Prediction of kidney depth and body thickness in renal scintigraphy

Objectives The aim was to validate predictors for estimation of kidney depth (KD) and body thickness (BT) in posterior and geometric mean renography in comparison with newly proposed predictor - body width (BW).

Methods KD, BT, and BW were measured in CT, MR, and SPECT transversal slices in 734 patients 1mo-85yrs old. In 554 of them, body weight (W) and height (H) were also available. Prediction error (PE) was calculated by cross-validation for individual predictors and their combinations including regression formulas published by Tauxe, Tonnesen, Taylor, Itoh, Gordon, and Raynaud.

Results In children 0-15 yrs, average KD of the right kidney (KDR) was 4.2±1.5 cm and of the left kidney (KDL) 4.0±1.3 cm. In adults, mean KDR was 8.3±2.1 cm and KDL 7.9±2.2 cm. KDR was significantly greater than KDL in all age groups except 0-5 yrs old children and 70< adults. Differences KDR-KDL greater than 1 cm were found in 6% children and 24% adults. Formula performing with the lowest PE was Tonnesen in children and Taylor in adults. The best individual predictor for both KD and BT was BW. It performed better than Tonnesen's formula in children and comparably with Taylor's formula in adults. BW measured in posterior view renography correlated well with that measured in tomographic slices (r=0.99).

Conclusions KD and BT required to calculate absolute renal uptake in posterior and geometric mean renography can be estimated by a single predictor BW that can be measured in posterior view without a need to record lateral projections. Comparison with KD and BT measured in lateral views and with transmission measurement remains to be done.

Research Support The work has been supported by the Czech Science Foundation grant no. 303/07/0950.