Free-breathing 3D cardiac function with accelerated magnetization transfer prepared imaging

  • Eric M Schrauben
  • Oliver Wieben
  • Kevin M Johnson
Open Access
Poster presentation
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Keywords

Magnetization Transfer Soft Thresholding Isotropic Spatial Resolution Phantom Scan Cardiac Time 

Background

3D cardiac MRI has long held promise for improved heart coverage, higher resolution, and reduced sensitivity to poor breath-hold reproducibility. However, its use has been limited by reduced blood pool to myocardium contrast for spoiled and balanced steady-state free precession (bSSFP) implementations. T2-preparation techniques [1] are capable of increasing contrast but are unfortunately limited by lengthy preparation periods and resulting scan inefficiencies. In this work, we develop a paradigm for high contrast 3D cardiac function that relies on the alternative use of magnetization transfer (MT) preparation [2] combined with accelerated 3D spoiled gradient echo imaging (SPGR).

Methods

An off-resonance RF pulse was interleaved with whole-heart, respiratory gated 3D radial SPGR sampling [3]. Simulations and phantom scans were performed to optimize MT saturation (power, off-resonance, and frequency). Phantom scans utilized 4% agar, fat, and doped water. After optimization, initial volunteer images were collected on a clinical 1.5T system (HDx, GE, Waukesha, WI) using: FOV = 64 × 32 × 32 cm3, 2.0 mm isotropic spatial resolution, TR/TE1/TE2 = 5.6/1.32/3.32 ms, α = 4°, free-breathing: scan time = 10 min, 50% acceptance window (bellows), number of projections = 39,000. In-vivo experiments utilized a 1600°, 20 ms Hamming-windowed Sinc pulse applied every 10 TRs. This pulse was applied at 210 Hz off-resonance providing some fat-saturation. In addition, two full echoes (TE1 and TE2) at ± 62.5 kHz were added to further remove fat signal while increasing SNR of water images. Twenty cardiac time frames were reconstructed using iterative soft thresholding of temporal differences with a spatial wavelet transform.

Results

Figure 1 shows images from phantom scans for a sweep of MT off-resonance frequencies and demonstrates the potential for simultaneous suppression of muscle (agar) and fat. In-vivo results are presented in Figure 2 for two reformats: vertical long axis in end-systole and end-diastole (left) and an end-systolic base to apex short axis stack (right). Excellent blood pool to myocardium contrast and fat suppression are observed. Isotropic spatial resolution allows for retrospective whole-heart reformats in any orientation.
Figure 1

Left: MT-prepared VIPR SPGR scans in phantoms with water, 4% agar, blood-mimicking fluid, and canola oil (fat) demonstrate signal saturations at various MT offset frequencies. Right: Signal calculations over a range of frequencies show maximum fat suppression near its peak at 1.5T.

Figure 2

Left: Vertical long axis reformats in end-systole (top) and end-diastole (bottom) display excellent suppression of fat and muscle without off-resonance induced banding artifacts seen in bSSFP. Right: End-systolic short-axis stack from apex to base displays benefits of isotropic spatial resolution for retrospective reformatting of the entire heart in any orientation.

Conclusions

The feasibility of a novel whole-heart functional cardiac acquisition using MT preparation with isotropic spatial resolution in a clinically reasonable scan time is presented. Further studies on optimization of acquisition parameters, including off-resonance frequency, number of projections, and acquired spatial resolution, will improve the applicability of the sequence for clinical situations.

Funding

NIH grant 2R01HL072260.

References

  1. 1.
    Brittain JH, et al: MRM. 1998Google Scholar
  2. 2.
    Henkelman RM, et al: NMR Biomed. 2001Google Scholar
  3. 3.
    Barger AV, et al: MRM. 2000Google Scholar

Copyright information

© Schrauben et al.; licensee BioMed Central Ltd. 2014

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/2.0), 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.

Authors and Affiliations

  • Eric M Schrauben
    • 1
  • Oliver Wieben
    • 1
    • 2
  • Kevin M Johnson
    • 1
  1. 1.Medical PhysicsUniversity of Wisconsin - MadisonMadisonUSA
  2. 2.RadiologyUniversity of Wisconsin - MadisonMadisonUSA

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