1. A method for determining imaging parameters for acquiring data from an examination subject for reconstructing a magnetic resonance image of the examination subject from the data, comprising the steps of: establishing initial imaging parameters for acquiring magnetic resonance data from an examination subject with a magnetic resonance data acquisition unit; supplying said initial imaging parameters to a computer and calculating signal intensities in said computer for tissue that exist in at least a portion of the examination subject, using said initial imaging parameters and without using any acquired magnetic resonance signals, by mathematically determining tissue proportions from a body region of the examination that is at least partially in a region of the examination subject from which said magnetic resonance data are to be acquired; and adapting said initial imaging parameters dependent on the calculated signal intensities, to obtain adapted imaging parameters, and operating said magnetic resonance data acquisition unit with the adapted imaging parameters to acquire said magnetic resonance data from the examination subject; and in said computer, processing said magnetic resonance data acquired from the examination subject using the adapted imaging parameters to obtain image data representing a magnetic resonance image of the examination subject, and making said image data available as a data file at an output of said computer.