Relative renal function estimate by renal scintigraphy with 99mTc-DMSA: influence of attenuation correction methods

Introduction – The estimate of relative renal function (RRF) through scintigraphy with dimercaptosuccinic acid labelled with Technetium-99 metastable (99mTc-DMSA) may be influenced by kidney depth (KD), due to attenuation by soft tissue surrounding the kidneys. Considering that rarely this KD is known, several methods for attenuation correction (AC) have been developed, namely those using empirical formulae, such as Raynaud, Taylor or Tonnesen methods, or by direct calculation of the geometric mean (GM). Objectives – To identify the influence of different AC methods on RRF estimateby scintigraphy with 99mTc-DMSA and to evaluate the respective KD variability. Methods: Thirty-one patients were referred for 99mTc-DMSA scintigraphy and underwent the same acquisition protocol. Processing was performed by 2 independent operators, three times per exam, changing for the same processing the methods for the FRR determination: Raynaud’s method, Taylor’s method, Tonnesen´s method, GM and without AC (WAC). Friedman’s test was used to identify the influence of the different AC methods on RRF estimate and Pearson’s correlation test was used to evaluate the association and significance between KD and the variables age, weight and height. Results – Friedman’s test indicated that there were significant differences between methods (p=0.000), except for WAC/Raynaud, Tonnesen/GM and Taylor/GM (p=1.000) comparisons, for both kidneys. Pearson’s test showed a strong positive correlation between weight and the three methods of KD estimation. Conclusions – Taylor’s method, regarding the three methods of KD calculation, is the closest to GM. The choice of the attenuation correction method influences significantly the quantitative parameters of FRR.