The effect of certain variables on the tumor and tissue distribution of tracers. IV. False carriers: ferric citrate.

The intravenous administration of Fe+3 -citrate (1.6 mg/kg body weight) was demonstrated to alter the concentration of carrier-free 67Ga and 54Mn in malignant and healthy tissues of the rat, Morris 7777 hepatoma model. When the Fe+3 was injected 2 hours before, simultaneously with, or 2 hours after 67Ga (and the rats sacrificed 4 hours after injection), the 67Ga in most normal tissues decreased, and the viable tumor concentrations increased by 135, 24, and 47%, respectively. Twenty-four hours after a simultaneous administration of Fe+3 and 67Ga, egress of 67Ga from the tumor was much less than from the healthy tissues. These changes resulted in significant improvements in viable tumor to background ratios, especially at 4 hours. These changes induced in the distribution of the two tracers by Fe+3 indicate that some kinetic characteristics are shared. This is discussed in the light of their response to carrier Ga and Mn. The use of Fe+3 shows promise as a means of improving tumor/background ratios for 68Ga and 52mMn, two short-lived positron emitters that can be used with positron scanners. Gallium-67 imaging may also be improved by these techniques. The Fe+3 increases excretion of 67Ga from the animal, and this could result in a lower radiation dose to a patient.