1. A method of magnetic resonance (=MR) imaging for the acquisition of a three-dimensional (=3D) dataset of an object of investigation, wherein spatial encoding by three mutually orthogonal magnetic field gradients is performed such that a signal is readout under a read-gradient in one spatial direction (k 1 ) and spatial encoding in the other two spatial directions (k 2 , k 3 ) is performed by applying phase encoding gradients in the other two spatial directions (k 2 , k 3 ) prior to signal acquisition with data acquisition being performed in a sequential manner such that, at each acquisition step, a signal is acquired under the readout gradient, but with different combinations of the two phase encoding gradients, the method comprising the steps of: a) applying a temporal sequence of spatial encoding such that a basic dataset containing N 3D(b) phase encoding steps is first acquired using a randomized sampling pattern in the two phase encoding directions, with the sampling density of the randomized sampling pattern decreasing monotonically from a center of k-space to generate a first dataset suitable for reconstruction of strongly undersampled data by use of a compressed sensing method to generate a first 3D image volume of the object of investigation with a predefined sufficient minimum quality; b) acquiring a complimentary dataset in which N 3D(c) additional phase encoding steps are acquired supplementing already acquired data such that a density of sampling points is increased, thereby allowing reconstruction of 3D-image volumes of increasing image quality until data are acquired with a predefined sampling density to reconstruct a final 3D-volume of optimum quality, wherein spatial encoding in acquisition of the basic as well as the complimentary dataset is performed in a segmented fashion in L segments with N seg phase encoding steps in each segment, a total k-space sampling pattern of the basic or complimentary dataset being subdivided into a predefined number of N seg sectors containing L phase encoding steps each and, for the acquisition of each phase encoding step in each segment, one phase encoding step is selected from each sector such that each segment contains one phase encoding step from each sector; c) monitoring motion of the object of investigation using navigators built into the measurement sequence or by extrinsic motion detection devices; and d) terminating data acquisition whenever involuntary motion exceeds a predefined threshold.