Comparison of interpolation methods of predominant cardiomyocyte orientation from in vivo and ex vivo cardiac diffusion tensor imaging data

FIGURE 1. Workflow. First, the cDTI input data are prepared in (I) a data pre‐processing step including (IA) data segmentation, followed by (IB) a mapping to a shape‐adapted coordinate system—HFCs or PSCs. Then, (II) interpolation of the ACO is performed, comparing five methods categorized into three interpolation strategies: shape‐based tensor interpolation, fitting a rule‐based method, and fitting a low‐rank model

FIGURE 2. Results of the ex vivo comparison: median angular interpolation error compared with the ex vivo, high‐resolution ground truth within the myocardium, averaged over the cases. Each subplot shows the error dependence on the number of ex vivo, short‐axis slices and the SNR of the input data. The rows present the results for the in‐plane resolution of 1.5 mm and 2.5 mm of the input data. The columns depict the five interpolation methods

FIGURE 3. Angular interpolation error mapped onto the myocardium for one exemplary test case. The ex vivo input data have a resolution of 1.5 × 1.5 × 8 mm3, SNR of 30 and consists of 7 short‐axis input slices, coinciding with the settings of the in vivo data used in in vivo comparison. The columns represent the results of the five interpolation methods

FIGURE 4. Comparison of median angular difference within the myocardium averaged over the cases for the five interpolation methods. The blue, green, and grey bars represent the results of the in vivo comparison (Section 2.5), the synthetic in vivo comparison (Section 2.4), being a replica of the in vivo comparison with ex vivo data, and the ex vivo comparison (Section 2.4). The setting with the same SNR and number of slices as in the in vivo data set and 1.5 × 1.5 × 8 mm3 resolution is considered for the ex vivo comparison. The symbols represent the median error of the individual test cases

FIGURE 5. Original (in grey) and interpolated (color coded by the angular interpolation error) in vivo diffusion tensors' first eigenvector field on a mid‐ventricular, short‐axis target slice, for one exemplary test case. The in vivo input data from seven input slices and SNR = 30 were interpolated onto the target slice. The columns represent the original DTI data and the five interpolation methods

FIGURE 6. Spatial error variation within the myocardium for the in vivo data in blue and the synthetic in vivo comparison with ex vivo data in green. The rows show the circumferential and transmural variations. The columns present the results using the interpolation with PSC and HFC, the rule‐based approximation, and the low‐rank PGD and POD model estimations. Along both directions, the data were assigned to 10 bins. Each box plot represents the case‐averaged median and 25th and 75th (box) and 5th and 95th (whisker) percentiles obtained within the bin