Nor is it necessary to administer exactly one atom of O-18 for every two atoms of D--a matter which in practice is governed by the economics of obtaining O-18 enriched water, and the sensitivity of the mass-spectrographic equipment available.
Nor is it necessary to administer exactly one atom of 18 O for every two atoms of deuterium. This matter in practice is governed by the economics of buying 18 O enriched water, and the sensitivity of the mass-spectrographic equipment available.