Tc-99m mercaptoacetyltriglycine clearance comparison of camera-assisted methods

Purpose: To compare the accuracy of three camera-assisted methods for the m easurement of Tc-99m mercaptoacetyltriglycine (MAG3) clearance. Materials and Methods: MAG3 renal scintigraphy was performed in 21 adults w ith different degrees of renal function. Posterior views were obtained that included the heart and the kidneys in the camera field of view. The syring e for injection was imaged before and after injection. Blood samples were d rawn 24 and 43 minutes after injection and plasma radioactivity was measure d. Three camera-assisted techniques to measure MAG3 clearance were tested: 1) Biexponential fitting of the left ventricular curve, normalized to plasm a activity at 24 minutes; 2) calculation of clearance by relating the integ ral of the plasma curve (normalized to plasma activity) to the kidney activ ity using the Rutland-Patlak space method; and 3) a regression equation mea suring clearance from the percentage of the injected dose accumulating in t he kidneys during the 1- to 2.5-minute period. The camera-assisted clearanc es were compared with the single-sample MAG3 clearances calculated using th e Russell equation. Linear regression analysis was used to measure the corr elation between the camera-based methods and the single-sample techniques. Results: Correlation with r > 0.900 was found for all three techniques. The difference in correlation coefficients between the three methods was not s ignificant; however, the regression line of method 3 was significantly clos er to the line of identity (P = 0.005). Conclusion: Method 3 most closely fits the line of identity and is probably the most practical because no blood sample is needed.