on the container pertains to the biologic properties of the material and not to the radioactivity level. it is important to make certain that the radioactivity in the dose at the time of administration is sufficient for the intended use. the patient dose should be measured by a suitable radioactivity calibration system immediately prior to administration. note: a shielded syringe should be used for withdrawing and injecting the iodinated i 131 albumin total blood and plasma volumes dosage may range from 5 to 50 microcuries. blood volume determination a. preparation of reference solution remove an aliquot of the contents of the vial to be used in the procedure identical in volume to the dose to be administered to the patient. prepare a reference solution using normal saline as a diluent. the recommended dilution is 1:4000 [dilution factor (df) = 4000]. determine the radioactivity concentration (net cpm/ml) of the reference solution. care must be taken to assure that the reference solution and the blood samples (step b3) are assayed using the same geometric configuration. a. administration of dose 1. inject the dose into a large vein in patient's arm. measure the residual radioactivity in the syringe and needle. 2. destroy the syringe after injecting. do not attempt to resterilize.caution: the syringe should be disposed of in accordance with the us nuclear regulatory commission or agreement state regulations pertaining to the disposal of radioactive waste. 3. at 5 and 15 minutes after injecting the dose, withdraw blood samples from the patient's other arm with a sterile heparinized syringe. b. calculation of blood volume 1. take a known aliquot from each blood sample and determine radioconcentration in net cpm/ml. 2. plot the 5- and 15-minute sample counts (net cpm/ml) on semilog graph paper using the average count value of each sample and determine the radioconcentration at injection time (zero time) by drawing a straight line through the 15- and 5- minute points to zero time. the x ordinate iof the graph is the sample withdrawal time and the logarithmic y ordinate is radioconcentration in net cpm/ml. 3. calculate the patient's blood volume (in ml) using the following formula: net cpm/ml reference solution × df = blood volume (in ml) net cpm/ml patient's blood sample sample blood volume calculations volume of blood sample aliquot = 1.0 ml volume of reference solution aliquot = 1.0 ml net counts at zero time = 48,100 net counts obtained from reference solution aliquot = 52,430 using the formula above gives 52,430 x 4000 = 4360 ml 48,100 serial blood volume determinations iodinated i 131 albumin injection is administered in sufficiently low dosage to permit repetitions as often as required by clinical circumstances. it must be remembered that it is always necessary to correct for background radioactivity remaining in the blood from former determinations. therefore, for each determination after the first one, a background blood sample must be taken just before the iodinated i 131 albumin is injected. background blood sample: 1. withdraw background blood sample from large vein in patient's arm with a sterile heparinized syringe. 2. leaving needle in patient's vein, detach syringe containing blood sample. 3. attach syringe containing the dose of megatope to the indwelling needle and administer (see instructions under blood volume determination, administration of dose ). 4. determine radioconcentration in net cpm/ml of aliquots taken from background and postinjection blood samples, and from the reference solution. the radioconcentration (net cpm/ml) per aliquot of the background blood sample must be subtracted from the radioconcentration per aliquot of the blood sample obtained after the injection of iodinated i 131 albumin. the formula for calculating each blood volume determination after the first one thus becomes: net cpm/ml reference solution × df = blood net cpm/ml net cpm/ml volume postinjection minus background blood sample blood sample (in ml) plasma volume determination the procedure is essentially the same as that for blood volume determination, except that the blood sample drawn from the patient is centrifuged, the red blood cells are removed, and net cpm/ml of the plasma is determined. the formula for calculation of plasma volume, therefore is: net cpm/ml reference solution × df = plasma volume net cpm/ml patient's plasma sample (in ml) cardiac output dosage generally ranges from 3 to 50 microcuries. cardiac and pulmonary blood volumes; circulation times dosages used have generally been 75 to 130 microcuries. protein turnover studies dosages used have ranged from 10 to 150 microcuries. after injection, a period of seven days should be allowed before determinations are made to permit the elimination of any degraded protein in the dose. heart and great vessel delineation the suggested dosage is 5 microcuries per kg of body weight, although doses up to 750 microcuries have been used, depending on the instrumentation available and the scanning technique employed. localization of the placenta for localization of the placenta in the differential diagnosis of placenta praevia, a 3 to 5 microcurie dose is recommended; this dose has proved adequate for excellent localization, and the fetal total body radiation is a fraction of that received during x-ray placentography. while fetal thyroid irradiation is higher with iodinated i 131 albumin injection than with x-ray placentography, the administration of lugol's solution is reported to eliminate this hazard. localization of celebral neospasms the suggested dosage is 5 microcuries per kg of body weight. although doses as large as 500 microcuries of iodinated i 131 albumin injection have been used, the dose should be kept as small as possible. dosage is administered six hours before the initial examination, and scans are repeated at periodic intervals. radiation dosimetry the estimated absorbed radiation doses to an average patient (70 kg) from an intravenous injection of 50 microcuries of iodinated i 131 albumin injection usp are shown in table 4. table 4

aried considerably in their reporting of this figure. it has ranged, in the literature, from below 10 days to over 20 days. one important factor affecting the biological half-life is the initial rate of excretion, and this depends in part on the quality of the iodinated i 131 albumin. with megatope, the biologic half-life in normal individuals has been reported to be approximately 14 days.`