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Late gadolinium enhancement imaging using spiral readouts at 3T
Journal of Cardiovascular Magnetic Resonancevolume 15, Article number: E8 (2013)
Breath-hold late gadolinium enhancement (LGE) imaging is commonly performed as a stack of 2D short-axis slices through the ventricles. Standard inversion recovery with Cartesian k-space coverage requires long acquisition windows of 140 - 200 ms which have potential to introduce artefacts due to longitudinal magnetisation recovery and blurring due to cardiac motion. Ghosting in the phase encoding direction from beat-to-beat signal variations and due to poor breath-holding may mimic enhancement and a phase swapped (PS) stack of slices is also acquired to confirm diagnosis, although this doubles the scan time.
Spiral data acquisition provides highly efficient coverage of k-space and would potentially allow a significant reduction of the acquisition window. This would reduce motion blurring and edge artefacts while at the same time, may eliminate the need for PS acquisitions. Its use for 2D LGE was investigated.
An interleaved spiral readout sequence was designed to match the current clinically-used standard inversion-prepared segmented gradient-echo sequence in terms of spatial resolution (1.4 x 1.4 x 6 mm (reconstructed 0.7 x 0.7 x 6 mm)) and breath-hold duration (14 cardiac cycles with alternate R-wave gating). The sequence consisted of 12 interleaves (13 ms duration) with 2 acquired per cardiac cycle (flip angles 45° & 90°). The acquisition window was 53 ms compared to 144 - 204 ms for the standard sequence. A water excitation pulse eliminated signal from fat and associated off-resonance blurring.
Spiral LGE imaging was performed after the completion of clinical LGE studies (with and without PS) in 9 patients on a Siemens 3T Skyra scanner. Basal, mid and apical short axis slices were acquired for paired comparison with the standard Cartesian images in terms of blood signal-to-noise ratio (SNR) and blood/myocardium contrast-to-noise ratio (CNR).
Figure 1 shows phantom scans with edge artefact using Cartesian k-space coverage (due to magnetisation recovery through the long acquisition window) which are not present on the spiral image.
In vivo, blood pool SNR and blood-myocardium CNR were significantly higher with the spiral acquisitions (SNR: 162.8+/-62.5 vs 238.8+/-112.0, p<0.05, CNR: 137.8+/-55.8 vs 201.8+/-105.1, p < 0.05) despite always being acquired later when the blood pool gadolinium concentration is lower. Example images from both sequences in 3 patients are shown in Figure 2.
Spiral readouts allow shorter acquisition windows then standard Cartesian LGE imaging (53 ms compared to 144-204 ms in this study) which has the potential to reduce edge artefacts and motion blurring. The higher flip angles used also result in increased SNR and CNR.
While beat to beat signal variations result in ghosting in the phase encode direction with Cartesian acquisitions, requiring the acquisition of a PS stack, their effect with spiral acquisitions is less obvious and will be a focus of future work.
Wellcome Trust Grant WT093953MA
NIHR - National Institute for Health Research