Several kinds of reductants have been used for labeling of various compounds with99mTc. Recently, Benjamin has reported the method of labeling by electrolysis. Al-though his method is very useful in comparison with the other conventional methods, there are still several points to be investigated. Then, we have further developed this method and devised a simplified apparatus for electrolysis which includes a timer and a stirrer so that we can easily get the constant current for electrolysis. For the preparation of99mTc-albumin, Pt-Zr electrodes showed a labeling efficiency of about 70% right after electrolysis, and by standing the electrolyte for about 10 min, more than 95% of99mTc was tagged to albumin. No differences in blood clearance rates in a rabbit could be observed between99mTc-albumin and131I-HSA at least for three hours after simultaneous administration. Pt-Sn electrodes gave good labeling efficiency for preparation of99mTc-millimicro-sphere. When this labeled compound was injected into mice, more than 90% of the activity was detected in liver 5 min after administration. As the results of these investigations, we concluded that electrolysis method for preparation of various99mTc-compounds is one of the most useful methods, and the preparation by the apparatus which we developed has many advantages such as simplicity, rapidity and reproducibility.
In order to investigate the tumor affinity radioisotope, Tin (Sn-113), Germanium (Ge-68), Zirconium (Zr-95) and Hafnium (Hf-175+181) -the elements of group IV in the periodic table-were examined, using the rats which were subcutaneously trans-planted with Yoshida's sarcoma. Six preparations, 113Sn-dichloride, 113Sn-citrate, 95Zr-nitrate, 95Zr-oxalate, 15+181Hf-chloride and68Ge-chloride were injected intravenously to each group of tumor bearing rats. These rats were sacrificed at various periods after injection of each prepara-tion: 3 hours, 24 hours and 48 hours in all preparations but68Ge-chloride, 1 hour, 3 hours and 24 hours in68Ge-chloride. The radioactives of tumor, blood, muscle, liver, kidney and spleen were measured by a well-type scintillation counter, and retention values in every tissue including tumor were calculated (in per cent of administered dose per g-tissue weight) . 113Sn had strong affinity for the malignant tumor, but it might have a disadvantage for the clinical application because retention value in the tumor was small and this element had very strog affinity for the bone and also considerably strong affinity for the inflammatory tissue.113Sn accumulated in the bone was very slowly excreted, but it disappeared rapidly from the blood and soft tissues.68Ge did not show any affinity for the malignant tumor, and disappeared very rapidly from the blood and soft tissue, and the majority of radioactivity was excreted in urine within first 3 hours.175+181Hf and95Zr did not have any affinity for the malignant tumor and disappeared slowly from the blood and soft tissue.
Serum iron was removed by Amberlite CG-400 ion exchange resin after lowering pH of the serum with citric acid. Recovering pH with sodium bicarbonate solution, the iron removed serum was incubated with radioactive ferric ammonium citrate solution and iron free transferrin was saturated with iron. Unbound iron ion in the iron solution serum mixture was removed with a resin strip made of Amberlite IRA-400, or with Amberlite CG-400. With a resin strip, ninety minutes were required for i, he removal of unbound iron ion, however, centrifugation can be omitted. With CG-400, 15 minutes were needed for the removal and then centrifugation. Clinical application of the above described method using a resin strip was per-formed with various patients and normals. The results showed a very good correlation between the TIBC by the present method and TIBC obtained by adding serum iron and unsaturated iron-binding capacity of the serum (UIBC) . Serum iron values obtained by subtracting UIBC from TIBC, and that obtained by colorimetry showed a very good correlation as well. TIBC by immunodifusion showed fairly good correlation with TIBC by the present method. The present method is simple, reproducible and can be used for the routine laboratory test.
Determination of unsaturated serum iron binding capacity using radioiron and resin strip was investigated. The resin strip was supplied from Daiichi Radioisotope Laboratories, Ltd. as a UIBC determination kit (Res-O-Mat Fe) . 0.5 ml of serum was added to a vial which contained59Fe labelled 3 μg of ferric ammonium chloride, and incubated for 20 minutes at room temperature. During this time, 59Fe radioactivity was counted (A cpm) . After the incubation, a resin strip was added to the vial and the vial was rotated continuously during 90 minutes. The resin strip was removed from the vial, and the radioactivity of the vial was counted again (B cpm) . Then UIBC (μg/dl) =B/A×3.0×200 About 93%io of 3 ig of unbounded iron in the vial was adsorbed by resin strip on the presence of iron saturated serum. Meanwhile, resin strip did not adsorb any transferrin bound iron from the59Fe ilabelled unsaturated serum. The changes of temperature 5°C-37°C during all course of this technique did not show any serious effects for the resulting UIBC values. The UIBC values showed excellent lineality according to various values. The UIBC values determined by magnesium carbonate method and Res-O-Mat Fe method showed good correlation (r=+0.99), but some of serum sample with high UIBC values showed lower values compared with that of magnesium carbonate method. Further investigation will be necessary to make clear the reasons of such discrepancy.