Robust large-volume fat suppression in whole-heart free-breathing self-navigated coronary MR angiography at 3T using lipid insensitive binomial off-resonant excitation (LIBRE) pulses
Jessica AM Bastiaansen1, Davide Piccini1,2, Ruud B van Heeswijk1,3, and Matthias Stuber1,3

1Department of Radiology, University hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland, 2Advanced Clinical Imaging Technology, Siemens Healthcare, Lausanne, Switzerland, 3Center for Biomedical Imaging, Lausanne, Switzerland


Large volume fat suppression is increasingly challenging at high magnetic field strengths due to B0 and B1 inhomogeneities. In this study, we developed a novel lipid-insensitive binomial off-resonant (LIBRE) radiofrequency excitation pulse to achieve near-complete fat suppression in large 3D volumes and applied it to whole-heart coronary imaging at 3T. In 6 healthy volunteers, we performed free-breathing self-navigated whole-heart 3D radial coronary MRA, and quantitatively compared the results to more commonly used methods for lipid nulling. We show that LIBRE significantly improves the signal nulling of lipid resonances resulting in both improved blood pool delineation for self-navigation and increased vessel conspicuity in the final images.


The signal suppression of unwanted lipid resonances is increasingly challenging at high magnetic field strengths due to increased B0 and B1 inhomogeneities. In a number of specific applications, e.g. coronary MRA, fat suppression is of vital importance, since vessels are embedded in lipid tissue layers and fat suppression needs to be homogeneous within a relatively large volume. Not only may residual off-resonance lipid signals hinder the correct anatomical visualization of the small-caliber coronary vessels, but the presence of such signal from static structures (e.g. chest) can also be a major issue when advanced motion compensation techniques are used. In particular respiratory self-navigation [1, 2] relies on the precise detection of the left-ventricular blood pool in a projection image of the whole thorax [3] to perform motion correction and achieve a 100% scan efficiency in free-breathing coronary MRA. When fat signal is not completely suppressed, the blood pool can no longer be isolated and correct tracking becomes increasingly challenging. The aim of this study was therefore to develop and test a novel lipid insensitive binomial off-resonant excitation (LIBRE) pulse for respiratory self-navigated whole-heart coronary MRA at 3T, and to quantitatively assess the resulting image quality in comparison to more commonly used lipid-nulling schemes.

Materials and Methods

Coronary MRA was performed in (n=6) healthy adult volunteers on a 3T clinical scanner (PRISMA, Siemens Healthcare, Erlangen, Germany). Data were acquired using a prototype respiratory-1D-self-navigated ECG-triggered free-breathing 3D radial gradient-recalled-echo (GRE) imaging sequence [3], preceded by an adiabatic T2 preparation module (T2Prep) to improve blood myocardium contrast [4]. All datasets were 1D motion-corrected, using the superior-inferior (SI) projection image of the thorax, and reconstructed at the scanner. Three different scans were performed in each volunteer: 1) a conventional lipid nulling using spectral presaturation of the lipid resonances (fat-sat, or FS), 2) a conventional 1-1 binomial water excitation scheme (WE), 3) the novel lipid insensitive excitation using LIBRE pulses. The pulse design was based on binomial rectangular pulses which are both frequency and phase modulated. Imaging parameters were: field-of-view (220 mm)3, matrix size 1923, TET2-Prep = 40 ms, RF excitation angle 18°, TE/TR = 2.5 ms/5.6 ms, with 24 to 32 radial readouts per heartbeat for a total of ~15k k-space lines. To compare the efficacy of the three different lipid nulling methods, the signal-to-noise ratio (SNR) of blood, myocardial and fat tissue, the contrast-to-noise ratio (CNR) between blood and myocardium, and between blood and fat tissue, and the vessel sharpness of the right coronary artery (RCA) were calculated using SoapBubble [5]. Statistics were computed via two-tailed student’s t-test for paired data corrected for multiple comparisons. Finally, the tracking signals of the algorithm for respiratory self-navigation were compared by visual inspection.

Results and Discussion

Data were successfully acquired and reconstructed in all volunteers. Representative MRA images show a clear visual difference between the three methods (Fig. 1, A to C). Both RCA and LAD could be clearly visualized using the LIBRE method (Fig. 1, A1 to A3). In all volunteers, the LIBRE method showed improved lipid nulling in the whole acquired volume when compared to conventional spectral fat suppression and water excitation techniques (Fig. 1). The value of all quantitative endpoints was significantly improved for the LIBRE method, with respect to the two other acquisition schemes. SNR and CNR measurements showed significant improvements comparing the LIBRE water excitation method with conventional water excitation and fat pre saturation (Fig. 2A and 2B). The vessel sharpness of the RCA was improved by 30% on average (Fig. 2C). These results are most likely due to the absence of ubiquitous streaking artifacts caused by unsuppressed chest fat. The effects of the different fat suppression techniques can also be appreciated in sagittal images (Fig. 3A-C), where the LIBRE excitation pulses achieve a near complete suppression of the chest fat, thus generating a clean tracking signal for the self-navigation algorithm (Fig. 3D). Conversely, the suboptimal fat suppression of the other two techniques resulted either in a dampened tracking due to the superimposition of static tissue (Fig. 3E), or to unreliable motion detection due to the lack of sharpness in the delineation of the blood pool (Fig. 3F). The suboptimal motion detection and correction in FS and WE also contribute to the lower final image quality.


These preliminary findings demonstrate that novel LIBRE excitation pulses achieve improved fat saturation for coronary imaging at 3T, higher CNR of blood/myocardium and increased vessel sharpness, leading to improved visualization of the coronary arteries. Respiratory self-navigation may particularly benefit from the improved efficacy of this novel pulse.


Center for Biomedical Imaging, Lausanne, Switzerland (CIBM), Nanotera


[1] Stehning, C., et al., Free-breathing whole-heart coronary MRA with 3D radial SSFP and self-navigated image reconstruction. Magn Reson Med, 2005. 54(2): p. 476-80.

[2] Piccini, D., et al., Respiratory self-navigated postcontrast whole-heart coronary MR angiography: initial experience in patients. Radiology, 2014. 270(2): p. 378-86.

[3] Piccini, D., et al., Respiratory self-navigation for whole-heart bright-blood coronary MRI: methods for robust isolation and automatic segmentation of the blood pool. Magn Reson Med, 2012. 68(2): p. 571-9.

[4] Nezafat, R., et al., B1-insensitive T2 preparation for improved coronary magnetic resonance angiography at 3 T. Magn Reson Med, 2006. 55(4): p. 858-64.

[5] Etienne, A., et al., "Soap-Bubble" visualization and quantitative analysis of 3D coronary magnetic resonance angiograms. Magn Reson Med, 2002. 48(4): p. 658-66.


Free-breathing self-navigated coronary MRI at 3T using three lipid nulling methods. The first used novel lipid insensitive RF excitation pulses (LIBRE, A1-A3), the second a standard fat suppression (FS, B1-B2), and the third a standard water excitation (WE, C1-C2). Displayed are the RCA (orange arrows) and LAD (yellow & green arrows). Note the depiction of the LAD branches (A2, green arrows), and the inhomogeneous fat suppression in B and C (red arrows).

Quantitative endpoints comparing three lipid suppression techniques, LIBRE, FS, and WE. SNR of muscle, myocardium and lipid signals (A). CNR between blood and myocardium and between blood and fat (B). Vessel sharpness of the RCA using three different methods for lipid nulling (C). * p<0.05 in respect to the LIBRE technique.

Sagittal images depicting the fat suppression in the chest wall of three different methods of lipid nulling (A-C). Note the inhomogeneous fat suppression in B and C compared with A. Display of the corresponding superior inferior (SI) projections used for self-navigation and online image reconstruction (D-F). Note how only LIBRE provides a clean and reliable tracking signal of the blood pool.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)