Abstract
This study was performed to evaluate a quantitative method based on <sup>99m</sup>Tc-DMSA renal planar scintigraphy performed during acute pyelonephritis (APN) to detect kidneys at risk of scarring. <b>Methods:</b> A total of 43 children (5.8 ± 3.6 y old [mean ± SD]) were examined by <sup>99m</sup>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 <i>n</i>% (region of interest containing all the pixels with a value ≥ <i>n</i>% of the value of the pixel with the maximal activity value) to the count density in a 20% isocount (C<sub><i>n</i>%</sub>) and the number of pixels in a given isocount to the number of pixels in a 20% isocount (S<sub><i>n</i>%</sub>). <b>Results:</b> All kidneys normal at DMSA 1 remained normal at DMSA 2. For the automatic index, the C<sub>70%</sub> ratio was considered the best index for the prediction of scarring. When this C<sub>70%</sub> 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. <b>Conclusion:</b> A cutoff value of 0.45 for the C<sub>70%</sub> ratio calculated for <sup>99m</sup>Tc-DMSA scintigraphy performed during APN may be useful for detecting kidneys at risk of scarring.
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