1. An MRI image data signal post-processing method for generating high-resolution diffusion-weighted imaging (DWI) images from multi-shot interleaved MRI pulse sequences, without relying on external navigator echoes, comprising: programmatically estimating motion induced phase variations and position changes of a patient or subject among multiple segments of acquired DWI image data using parallel image reconstruction by 1) performing parallel MRI reconstruction of k-space data from each segment of DWI, 2) producing a full-FOV image from each DWI segment, and 3) measuring inter-segment phase variation and position change from the produced DWI images; programmatically incorporating (i) shot-to-shot phase and position variations from the estimated motion induced phase variations and position changes and (ii) defined coil sensitivity profile data into a mathematical model that can jointly calculate magnitude-value source density signals that overlap in acquired uncorrected interleaved DWI image data to generate corrected DWI image data; and Programmatically generating high-resolution DWI images based on the corrected DWI image data to thereby generate images free from aliasing artifacts, wherein the multi-shot interleaved MRI pulse sequences are associated with interleaved echo-planar imaging (EPI) which generates EPI segments as the multiple segments or interleaved fast spin-echo (FSE) imaging which generates FSE segments as the multiple segments, wherein the estimating motion induced phase and position variations from the acquired data comprises: i. reconstructing images corresponding to different EPI or FSE segments by applying the parallel reconstruction to each individual EPI or FSE segment as the each DWI segment; ii. mathematically quantifying phase and position changes among multiple images generated by the reconstruction as the measured inter-segment phase variation and position change; then iii. spatially smoothing a shot-to-shot phase variation map derived from the mathematic quantification to produce phase information of high signal-to-noise ratio.