1. n. [Formation Evaluation]

The time between each echo in a nuclear magnetic resonance (NMR) measurement. The time is also the time to the first echo and is therefore an important parameter in defining the fastest relaxation time that can be measured. In standard measurements, the echo spacing ranges from 0.2 to 1 ms.

See: CPMG,  diffusion relaxation,  nuclear magnetic resonance measurement,  relaxation time,  shifted spectrum