1. A method for acquiring a diffusion-weighted image in diffusion-weighted MRT imaging, comprising the steps of: (a) in a diffusion-weighted measurement, acquiring and storing a non-diffusion-weighted data set from a subject a diffusion-weighted data set by using a DESS sequence by switching two readout gradients successively for acquiring the non-diffusion-weighted data set, and by switching a bipolar diffusion gradient pulse sequence between two readout gradients for acquiring the diffusion-weighted data set; and (b) calculating a diffusion-weighted MRT image based on the non-diffusion-weighted data set and the diffusion-weighted data set, and based on a value characterizing the diffusion-weighted measurement.