1. A method to supplement acquired magnetic resonance (MR) data comprising: operating a magnetic resonance data acquisition unit comprising a plurality of acquisition coils to acquire a reduced MR data set with each coil, with said coils operated in parallel to acquire multiple reduced MR data sets with an accelerated acquisition procedure that undersamples k-space; in a processor, for a specific one of said acquisition coils, applying a reconstruction kernel for said specific one of said acquisition coils to said multiple reduced data sets to calculate, from the multiple reduced MR data sets, a reconstructed MR data set comprising supplemented MR data for said specific one of said acquisition coils, by using said reconstruction kernel to reconstruct, from the multiple reduced MR data sets, at least some MR data that are absent from the reduced MR data set acquired by said specific one of said acquisition coils; in said processor, determining statistical variances of the reduced MR data set acquired with said specific one of said acquisition coils, as MR data variances; in said processor, determining statistical variances of the MR data set reconstructed for said specific one of the acquisition coils, as reconstruction data variances; and in said processor, reusing the reduced MR data set acquired with said specific one of the acquisition coils in the reconstructed MR data set to determine a supplemental MR data set for said specific one of said acquisition coils, by combining the reduced MR data set weighted with the MR data variances and the reconstructed MR data set weighted with the reconstruction data variances, and making said supplemental MR data set available in electronic form as a data file.