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The influence of four pH adjustment agents on the biologic behavior of osmium-191 (191Os) impurity in 191Os/191mIr generator eluates was studied. Extended body clearance and biodistribution studies were performed in mice. The solutions to be injected were obtained by eluting generators with a 0.9% NaCl solution at pH 1. The pH of these eluates was adjusted to 5-9 with succinate, phosphate, lysine or NaOH solution. Our results demonstrate that the biologic behavior of these generator eluates is significantly dependent on the agent used for pH adjustment. Buffering with lysine leads to the best results: (a) the mice show no adverse reaction after injection of 150 human doses and the body clearance is very rapid and (b) more than 75% I.D. at 24 hr postinjection. Preliminary calculations based on these results suggest a significant decrease in the estimated patient radiation dose when lysine buffered 191Os/191mIr generator eluates are used for radionuclide angiography.

Ninety patients, 85 of them jaundiced, were examined after the injection of Tc-99m pyridoxylidene glutamate, a substance rapidly concentrated by normal hepatocytes and excreted into the biliary tract. It appears in the gallbladder after 10-15 min, and in the gastrointestinal tract at 30 min. On the basis of the time of appearance in the intestine, four groups of patients were recognized: 1. Seventeen patients with a normal pattern, with visualization of the gut at 30 min. 2. Nineteen patients with a slight delay in passage, with appearance in the gut between 30-180 min. 3. Twenty-nine patients showing very slow excretion visualized only at 24 hr; 21 of these had parenchymatous disease of the liver, three choledocholithiasis and five had malignant disease causing partial obstruction. 4. Twenty-five patients with no visualization of the intestine; eight of them proved to be cases of medical jaundice, and 17 were surgical cases. Groups 3 and 4 comprise 54 patients where the question of medical or surgical jaundice was critical. If lack of intestinal activity is considered an indicating surgical jaundice, the accuracy of this study was only 72.4%.

A new separation system for an 191Os/191mIr generator is described. The system is composed of two columns in a series: a main column, packed with silica gel impregnated with tridodecylmethylammonium chloride (loaded with high activity 191Os as an osmyl chloride); and a scavenger column, packed with activated charcoal. Iridium-191m is eluted from the generator by pH 1 saline. For clinical use the eluate is buffered by succinate solution before injection. This new system is characterized by high performance (approximately 25% 191mIr recovery with 5 X 10(-4)% 191Os breakthrough) and long shelf-life (3 wk). The buffered eluate is sterile, pyrogen-free, and nontoxic, and contains no 192Ir. It is suitable for first-pass radionuclide angiocardiography with a very low radiation dose to the patient.

Iridium-191m would appear to be a highly useful agent for first-pass radionuclide angiocardiography (FPNA), with its very short half-life (4.96 sec), dual photopeaks (65 and 129 keV), and high injectable activity levels (greater than 100 mc). In order to compare 191mIr FPNA to current methods used to define cardiac function, 20 patients referred for cardiac catheterization were studied. Count rate data, right ventricular (RV), and left ventricular ejection fraction (LVEF), LV and diastolic volume (EDV), and end diastolic long axis (AXIS) were evaluated. Count rate data using 191mIr FPNA was consistently better than similar data obtained by 99mTc FPNA. There were acceptable correlations between 191mIr and 99mTc FPNA RVEF (r = 0.848), 191mIr FPNA and contrast angiography LVEF (r = 0.944), LVEDV (r = 0.917), and LV AXIS (r = 0.866). The data thus suggests that 191mIr FPNA has great potential in the evaluation of cardiac function.