100% efficient motion corrected coronary MR angiography using a gradient echo sequence in a 3T PET-MR system
Camila Munoz1, Radhouene Neji2, Peter Weale2, Rene Botnar1, and Claudia Prieto1

1Department of Biomedical Engineering, King's College London, London, United Kingdom, 2MR Research Collaborations, Siemens Healthcare, Frimley, United Kingdom


Respiratory motion remains a challenge for coronary MR angiography at 3T. Here we propose an inline 2D translational motion correction scheme using an image-based navigator. Low-resolution navigators are acquired at each heartbeat by spatially encoding the start-up echoes of an ECG-gated gradient echo sequence, allowing for 100% scan efficiency. Results from healthy volunteers show that motion correction improves visualization of the right and left anterior descending coronary arteries. The proposed scheme potentially allows for performing a comprehensive diagnosis of coronary artery disease by acquiring both diagnostic and motion information from MR, that can also be used to correct PET data.


Recent development of simultaneous whole-body PET-MR scanners has the potential of performing non-invasive diagnosis of coronary artery disease, including assessment of myocardial perfusion, coronary angiography and ventricular function in one comprehensive exam1. However, image quality degradation due to physiological motion of both PET and MR images remains a major challenge. For cardiac MR imaging, image-based navigators have been proposed in order to address the problem of respiratory motion for 3D whole heart coronary MR angiography (MRA)2-3. These approaches reduce the MR acquisition time, since all acquired data is used for reconstruction (100% scan efficiency) and correct for the complex motion of the heart during free-breathing acquisition. One of these approaches spatially encodes the start-up echoes of a balanced steady state acquisition sequence to reconstruct an image navigator2. Here we propose to extend this approach to a gradient echo sequence, so that start-up echoes can be used to acquire image-based navigators for inline 2D translational motion corrected coronary MRA imaging in a 3T PET-MR system.


An ECG-triggered 3D T1-weighted gradient echo sequence using a fully sampled golden-step Cartesian spiral profile order4 was implemented. This trajectory samples the phase encoding plane following approximate spiral interleaves on the Cartesian grid. A user-defined number of start-up echoes were used to acquire a coronal-oriented low-resolution 2D Cartesian navigator at each heartbeat. Additionally, an adiabatic T2 preparation pulse was implemented to improve the contrast in the images, and a fat saturation prepulse was applied before 3D coronary MRA acquisition (Fig. 1). Translational motion in foot-head (FH) and left-right (RL) directions was estimated from the 2D navigator in a beat-to-beat fashion using normalised cross correlation of a template covering the apex of the heart (Fig. 2). Motion estimates were used to correct data acquired at each heartbeat prior to image reconstruction by multiplying the k-space data with corresponding linear phase factors. Inline motion correction was implemented in the scanner, so that a high-resolution 3D motion corrected coronary MR angiography was obtained. Acquired data was also reconstructed inline without motion correction for comparison purposes.

Three healthy subjects were scanned during free-breathing on a 3T PET-MR scanner (Biograph mMR, Siemens Healthcare, Erlangen, Germany) using a prototype implementation of the proposed gradient echo sequence (field of view = 300x300x80mm3, resolution = 1x1x2mm3, TR/TE = 3.75/1.72ms, flip angle = 15°). A subject-specific acquisition window (82–90ms) was obtained by varying the segments acquired per each spiral interleave (22-24 profiles per cardiac cycle), and a trigger delay was set targeting the mid-diastolic rest period. For the 2D image navigator acquisition, 14 start-up echoes (same FOV, flip angle = 3º) were used.


3D coronary MRA images were reformatted to simultaneously visualize the left anterior descending (LAD) and right coronary artery (RCA) using custom made software5. A significant improvement in recovering the distal segment of the RCA (red arrow) and the proximal segment of the LAD (blue arrow) can be observed in Fig. 3 (top) for the first subject. However, lack of contrast prevented to observe the distal LAD. A similar behaviour can be observed in Fig. 3 (bottom) for a second subject. Additionally, blurring of the RCA (green arrow) is reduced when applying the proposed motion correction.


We have presented an MR acquisition scheme that allows for inline translational motion correction for coronary MR angiography in a 3T PET-MR scanner. By spatially encoding the start-up echoes of a gradient echo sequence, motion was estimated in a beat-to-beat fashion, achieving 100% scan efficiency. A golden-step Cartesian spiral profile order acquisition was used for acquiring high-resolution 3D MR data. Motion correction improves image quality and contrast compared with uncorrected images. Further work includes incorporating non-rigid bin-to-bin motion correction to further improve image quality, and use of the MR-measured motion estimates to correct simultaneously acquired cardiac perfusion PET data and corresponding attenuation correction maps.


This work was supported by the EPSRC Centre for Doctoral Training in Medical Imaging.


1. Rischpler, C et al. Hybrid PET/MR imaging of the heart: potential, initial experiences, and future prospects. JNM 2013, 54(3):402–15

2. Henningsson, M et al. Whole-heart coronary MR angiography with 2D self-navigated image reconstruction. MRM 2012, 67(2):437–45

3. Wu, HH et al. Free-breathing multiphase whole-heart coronary MR angiography using image-based navigators and three-dimensional cones imaging. MRM 2013, 69(4): 1083–93

4. Prieto, C et al. Highly efficient respiratory motion compensated free-breathing coronary MRA using golden-step Cartesian acquisition. JMRI 2015, 41(3):738–46

5. Etienne, A et al. “Soap-Bubble” visualization and quantitative analysis of 3D coronary magnetic resonance angiograms. MRM 2002, 48(4):658–66


Fig1.Schematic diagram of the implemented coronary MR angiography sequence. A coronal 2D navigator (2D nav) is acquired by spatially encoding the start-up echoes of the high-resolution 3D gradient echo (GRE) imaging sequence. The template for motion estimation is manually placed during acquisition planning.

Fig2.Example 2D image navigators acquired with 14 start-up echoes. Template tracking of the apical region of the heart is also displayed (red boxes). The maximum FH displacement between these image navigators was 8 mm. FH: foot-head.

Fig3.Reformatted images along the RCA and LAD artery from two subjects. (a) Uncorrected images (b) Motion correction approach. Proximal segments of the RCA and LAD can be observed in the uncorrected images, however, blurring prevents visualisation of distal segments. Both arteries are better depicted after applying 2D translational motion correction.

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