Optimization of Gate’s technique for measurement of GFR during routine renal scan [Persian]

Using Gate’s technique for GFR measurement with Gamma camera, the patient is received 5mCi of Tc-99m-DTPA. By this amount of radioactivity, good quality renal scan is not possible. This study tries to optimize Gate’s technique for GFR measurement during routine renal scan (with 10-15 mCi). Methods and materials: Scanning was performed for 60 seconds from samples of Tc-99m with activities of 3, 9, 12, 15 and 18 mCi in a small syringe, with a 30 cm distance from the detector. Another sample of 12 mCi of Tc-99m was imaged for 5, 10, 15, 20 and 30 seconds. The same sample was again imaged for 10 seconds in different distances (10, 20, 30 and 40 cm) from the detector. Each image was acquired 10 times. Using rectangular region of interest (ROI), total count and maximum count per pixel were recorded for all images. Results: The total count revealed rising in the images form 3 mCi to 15 mCi samples while declining thereafter, suggesting paralysis of the Gamma camera in high activities. Maximum count per pixel was 32767 (2 in 15 power minus one) in all images except for the 3 mCi sample image, suggesting saturation of the pixels in high activities. Also saturation of the pixels was note in images of 12 mCi sample for more than 15 seconds. No saturation of pixels was noticed within 20-40 cm distance from the detector. Conclusion: By optimization of the Gate’s technique for GFR measurement, GFR can be calculated during routine renal scan. We suggest using 10-15 mCi of Tc-99m-DTPA, with 5-15 seconds preinjected syringe count, 30 cm distant from the detector. Comparison of GFR calculation using suggested technique with GFR estimation by creatinine clearance in 9 patients, resulted in a significant and good correlation coefficient (R=0.883, P=0.005).