The Value And Significance Of Renal Parenchymal Volume And Thickness By Noncontrast Helical CT In Evaluating Differential GFR For Chronic Obstructed Kidneys

Objective The purpose of the study is to evaluate the value of renal parenchymal volume and thickness by noncontrast helical CT in evaluating the differential GFR for chronic obstructed kidneys. The correlations between the two morphology indices of renal parenchyma and the GFR for chronic obstructed kidneys were analyzed.Methods Seventy-one patients that had a diagnosis of unilateral chronic upper urinary tract obstruction were included for analysis. 1. The renal parenchymal volume and thickness were measured by noncontrast helical CT. Both the kidneys were scanned by noncontrast helical CT. The renal parenchymal area of each section was marked manually. Renal parenchymal volume was calculated as the sum of renal parenchymal area multiplied by the width of each section. The volume percentage of obstructed kidney (%CTvol) was calculated also. 2. Renal parenchymal thickness was measured by two methods respectively.⑴Renal parenchymal thickness measurements were made on the first and last image levels from the anterior, posterior and lateral locations of the kidney that contained the collecting system;⑵Renal parenchymal thickness was taken at an angle exactly perpendicular to the axis of the kidney laterally on three levels. The mean of these measurements was defined as the renal parenchymal thickness. The differential renal parenchymal thickness of the obstructed kidney (%CTt1 and %CTt2) was defined as the percentage of the obstructed renal parenchymal thickness as of the total renal parenchymal thickness for both kidneys respectively. 3. GFR was determined with 99mTc-DTPA dynamic imaging system by Gates method, the differential GFR for obstructed (%GFR) was the GFR percentage of obstructed kidney as of the total GFR for both kidneys. The relation test was carried out between the %CTvol, %CTt and the %GFR respectively. The actual value of the renal parenchymal morphology indices (CTvol, CTt1 and CTt2) and the GFR in chronic obstructed kidney were carried out, too. 4. The glomerular filtration rate was estimated by the Cockcroft-Gault equation (eGFR). The estimated glomerular filtration rate for chronic obstructed kidneys (eGFRvol, eGFRt1 and eGFRt2) were calculated based on the %CTvol, %CTt1 and %CTt2. The relation test was carried out between the eGFR and GFR respectively.Results 1. CTvol and %CTvol correlated well with the GFR in chronic obstructed kidney and %GFR respectively. Pearson correlation coefficient r respectively are 0.53(Pearson relation test, t = 5.13, P < 0.05) and 0.70(Pearson relation test, t = 8.14, P < 0.05), The correlation is much better between %CTvol and %GFR. The liner correlation equation respectively are the GFR in chronic obstructed kidney = 10.04 + 0.21*CTvo(lF = 26.27, P < 0.05)and %GFR = 0.04 + 0.80*%CTvo(lF = 66.29, P < 0.05). 2. Both CTt1 and CTt2 correlated with GFR in chronic obstructed kidneys, Pearson correlation coefficient r respectively are 0.52(Pearson relation test, t = 5.12, P < 0.05) and 0.45(Pearson relation test, t = 4.23, P < 0.05). The liner correlation equation respectively are the GFR in chronic obstructed kidney = 9.3 + 2.24*CTt(1F = 26.2, P < 0.05)and the GFR in chronic obstructed kidney = 13.84 + 14.3*CTt2(F = 17.87, P < 0.05). Both %CTt1 and %CTt2 also correlated well with GFR in chronic obstructed kidneys. Pearson correlation coefficient r respectively are 0.66(Pearson relation test, t = 7.26, P < 0.05) and 0.57(Pearson relation test, t = 5.71, P < 0.05). The liner correlation equation respectively are %GFR = 0.08 + 0.76*%CTt1(F = 52.68,P < 0.05) and %GFR = 0.13 + 0.59*%CTt2(F = 32.56,P < 0.05). Paired-samples t test showed that there was insignificant difference (t = -0.07,P = 0.95 > 0.05) between %CTt1 and %CTt2, but there was significant differences between CTt1 and CTt(2t = -5.68, P < 0.05). 3. eGFRvol(26.17±21.27)ml/min, eGFRt1(23.74±19.93) ml/min and eGFRt2(23.81±20.76) ml/min correlated well with GFR in chronic obstructed kidneys, Pearson correlation coefficient r respectively are r = 0.66(Pearson relation test, t = 7.34, P < 0.05), r = 0.65(Pearson relation test, t = 7.08, P < 0.05) and r = 0.61(Pearson relation test, t = 6.32, P < 0.05). These correlation coefficient are approximation. The liner correlation equation respectively are the GFR in chronic obstructed kidney = 8.64 + 0.75*eGFRvol(F = 53.94, P < 0.05), the GFR in chronic obstructed kidney = 8.63 + 0.83*eGFRt1(F = 50.15, P < 0.05)and the GFR in chronic obstructed kidney = 11.03 + 0.73*eGFRt2(F = 39.93, P < 0.05).Conclusion 1. Renal parenchymal volume and thickness by noncontrast helical CT might be used as clinical practical parameters to evaluate the differential GFR for chronic obstructed kidneys. 2. Renal parenchymal volume is much more accurate than renal parenchymal thickness by noncontrast helical CT to evaluate the differential GFR for chronic obstructed kidneys. 3. %CTvol or %CTt significantly correlated with %GFR in chronic obstructed kidneys. 4. As regards the method used to measure the renal parenchymal thickness. The renal parenchymal thickness was measured on the first and last image levels of the kidney that clearly contained the collecting system correlated much better with GFR of the obstructed kidney than the method (2).