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.