Free-breathing respiratory self-gated Golden angle RAdial Three-dimensional whole-heart isotropic cine imaging for left ventricular volumetric Evaluation (GRATE) - comparison with conventional 2D breath-hold cine imaging

Methods: Acquisition. A balanced steady-state free precession (bSSFP) sequence using a 3-dimensional (3D) golden angle radial acquisition order was implemented for acquisition of an image volume covering the whole heart (GRATE). The sequence was used to image 8 healthy volunteers during free breathing and over several cardiac and respiratory cycles. A stack of short-axis (SA) slices, as well as 4-, 3and 2-chamber views, were acquired with a conventional Cartesian 2-dimensional (2D) breath held cine bSSFP for comparison. Both methods were applied twice on each subject with a break outside the scanner in between. GRATE parameters were: FOV 352 mm, isotropic voxels 2 × 2 × 2 mm, TR/TE 2.7/1.3 ms, flip angle 65°, 900,000 radial spokes. Respiratory Self-gating. Respiratory self-gating (SG) signals from the data were extracted retrospectively from the k-space center point in each radial spoke using a twosided low-pass filter adapted to each dataset. Trigger points for each respiratory cycle were derived from the angle of the analytic signal, i.e. filtered using a quadrature low-pass filter that only kept positive frequencies. Image reconstruction. The respiratory SG signal and recorded ECG were used to bin each radial spoke into 3 respiratory phases and 25 cardiac phases. For whole heart image reconstruction of each bin, selected spokes from neighboring bins were also used, chosen to give a more evenly distributed k-space sampling. From each image volume multi-planar reformatting was used to extract a SA stack with the same resolution as the breath held SA stack (2 × 2 × 8 mm). LV volumes were obtained from manual segmentation of each SA stack. Data are given as mean ± SD.