About the undersampling rate

[rederxz]

First of all, thanks for such great work! And I have a question about data used in this work.

In the paper "k-t NEXT: Dynamic MR Image Reconstruction Exploiting Spatio-temporal Correlations", you state that "The undersampling rate mentioned is stated with respect to the matrix size of the data, which is 192 × 190." in section 3.1. And as stated in the paper, the undersampling is done retrospectively after zero-padding the matrix size to 256x256, in other words, the original sampling matrix size is 192x190, but the undersampling is done to a 256x256 matrix. So what is the exact definition of "undersampling rate" here? Since the full sampling matrix and undersampled matrix have different matrix size, I think the definition is not straightforward.

Hoping for your reply! Thanks!