Head to Head Comparison of 99mTc(CO)3(NTA) and 99mTc-MAG3 in Patients with Suspected Obstruction
Abstract Purpose 99mTc-tricarbonyl-nitrilotriacetic acid, 99mTc(CO)3(NTA), is a new 99mTc-renal radiopharmaceutical with a clearance equal to that of 131I-ortho-iodohippuran. Our purpose was to compare the performance of 99mTc(CO)3(NTA) and 99mTc-MAG3 in patients with suspected obstruction.Methods 99mTc(CO)3(NTA) was prepared with commercially available NTA and CRS Isolink kit, and isolated by HPLC. Eighteen adult patients referred for diuretic renography received an intravenous injection of approximately 40 mg of furosemide 15 min prior to either 99mTc(CO)3(NTA) or 99mTc-MAG3 (mean activity of 47 ± 4.4 MBq). Data were acquired for 24 minutes followed by an anterior image of the liver and gall bladder and a measure of voided volume. Patients received a second furosemide injection equal to one third of the original dose followed fifteen minutes later by administration of the alternate tracer, mean activity of 320 ± 34 MBq. Clearances were measured using a camera-based technique.Results The clearance of 99mTc(CO)3(NTA) was greater than that of 99mTc-MAG3, 331 ± 146 vs 271 ± 105 mL/min/1.73 m2, respectively, p < 0.0001. The kidney to background ratio for 99mTc(CO)3(NTA) was greater than that of 99mTc-MAG3 for both left and right kidneys, p < 0.001; the 20 min/maximum count ratio was significantly less, p < 0.0001. There was no significant difference in the voiding volumes following 99mTc(CO)3(NTA) and 99mTc-MAG3 administration, 598 ± 237 mL vs 498 ± 170 mL, respectively, p = 0.07. Gall bladder activity was not observed with 99mTc(CO)3(NTA) but was present in 6/17 99mTc-MAG3 studies. Images and renogram curves were comparable except for two patients where the 99mTc(CO)3(NTA) study excluded obstruction but the 99mTc-MAG3 study suggested an indeterminate or obstructed kidney.Conclusions Unlike 99mTc-MAG3, 99mTc(CO)3(NTA) is not eliminated via the hepatobiliary track. Moreover, 99mTc(CO)3(NTA has a higher kidney to background ratio and more rapid clearance than 99mTc-MAG3. These advantages should allow more robust camera-based clearance measurements and may lead to better discrimination between obstructed and non-obstructed kidneys.