A majority of radar algorithms leverage frequency domain image reconstruction, based on Fourier transformation, to achieve fast image acquisition. Particularly, in applications like security screening, real-time operation is a key-characteristic, hence the execution time of the reconstruction algorithm is a significant aspect. This paper proposes two computationally efficient techniques to address three-dimensional (3D) image reconstruction in the frequency domain when sparse Multiple-Input Multiple-Output (MIMO) apertures are used. The reconstruction fidelity of both methods is demonstrated by simulation results. The proposed algorithms are readily compatible with Synthetic Aperture Radar (SAR) measurement setups as well, hence their performance is also validated using an available set of experimental measurements. This paper focuses on the execution time of each method, when the algorithm is parallelized and executed on a single graphical process unit (GPU), arguing that three-dimensional scenes can be reconstructed with high accuracy in a few milliseconds using very low-cost hardware.