Use of persistent free-radicals in magnetic resonance imaging

A method of electron spin resonance enhanced nuclear magnetic resonance investigation of a sample, said method comprising introducing into said sample a persistent, water-soluble cyclic .pi.-system radical, said radical having an inherent linewidth in its esr spectrum of less than 500 mG, said radical having an electron delocalising .pi.-system which comprises at least one homo- or hetero- tricyclic ring, and said radical comprising at least one pair of adjacent ring carbons of a (C.dbd.C).sub.n moiety, where n is a positive integer, or an aryl substituent is substituted to form a fused ring of formula ##STR126## where X.sub.3 is oxygen, sulphur, or SO.sub.2, and Z is C(CH.sub.3).sup.7.sub.2 or CRT.sup.7.sub.2 wherein R.sup.7 is hydrogen or optionally hydroxylated methyl, with a center ring substituted by two oxygen atoms, together with at least one pharmacologically acceptable carrier or excipient,

• exposing said sample to a first radiation of a frequency selected to excite electron spin transitions in said free radical, exposing said sample to a second radiation of a frequency selected to excite nuclear spin transitions in selected nuclei in said sample, detecting free induction decay signals from said sample, and, optionally, generating an image or dynamic flow data from said detected signals.

A non-radical precursor to a physiologically tolerable, persistent, water-soluble cyclic .pi.-system free radical, said radical having an inherent linewidth in its esr spectrum of less than 500 mG, said radical having an electron delocalising .pi.-system which comprises at least one homo- or hetero- tricyclic ring, and said radical comprising at least one pair of adjacent ring carbons of a (C.dbd.C).sub.n moiety, where n is a positive integer, or an aryl substituent is substituted to form a fused ring of formula ##STR127## where X.sub.3 is oxygen sulphur, or SO.sub.2, and Z is C(CH.sub.3).sub.2 or CR.sup.7.sub.2 wherein R.sup.7 is hydrogen or optionally hydroxylated methyl, with a center ring substituted by two oxygen atoms.

A process for preparing a physiologically tolerable, persistent, water-soluble cyclic .pi.-system free radical, said radical having an inherent linewidth in its esr spectrum of less than 500 mG, said radical having an electron delocalising .pi.-system which comprises at least one homo- or hetero- tricyclic ring, and said radical comprising at least one pair of adjacent ring carbons of a (C.dbd.C).sub.n moiety, where n is a positive integer, or an aryl substituent is substituted to form a fused ring of formula ##STR128## where X.sub.3 is oxygen, sulphur, or SO.sub.2, and Z is C(CH.sub.3).sub.2 or CR.sup.7.sub.2 wherein R.sup.7 is hydrogen or optionally hydroxylated methyl, with a center ring substituted by two oxygen atoms,

• comprising subjecting a non-radical precursor therefor to a radical generation procedure.

A persistent, water-soluble cyclic .pi.-system free radical, said radical having an inherent linewidth in its esr spectrum of less than 500 mG, said radical having an electron delocalising .pi.-system which comprises at least one homo- or hetero- tricyclic ring, and said radical comprising at least one pair of adjacent ring carbons of a (C.dbd.C).sub.n moiety, where n is a positive integer, or an aryl substituent is substituted to form a fused ring of formula ##STR129## where X.sub.3 is oxygen, sulphur, or SO.sub.2, and Z is C(CH.sub.3).sub.2 or CR.sup.7.sub.2 wherein R.sup.7 is hydrogen or optionally hydroxylated methyl, with a center ring substituted by two oxygen atoms.