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New Parameter for obstruction in Tc-99m MAG3 renogram.
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New Parameter for obstruction in Tc-99m MAG3 renogram.
Justin J. De Grado, MD, MS, Robert M. Weiss, MD, Guy J. Manetti, MD, JeeHee Kim, BS, Sun H. Kim, MD.
Yale University, New Haven, CT, USA.
Background :
The clearance half time (T1/2) value has been used as a standard criteria in radionuclide diuretic renograms. However, in the presence of hydronephrosis, the accuracy of T1/2 as a reference in differentiating between obstruction and nonobstruction is compromised because of falsely prolonged T1/2 values associated with the reservoir effect of the dialated collecting system. The purpose of this study is to find a better criteria in delineating obstruction in groups with intermediate diuretic response.
Methods :
From 2002 to 2007, Tc-99m MAG3 diuretic renograms with intermediate diuretic response (T1/2 10-25 minutes)were selected (n= 36 patients, 45 kidneys, M: F=26:19, mean age 13.1 years old, 3 month-88 yr). T1/2 and RCA5 (residual cortical activity which equals activity at 5 min after lasix administration/peak activity)-RCA20 were compared in the obstruction and nonobstruction groups. The final diagnosis of obstruction was based on clinical findings and improvement in the degree of hydronephrosis on ultrasound follow up.
Results :
The results are summarized in the table. There is no significant difference in T1/2 values between the obstruction group (19.5min) and the nonobstruction group (20.1 min) (p<0.05). However, RCA5 is significantly higher in the obstruction group (0.9) than in the nonobstruction group (0.7). Other parameters such as RCA10. 15. 20 demonstrate less significant differences between the 2 groups.
Comparison of T1/2 &RCA 5 between the obstruction and nonobstruction groups
| Nonobstruction T1/2 (min)(n=37) | Nonobstruction
mean T1/2
=20.1
meanRCA5
=0.7
meanRCA10
=0.7
meanRCA15
=0.6
meanRCA20
=0.5 | Obstruction T1/2 (min) (n=8) | Obstruction
meanT1/2
=19.5
meanRCA5
=0.9
meanRCA10
=0.8
meanRCA15
=0.7
meanRCA20
=0.5 | | Normal | 16.4 min(n=3) | 14.2 min
(n=2) | | Mild hydronephrosis | 15.8 min
(n=4) | none | | Moderate hydronephrosis | 19.7 min(n=16) | 21.4 min
(n=5) | | Severe hydronephrosis | 22.7 min(n=14) | 20.6 min
(n=1) |
Conclusions :
In diuretic renograms with intermediate diuretic responses, RCA5 is a better criteria for delineating obstruction rather than the current parameter of T1/2. |
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