André Fischer1,2, Anne Menini1, Aurelien Bustin1,3, Kevin M Johnson4, Christopher J Francois5, and Anja C.S. Brau2
1GE Global Research, Garching bei München, Germany, 2Cardiac Center of Excellence, GE Healthcare, Garching bei München, Germany, 3Computer Science, Technical University Munich, München, Germany, 4Medical Physics, University of Wisconsin, Madison, WI, United States, 5Radiology, University of Wisconsin, Madison, WI, United States
Synopsis
Cardiac MRI is affected by both cardiac and
respiratory motion. While ECG-gated imaging in breath hold is the clinical
method of choice, free-breathing methods are needed in patients with limited
breath hold capability. This works describes a method to obtain free-breathing cine
datasets with high SNR and high spatial resolution (1.4mm in-plane) from a
completely self-gated Golden Angle radial scan within an 11s scan time. The
motion compensated reconstruction technique takes advantage of calibrated displacement
fields extracted from the radial data to recover motion artifact-free cardiac
phases. Beyond cine imaging, contrast-enhanced cardiac imaging can also be
expected to benefit from this motion compensated reconstruction strategy.Motivation
Cardiac
magnetic resonance imaging (CMR) is affected by both cardiac and respiratory
motion which are commonly compensated with ECG-gated imaging during a breath
hold. However, free-breathing methods are preferred or even required in
patients with limited breath hold capability. Free-breathing approaches utilize
either rapid single-shot scans to reduce respiratory motion artifacts at the
expense of spatial resolution or segmented respiratory-gated scans at the
expense of scan time efficiency. Golden
Angle radial [1] sampling has favorable properties for free-breathing
CMR, including motion robustness and flexible reconstruction options. These
properties also make Golden Angle radial sampling a good sampling strategy for motion
compensated reconstructions [2,3]. In this work, we propose the combination of
a self-gated 2D radial Golden Angle data acquisition scheme with a recently
introduced motion compensated reconstruction strategy [4] to obtain high-resolution
motion compensated CMR data in every desired cardiac phase.
Methods
A 2D golden
angle radial spoiled gradient echo sequence was employed to collect short-axis
cardiac data from four volunteers using the following parameters: 3.0T scanner
(MR750w, GE Healthcare, Waukesha/WI, USA), α=15°,BW=±125kHz,256
readout points,TR=4.3ms,TE=1.5ms,slice thickness=8mm, FOV=360mm circular,
resolution 1.4x1.4mm
2, 2584 projections resulting in 11s total scan
time. Self-gating signals for cardiac and respiratory motion were obtained from
the k-space DC signal [5] and compared by regression to simultaneously recorded
peripheral gating (PG) and respiratory belt signals. Using the derived self-gating signals, images
in various cardiac and respiratory phases were reconstructed using a binning
scheme as described previously, e.g., in [5] (Figure 1, step 1). For each
cardiac phase, four images were reconstructed as follows: 1) Combining all
free-breathing data per cardiac phase without motion management (NoMCR); 2) Retrospective
self-gating selecting data (approx. 20-25%) closest to end-expiration of the
desired cardiac phase (RG); 3) Motion Compensated Reconstruction (MCR); and 4) a
filtered backprojection (FBP) of the RG data, which was viewed as ground truth
to assess whether MCR accurately reconstructs the desired cardiac phase. NoMCR
and RG recovered missing data using a non-Cartesian iterative SENSE [6].
The MCR was accomplished
in four steps using the cardiac and respiratory self-gating signals: 1) clustering
of all data of the desired cardiac phase into eight respiratory bins; 2) filtered
backprojection of these eight respiratory states; 3) extraction of the calibration
displacement fields between the bins by applying a non-rigid registration; 4)
motion compensated SENSE-like reconstruction using the previously extracted
calibration motion fields [4,7,8] (Figure 1).
Results
A very
high correlation (R
2 = 95.9%) between the self-gating signals, the
recorded PG curve, and respiratory belt was observed (Figure 2). Data from 11s scan
time were found sufficient to result in high-quality motion compensated cine
images. Figures 3 and 4 show representative images and temporal profiles of the
four different reconstruction schemes. Combining all free-breathing data into
one dataset (NoMCR) leads to high SNR images with significant respiratory
motion induced blurring. RG improves
apparent sharpness (e.g. diastole), but can suffer artifacts from severe
undersampling (e.g. systole). MCR takes advantage of all projections in all respiratory
states by including the calibration displacement fields into the reconstruction.
Thus it recovers a sharp image with high SNR where small anatomical features
are preserved. Furthermore, the cardiac phases in the MCR are in good agreement
with the FBP ground truth images (Figure 4c), demonstrating the ability of the
MCR to accurately recover the desired cardiac phases.
Discussion
Cardiac
cine images from 11s fully self-gated, free-breathing Golden Angle radial datasets
were successfully reconstructed using MCR. This scheme proved to be superior to
non-Cartesian iterative SENSE reconstructions without motion correction (NoMCR,
RG). The described technique offers several potential advantages: improved
patient comfort and clinical workflow since neither breath holds nor ECG leads
are necessary; high image quality with both
high SNR and high spatial resolution; time-efficient acquisition since no data
are discarded– instead, every acquired sample is used in the motion compensated
image. The presented technique could also be extended to simplify and improve
contrast-enhanced cardiac exams such as perfusion or late enhancement.
Acknowledgements
No acknowledgement found.References
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