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Normalized residual activity: usual values and robustness of the method.
Amy Piepsz1, Jacob D Kuyvenhoven, Marianne Tondeur
1Department of Radioisotopes, Centre Hospitalo-Universitaire St. Pierre, Brussels, Belgium. amypiepsz@yahoo.com
Summary
Normalized Residual Activity (NORA) is a robust parameter for assessing renal emptying in renography. Standardized NORA effectively evaluates kidney function, even in operated, unobstructed kidneys with potentially high values.
Area of Science:
- Nuclear medicine
- Renal physiology
- Medical imaging analysis
Background:
- Renography is crucial for assessing renal function.
- Estimating renal emptying requires robust parameters.
- Normalized Residual Activity (NORA) is a novel parameter for renography.
Purpose of the Study:
- To investigate the robustness of the Normalized Residual Activity (NORA) for renal emptying estimation.
- To define NORA values in normal and dilated, unobstructed kidneys.
Main Methods:
- NORA calculation: renal activity at a specific time point divided by activity between 1-2 minutes.
- Evaluation of background correction and time interval for NORA calculation.
- Analysis of NORA in normal kidneys and surgically altered, unobstructed kidneys.
Main Results:
- Background correction significantly impacts NORA values (67-83% of uncorrected).
- Time interval variations cause 10-15% NORA underestimation.
- 90th percentile NORA values differed significantly between normal and operated kidneys, with higher values in the latter.
Conclusions:
- Standardized NORA is a robust and simple parameter for evaluating renal emptying.
- High NORA values in operated, unobstructed kidneys indicate poor emptying, even post-micturition.