MEASURING TECHNETIUM-99M-MAG3 CLEARANCE WITH AN IMPROVED CAMERA-BASEDMETHOD

Because commercially available camera-based methods are not optimized, they fail to account for dose infiltration, table attenuation and cor respondence between time of injection and starting the camera. We have developed a more optimized technique to calculate camera-based cleara nces and applied this technique in the design of a camera-based cleara nce method for Tc-99m-MAG3. Methods: Technetium-99m-MAG3 scintigraphy was performed in 20 patients who had varying degrees of renal function . Data were acquired posteriorly in supine patients at 2 sec/frame for 24 frames, 15 sec/frame for 16 frames and 30 sec/frame for 40 frames. Background correction was performed using an automated elliptical reg ion of interest. Renal depth was estimated using improved regression e quations and an empirically determined attenuation coefficient derived from phantom studies. Corrections were made for table attenuation and time discrepancies between dose injection and starting the camera. Th e percent injected dose in the kidney at 1-2, 1-2.5 and 2-3 min postin jection and the percent injected dose at those time periods corrected for body surface area were correlated with MAG3 clearance based on a s ingle injection, two-compartment model. Results: There was high correl ation between the percent injected dose in the kidney at all three tim e periods and the multisample clearance. Correcting for body surface a reas significantly improved the correlation coefficients. Consequently , regression equations were developed to predict multisample clearance based on percent dose and body surface area. Conclusion: The optimiza tion features described in this method should improve precision when s equential studies are conducted in the same patient.