DMSA-scintigraphy in paediatrics: Is the evaluation of the geometric mean necessary for the calculation of the differential renal function?

For assessment of differential renal function (PF) by means of static renal scintigraphy with Tc-99m-dimer-captosuccinic acid (DMSA) the calculation o f the geometric mean of counts from the anterior and posterior view is reco mmended. Aim of this retrospective study was to find out, if the anterior v iew is necessary to receive an accurate differential renal function by calc ulating the geometric mean compared to calculating PF using the counts of t he posterior view only. Methods: 164 DMSA-scans of 151 children (86 f, 65 m ) aged 16 d to 16 a (4.7 +/- 3.9 a) were reviewed. The scans were performed using a dual head gamma camera (Picker Prism 2000 XP, low energy ultra hig h resolution collimator, matrix 256 X 256, 300 kcts/view, Zoom: 1.6-2.0). B ackground corrected values from both kidneys anterior and posterior were ob tained. Using region of interest technique PF was calculated using the coun ts of the dorsal view and compared with the calculated geometric mean [SQR( Cts(dors) X Cts(ventr))]. Results: The differential function of the right k idney was significantly less when compared to the calculation of the geomet ric mean (p <0.01). The mean difference between the PF a m and the PFdors w as 1.5 +/- 1.4%. A difference greater than or equal to5% (5.0-9.5%) was obt ained in only 6/164 scans (3.7%). Three of 6 patients presented with an und erestimated PFdors due to dystopic kidneys on the left side in 2 patients a nd on the right side in one patient. The other 3 patients with a difference >5% did not show any renal abnormality. Conclusion: The calculation of the PF from the posterior view only will give an underestimated value of the r ight kidney compared to the calculation of the geometric mean. This effect is not relevant for the calculation of the differential renal function in o rthotopic kidneys, so that in these cases the anterior view is not necesssa ry. However, geometric mean calculation to obtain reliable values for diffe rential renal function should be applied in cases with an obvious anatomica l abnormality.