Table 2 Parameters used for B-spline registration
Cost function | |
|---|---|
Metric of the similarity measure | Advanced Mattes mutual information |
Number of grey level histogram bins in each resolution level | 32 |
Transformation | |
Transformation | Cubic B-spline |
Knot spacing at the highest resolution levels (mm) | Same spacing for all three dimensions. |
The effect of various spacings was investigated | |
Knot spacing schedule in resolution levels 1, 2 and 3 | 4, 2, and 1 |
Optimization | |
Optimizer | Adaptive Stochastic Gradient Descent |
Maximum number of iterations in each resolution level | Ratio iterations between levels: 1 2 2 |
The effect of the number of iterations was investigated | |
Parameter values for determination step size a k (mm) of the optimizer for each resolution level | Same values for all three dimensions. |
a = 6400, A = 50, α = 0.60 | |
Image sampling | |
Spatial samples used to compute the mutual information in each iteration | Randomly off the voxel grid |
Number of spatial samples in each iteration | 2048 |
Hierarchical strategies | |
Number of resolutions levels | 3 |
Fixed image pyramid | Fixed recursive |
Moving image pyramid | Moving recursive |
Downsampling factor for multi-resolution image data | Gaussian pyramid with factor 2 |
Downsampling factor for the image pyramid for each resolution level | 4 (resolution 1), 2 (resolution 2), 1 (resolution 3) |
For multi-grid transformation model | Knot spacing halved every resolution level |