1. A method to process complex image data, comprising: providing, to a processor, complex image data, comprising phase and amplitude information, acquired as signals emitted from an examination subject during a plurality of echo times in a magnetic resonance (MR) data acquisition using a plurality of individual acquisition components selected from the group consisting of individual reception coils and respective portions of a multi-coil reception array, said complex image data having been acquired according to at least one MR parameter, of an MR data acquisition unit that executes said MR data acquisition, that affects said signals representing said complex image data, said examination subject comprising a first spin species and a second spin species that emit said signals, said second spin species differing from said first spin species, and a phase difference between precessing spins of said first spin species and precessing spins of said second spin species being different in at least two of said echo times; and in said processor, determining a value of said at least one MR parameter, with spatial resolution for a plurality of image points in said complex image data, that causes a function, which depends on said at least one MR parameter and a corresponding image point in said complex image data acquired during said at least two of said echo times, to satisfy an extreme condition at which said function has an extreme function value, by solving, for the multiple image points, an equation system that represents an extreme condition or multiple extreme conditions of a probability distribution depending on the at least one MR parameter, wherein the equation system represents the condition 0 = ∑ a = 1 N ⁢ ∑ b = 1 N ⁢ ( τ a - τ b ) ⁢ Exp ⁡ [ ⅈω Δ ⁢ ⁢ B ⁢ ⁢ 0 ⁡ ( τ a - τ b ) ] ⁢ g a ⁢ g b * ⁢ d a ⇀ † ⁢ d b ⇀ ( 1 ) wherein N is a number of the echo times and τ n represents the n-th echo time, wherein a vector {right arrow over (d)} n associated with the n-th echo time τ n has matrix elements that depend on image data acquired with plurality of acquisition units at the echo time τ n , wherein ω ΔB0 is a spatially resolved shift to be determined of a precession frequency, and wherein: 
 g n =r 1 Exp[(−1/[ T 2 *] 1 )τ n ]+(1− r 1 )Exp[(−1/[ T 2 *] 2 +iω 2 )τ n ]  (2) wherein r 1 is the local proportion of the first spin species [T 2 *] 2 is the T 2 * time of the first spin species, [T 2 *] 2 is the T 2 * time of the second spin species, and ω 2 is a difference between a precession frequency of the second spin species and a precession frequency of the first spin species; and making said value of said at least one MR parameter that causes said function to have said extreme function value available in electronic form at an output of said processor.