A method for generating a synthetic diffusion image, the method comprising: - acquiring initial diffusion scan data by means of diffusion weighted magnetic resonance scans at a plurality of initial b-values; - deriving an initial diffusion image from at least part of the initial diffusion scan data; - acquiring target diffusion scan data by means of a diffusion weighted magnetic resonance scan at a target b-value higher than each of the initial b-values; and - generating the synthetic diffusion image by performing a cost function based reconstruction using at least the initial diffusion image and the target diffusion scan data to apply a fidelity term in k space to the synthetic diffusion image, wherein the synthetic diffusion image is at least one of a synthetic diffusion parameter map and a synthetic diffusion weighted imaging = DWI image at the target b-value, characterized in that: when the synthetic diffusion image is the synthetic diffusion parameter map, an initial diffusion parameter map is derived from the at least part of the initial diffusion scan data to provide the initial diffusion image by the following steps: - reconstructing at least two initial DWI images based upon the initial diffusion scan data associated with at least two different initial b-values; and - calculating the initial diffusion parameter map based upon the at least two initial DWI images; and when the synthetic diffusion image is the synthetic DWI image at the target b-value, an initial computed DWI image at the target b-value is derived from the at least part of the initial diffusion scan data to provide the initial diffusion image by the following steps: - reconstructing at least two initial DWI images based upon the initial diffusion scan data associated with at least two different initial b-values; - calculating an apparent diffusion coefficient = ADC map based upon the at least two initial DWI images; and - calculating the initial computed DWI image at the target b-value based on the calculated ADC map. - acquiring initial diffusion scan data by means of diffusion weighted magnetic resonance scans at a plurality of initial b-values; - deriving an initial diffusion image from at least part of the initial diffusion scan data; - acquiring target diffusion scan data by means of a diffusion weighted magnetic resonance scan at a target b-value higher than each of the initial b-values; and - generating the synthetic diffusion image by performing a cost function based reconstruction using at least the initial diffusion image and the target diffusion scan data to apply a fidelity term in k space to the synthetic diffusion image, - reconstructing at least two initial DWI images based upon the initial diffusion scan data associated with at least two different initial b-values; and - calculating the initial diffusion parameter map based upon the at least two initial DWI images; - reconstructing at least two initial DWI images based upon the initial diffusion scan data associated with at least two different initial b-values; - calculating an apparent diffusion coefficient = ADC map based upon the at least two initial DWI images; and - calculating the initial computed DWI image at the target b-value based on the calculated ADC map.