Application of renal depth by CT for the measurement of GFR using SPECT/CT

Abstract

Objective To investigate the necessity and feasibility of renal depth measured by CT for the measurement of GFR with SPECT/CT.Methods CT and lateral planar imaging of SPECT along with dynamic 99Tcm-DTPA renal scintigraphy (DRS) was performed in 49 patients.The renal depth estimated by Tonnesen formula and SPECT was compared with that measured by CT using paired t-test.GFR was recalculated by the Gates method using the renal depth measured by CT,Tonnesen formula and SPECT.Linear correlation analysis was used between the renal depth by CT and measurement error caused by Tonnesen formula and lateral planar imaging of SPECT.Paired t-test was also performed with software SPSS 15.0.Results Compared with CT,the renal depth was substantially underestimated by Tonnesen formula ( right kidney:(5.77±0.90) cm,t=-11.50,P＜0.01; left kidney:(5.74±0.88) cm,t =12.20,P＜0.01),which resulted in the underestimation of GFR (right kidney:( -20.92 ± 11.28)％,t =-6.99,P＜0.01 ;left kidney:( -23.71 ±7.71 )％,t =-8.73,P ＜0.01 ) ; while,it was overestimated by SPECT ( right kidney:(7.40 ± 1.15) cm,t =5.19,P ＜0.01 ; left kidney (7.49 ± 1.19) cm,t =5.14,P ＜0.01 ),which resulted in the overestimation of GFR ( right kidney:( 5.23 ± 9.64 ) ％,t =2.72,P ＜ 0.01 ; left kidney:(8.93 ±9.29) ％,t =5.21,P ＜0.01 ).The error for the calculation of renal depth by Tonnesen formula was positively correlated with the true value (right kidney r =0.62,P ＜0.01 ; left kidney r =0.73,P ＜ 0.01 ).However,there was no correlation between the error of the renal depth measured by SPECT and the true value (right kidney:r =0.26,P ＞0.05; left kidney:r =0.38,P ＜0.01 ).Conclusion SPECT/CT can improve the accuracy of GFR measurement by the Gates method using renal depth measured by CT. Key words: Glomerular filtration rate; Tomography, emission-computed, single-photon; Tomography, X-ray computed; Renal depth; Tonnesen formula