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ABSTRACT
Year : 2010  |  Volume : 25  |  Issue : 3  |  Page : 109-110 Table of Contents   

Dosimetry


Date of Web Publication25-Nov-2010

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How to cite this article:
. Dosimetry. Indian J Nucl Med 2010;25:109-10

How to cite this URL:
. Dosimetry. Indian J Nucl Med [serial online] 2010 [cited 2019 Dec 10];25:109-10. Available from: http://www.ijnm.in/text.asp?2010/25/3/109/72761

DOS 1 (ORAL)

Kinetic modeling of PET-tracers for dopamine receptors

Pal Sunil, Kumar Nitin, Tiwari Anjani K, Kaushik A, Mishra AK


Institute of Nuclear Medicine & Allied Sciences (INMAS, DRDO), Delhi, India

Traditional tracer kinetic models have formal compartmental structures and the rate constants are fitted for using standard techniques. Using one scan, derived parameters such as the distribution volume (DV) (the ratio of ligand concentration between tissue and blood at equilibrium) or binding potential (BP) can be obtained and both are proportional to the Bmax (concentration of available receptors) and Ka (affinity constant of the radioligand). These models have generally been applied to region of interest analysis which is prone to errors due to variations in the selection of the image segments to be analyzed and which effectively further reduces considerably the spatial resolution of the imaging techniques. We have tried to utilize these model for Dopamine receptor analysis. There is a range of parametric imaging analysis techniques, typically based on a compartmental description of the tracer. These range from explicitly specified compartmental structures (model driven) to more flexible models derived from a general compartmental description (data driven). Examples of model-driven approaches include a one-tissue compartmental model for the estimation of blood flow and two-tissue compartment models for glucose metabolism and receptor ligand binding. Another aspect of modeling, is to adjust the PET-acquisition protocol to better fit the model. Instead of just injecting the radioactive tracer in a single intravenous bolus, the bolus injection may be followed by a continuous infusion of the tracer. Such a bolus-infusion protocol has the advantage of reaching a steady state earlier which is maintained throughout the PET-acquisition. The steady-state reached with the bolus infusion protocol has also proved advantageous in studies of tracer displacement, measuring dynamic changes of receptor binding levels.

Keywords: PET, dopamine receptor, tracer

DOS 2 (ORAL)

Biodistribution and radiation dosimetry of amino acid analogue of classical/PET radiopharmaceuticals in cancer patients

Tiwari Anjani K, Singh L, Datta A, Mishra AK


Institute of Nuclear Medicine & Allied Sciences, DRDO, Delhi, India

Purpose amino acid analogues are very important agents used for the treatment of several cancer types. As radiolabelled anticancer agents provide a potential means for personalized treatment planning, DTPA (amino acid)2 were labelled with the 99mTc. Non-invasive measurements of these uptake in organs and tumors may provide additional information on pharmacokinetics and pharmacodynamics of the drugs. The purpose of the present study was to determine the biodistribution and radiation absorbed dose of these analogues in humans. Methods biodistribution of DTPA (amino acid)2 were measured in patients with use of Scintigraphic imaging. Venous blood samples were collected to measure activity in blood and plasma. Regions of interest (ROI) for various source organs were defined and used to generate time-activity curves and to calculate percentage injected dose and residence times. Radiation absorbed doses were calculated according to the MIRD method. Gall bladder and liver demonstrated high uptake, whilst uptake in brain and normal lung was low. The percentage injected dose at 1 h in the liver was rapidly cleared from plasma and no radiolabelled metabolites were detected.

Keywords: Biodistribution, radiation dose, cancer

DOS 3 (POSTER)

A comparative investigation of 18F kinetics in receptors: A compartment model analysis

Tiwari Anjani K, Swatantra, Kaushik A, Mishra AK


Institute of Nuclear Medicine & Allied Sciences (INMAS, DRDO), Delhi, India

Some authors reported that 18F kinetics might be useful for evaluation of neuro receptors. We hypothesized that 18F kinetics may show some information about neuronal damage, and each rate constant might have statistically significant correlation with WO function. The purpose of this study was to investigate Tc-99m MIBI kinetics through a compartment model analysis. Each rate constant from compartment analysis was compared with WO, T1/2, and (H/M) ratio in early and delayed phase. Different animal model were studied. After an injection the dynamic planar imaging was performed on a dual-headed digital gamma camera system for 30 minutes. An ROI was drawn manually to assess the global kinetics of 18F. By using the time-activity curve (TAC) of ROI as a response tissue function and the TAC of Aorta as an input function, we analysed 18F pharmacokinetics through a 2-compartment model. We defined k1 as influx rate constant, k2 as out flux rate constant and k3 as specific uptake rate constant. And we calculated k1/k2 as distribution volume (Vd), k1k3/k2 as specific uptake (SU), and k1k3/(k2+k3) as clearance. For non-competitive affinity studies of PET two modelling parameters distribution volume (DV) and Bmax / Kd are also calculated. Results: Statistically significant correlations were seen between k2 and T1/2 (P<0.06), k1, Vd, SU, clearance had significant correlation with not only early H/M but also delayed H/M (P<0.002 in each others). The pharmacokinetics of 18F at the injection had relation to the uptake of it at 30 minutes and 2 hours after the injection. Furthermore, some indexes had statistically significant correlation with DV and Bmax. These compartment model approaches may be useful to estimate the other related studies.

Keywords: 18F, PET, compartmental model

DOS 4 (POSTER)

Application of radiotracers in the assessment of prophylactic role of zinc in experimental model of colon carcinogenesis

Vijayata Dani, Vaiphei K 1 , Dhawan DK 2


Nuclear Medicine, Centre for Emerging Areas in Science and Technology, 1 Department of Biophysics, Panjab University, Chandigarh-160 014. 2 Department of Histopathology, Post graduate Institute of Medical Education and Research, Chandigarh 160 014, India

The present study elucidated the modulatory effects of zinc in 1,2 dimethylhydrazine (DMH) induced colon carcinogenesis using radiotracer techniques. Rats were segregated into four groups viz., untreated control, DMH treated, zinc treated, DMH+zinc treated. Colon carcinogenesis was induced through weekly subcutaneous injections of DMH (30mg/Kg body weight) for 16 weeks. Zinc was supplemented to rats at a dose level of 227mg/L in drinking water, ad libitum. The prophylactic role of zinc was assessed by following radiotracer techniques viz: whole body biological half life of 65 Zn and 65 Zn biodistribution, subcellular distribution, uptake of 3 H-Thymidine to assess rate of DNA synthesis, radiorespirometric determination of 14 C-D-Glucose metabolism and in-vitro uptake of labeled aminoacids. The statistical significance of the data has been determined by using one way analysis of variance (ANOVA) followed by multiple post - hoc test. The carcinogenic state in the animals was confirmed by histopathological examination, whereby, well-differentiated signs of dysplasia were evident in colonic tissue sections of DMH treated rats. The biokinetics study of zinc revealed a significant decrease in the biological half life of 65 Zn. Also, DMH treatment caused a significant increase in the percent uptake values of 65 Zn in the colon, small intestine, kidney and blood, whereas a significant decrease was observed in the liver. The uptake rates of amino acids viz: 14 C-glycine, 14 C-alanine and 14 C-lysine were significantly higher in the DMH treated colons. Moreover, a significant increase in the uptake and turnover of 14 C-D-Glucose was also observed after DMH treatment. A significant increase in the [ 3 H]-thymidine uptake was observed following 16 weeks DMH treatment. However, supplementation of zinc significantly reversed the proliferative effect of DMH as evidenced by ameliorating the altered parameters. Radiotracer techniques play an important role in assessing positive beneficial effect of zinc against chemically induced colonic preneoplastic progression.

Keywords: Zinc, colon carcinogenesis, radiotracer techniques

DOS 5 (POSTER)

Elucidation of the mechanism of reduced uptake of 99mTc labeled bone seeking radiopharmaceutical due to iron overload

Nishad DK, Singh T, Kumar N, Swaroop K, Soni S, Sharma BG, Mittal G, Bhatnagar A


Institute of Nuclear Medicine & Allied Sciences (DRDO), Brig. S.K. Mazumdar Road, Timarpur, Delhi-54, India

It has been postulated that biodistribution of radiopharmaceutical get altered in iron overload conditions. Researchers have proposed different probable mechanisms to explain the above mentioned finding. Few believes that; radiopharmaceutical may alter by in vivo reaction, particularly the exchange reactions in which the radionuclide detaches from the pharmaceutical and adheres to another compound which may have different organ specificity or biological fate. It is also possible that the renal uptake may be due to the displacement of radioactive component from radiopharmaceutical in a form preferentially excreted or to the creation of a new complex which has kidney seeking properties. Still the exact mechanism behind this is unknown and yet to be discovered. In our present study we have confirmed the reduced bone uptake of radiopharmaceutical in an iron overload condition using rabbits as an experimental model. Two groups of Newealand white rabbits (three in each) were taken for the study i.e. Control and Test respectively. Control group rabbits were kept without any pre-treatment while the rabbits of test group were injected intramuscularly with a single dose (30 mg) of iron-sorbitol-citrate complex. After 2 hrs when the plasma iron concentration is at peak, 92.5 MBq of 99mTc-Methylene diphosphonate (MDP) was injected intravenously in the animals of both groups. Scintigraphic images using gamma camera were taken at 1, 2, 3 and 24 Hrs. The scintigraphic images obtained showed a significant difference in uptake pattern of radiopharmaceutical between control and test group animals. Reduced bone uptake of radiopharmaceutical and prominent hot kidneys were observed in the test group animals in comparison to control group. Further in vitro and in vivo studies are in progress to elucidate the exact mechanism involved. Based on the findings of our present studies we may be able to either re-confirm the earlier hypothesis or get a new aspect as a preventive approach for decorporation of radionuclides and heavy metals.

Keywords: Iron overload, 99mTc-MDP, gamma scintigraphy, iron-sorbitol-citrate, intravenous






 

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