R. S. Mani

Production of96Tc and95mTc via the93Nb(α, xn) Reactions

Relatively longer liver technetium tracers such as95mTc (61 d) are useful for the development, evaluation and comparison of new technetium complexes for eventual development of99mTc radiopharmaceuticals. The feasibility of producing96Tc (4.35 d) and95mTc (61 d) was studied by the alpha bombardment of pure Nb targets (93Nb-100%).96Tc was obtained in a yield of 30 μCi/μAh using 16 MeV alphas, but it contained significant activity of95Tc (20 h) Relatively pure96Tc and95mTc was produced in yields of 18 μCi/μAh and about 1 μCi/μAh respectively with alphas of suitable energy and after allowing for suitable cooling periods after the end of bombardment (EOB).

A new method for99mTc generator preparation

The authors report here a new approach for making99mTc generators based on neutron irradiation of metallic molybdates and direct elution eliminating intermediate chemical processing steps. This approach tested using zirconium molybdate was found to yield99mTc with good yield and purity. This seems to be the simplest way of making column type99mTc generator even using low flux reactors and merits further detailed evaluation.

Preparation of a sterile closed system99mTc generator based on zirconium molybdate

A procedure for preparation of a sterile closed system generator for99mTc based on conversion to zirconium molybdate of99Mo produced by neutron activation is reported. The generator is sterilized by autoclaving.99mTc is eluted using 0.9% NaCl with high yield and purity in successive elutions.

Chemical and radiochemical evaluation of the purity of99mTc extracted by MEK

Solvent extraction separation of99mTc from99Mo using methyl ethyl ketone(MEK) has been found to be an effective method of obtaining99mTc of medicinal purity from low specific activity99Mo. The authors have investigated the effect of alkali and molybdenum concentration on the extraction of99Mo and99mTc into methyl ethyl ketone. The possibility of methyl ethyl ketone forming enol and condensation products and its effect on the final extraction efficiency and purity of99mTc has been studied. Sodium molybdate has been found to have a good salting out effect on99mTc pertechnetate and hence99mTc extraction can be better accomplished from low specific activity99Mo solutions. The ketone seems to form traces of condensation products in the extraction procedure. These have been found to be coextracted with99mTc into MEK but did not affect the extractability of99mTc. It was observed that neutral alumina column removes these condensation products from MEK containing99mTc. Alternately these could be filtered off by acidification of the final aqueous99mTc solution. The studies indicate that under optimum experimental conditions methyl ethyl ketone separates99mTc from99Mo with high efficiency and yields99mTc of high purity suitable for use in nuclear medicine in the form of various labelled compounds.

A simple method for the determination of the specific activity of125I-tracer used in radioimmunoassay

Knowledge of the specific activity of the125I-tracer is essential for optimization and for calculation of RIA parameters. The specific activity of the125I-thyroxin used in thyroxin radioimmunoassay /RIA/ has been determined by a simple method involving combination of RIA and displacement analysis. It has been compared with the value obtained by the conventional method based on radioiodination data. Our studies indicate that even for a non-protein hormone like thyroxin the specific activity of125I-thyroxin derived from iodination data is not reliable. The specific activities obtained by displacement analysis were consistent with the experimental findings.

Radioimmunoassay of Human Follicle Stimulating Hormone /HFSH/

A method for determining Human FSH in blood/serum by RIA is described. The radioiodination of FSH with125I is carried out under carefully controlled conditions such as, amount of initial activity of125I take for iodination, the reaction volume, and the reaction time, etc. The tracer FSH obtained thus is with minimum damage and optimum specific activity which is ideally suited for RIA. The shelf-life of the tracer is enhanced by the addition of benzyl alchol. The tracer can be conveniently stored at+4–6°C upto 10 weeks, avoiding the repeated freezing and thawing process. Antiserum to FSH is raised in rabbits by repeated injections via intramuscular route. The method utilizes polyethylene glycol /PEG/ as the separation system. Using this method, a number of control samples of men and women of reproductive age group are screened. This sensitive assay has a good validity and has an inter-assay variation less than 15%.

Preparation of radioidinated insulin and thyroid stimulating hormone using 1,3,4,6-tetrachloro-3α, 6α-diphenylglycouril (Iodogen) for radioimmunoassay

Radioiodinated insulin and thyroid stimulating hormones were prepared using 1,3,4,6-tetrachloro-3α, 6α-diphenylglycouril (Iodogen). Conditions of iodination like concentration of iodogen, reaction time, etc., were optimized to get maximum yield. Stability studies of iodogen coated tubes were carried out over a period of time. The dependence of iodination yield on varying amounts of activity and protein concentration were investigated. Iodination yield over a range of pH was also studied. The radiolabelled hormones prepared by this method were used in radioimmunoassay and were compared with tracers prepared by the Chloramine-T method.

Radioimmunoassay of somatotropin using second antibody polyethylene glycol combination separation system

We describe a radioimmunoassay procedure for human somatotropin using second antibody — polyethylene glycol (PEG) combination for the separation of antibody bound and free antigen. The assay is done by a single incubation of 18 hours or with one hour pre-incubation and 3 hours post-incubation at room temperature (25 °C) and uses 0.1 mℓ of serum sample. The assay covers a range of 0–40 μg/ℓ and has a sensitivity of 0.6 μg/ℓ of somatotropin. The assay is validated by inter-assay and intra-assay variations, recovery and parallelism tests.

A single reagent thyroxine radioimmunoassay

An homogenous radioimmunoassay of thyroxine using labelled antigen antibody complex as a single reagent is described. Variation of dose response curve slope with assay incubation time has been studied at two different antisera concentrations. The dissociation constant of the complex was found to be 3.5·10−4 s−1. The assay involves only three pipettings and requires 45 minutes incubation at 37 °C and 10 μl of serum. Though the assay is essentially a nonequilibrium type, apparent increase in sample values, due to the drift of dose response curve for 45 minutes delay was less than 7.5%. Within and between assay variations were both less than 5% c. v. Assay has been validated by recovery experiments. Analysis of 40 serum samples by the proposed method and by an equilibrium assay gave similar values; r=0.957, Y=0.955X+0.478.

Solid phase radioimmunoassay of triiodothyronine (T3) using antibody coupled carboxymethylcellulose powder

The paper describes a solid-phase radioimmunoassay for triiodothyronine (T3) using antibody coupled to carboxymethylcellulose powder. The free carboxylic acid groups of cellulose are covalently coupled to the amino groups of the antibody using 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide hydrochloride. Immobilized antibody thus prepared was used in a solid-phase radioimmunoassay of T3. The assay has a sensitivity of 0.18 μg/l, and a range of 0.18–4 μg/l. Satisfactory correlation was obtained when this assay was compared with a T3 assay based on dextran coated charcoal separation system (Y=0.95X+0.15 μg/L; r=0.98).