A method for the preparation of an imaging medium suitable for use in magnetic resonance, said method comprising the steps of: (i) preparing a system containing: a solvent; parahydrogen; a magnetisation transfer metal complex, with a molecular symmetry that allows the creation of a singlet state between spin pairs within it, said complex including a reversibly bound small molecule transference substrate containing pairs of spin 1⁄2 nuclei that can form a singlet state across the spin-pair; applying a magnetic field such that hyperpolarisation is transferred into the magnetisation transfer metal complex, including the reversibly bound small molecule transference substrate; (ii) separately or simultaneously introducing a recipient transition metal complex comprising pairs of spin 1⁄2 nuclei that can form a singlet state across the spin-pair and has different ligating properties than the magnetisation transfer metal complex; said recipient transition metal complex being capable of binding the small molecule transference substrate, said recipient transition metal complex including a recipient substrate, such that the recipient complex and recipient substrate, including the bound small molecule transference substrate, is hyperpolarised; and (iii) providing an imaging medium by: (a) separating the hyperpolarised recipient transition metal complex; or (b) separating the hyperpolarised recipient substrate; or (c) separating the small molecule transference substrate (i) preparing a system containing: a solvent; parahydrogen; a magnetisation transfer metal complex, with a molecular symmetry that allows the creation of a singlet state between spin pairs within it, said complex including a reversibly bound small molecule transference substrate containing pairs of spin 1⁄2 nuclei that can form a singlet state across the spin-pair; applying a magnetic field such that hyperpolarisation is transferred into the magnetisation transfer metal complex, including the reversibly bound small molecule transference substrate; a solvent; parahydrogen; a magnetisation transfer metal complex, with a molecular symmetry that allows the creation of a singlet state between spin pairs within it, said complex including a reversibly bound small molecule transference substrate containing pairs of spin 1⁄2 nuclei that can form a singlet state across the spin-pair; applying a magnetic field such that hyperpolarisation is transferred into the magnetisation transfer metal complex, including the reversibly bound small molecule transference substrate; (ii) separately or simultaneously introducing a recipient transition metal complex comprising pairs of spin 1⁄2 nuclei that can form a singlet state across the spin-pair and has different ligating properties than the magnetisation transfer metal complex; said recipient transition metal complex being capable of binding the small molecule transference substrate, said recipient transition metal complex including a recipient substrate, such that the recipient complex and recipient substrate, including the bound small molecule transference substrate, is hyperpolarised; and (iii) providing an imaging medium by: (a) separating the hyperpolarised recipient transition metal complex; or (b) separating the hyperpolarised recipient substrate; or (c) separating the small molecule transference substrate (a) separating the hyperpolarised recipient transition metal complex; or (b) separating the hyperpolarised recipient substrate; or (c) separating the small molecule transference substrate <EOS>