Strontium 85 as strontium nitrate is at present used to detect occult neoplasm of bone (1). Because of its long physical and biological half-time the amount of radioactivity given to the patient must be limited in order to keep the dose to the patient at an acceptable minimum level. The low photon yield makes the scanning procedure long and tedious, often exhausting an already ill patient and imposing limitations on the areas that can be scanned. The recent development of gallium citrate using the short-lived positron emitter, gallium 68, as a bone-scanning agent led us to examine indium 113m as a possible agent for bone and kidney scanning. The group at Oak Ridge Institute of Nuclear Studies found that addition of carrier gallium prevents binding of the radioactive gallium by the beta globulin, transferrin, and gives gallium citrate bone-seeking properties similar to calcium, strontium, and fluoride (2–4). Since indium lies in the same group, III B, as gallium and because initial studies suggest that it also is transported by the beta globulin transferrin (5), it is reasonable to assume that the two isotopes behave similarly. A more direct approach to inhibiting the binding of indium by transferrin is intravenous administration of ferric ion to saturate the protein. Methods Ferric chloride was prepared by dissolving 5 mg of FeCl3·6H20 per milliliter of 0.1 N HCl to give a concentration of about 1 mg of ferric ion per milliliter. The solution was sterilized by passage through a 45-micron millipore filter, since auto-claving was found to alter the composition. U3mInCl3 was prepared after the method of Stern et al. (5) by adding to 10 ml of the generator2 eluate in 0.05 N HCl 1 ml of 10 per cent gelatin and 0.5 ml of NaCl (120 mg/cc) in a 50° C water bath. After a brief stirring, the mixture was titrated to pH. 4 with 1 N NaOH. The final mixture was sterilized by passage through a 45-micron millipore filter. In the rabbit, 1 mg of ferric ion (1 ml of a solution containing 5 mg FeCl3-6H20 per ml) was administered intravenously followed in one-half hour by 4 mCi of 113mIn chloride. Scanning was performed one hour later by means of a commercially available dual 8-inch crystal scanner with a fine focusing collimator (Fig.1). The scan shows good localization of indium chloride in the bone and kidney. Since ferric ion has considerable toxicity, it will be necessary to find a less toxic form, or perhaps substitute a less toxic ion such as Cr + + + or Ga+ + + in future studies. The desirable physical properties of 113mIn, namely, a short 1.6 hour half-life, a pure 390 keV gamma emission without associated particulate emission, and a ready availability from a tin-indium generator, make it a desirable agent for scanning bone and kidney.
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Dec 1, 1977
M Ahmon 
