1. A method of forming an optimally gated medical image comprising: acquiring a list mode data set for medical imaging of a patient; simultaneously acquiring from said patient a respiration correlated amplitude measurement S(t), said respiration correlated amplitude measurement S(t) including respiration amplitude threshold value pairs; selecting a lower respiration amplitude threshold value and an upper respiration amplitude threshold value pair that has a narrowest interval from among all respiration amplitude threshold value pairs in said measurement S(t); synchronizing the list mode data set and the respiration correlated amplitude measurement; and using list mode data of said list mode data set obtained when said measurement S(t) was within a range defined by said lower and upper threshold values to form a medical image.