Computed Tomography Based Renal Volume Measurements:Correlation With Renal Function In Patients With Renal Tumors

Part I Effect of CT Scanning Parameters on Renal Volume Measurements in Vitro:A Phantom StudyObjective:To evaluate the influence of various environments, tube voltages, tube currents and slice thicknesses on the accuracy of a home-made segmentation program in determining renal volume on computed tomography (CT) images.Materials and Methods:Volumes of potatoes and porcine kidneys measured on CT images were compared with actual volumes which were determined by water displacement method. CT scans were performed under various conditions:environments (air and oil); tube voltages/tube currents (80kVp/200mAs,120kVp/200mAs,120kVp/100mAs); and reconstructed slice thicknesses (0.75mm,1.5mm). Percentage errors (PEs) were applied to evaluate the accuracy of volume measurements, and PEs were defined as dividing the differences between CT based volume and the actual volume by the actual volume. Student’s paired sample t test was used for analyzing the influence of various conditions and parameters on image quality and volume measurements.Results:The volumes measured in oil were closer to actual volumes (P<0.001). Under the same tube current and slice thickness, the mean PEs between 120kVp and 80kVp were not significantly different (0.8±1.9 vs.0.9±1.8, P=0.240,0.75mm slice thickness; 0.4±1.9 vs.0.5±1.9, P=0.421,1.5mm thickness). Under the same tube voltage and slice thickness, the mean PEs between 200mAs and 100mAs were significantly different (0.8±1.9 vs.1.0±1.8, P=0.002,0.75mm slice thickness; 0.4±1.9 vs. 0.6±1.9, P<0.001,1.5mm thickness). Significant difference of PEs existed between 0.75mm and 1.5mm slice thickness, the mean PEs were smaller under 1.5mm slice thickness (P<0.001).Conclusions:Various environments, tube currents and reconstructed slice thicknesses could affect the volume measurements. The best performances of volume measurement in vitro were obtained at oil,120kVp/200mAs and 1.5mm thickness.Part II Computed Tomography Based Renal Volume measurements:Correlation with Renal Function in Patients with Renal TumorsObjective:To evaluate the correlations between renal cortical volume (RCV)/renal parenchymal volume (RPV) and renal function in patients with renal tumors before and after laparoscopic partial nephrectomy (LPN).Materials and Methods:Thirty-five patients with a single unilateral renal tumor managed with LPN were enrolled in this study. Pre and post-operative RCV/RPV were measured on the arterial phase of contrast-enhanced CT by a semiautomatic segmentation program. Pre and post-operative glomerular filtration rate (GFR) were measured by renal nuclear scintigraphy. The correlations between RCV/RPV and GFR preoperatively and postoperatively were done using the Pearson correlation coefficient.Results:A moderate correlation was observed between the preoperative virtually preserved RCV (r=0.502,p=0.002)/RPV (r=0.527,p=0.001) and the preoperative GFR for the operated kidneys. A moderate correlation was observed between the preoperative RCV(r=0.384,p=0.023)/RPV (r=0.412,p=0.014)and the preoperative GFR for the contralateral kidneys. Postoperative residual RCV (r=0.619,p<0.001)/ RPV (r=0.593,p<0.001) correlated moderately with postoperative GFR for the operated kidneys. Postoperative RCV (r=0.434,p=0.009)/RPV (r=0.522, p=0.001) correlated moderately with postoperative GFR for the contralateral kidneys. The correlation between the percent change in RCV/RPV and the percent change in GFR of the operated kidneys presented r=0.416,p=0.013/r=0.477,p=0.004. There were no correlations between the percent change in RCV/RPV and the percent change in GFR of the contralateral kidneys..Conclusions:Both CT based RCV and RPV were associated with renal function moderately, that is, renal volume, to some extent, could reflect renal function in patients with renal tumors before and after LPN. The use of RCV as a measure of renal function performed no better than the use of RPV in this study. The correlations between renal volume and renal function for the operated kidneys were better than those for the contralateral kidneys both before and after LPN. CT based renal volume measurements could serve as an effective method to evaluate long term renal function after LPN.