Improved Quantification of Glomerular Filtration Rate and Differential Renal Function of Ectopic Kidneys in a Dual Head Gamma Camera

Abstract

Introduction: Tc-99m Di-ethylene Tri-amine Penta Acetic Acid (DTPA) renogram is an accepted method to measure Glomerular Filtration Rate (GFR) of the kidneys. The depth and position of ectopic kidneys may vary. This may lead to variation in tissue attenuation and error in the computed GFR and Differential Renal Function (DRF) of each kidney. Objective: The present study was undertaken in patients with ectopic kidneys to improve the accuracy of GFR and DRF calculation in a renogram with single injection of Tc-99m DTPA on a dual head gamma camera. Materials and Method: The study was conducted on 55 patients with ectopic kidneys. Images were acquired on a dual head gamma camera simultaneously in anterior and posterior views. Both anterior and posterior image datasets were used to compute the GFR of the ectopic kidney by Gates method. Depth correction of the ectopic kidney was done using the lateral view image. Total GFR was calculated as the sum of the anterior dataset ectopic kidney GFR and the posterior dataset normal kidney GFR. DRF was calculated again, by using the anterior dataset GFR of the ectopic kidney and posterior dataset for normal kidneys. The total GFR calculated by our method was compared to the patient's eGFR (based on serum creatinine, age and sex). Result: The GFR calculated by anterior data set in the ectopic kidney was significantly higher than that calculated by posterior dataset (p < 0.001). Similarly, the differential GFR of the ectopic kidney was higher when the anterior dataset was used (p < 0.001). The ectopic kidney GFR of 34 (61.8%) of the 55 patients was greater than 35 ml/min, whereas in 21 patients (38.2%), it was less than 35 ml/min. The total GFR calculated by using both anterior and posterior data set was compared with the eGFR; the correlation coefficient was 0.74 in patients with ectopic kidney GFR of >35 ml/min and 0.83 in those with <35ml/min. Conclusion: The GFR of ectopic kidney as calculated from the anterior data set was significantly higher in comparison to the GFR calculated from the posterior data set (p < 0.001). Using the ante-* Corresponding author.G. S. Muthu, S. Mitra 15 rior dataset GFR, the DRF values for the ectopic kidneys was also significantly higher (p < 0.001). This method improves the accuracy of the GFR and DRF values and helps to differentiate a normally functioning ectopic kidney from a poorly functioning one. Compared to the total GFR as calculated by the present method, the eGFR showed a better correlation in patients with ectopic kidney GFR < 35.0 ml/min.

Comparison between GFR Values Obtained by CG-formula and DTPA Renography in Different Renal Disorders

“…The total GFR in ml/min is computed as follows [3] . GFR = RU · (9.8127) -(6.82519) From the above mentioned equation, it is evident that the depth of the kidneys is an important factor in the computation of GFR by Gates method.…”