1348590 - Rapid 3D SPirAl Respiratory and Cardiac Self-gated (3D-SPARCS) Cine Imaging Using Randomized Stack-of-Spirals

Breath-held segmented cine imaging is the gold standard for analyzing cardiac function, but it uses ECG gating and requires 10-12 breath-holds to cover the left ventricle. Our group has developed a continuous-acquisition respiratory and cardiac self-gated cine sequence for free-breathing cardiac function acquisition using 2D stack spiral acquisition¹. However, the acquisition still takes 2-3 min to cover the left ventricle, and it would benefit from the SNR efficiency of 3D imaging. Thus, we develop a rapid 3D self-gated cine, using randomized stack of spiral gradient echo sequence to perform 3D cine evaluation of the left ventricle².

Methods:

8 volunteers were imaged on a 3T scanner. Imaging occurred 3 minutes after the injection of 0.15 mmol/kg of Clariscan.  Stack of spiral gradient echo parameters are in Table 1. Stack-of-spiral sampling scheme consisted of a variable kz-density stack of dual density spirals rotated by the golden angle. The kz-t sampling pattern is shown on the top panel of Figure 1(A).  We acquired 3, 5, or 7 partitions out of 10 total partitions. The first partition (shown in rectangles and black spirals) of each measurement is set to kz=0 and used as a self-gating navigator. Other sampled kz partition in each measurement are randomly picked from a Bates distribution3 and without replacement to prevent the same partition to be repeated within a single measurement.

The automatic cardiac self-gating pipeline is shown in Figure 1(A): Self-gating cardiac signals were determined using the center point of the central partition each group of spiral partitions for all receiver coils. PCA was performed to separate the cardiac and respiratory components followed by frequency spectrum analysis to extract filtered cardiac and respiratory signals. Figure1(B) shows the auto coil selection. Figure 1(C) shows the retrospective cardiac binning was performed by motion corrected k space and non-Cartesian spiral L1-SENSE reconstruction^4,5,6. The objective function was solved using non-linear conjugate gradient algorithm with 30 iterations.

Results:

Figure 2(a) shows reconstructed short axis images of sampling 3, 5 and 7(out of 10) partitions with an 80s acquisition. Sampling 5 partitions provided a reasonable trade-off between adequately sampling the kz=0 partition for self-gating while preserving a temporal resolution of 40ms.

Figure2(b) shows reconstructed cine images covering the left ventricle with 5 partitions with a flip angle 7° and 15°. 7° has a better performance for improving contrast between the myocardium and the cavity during systole due to the GRE readout

Conclusion:

Our proposed self-gated free-breathing 3D stack of spiral cardiac cine imaging strategy acquires cine images with desirable temporal and spatial resolution in short acquisition time. Using a 7° flip angel with a self-gating signal every 5 interleaves produced the best image quality for GRE acquisition. This strategy could provide a faster and more efficient protocol for cardiac cine imaging.