Volume 12 Supplement 1

Abstracts of the 13thAnnual SCMR Scientific Sessions - 2010

Open Access

Coronary MRA at 3 T using 3d multi-interleaved multi-echo acquisition with varpro fat-water separation

  • Saurabh Shah1,
  • Xiaoming Bi1,
  • Diego Hernando2,
  • Peter Weale1,
  • Sonia Nielles-Vallespin3,
  • Peter Kellman4 and
  • Sven Zuehlsdorff1
Journal of Cardiovascular Magnetic Resonance201012(Suppl 1):P42

DOI: 10.1186/1532-429X-12-S1-P42

Published: 21 January 2010

Introduction

Coronary MR Angiography is a valuable tool for non-invasive assessment of coronary arteries. Presently, contrast-enhanced, fat-saturated, ECG-triggered and navigator-gated 3D spoiled gradient-echo sequence is employed for whole-heart Coronary MRA at 3 T[1]. However, large static field variations at 3 T frequently result in non-uniform fat-suppression over the field-of-view (FOV), obscuring the delineation of coronary arteries. Multi-echo Dixon approaches utilizing iterative decomposition have been shown to provide robust fat-water separation even in the presence of large field inhomogeneities. In this study, an ECG-triggered navigator-gated 3D spoiled gradient-echo multi-interleaved multi-echo (GRE-MEMI) pulse sequence is introduced which utilizes VARPRO[2] fat-water separation to achieve reliable fat-suppression and provides enhanced visualization of coronary arteries.

Methods

A 3D GRE-MEMI sequence (Fig. 1) was implemented on a 3 T whole-body MR scanner (MAGNETOM Trio, Siemens AG) with support for navigator-gating and ECG-triggering. Water-only and fat-only images were reconstructed using VARPRO. Four healthy volunteers were imaged pre- and during contrast agent administration targeting right coronary artery (RCA). Typical imaging parameters for pre-contrast GRE-MEMI scan are listed in Table 1. Additionally, a conventional single-echo fat-saturated GRE scan was acquired for comparison. Thereafter, 0.2 mmol/kg Gd-DTPA (Magnevist®, Bayer Healthcare) was slowly injected at a rate of 0.3 ml/s followed by 20 ml of saline solution injected at the same rate. GRE-MEMI acquisition with inversion preparation (TI = 300 ms) was started 30 s after injection.
Table 1

Typical imaging parameters for conventional 3D fat-saturated GRE and 3D GRE-MEMI measurements.

Paramater name

Fat-saturated GRE

GRE-MEMI

No. of Echoes

1

4

TE

1.54 ms

1/2/3/4 = 1.35/2.47/3.6/4.7 2 ms

TR

3.4 ms

5.42 ms

Flip angle

18°

18°

Resolution

1.3 mm × 1.3 mm × 1.5 mm

1.3 mm × 1.3 mm × 1.5 mm

No. of Slices

32

32

Parallel acquisition/acceleration/reference lines

GRAPPA/2/24

GRAPPA/2/24

https://static-content.springer.com/image/art%3A10.1186%2F1532-429X-12-S1-P42/MediaObjects/12968_2010_Article_1142_Fig1_HTML.jpg
Figure 1

Pule Sequence Diagram for 3D ECG-triggered, navigator gated, spoiled gradient echo sequence with multi-echo multi-interleave readout (GRE-MEMI). Multiple echoes are used during reconstruction by VARPRO for iterative water-fat decomposition. No fat-saturation prepulse is applied separately. Multi-interleaved scheme achieves shorter echo time increments between multiple echoes, which improves the fat-water separation.

Results

Targeted RCA images were successfully acquired in all volunteers with effective fat-water separation. The average total imaging time was 8.93 ± 1.2 min with navigator efficiency of 33.8 ± 4.6%. Fig. 2 shows pre-contrast coronary artery images from a healthy volunteer. Conventional fat-saturation yields suboptimal fat-suppression whereas robust fat-suppression is evident in water-only images which provide clear depiction of coronary artery. Fig. 3 illustrates enhanced contrast-to-noise with the use of contrast agent.
https://static-content.springer.com/image/art%3A10.1186%2F1532-429X-12-S1-P42/MediaObjects/12968_2010_Article_1142_Fig2_HTML.jpg
Figure 2

Conventional fat saturation (chemical selective saturation) image (a) and fat-water separated images (b, c) from a targeted right coronary artery (RCA) measurement at 3 T in a healthy volunteer without any contrast agent administration. Conventional fat saturation yields suboptimal results in some areas (a - red arrows), however, robust fat suppression is achieved over the entire FOV using the proposed technique. Moreover, the use of multiple echoes increases the signal-to-noise ratio (SNR). Water-only (d) and fat-only (e) pre-contrast images from another health subject demonstrate excellent fat suppression and clearly depict RCA (red arrows).

https://static-content.springer.com/image/art%3A10.1186%2F1532-429X-12-S1-P42/MediaObjects/12968_2010_Article_1142_Fig3_HTML.jpg
Figure 3

Water-only (a) and fat-only (b) images acquired from a healthy subject during slow infusion of contrast media. Note that water and fat signals are effectively separated and the RCA (a - red arrows) is sharply delineated. Compared to pre-contrast GRE measurements, use of contrast agent increases contrast-to-noise ratio between blood and background tissues.

Conclusion

3D GRE-MEMI sequence was successfully utilized for targeted fat-water separated coronary artery imaging in healthy volunteers. VARPRO fat-water separation provides reliable fat-suppression at 3 T and improves the delineation of coronary arteries. Moreover, without the use of a fat-saturation prepulse, readout duration within a heartbeat can be extended to cover the entire quiescent period without any degradation in fat-suppression. Multi-echo acquisition results in increased acquisition time, however, the resulting water-only image provides the benefit of increased SNR due to intrinsic averaging effect of fat-water separation. Further improvement in acquisition speed using higher parallel imaging factors is required to achieve 3D whole-heart coverage.

Authors’ Affiliations

(1)
Siemens Healthcare
(2)
University of Illinois at Urbana-Champaign
(3)
Royal Brompton And Harefield NHS Foundation Trust
(4)
National Institutes of Health/NHLBI

References

  1. Bi X et al: MRM. 2007, 58:Google Scholar
  2. Hernando D et al: MRM. 2008, 59:Google Scholar

Copyright

© Shah et al; licensee BioMed Central Ltd. 2010

This article is published under license to BioMed Central Ltd.

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