1. A method for data sampling and image reconstruction, comprising: acquiring magnetic resonance data corresponding to an area of interest of a subject, wherein acquiring the magnetic resonance data comprises: determining a two-dimensional (2D) multi-level undersampling pattern based on: a distance, r k , between each sampling point of a plurality of sampling points in k-space and a center of the k-space, and a probability that each of the sampling points is acquired; determining a desired variable-density spiral trajectory based on the multi-level undersampling pattern, wherein the desired variable-density spiral trajectory has a density according to a function of r k ; generating one or more spiral gradient waveforms based on the desired variable-density trajectory; tracing a variable-density spiral trajectory using the one or more spiral gradient waveforms; and sub-sampling the magnetic resonance data based on the variable-density spiral trajectory; and reconstructing, using one or more image reconstruction functions that comprise compressed sensing, one or more images of the area of interest based on the acquired magnetic resonance data.