Determination Of Single-Kidney Glomerular Filtration Rate With CT Urography Versus Isotope Renogram

Glomerular filtration rate（GFR）is the quantitative indicator of renal function.There were many methods to evaluate glomerular filtration rate,some of them are able to assess overall（bilateral）renal function,such as inulin clearance,serum creatinine（Scr）assessment,dual plasma method,etc.,others are able to evaluate split（unilateral）renal function,such as99mTc-DTPA renal dynamic imaging Gates method（isotope renogram）,CT renal function measurement（Patlak method）,etc..The evaluation of split renal function plays an important role in the surgical treatment planning of renal diseases such as renal tumors,stones,infections and transplantation,etc..CT examination and isotope renogram can provide the morphological and functional information of the kidney,respectively.Typically,both of them are the preoperative clinical routines for renal diseases.CT examination could serve as a one-stop-shop method for morphological and functional evaluation,so,has clinical importance potentially.However,the previously reported Patlak method cannot be applied in clinical practice because of the great radiation dose due to dynamic CT scanning.Therefore,the methodology of CT renal function evaluation needs to be further improved.The purpose of this study is to develop and validate a CT method for evaluation of single-kidney GFR（CT-GFR）by using the image data of computed tomographic urography（CTU）without additional radiation dose to the patients.The experimental method was as following.Thirty-six patients referred for CTU and isotope renogram by clinicians were randomly enrolled into this investigation.Informed consent was obtained from all patients.The CTU protocol included non-contrast,nephrographic,and excretory phase imaging.The nephrographic phase images were acquired at 100s after the iodine contrast injection,then the excretory phase images were acquired at 600s（i.e.,10 min）.The total CT-GFR was calculated by dividing the CT number increments of the total urinary system by the area under the aortic time density curve.The total CT-GFR was then spilt into single-kidney CT-GFR by a proportional factor.The single-kidney CT-GFR were compared with single-kidney Gates-GFR by using paired t-test,correlation analysis,and Bland-Altman plots to evaluate the agreement of the two methods.This process was done independently by two radiologists,with results blinded to each other.The final results were the average of the two observers.The experimental results showed that the paired difference between single-kidney CT-GFR（45.04±13.91）ml·min^-1and single-kidney Gates-GFR（51.21±14.76）ml·min^-1 was（6.19±5.63）ml·min^-1,P<0.001,demonstrating 12.1%system underestimation with（±11.03）ml·min^-1 measurement deviation,indicating the two methods agreed well.In addition,a good correlation was revealed between both measurements（r=0.87,P<0.001）.We concluded that the proposed single-kidney CT-GFR measurement demonstrated a good agreement with isotope renogram,could accurately quantify the split renal function while providing morphological evaluation,so has important clinical relevance.