A magnetic imaging technique which is resistant to changes in breathing while allowing the use of phase ordering to provide effective motion artifact reduction in an optimal time. This is provided by apparatus for magnetic resonance imaging a target object subject to periodic motion, comprising a magnetic resonance imaging scanner for exciting said target object and recovering imaging data in k-space; a sensor for detecting a signal indicative of a position of said target object; classifying logic for classifying said at least one line of imaging data into one of a plurality of groups of lines of imaging date in dependence upon said position detected by said sensor as said target object was excited, each group of lines corresponding to one of a plurality of contiguous ranges of position and scan terminating logic for detecting when two or more groups of lines corresponding to contiguous ranges of position together containing a set of lines of imaging date spanning k-space from which an image can be derived.