Motion quantification is essential for successful MR imaging and MRI guided radiotherapy of mobile organs. Currently, 3D MRI is too slow to quantify organ displacements and a motion model could alternatively be used for tracking and/or motion compensation. A motion model trained on MRI data and driven by the noise covariance matrix (NCM) of a receive array is proposed to quantify internal anatomy motion. Passive thermal noise measurements have a high temporal resolution (~10ms) and do not interfere with or rely on MR signal. Abdominal organ displacement can be accurately estimated in 3D, through the NCM of the receive array.