Gopal B. Saha

In Vitro Tests

The radioimmunoassay (RIA) method was first developed by S. A. Berson and R. S. Yallow in the late 1950s for the determination of insulin in human serum. Presently, the method is employed extensively to determine numerous hormones, enzymes, and drugs in minute quantities (10-9–10-12 M) in human plasma in order to assess various disease conditions. The general term for this method in both immune and nonimmune systems is the competitive binding assay (CBA).

A study of protein-binding of 99mTc-methylene diphosphonate in plasma

Abstract The extent of plasma protein-binding of 99m Tc-methylene diphosphonate (MDP) at 10 min, 1, 2 and 3 h after injection into patients has been determined by trichloroacetic acid and ammonium sulfate precipitation, dialysis and Sephadex gel chromatography. The percent administered dose bound to plasma proteins decreases with time, whereas the fraction of the plasma activity bound to plasma proteins increases with time after injection. Urinary excretion of the tracer is about 38% at 2 h and 62% at 24 h. The results suggest that the rate of removal of 99m Tc-MDP by bone uptake and urinary excretion is much faster than the rate of disappearance of the protein-bound tracer.

Plasma protein binding of 99mTc-pyrophosphate

Abstract In 10 patients, the extent of plasma protein-bound 99mTc-pyrophosphate has been determined at 15 min, 2h and 3h after injection by trichloroacetic acid and ammonium sulfate precipitation, dialysis and Sephadex gel chromatography. The per cent administered dose bound to plasma protein, determined by TCA precipitation, decreases with time initially and then remains constat at 2h and 3h, while it remains the same at 1.1%l.−1 at all times after injection in the case of (NH4)2SO4 precipitation. The results suggest that the rate of release of the tracer from the protein-bound fraction is slower than the rate of bone uptake and urinary excretion of free 99mTc-PYP. It is also found that the heavy mol. wt. proteins release the tracer faster than the lighter proteins.

Unusual In Vivo Distribution of 99mtc-diphosphonate

An unusual accumulation of 99mTc diphosphonate appeared within the stomach, thyroid and lungs of a patient along with minimal uptake in the bone. Many factors involving the patients disease processes and medications might result in in vivo radiopharmaceutical changes producing the observed atypical bone scans.

Measurement of renal function with 111In-DTPA in dogs

Abstract The renal clearances of 111 In-DTPA were measured and compared with those of 125 I-iothalamate in dogs using three methods: (a) constant infusion method, (b) single injection UV/P method, and (c) single injection slope method. The renal clearances of 111 In-DTPA were on the average 9% higher than those of 125 I-iothalamate. Its urinary excretion was approximately 50% at 1 hr and about 80% at 4 hr, and bilary excretion was negligible. Sequential scintophotography of the renal system in dogs revealed the flow of the tracer through the kidneys, and excretion into the ureter and bladder.

Radiopharmacology in Nuclear Medicine

Radiopharmacology is a new field of interest and offers a wide scope for further research and investigation into the design and use of radiopharmaceuticals. Radiopharmacology deals with the physiopathologic handling of radiopharmaceuticals in the living system. The study of the distribution and the mechanism of localization of a radiopharmaceutical in different organs is the essence of radiopharmacology. Knowledge of radiopharmacology provides more information and accuracy in the diagnosis of human diseases.

Radiation Dosimetry, Safety, and Regulations

Radiation can cause deleterious effects in living systems. It is therefore essential to assess these effects in humans for a given nuclear medicine procedure involving the administration of a radiopharmaceutical. The damaging effects arise from the absorption of energy in tissues and depend on a number of factors: (1) the activity of the administered radiopharmaceutical, (2) the physical and biologic half-lives of the radiopharmaceutical, (3) the distribution and metabolic fate of the radiopharmaceutical in the body, (4) the fraction of energy released per disintegration from a source region that is absorbed in the particular target volume, and (5) the shape and mass of the target organ. The physical characteristics of a radiopharmaceutical are well established. Information concerning the proper biologic handling of a radiopharmaceutical can be obtained from various experimental studies in humans and animals. Because there are variations from one individual to another in physiologic functions and in the shape, size, density, and relative location of different organs, the factors 3–5 listed above are approximated for a “standard” or “average” 70-kg man.