Accelerated 3D self-gated cardiac cine imaging at 3T using a tiny golden angle and compressed sensing

Background 3D self-gated (SG) cine imaging with TrueFISP not only provides excellent contrast between myocardium and blood, but also eliminates the need for ECG set up and permits free-breathing acquisitions [1]. However, such Cartesian sampling-based techniques are commonly used at 1.5 T due to the eddy current and SAR problems as well as time-consuming on data acquisition under the Nyquist sampling criteria. To achieve time-efficient 3T cine imaging, a novel accelerated SG method, named SparseSG, was proposed using a tiny golden angle and compressed sensing [2].


Background
3D self-gated (SG) cine imaging with TrueFISP not only provides excellent contrast between myocardium and blood, but also eliminates the need for ECG set up and permits free-breathing acquisitions [1]. However, such Cartesian sampling-based techniques are commonly used at 1.5 T due to the eddy current and SAR problems as well as time-consuming on data acquisition under the Nyquist sampling criteria. To achieve time-efficient 3T cine imaging, a novel accelerated SG method, named SparseSG, was proposed using a tiny golden angle and compressed sensing [2].

Methods: Sequence
A 3D hybrid radial sampling pattern was adopted for the SparseSG [1]. In order to reduce the eddy current effect, a tiny golden angle of 32.039°, instead of 111.246°, was used for data acquisition ( Figure 1). After the respiratory and cardiac motions were determined by processing the SG data as [1], the acquired data was retrospectively sorted into different respiratory and cardiac phases. A compressed sensing method exploiting the image sparsity in k-t space was used for image reconstruction, thus effectively shortening the scan time and reducing SAR.

Experiment
IRB-approved cardiac imaging was performed on 5 healthy subjects (2M, 3F, age 20~26) at 3 T (Siemens Tim Trio, Germany) with a standard 6-channel body coil and a spine coil. Scan parameters included: 3D imaging with standard short-axis, TR = 3.8 ms, TE = 1.9 ms, spatial resolution = 1.3 × 1.3 × 8.0 mm 3 , bandwidth = 1502 Hz/Pixel, partition number = 10. The acceleration factors were R = 4 and 8, corresponding to scan time 0.76 min and 0.38 min. The standard 2D multi-slice ECG-triggering and conventional self-gating methods with the same spatial and temporal resolutions were also conducted for comparison.

Results
All MR scans were successfully conducted. SparseSG allowed a whole-heart coverage of 3D cine imaging within 1 min, which was much shorter than those of the ECG-triggering and SG methods (Figure 2.b). As the acceleration factor increased, the reconstructed cine images of SparseSG become a little blurry. However, the left ventricle ejection fraction (LVEF) and cardiac structure obtained from SparseSG were in good agreement with those from conventional ECG-triggering and SG methods, even if a high acceleration factor R = 8 was used (Figure 2.a&c).

Conclusions
An accelerated SG technique, SparseSG, was developed to realize 3D cardiac cine imaging at 3T without ECG and breath-holding. Preliminary in vivo study demonstrated that whole heart coverage of 3D cine imaging can be achieved within 1 min and the technique has excellent performance compared to the standard ECGtriggering and conventional SG methods. This warrants further evaluation of SparseSG on more volunteers and patients.  Compared to the standard ECG-triggering and conventional SG methods, cardiac structure obtained by SparseSG were well agreement with those by standard ECG-triggering and conventional SG methods. (b) Whole heart coverage of 3D cine imaging can be achieved within 1 min by SparseSG, which is much shorter than the standard ECG-triggering and conventional SG methods.(c) The left ventricular ejection fraction calculated from the images obtained by SparseSG was well agreement to the standard ECG-triggering method.