Initial comparison of Tc-99m-NTA and Tc-99m-MAG3 in patients with suspected obstruction

539 Objectives Tc-99m-tricarbonyl-nitriloacetic acid, Tc-99m-NTA, is a new Tc-99m renal radiopharmaceutical with pharmacokinetic properties comparable to I-131 ortho-iodohippuran including a more rapid plasma clearance than the widely available tracer, Tc-99m MAG3. The objective of this study was to compare the performance of Tc-99m-NTA and Tc-99m-MAG3 in the clinically relevant setting of patients undergoing diuretic renography for suspected obstruction. Methods An eIND was obtained and the study approved by the Emory IRB. Tc-99m-NTA was prepared in house as previously described (J Nucl Med 2009:50:454). Adult patients referred for diuretic renography were invited to participate. Informed consent was obtained from all participants and patients entering the study were asked to arrive well hydrated. They were given an additional 200 mL of water on arrival. An intravenous line was placed and connected to a one liter bag of normal saline. Patients received an IV injection of 40-60 mg of furosemide 15 min prior to the administration of either Tc-99m-NTA or Tc-99m-MAG3; the tracer order was randomized with a mean ± SD initial dose of 47 ± 4.4 MBq. Data were acquired for 24 minutes followed by a measure of voided volume, an anterior image of the liver and gall bladder and a post-void image of the kidneys. Clearances were measured using a camera based technique (Radiology 1997;204:47). Patients received an additional 200 mL of oral hydration in addition to the normal saline infusion prior to a second IV injection of furosemide equal to 35% of the original dose. Fifteen minutes following furosemide, the tracer not used initially was administered, mean dose of 320 ± 34 MBq, and the initial acquisition protocol was repeated. Results Ten patients (7 females), mean age ± SD of 49 ± 18.7 years, have entered the study. In 6 of 20 acquisitions, the patient had to void before the 24 min acquisition was complete. Two studies demonstrated substantial tracer retention in the arm following injection and there was marked motion during another acquisition. Hydration was comparable as indicated by the fact that there was no significant difference in the voiding volumes following the Tc-99m-NTA and Tc-99m-MAG3 acquisitions, 638 ± 215 mL vs 561 ± 162 mL, respectively, p=0.22. Taking into account differences in dose administered, images and curve parameters were comparable. Relative uptake was comparable for the two tracers; the mean percent uptake of the left kidney for Tc-99m-NTA was 53.1 ± 27.7% compared to 52.1 ± 28.1% for Tc-99m-MAG3, p = 0.19. The mean (± SD) postvoid/maximum count ratio, an important parameter for evaluating suspected obstruction (AJR 2011;197:325), was 0.22 ± 0.30 for the left kidney for Tc-99m-NTA and 0.23 ± 0.21 for Tc-99m-MAG3. For the right kidney, the mean postvoid /max ratio was 0.25 ± 0.30 for Tc-99m-NTA and 0.36 ± 0.25 for Tc-99m-MAG3. The Wilcoxon rank sum test suggested a trend toward lower postvoid /max values for Tc-99m-NTA, p =0.13 and 0.07 for the left and right kidneys, respectively. The plasma clearance of Tc-99m-NTA was significantly greater than the plasma clearance of Tc-99m-MAG3, 330 ± 145.vs 255 ± 107 mL/min/1.73 m2 , respectively, p Conclusions : Initial comparison of Tc-99m-MAG3 and Tc-99m-NTA suggests that image and renogram curves are comparable but that Tc-99m-NTA has a more rapid clearance, a tendency toward lower postvoid/max count ratios and fewer subjects with gallbladder visualization.