Carbon-11 in Bone and Lung Scanning

Radiocarbon-11 decays with 20.3-min half-life by emitting positrons with 1.0-MeV maximum energy. Two 511-keV ±γ-photons almost always are emitted coincidentally with each disintegration, at 180° to each other. This 'back-to-back' relationship makes it possible readily to locate small accumulations of 11C in vivo by opposed detectors connected by coincidence circuitry. The calculated narrow-beam half-thickness in water is more than 7 cm, to provide good penetration from deep organs, and with little scatter. Multimillicurie amounts of a mixture of 11CO and 11CO2 are generated readily in our small cyclotron when probe targets of B2O3 are bombarded with protons, deuterons, or 3He++ ions. The 11CO is oxidized to 11CO2 by hopcalite placed in the vacuum line. Dogs with primary or metastatic bone tumours received 11CO2, either by inhalation in a closed system, or in slightly basic solution in travenously. Scintigraphs, that were obtained within 10-20 min by means of a Nuclear-Chicago focused-collimator scanning machine, revealed significant accumulations of 11C at sites where bone erosion was demonstrable roentgenographically. Good pictures of dog lungs were obtained either with the mechanical scanner, or with our Nuclear-Chicago scintillation camera, after intravenous injection of 4-12 μm diam. smoothly-rounded aggregates of SrCO3 that were formed in dextran-saline solution. These 'photon-carrier' aggregates have been made either with 11C; or with 2.8-h 87mSr, which emits 388-keV gamma-rays. Alternatively, they might be made to 'carry' the 231-keV gamma-rays of 70-m in 85mSr, that are advantageous for scintigraphy. The advent of Anger's positron camera, with choice of plane of prime interest, will provide opportunities to emphasize the maximum target/nontarget ratio in pictures of localized accumulations of 11C, as well as of 13N, 15O and other cyclotron-produced short-lived β+-isotopes of abundant physiologically important elements. (author)