Quantitative analysis of 99mTc-DMSA during acute pyelonephritis for prediction of long-term renal scarring

This study was performed to evaluate a quantitative method based on (99m)Tc-DMSA renal planar scintigraphy performed during acute pyelonephritis (APN) to detect kidneys at risk of scarring.

A total of 43 children (5.8 +/- 3.6 y old [mean +/- SD]) were examined by (99m)Tc-DMSA scintigraphy during (DMSA 1) and 8 +/- 2 mo after (DMSA 2) APN. Two levels of interpretation were performed independently: first, a semiquantitative analysis to classify the kidneys by considering the evolution between DMSA 1 and DMSA 2 (i.e., to determine which kidneys had developed scarring), and second, an automatic quantitative analysis of DMSA 1 to define and to evaluate a predictive index for kidney evolution from DMSA 1 to DMAS 2. The method consisted of determining an automatic threshold for the kidney and then calculating ratios of the count density in a given isocount n% (region of interest containing all the pixels with a value > or = n% of the value of the pixel with the maximal activity value) to the count density in a 20% isocount (C(n%)) and the number of pixels in a given isocount to the number of pixels in a 20% isocount (S(n%)).

All kidneys normal at DMSA 1 remained normal at DMSA 2. For the automatic index, the C(70%) ratio was considered the best index for the prediction of scarring. When this C(70%) ratio was used, a cutoff value of 0.45 was able to predict scarring with a sensitivity of 0.83, a specificity of 0.78, a positive predictive value of 0.85, and a negative predictive value of 0.77.

A cutoff value of 0.45 for the C(70%) ratio calculated for (99m)Tc-DMSA scintigraphy performed during APN may be useful for detecting kidneys at risk of scarring.