August 1990, Volume 40, Issue 8

Original Article

Tc<sup>99m</sup>-RENAL IMAGING AGENT - THE PREPARATION AND COMPARATIVE CLINICAL EVALUATION

M. Jehangir  ( Pakistan Institute of Nuclear Science and Technology, Islamabad. )
Amin Wiqar  ( Nuclear Medical Centre, Armed Forces Institute of Pathology, Rawalpindi. )
M. Safdar  ( Pakistan Institute of Nuclear Science and Technology, Islamabad. )
Manzoor Ahmad  ( Nuclear Medical Centre, Armed Forces Institute of Pathology, Rawalpindi. )

ABSTRACT

Radionuclide Tc99m DTPA (Diethylenetriaminepenta Acetic Acid) renal imaging is being used to assist in the evaluation of overall GFR, the separate GFR, the intra-renal transit time, the cortical transit time, response to frusimide injection, diagnosis of ATN and rejection in renal transplant cases. A study was conducted at PINSTECH in order to prepare DTPA kit locally and evaluate the labeling efficiency as well as the invitro and invivo stability of Tc99m DTPA preparation. The results were comparable with th9se of imported Renal imaging (pentetate-Il Technetium 99m) agent. The shelf life of the kit at room temperature recorded is around 3 months, the labeling efficiency with Tc99m pertechnetate is more than 99% and the fraction of hydrolyzed Tc99m recorded is less than 1%. On clinical trials no artifacts were seen on scintigraphic images (JPMA 40:185, 1990).

INTRODUCTION

Tc99m DTPA has been described as the best kidney imaging agent1-3 and is in use in our country for the past several years. But as the reagent has to be imported from U.K. in the form of freeze dried kit4 the cost of the kits constitutes a major fraction of the recurring expenditure borne by nuclear medicine departments. The expenses can be reduced considerably by preparing them locally. A procedure for the preparation of Tc99m DTPA kit adopted at PINSTECH is submitted and the steps taken to ensure the quality control of these kits are also described. A comparative study was also conducted over a selected group of normal volunteers and in renal disorder patients with locaily prepared DTPA kits as well as the imported ones (Amersham UK) in order to evaluate their clinical efficiency. There is controversy about the stability of these kits5 therefore radiochemical purity and labeling efficien­cy of these kits at different time and temperature were studied in detail to check the efficiency, stability and shelf life.

MATERIAL AND METHODS

A stock solution (A) of DTPA (Fluka-750 mg) in sterile distilled water (60 ml) was prepared by raising the pH to 7.0 with NaOH. A solution B (20 ml) of SnC12 2H2O (E. Merck) (800 mg) in HCL was also prepared. With rapid stirring so!. B (1 ml) was added to sol. A. pH was readjusted to 6.8 and volume was brought to 75 ml with sterile distilled water 1.0 ml aliquot after passing through 0.22 micrometer millipore was dispensed in 70 vials and freeze dried for 48hrs. The vials were then sealed under saline as solvents. 1 cm strips were cut and counted in Gamma counter to calculate activity at different retention values. In order to check stability DTPA was mixed with reducing agent, labeling was carried out on DTPA in solution form, in freeze dried form and at different time intervals (Table-I).

RESULTS AND DISCUSSION

Results shown in Table 1 and Figures 1,2,3,4




demonstrate labeling efficiency to be more than 99% which is comparable to that of imported kit (Amersham ‘UK). The amount of free pertechnetate and hydrolyzed Technetium recorded is less than 1%. There has been some controversy about the stability of these kits5. We found (Figure 5)

that the kit containing reducing agent and NaTcO4-99m (after labeling is stable upto 24 hrs., whereas literature5 value is 6 hrs. Similarly our results (Figures 6,7)


showed that DTPA in the stock solution state (with reducing agent) is also stable upto 24 hrs. at 5°C while labeling of this stock solution with TCo4 after 48 hrs gave free TC04 6.9% and hydrolysed 3%. Stability of the DTPA kits in the freeze dried form kept at 5Co and 2OCo has also been studied (Figures 8-10).



Therefore shelf life of the kit at room temperature can easily be given upto 3 months. A clinical comparative study was also performed in order to evaluate the invivo stability of Tc99m DTPA preparations. The Tc99m was obtained from a Mo-Tc99m generator (Amersham UK). The equipment used was a large field of view gamma camera (Scintronix UK) coupled with a general purpose high resolution low energy col­limator. The camera was interfaced to an on-line computer (NoVa 4c). The study group included normal volunteers, normal functioning transplant and transplant with ATN and rejection. These groups were studied under similar conditions at an interval of 24 hrs with Tc99m pentetate II Amersham kit and Tc99m DTPA PINSTECH kit. Tc99m renal imaging agent injected in bolus dose of 5 mCl. The study was recorded on a computer at a frame rate of one frame per sçcond for the first 30 sec and then 30 sec frames for the next30 min. Processing of the study was performed by drawing region of interest over the kidneys background and bladder areas. In case of transplant kidneys additional area of interest was drawn over the iliac artery distal to transplant. Time activity curves for these regions were generated from derived data and curves “up slope” (CPS/Sec), “peak” (min) and “down slope” (CPS/Sec) were calculated. Thyroid activity was also recorded in each case. On analysis of these time activity curves results were comparable with those of imported kits (Table II).

The scintigraphic images (Figures 11,12)


also showed perfect labeling, stability of Tc99m DTPA prepara­tion with no image artifact.

CONCLUSION

Regular production of these kits locally has resulted into saving of foreign exchange and the facility of radionuclide renal imaging has been extended to large number of patients.

REFERENCES

1. Hauser, W., Atkins, H., Nelson, KG. and Richards, P. Tc99m DTPA, a new radiopharmaceutical for brain and kidney scanning. Radiology, 1970; 94: 679-684.
2. Carlsen, i.E., Moller, M.L., Lund, J.O. Comparison of four com­mercial Tc99m DTPA preparations used for the measurement of GFR. J. Nucl. Med., 1980; 21: 126-129.
3. Fritzberg, Alt Current status of renal radiopharmaceuticals. J. NucI. Med., 1980; 21: 177-188.
4. Hosain, F. Quality contrn of Tc99m DTPA by double tracer clearance technique J. Nucl. Med., 1974; 15: 442-445.

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