1. A method for correcting for artifacts generated by relative motion between an imaging system and items within a subject being imaged, the motion causing misregistration between different images of the same subject temporally separated and the misregistration causing the artifacts when the different images are merged, said method comprising the steps of: obtaining gray level density data for different images of the same subject, said gray level density data including items wherein the gray level density data normally changes as a function of time during a scan period and items wherein the gray level denstiy normally remains substantially the same as a function of time during a scan period; said items wherein the gray level density data normally remains substantially the same displaying primary and possibly secondary characteristics; selecting a point on an item displaying gray level density data that normally remains substantially the same, locating said point in said different images; reducing the effects of the secondary characteristics in the step of locating said point; obtaining a vector value of the motion causing the misregistration to determined differences between the locations of the point in said different images; and using said vector value to correct the misregistration between the different images.