Influence of Early Bladder Imaging in Experimental Rabbits on the Quantitative Determination of Glomerular Filtration Rate by the Gates Method

Abstract

Objective: To investigate the influence of early bladder imaging (EBI) in experimental rabbits on the quantitative calculation of glomerular filtration rate (GFR) by the Gates method.

Methods: We retrospectively analyzed the data of dynamic renal scintigraphy (DRS) in experimental rabbits. We calculated renal uptake during minutes 1-2 and 2-3 by correcting bladder radioactivity and computed the split GFR by renal uptake. Then, the EBI and GFR between 1-2 min and 2-3 min were compared, respectively.

Results: The EBI proportion (57.3%) at 2-3 min of DRS was higher than that (8.5%) at 1-2 min (P < 0.05). The correlations between the 1-2 min and 2-3 min uptake rates of unobstructed kidneys after correction (r = 0.952-0.979) were higher than those before correction (r = 0.859-0.936). However, the correlation between the two in obstructed kidneys was not improved (r _before = 0.967 versus r _after = 0.968). For unobstructed kidneys, the difference in GFR based on 2-3 min uptake between before and after correction was significant (P < 0.05), but not in obstructed kidneys (P > 0.05). For GFR based on 1-2 min uptake, the difference between before and after correction was not significant in obstructed or unobstructed kidneys (P > 0.05). Before correction, the GFR of unobstructed kidneys of 10.5% of the rabbits in the protein load test was lower than that in the baseline status, but not so after correction.

Conclusion: The 2-3 min EBI on DRS has a significant influence on the GFR calculated by the Gates method in experimental rabbits. Controlling water intake or calculating the GFR by 1-2 min renal uptake helps to avoid the influence of EBI on GFR.

Figure 1

Linear regression results and scatter plots between 1-2 min and 2-3 min renal uptake rates. (a) Total kidney: (a1) the total renal uptake rate without correction by bladder radioactivity; (a2) the total renal uptake rate with correction by bladder radioactivity. (b) Left kidney: (b1) the left renal uptake rate without correction by bladder radioactivity; (b2) the left renal uptake rate with correction by bladder radioactivity. (c) Right kidney: (c1) the right renal uptake rate without correction by bladder radioactivity; (c2) the right renal uptake rate with correction by bladder radioactivity.

Figure 2

Results of dynamic renal scintigraphy at baseline in the rabbit. The examination was performed on the 82nd day of right ureteral obstruction; the time below each frame of the images in panels (a) and (b) indicates the start time of acquisition. (a) The phase of blood flow perfusion. (b) The phase of renal function. No radioactivity is observed in the bladder in 60-120 s, and a small amount of urine radioactivity distribution is observed in the bladder in 120-180 s. (c) The renogram and the functional parameters. The GFR of the left kidney is 78.6 ml/min, and the GFR of the right kidney is 22.6 ml/min. (d) The outlined ROI of the kidney and background.

Figure 3

Results of dynamic renal scintigraphy in the protein load test in the rabbit. The examination was performed on the 83rd day of right ureteral obstruction; the time below each frame of the images in panels (a) and (b) indicates the start time of acquisition. (a) The phase of blood flow perfusion. (b) The phase of renal function; a small amount of urine radioactivity appeared in the bladder during 60-120 s, and much radioactivity appeared in the bladder during 120-180 s. (c) The renogram and the functional parameters. The GFR of the left kidney is 51.7 ml/min; the GFR of the right kidney is 19.9 ml/min. The left renal GFR is significantly lower than the GFR 78.6 ml/min of baseline status (Figure 2). After the renal uptake rate is corrected by bladder radioactivity, the left kidney GFR increases significantly to 88.5 ml/min, and the right kidney GFR is 20.9 ml/min. (d) The outlined ROI of the kidney and background.