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  • 1
    Publication Date: 2015-08-27
    Description: Purpose To identify and reduce image artifacts in non–contrast-enhanced velocity-selective (VS) magnetization-prepared peripheral MR angiography (MRA) at 3T. Methods To avoid signal loss in the arteries, double and quadruple refocused VS excitation pulse sequences were designed that were robust to a wide range of B 0 and B 1 offset. To suppress stripe artifact and background signal variation, we successively applied two VS preparations with excitation profiles shifted by half the period of the stripes. VS-MRA using single, double, and quadruple refocused VS preparations was tested in healthy subjects and a patient. Results In the regions of large B 0 and B 1 offsets, arterial signal loss was yielded by single refocused VS preparation, but was avoided with double or quadruple refocused preparations. Compared with single VS preparation, the two consecutive preparations with shifted excitation profiles substantially reduced the stripe artifact and background signal variation, as demonstrated by increased mean and decreased standard deviation of relative contrast-to-noise ratio. The proposed VS-MRA identified multilevel disease in the femoral arteries of the patient, as validated by digital subtraction angiography. Conclusion Two multiple refocused VS magnetization preparations with shifted excitation profiles yield artifact-free peripheral angiograms at 3T. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.
    Print ISSN: 0740-3194
    Electronic ISSN: 1522-2594
    Topics: Medicine
    Published by Wiley-Blackwell
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  • 2
    Publication Date: 2018-03-14
    Description: Purpose To characterize and suppress stripe artifact associated with velocity-selective (VS) magnetization for unenhanced MRA. Methods Extended phase graph formalism was used to show that the stripe artifact contains multiples of the fundamental frequency that is determined by the area of unipolar VS gradient. Four VS preparation pulses whose excitation profiles are spatially shifted by quarter the fundamental period of the stripes, were applied alternately. For further suppression of the artifact, k-space data at k z  = 0 were averaged over the 4 VS preparations. The proposed schemes were tested in a chicken breast phantom and healthy human subjects. Results When the standard VS preparation scheme was used, stripe artifact was shown in all the reconstructed images and appeared as artifactual peaks in k-space that corresponded to the first and second order harmonics of the fundamental frequency. Alternate application of the 4 phase-shifted VS preparation pulses suppressed the stripes, but not completely, as evidenced by residual erroneous peaks in k-space. After the k-space averaging, the stripe artifact was nearly eliminated. Conclusion Stripe artifact in VS-MRA consists of multiples of the fundamental frequency and can be effectively suppressed through alternate application of phase-shifted VS preparations along with k-space averaging.
    Print ISSN: 0740-3194
    Electronic ISSN: 1522-2594
    Topics: Medicine
    Published by Wiley-Blackwell
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
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