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Volume 18 Supplement 1

19th Annual SCMR Scientific Sessions

  • Poster presentation
  • Open Access

CAIPIRINHA-accelerated 2D bSSFP imaging with improved banding behavior using Gradient-Controlled Local Larmor Frequency (GC-LOLA)

  • 1,
  • 3, 2 and
  • 1
Journal of Cardiovascular Magnetic Resonance201618 (Suppl 1) :P301

https://doi.org/10.1186/1532-429X-18-S1-P301

  • Published:

Keywords

  • Larmor Frequency
  • Slice Position
  • Healthcare GmbH
  • bSSFP Sequence
  • bSSFP Imaging

Background

Cardiac MRI often requires a careful trade-off between SNR, spatio-temporal resolution and slice coverage. Providing fast acquisitions, high SNR and flow/motion robustness, bSSFP has become the dominant sequence. Drawbacks are high SAR levels and sensitivity to B0 inhomogeneities. For improving slice coverage, MS-CAIPIRINHA [1] has emerged as a standard method. By simultaneously scanning multiple slices, it provides acceleration in slice direction with minimal SNR penalty.

When combining MS-CAIPIRINHA with bSSFP, the sequence steady-state and contrast have to be maintained. Two methods are available: The first [2] employs RF-based multi-slice encoding [1], generating slice-specific shifts in the bSSFP pass-band structure effectively reducing the off-resonance robustness by a factor of two. The second [3] applies balanced gradient encoding during readout, potentially increasing the sensitivity to eddy currents for small inter-slice distances because encoding changes from excitation to excitation.

Methods

We propose a new method, called gradient-controlled local larmor adjustment (GC-LOLA), that eliminates the drawback of the RF-encoded combination in two steps: (1) By slightly unbalancing the slice select gradient, the Larmor frequency is made locally dependent, which compensates the relative shift between the pass-bands. (2) In addition, the RF phase cycles are modified to shift the centers of the aligned pass-bands to resonance. The method is illustrated in Figure 1 for two slices S0 and S1 at slice positions D0 and D1. The pass-band shifts are fully corrected by unbalancing the slice gradient by the moment M, distributed evenly on slice pre- and rephaser, and subtracting the residual off-resonance ΦG from the RF phase increments in both slices. To test the concept, phantom and in-vivo measurements were performed using a bSSFP sequence prototype, modified in-house to support MS-CAIPIRINHA and GC-LOLA (MAGNETOM Aera and Skyra, Siemens Healthcare GmbH, Erlangen).

Results

The Phantom results (Figure 2 top row, slice thickness 5 mm, slice positions S0: 55 mm, S1: 70 mm, flip 40°) demonstrate the successful restoration of the original band pattern. Due to the gradient unbalancing, the stop-bands appear slightly blurred. The benefit of increasing the off-resonance robustness can be seen from the volunteer scan (Figure 2 bottom row, slice thickness 5 mm, gap 100%, TR 2.9ms, TE 1.3ms): A stop-band is shifted out of the posterior of the left ventricle (LV) and the signal in the LV blood pool is more homogeneous.
Figure 1
Figure 1

bSSFP with GC-LOLA for two slices.

Figure 2
Figure 2

Top row: bSSFP band structure in a phantom with linear gradient for RF-encoded MS-CAIPIRINHA with two simultaneously excited slices without (left) and with GC-LOLA (right) compared to two single-slice acquisitions (center). Conventional MS-CAIPIRINHA shifts the stop-bands by +¼ and -¼ of the band distance in slice 1 and 2, respectively. The application of GC-LOLA shifts the stop-bands back to their original positions and blurs them. The common central pass-band is indicated with orange bars. Bottom row: One of two slices of an MS-CAIPIRINHA scan of a healthy volunteer at 3T without (left) and with (right) GC-LOLA. The stop-band indicated by the arrow has successfully been moved out of the posterior wall.

Conclusions

Our preliminary results indicate that GC-LOLA stabilizes MS-CAIPIRINHA-accelerated bSSFP with respect to field inhomogeneities, without the need for toggled gradients from TR to TR.

Authors’ Affiliations

(1)
Siemens Healthcare GmbH, Erlangen, Germany
(2)
Department of Diagnostic and Interventional Radiology, University of Wuerzburg, Wuerzburg, Germany
(3)
Centre for Advanced Imaging, The University of Queensland, Brisbane, QLD, Australia

References

  1. Breuer : MRM. 2005, 53: 684-691.View ArticlePubMedGoogle Scholar
  2. Stäb : MRM. 2011, 65: 157-164.View ArticlePubMedGoogle Scholar
  3. Duerk : 2013, US2013/0271128 A1Google Scholar

Copyright

© Speier et al. 2016

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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