Parametric clearance kidney scintigrams; diagnostic potential in diabetes

摘要

BACKGROUND: The diagnostic usefulness of parametric clearance kidney images was studied in the early diagnosis of diabetic nephropathy, juxtaposed with conventional dynamic urinary investigation (renoscintigraphy) combined with deconvolution procedure of renal and blood time activity curves and determination of plasma clearance of 99m Tc-ethylenedicysteine ( 99m Tc-EC). MATERIAL AND METHODS: The investigation was performed on a group of 70 individuals (41 males, 29 females) in whom diabetes type 1 was diagnosed (age 10 to 30 y.; mean 19 y.) and on a control group of 35 healthy individuals (15 males, 20 females) in the age-bracket of 18-25 years (mean 19 y.). In all subjects studied, renoscintigraphy was performed after administration of 99m Tc-EC (activity 40-120 MBq) combined with determination of urinary clearance (ERPF) of the radiopharmaceutical. The renographic curves were evaluated taking into account their shape and individual share of each kidney, and the clearance function was calculated (RClr). From analysis of the time-activity, kidney curves T max and T 1/2 were assessed. In addition, the mean 99m Tc-EC transport time through the complete kidney (MTT) and organ’s parenchyma (PTT) were calculated from results of deconvolution of the curve. From the dynamic urinary system study, conventional images of radiopharmaceutical distribution in the kidneys in the secretion phase were obtained. The parametric clearance images were also computed on the basis of relative clearance values in all the pixels of both kidney regions of interest. The disturbances in kidney function were assessed separately by means of conventional scintigram analysis and of corresponding parametric images. A three-stage classification was used in both cases for the evaluation of abnormal findings in the kidneys RESULTS AND CONCLUSIONS: In all studied individuals, the 99m Tc-EC (ERPF) clearance values were within the normal range. When renographic time activity curves were considered the flattening of the curves (III phase) was more frequent in diabetic individuals than in the controls (39.3% vs. 15.7%; p = 0.001). The shape of the curves in phases I and II were normal in all studied individuals of both groups. There were no differences observed between mean values of T max , T 1/2 and PTT in diabetics and controls. However, mean MTT values were significantly higher in diabetics than in controls (p = 0.02). In conventional summation images (phase II of the renograms), there were no significant differences in frequency of defects in kidney parenchyma diabetics and controls (4.3% vs. 2.9%). In contrast, analysis of parametric kidney clearance images revealed that parenchyma defects were found with significantly greater frequency in diabetic individuals (35.7%) than in control subjects (8.6%; p < 0.001). Summarizing the findings, it appears that parametric clearance kidney images reveal local deviations of renal uptake and secretory function while conventional indicators of renal function are still in the normal range. This observation points to the fact that clearance parametric images may have potential value in the early diagnosis of diabetic nephropathy, and perhaps in other types of renal damage. Incorporation of parametric images into the dynamic study of the urinary system may be promising when early detection of kidney damage seems vital.