Attenuation correction in evaluating renal function in children and adultsby a camera-based method

Correction for soft-tissue attenuation is required to evaluate absolute ren al function by a camera-based method, and an estimate of renal depth and an attenuation coefficient are commonly used for attenuation correction. The first goal of this study was to develop formulas for the calculation of ren al depth in both children and adults. The second goal was to optimize the a ttenuation coefficient for the estimation of renal accumulation of a Tc-99m -labeled agent. Methods: Renal depth was measured by CT in 74 children and 232 adults and compared with the depth calculated using previously publishe d equations. Multiple stepwise linear regression analysis was conducted usi ng data from children and adults together, and new formulas to calculate re nal depth were derived. Using the resulting equations, percentage renal upt ake at 2-2.5 min was computed from Tc-99m-diethylenetriamine pentaacetic ac id (DTPA) renography in 40 children and 92 adults. Percentage renal uptake was assessed using Various values of an attenuation coefficient, and an opt imized attenuation coefficient was determined to maximize the correlation c oefficient between percentage renal uptake and glomerular filtration rate ( GFR) measured from 2 blood samples. Results: Although the previously publis hed equations appeared to be acceptable in predicting adult renal depth, th ey substantially underestimated pediatric renal depth. Renal depth (D, cm) was shown by stepwise regression analysis to depend on the ratio of body we ight (W, kg) to body height (H, cm) and was successfully calculated in both children and adults using the derived equations (right: D = 16.778 x W/H 0.752; left: D = 16.825 x W/H + 0.397). The correlation coefficient betwee n percentage renal uptake of Tc-99m-DTPA and measured GFR varied substantia lly according to the attenuation coefficient used and was the highest (0.94 7) with an attenuation coefficient of 0.087/cm. Conclusion: The equations p resented here enabled estimation of renal depth irrespective of the patient 's age. Attenuation correction using these equations and the optimized atte nuation coefficient appears to aid in evaluating renal accumulation and, co nsequently, renal function in both children and adults.