R.D. Ganatra

Influence of initial large dose on subsequent uptake of therapeutic radioiodine in thyroid cancer patients

Fifty-two patients with differentiated thyroid cancer, following thyroidectomy were studied by administering a quantity of up to 5 mCi of [131I]sodium iodide. In most of these patients, radioiodine uptake values obtained with the subsequent therapeutic dose were markedly lower than those observed with the initial doses. This observation was verified in seven of the patients with differentiated thyroid cancer, by measuring the radioiodine uptake with a second dose of 4.5 mCi of [131I]sodium iodide. Calculations showed that the major etiology was probably therapeutic irradiation of the thyroid by the first dose.

Factors affecting the preparation of 99mTc-sulfur colloid.

Some factors, such as the effect of mannitol as ‘stabilizer’, increased concentration of thiosulfate, autoclaving conditions, etc., that can affect the preparation of 99mTc-sulfur colloid and consequently its biodistribution into different tissues are discussed. Also discussed are parameters, such as distribution with respect to time, effect of storage, preloading dose, etc., that can influence the uptake of the radiopharmaceutical by the RES in animals and humans.

Modified rapid radiometric method for detection of Mycobacterium tuberculosis from sputum samples

A modified, simple and radiometric method for early detection of M. tuberculosis from sputum samples has been developed using a biphasic vial system for detection of 14C-CO2 produced by the metabolism of 14C-U-acetate on glycerol-free Lowenstein-Jensen medium (LJM). Of the 84 smear positive sputum samples examined, 85.7% and 86.9% were scored positive by radiometric and visual methods respectively. The detection rates at 1st, 2nd and 3rd week of the test were 53.3%, 60.7% and 82.1% by radiometry and 1.2%, 11.9% and 54.8% by visual methods respectively. The mean detection time was 10.7 days by the radiometric and 21.0 days by the visual method. An average replication time of primary culture from 54 sputum samples was 25.58 +/- 6.92 h (range 10.0-39.1 h).

Transit time of a radionuclide bolus through inferior vena cava.

The effect of an intrinsic block or extrinsic pressure on blood flow through the inferior vena cava (IVC) was studied after rapid injection of 99mTc-pertechnetate or 99mTc-phytate into the femoral vein. Peak-to-peak transit time (PTT) between the curves generated at IVC origin and over the cardiac blood pool was measured in twelve normal patients (PTT=2.0±0.7 s) and six patients clinically suspected of circulatory impediment through the IVC (PTT=3.0 to 30.0 s). PTT measurements augmented the information obtained from sequential scintiphotos of IVC circulation. It is felt that this may be a more objective parameter for follow-up of patients having a progressive, primary disease of this vessel.

Thyroid function and thyrotropin levels in rabbits immunized to produce antibodies against thyroid hormones

Various parameters of thyroid function were studied in 27 rabbits, out of which 10 were immunized to produce antibodies against triiodothyronine (T3), 9 against thyroxine (T4) and 8 were normals. Estimations of T3, T4, Free T4 (FT4) and thyrotropin (TSH) in blood, qualitative and quantitative analysis of iodoamino acids in serum, protein bound iodine-131 (PB131I), butanol extractable iodine-125 (BE125I) and measurement of the disappearance rates of 125I-labelled T3 and T4 from plasma were done. In addition, glandular changes were also studied by measurement of 131I uptake, thyroid scanning and chromatographic analysis of hydrolysate of soluble iodoproteins. In T3 immunized animals, levels of T3 in serum increased by 38 to 125 times, levels of TSH also showed a significant rise (7.4 +/- 1.2 vs 28 +/- 9 ng/mL). Chromatographic analysis of iodoamino acids in serum as well as in the hydrolysate of the thyroid gland demonstrated a selective increase in synthesis of T3. Rate of disappearance of T3 from blood showed a significant decline. Thyroid glands in the immunized rabbits showed signs of hypertrophy and hyperplasia. Identical studies done in rabbits immunized to produce antibodies against T4 showed a similar pattern though of variable degree. Our studies indicate that the thyroid glands of the immunized rabbits undergo marked alterations resulting in selective increase in the synthesis and secretion of the particular thyroid hormone against which they were immunized. They do so under the influence of increased levels of TSH.

Increased sensitivity of triiodothyronine antibodies for radioimmunoassay after removal of endogenous antigen by simple laboratory procedures

Conventionally produced antibodies against triiodothyronine (T3) are known to possess high amounts of endogenously produced T3 associated with them. We felt that such antibodies would work better for T3 radioimmunoassay (RIA) after prior removal of the antigen. With this in view, we attempted dissociation and subsequent removal of T3 from antisera by two different methods, viz. dialysis and alcohol extraction. It was possible to remove T3 to an extent of 77% by alcohol extraction and 60% by dialysis. Resultant antisera fail to demonstrate any increase in the titre. However, when standard curves were generated using these antisera, the assays became more sensitive and it was possible to detect T3 in concentrations as low as 6.25 pg. The affinity constants of these antisera calculated from the respective Scatchard plots were found to have increased after both dialysis treatment was well as alcohol extraction. This was thought to be due to rendering some of the high affinity binding sites on the antibodies free of antigen after treatment. Serum T3 levels were measured in 68 patients with various thyroid status using both treated as well as untreated antiserum. The difference between the average values of serum T3 concentration estimated using various antisera before and after the treatment was not statistically significant. Our results suggested that a simple procedure like stripping of antigen from antibodies could be of help for acquiring high affinity and high sensitivity antibodies for this purpose.

Serum triiodothyronine levels in thyroid disorders and their diagnostic usefulness

Abstract Triiodothyronine concentrations were measured by radioimmunoassay in sera of 252 patients with various thyroid disorders after alcohol extraction. The serum triiodothyronine levels were found to be 155.5 ± 37.8 (1 S.D.) ng% in 160 euthyroid subjects, 77.6 ± 16.0 (1 S.D.) ng% in 30 hypothyroid patients and 331 ± 112 (1 S.D.) ng% in 62 thyrotoxics. The diagnostic accuracy of serum triiodothyronine level was found to be somewhat better for diagnosis of hyperthyroidism in comparison to that of serum thyroxine. The incidence of T-3 toxicosis in this series was 4.8%, which was not different from that reported by others, in spite of mild iodine deficiency prevailing in this region.