Process for preparing a liquid pharmaceutical formulation containing a complex of macrocyclic chelate with a lanthanide and a mol/mol amount of free macrocyclic chelate of between 0.002% and 0.4%, said process comprising the following successive steps: b) preparation of a liquid pharmaceutical composition containing the complex of macrocyclic chelate with a lanthanide, free macrocyclic chelate that is not under the form of an excipient X[X',L] in which L is the macrocyclic chelate and X and X' are a metal ion, in particular chosen independently from calcium, sodium, zinc and magnesium, and/or free lanthanide, by mixing a solution of free DOTA as the free macrocyclic chelate and of free gadolinium as the free lanthanide, so as to obtain complexation of the lanthanide by the macrocyclic chelate, the amounts of free macrocyclic chelate and of free lanthanide being such that all the lanthanide is complexed and that C ch 1 > C t ch 1, with C ch 1 representing the concentration of free macrocyclic chelate and C t ch 1 representing the target concentration of the free macrocyclic chelate in the final liquid pharmaceutical formulation, Ct ch 1 being selected in the range of between 0.002 % and 0.4 % mol/mol; c) measurement in the pharmaceutical formulation obtained in step b) of C ch l, the concentration of free lanthanide C lan 1 being equal to 0; d) adjustment of C ch 1 and of C lan 1 by eliminating free macrocyclic chelate from and/or by adding free lanthanide to and/or by modifying the pH of the formulation obtained in step b) so as to obtain C ch 1 = C t ch 1 and C lan 1 = 0, wherein Ct ch 1 is the target concentration of the free macrocyclic chelate in the final liquid pharmaceutical formulation and is selected in the range of between 0.002 % and 0.4 % mol/mol, wherein the amount of free macrocyclic chelate in the final liquid pharmaceutical formulation corresponds to the proportion of free macrocyclic chelate relative to the amount of complexed macrocyclic chelate DOTA-Gd in the final liquid pharmaceutical formulation in mol/mol, wherein the macrocyclic chelate is DOTA and the lanthanide is gadolinium. b) preparation of a liquid pharmaceutical composition containing the complex of macrocyclic chelate with a lanthanide, free macrocyclic chelate that is not under the form of an excipient X[X',L] in which L is the macrocyclic chelate and X and X' are a metal ion, in particular chosen independently from calcium, sodium, zinc and magnesium, and/or free lanthanide, by mixing a solution of free DOTA as the free macrocyclic chelate and of free gadolinium as the free lanthanide, so as to obtain complexation of the lanthanide by the macrocyclic chelate, the amounts of free macrocyclic chelate and of free lanthanide being such that all the lanthanide is complexed and that C ch 1 > C t ch 1, with C ch 1 representing the concentration of free macrocyclic chelate and C t ch 1 representing the target concentration of the free macrocyclic chelate in the final liquid pharmaceutical formulation, Ct ch 1 being selected in the range of between 0.002 % and 0.4 % mol/mol; c) measurement in the pharmaceutical formulation obtained in step b) of C ch l, the concentration of free lanthanide C lan 1 being equal to 0; d) adjustment of C ch 1 and of C lan 1 by eliminating free macrocyclic chelate from and/or by adding free lanthanide to and/or by modifying the pH of the formulation obtained in step b) so as to obtain C ch 1 = C t ch 1 and C lan 1 = 0,