Optimum acquisition times of two spin echoes for MR image synthesis

Spin‐echo images can be synthesized at arbitrary values of echo time T Es if two images are acquired at the same repetition time and two different echo times T EI and T E2 . Depending on the value of T Es , the noise in the synthetic images can either be greater or less than the acquisition noise. This note shows that if the time between the acquired echoes T E2 ‐ T E1 is equal to T 2 , the noise level in the synthetic images is no larger than the acquisition noise for T Es ⩾ T E1 . This is the lowest possible noise bound for two‐echo acquisition. Also, the noise bound for images synthesized with O ⩽ T Es ⩽ T E1 is minimized by making T E1 as short as possible. © 1986 Academic Press, Inc.