Field focusing n.m.r. (FONAR) and the formation of chemical images in man.

The first proposals for n.m.r. scanning in medical diagnosis was made by Damadian (1971a; 1972) and were followed by Lauterbur (1973). Damadian's method of scanning used the principle that the forced precessions of a nuclear magnetization under radio frequency (r.f.) driving field specify the conditions for obtaining spatial resolution of the signal producing domains of a nuclear resonance sample. Sufficient coupling of the nuclear spins to the radiation field to produce a signal detectable by r.f. spectroscopy requires that the stringent Bohr frequency condition, hv = microH0/I, be met. It became possible to construct, with the aid of direct current auxiliary coils, a small volume, called the resonance aperture, inside the applied static field of the magnetic resonance experiment. The correct value of H0 for the applied frequency is restricted to this aperture. The technique (Damadian 1972) was developed to provide a method for non-surgically detecting chemical abnormalities in the diseased organs of patients (Damadian 1971a). The first n.m.r. scans of normal patients and of those with malignant disease are discussed.