T1-weighting of Hahn echo-trains in the stray-field for deuterium: prospects for imaging using long echo-train summation

Hahn-echoes have been observed in stray-field gradients of 37.5 T/m and 74.5 T/m for deuterium in heavy water in a number of forms: liquid, ice, and coordinated in solid copper sulfate and silica gel. In the diamagnetic samples, the application of many pulses (>1000 or more) in long pulse-trains produced many sustained echoes. This lengthening of T_echo is caused by T₁-weighting of the components of the Hahn echo (even in the absence of spin-locking). In contrast, for the paramagnetic complex, the shortening of T₁ greatly reduces T_echo and only few echoes are obtained. A new protocol for stray field imaging is suggested when T₁ is long: long echo-train summation (LETS). The observed magnetisation is much greater for heavy ice than for heavy water because the line-width, and hence the thickness of the excited slice, is greater.