ESTIMATION AND RELEVANCE OF DEPTH CORRECTION IN PEDIATRIC RENAL STUDIES

Measurement of absolute renal function by gamma camera techniques requ ires knowledge of kidney depth to correct for soft tissue attenuation, there is debate about the need to take depth into account when only r elative renal function is estimated. The aim of this study was to deri ve a formula for renal depth in children and to assess the importance of depth correction when relative renal function is assessed with dime rcaptosuccinic acid (DMSA) on the gamma camera. In this study, kidney depths were derived from measurements on abdominal computerised tomogr aphy (CT) images in 57 children in the supine position with two normal ly located kidneys. Using best-subset regression analysis, one formula for both left and right kidney depth (KD, cm) was developed based on the easily measured parameters of height (H, cm) and body weight (W, k g), The inclusion of extra variables was found to significantly improv e the model compared with a model using weight alone (P<0.005). A seco nd group of 19 children who underwent technetium-99m DMSA scans, had d ifferential function estimated from both anterior and posterior views and the geometric mean method. The mean difference in differential ren al function calculated by the geometric mean method versus the posteri or image was only 1.2%. In conclusion, we present a new formula for th e estimation of paediatric kidney depth for the absolute quantitation of kidney uptake. Further, for normally located kidneys it appears unn ecessary to use the geometric mean method or to correct for individual renal depth when calculating differential function.