (bottom row). Severe signal-loss occurs (red arrow) if the echo center is shifted toward the shorter k-space edge (kmin for the blip-down data). As hypothesized, this signal-loss can be recovered if the PE direction is reversed (blip-up image). Note that the blip-up image shows also rudimentary signal-loss artifacts, however, in another region of the brain (yellow arrow) meaning that a partition of the echo is shifted towards kmax, that is, the shorter k-space edge for the blip-up data. b: The reference data were acquired as in (a) but using a longer TR = 170 ms to reduce the vibration-induced echo shift effect. As expected, the diffusion-weighted images (top row) show no signal-dropout. Note that the geometrical distortions (due to susceptibility and eddy current effects) in blip-up and blip-down images (top row in a and b) have not been corrected to avoid interpolation artifacts. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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fig02: a: Example of signal-dropout due to vibration on an axial slice of a diffusion-weighted image (top row) as well as the corresponding shift in k-space (middle row, amplitude of complex raw data) and the projection of the k-space signal along the dashed line (bottom row). Severe signal-loss occurs (red arrow) if the echo center is shifted toward the shorter k-space edge (kmin for the blip-down data). As hypothesized, this signal-loss can be recovered if the PE direction is reversed (blip-up image). Note that the blip-up image shows also rudimentary signal-loss artifacts, however, in another region of the brain (yellow arrow) meaning that a partition of the echo is shifted towards kmax, that is, the shorter k-space edge for the blip-up data. b: The reference data were acquired as in (a) but using a longer TR = 170 ms to reduce the vibration-induced echo shift effect. As expected, the diffusion-weighted images (top row) show no signal-dropout. Note that the geometrical distortions (due to susceptibility and eddy current effects) in blip-up and blip-down images (top row in a and b) have not been corrected to avoid interpolation artifacts. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Mentions: Figure 2a shows an example of the signal-dropout due to vibration in an axial slice of a diffusion-weighted image (top row) as well as the corresponding shift of the echo in k-space (middle row) and its k-space signal profile along the dashed line (bottom row). The signal-dropout was most apparent when the echo center was shifted towards the shorter k-space edge (red arrow). For the reference DTI data (Fig 2b), which were acquired using a longer slice TR = 170 ms to reduce the vibration effects, the echo center was only marginally shifted and no signal-dropout was visible in the diffusion-weighted image of either blip direction.


Correction of vibration artifacts in DTI using phase-encoding reversal (COVIPER).

Mohammadi S, Nagy Z, Hutton C, Josephs O, Weiskopf N - Magn Reson Med (2011)

a: Example of signal-dropout due to vibration on an axial slice of a diffusion-weighted image (top row) as well as the corresponding shift in k-space (middle row, amplitude of complex raw data) and the projection of the k-space signal along the dashed line (bottom row). Severe signal-loss occurs (red arrow) if the echo center is shifted toward the shorter k-space edge (kmin for the blip-down data). As hypothesized, this signal-loss can be recovered if the PE direction is reversed (blip-up image). Note that the blip-up image shows also rudimentary signal-loss artifacts, however, in another region of the brain (yellow arrow) meaning that a partition of the echo is shifted towards kmax, that is, the shorter k-space edge for the blip-up data. b: The reference data were acquired as in (a) but using a longer TR = 170 ms to reduce the vibration-induced echo shift effect. As expected, the diffusion-weighted images (top row) show no signal-dropout. Note that the geometrical distortions (due to susceptibility and eddy current effects) in blip-up and blip-down images (top row in a and b) have not been corrected to avoid interpolation artifacts. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3569871&req=5

fig02: a: Example of signal-dropout due to vibration on an axial slice of a diffusion-weighted image (top row) as well as the corresponding shift in k-space (middle row, amplitude of complex raw data) and the projection of the k-space signal along the dashed line (bottom row). Severe signal-loss occurs (red arrow) if the echo center is shifted toward the shorter k-space edge (kmin for the blip-down data). As hypothesized, this signal-loss can be recovered if the PE direction is reversed (blip-up image). Note that the blip-up image shows also rudimentary signal-loss artifacts, however, in another region of the brain (yellow arrow) meaning that a partition of the echo is shifted towards kmax, that is, the shorter k-space edge for the blip-up data. b: The reference data were acquired as in (a) but using a longer TR = 170 ms to reduce the vibration-induced echo shift effect. As expected, the diffusion-weighted images (top row) show no signal-dropout. Note that the geometrical distortions (due to susceptibility and eddy current effects) in blip-up and blip-down images (top row in a and b) have not been corrected to avoid interpolation artifacts. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Mentions: Figure 2a shows an example of the signal-dropout due to vibration in an axial slice of a diffusion-weighted image (top row) as well as the corresponding shift of the echo in k-space (middle row) and its k-space signal profile along the dashed line (bottom row). The signal-dropout was most apparent when the echo center was shifted towards the shorter k-space edge (red arrow). For the reference DTI data (Fig 2b), which were acquired using a longer slice TR = 170 ms to reduce the vibration effects, the echo center was only marginally shifted and no signal-dropout was visible in the diffusion-weighted image of either blip direction.

Bottom Line: We refined the model of vibration-induced echo shifts, showing that asymmetric k-space coverage in widely used Partial Fourier acquisitions results in locally differing signal loss in images acquired with reversed phase encoding direction (blip-up/blip-down).COVIPER was validated against low vibration reference data, resulting in an error reduction of about 72% in fractional anisotropy maps.COVIPER can be combined with other corrections based on phase encoding reversal, providing a comprehensive correction for eddy currents, susceptibility-related distortions and vibration artifact reduction.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, United Kingdom. siawoosh.mohammadi@ucl.ac.uk

Show MeSH
Related in: MedlinePlus