Effect of background region of interest and time-interval selection on glomerular filtration ratio estimation by percentage dose uptake of ^99mTc-DTPA in comparison with ⁵¹Cr-EDTA clearance in healthy cats

Abstract

Evaluation of glomerular function is a useful part of the diagnostic approach in animals suspected of having renal disease. Time-interval and background region of interest (bg ROI) selection are determining factors when calculating the glomerular filtration ratio (GFR) based on percentage uptake of (99m)technetium-labelled diethylene triamine penta-acetic acid ((99m)Tc-DTPA). Therefore, three different time intervals (60-120 s, 120-180 s, 60-180 s) and three different bg ROIs (C-shape, caudolateral, cranial + caudal) were investigated. In addition, global GFRs based on percentage dose uptake of (99m)Tc-DTPA for the different time-intervals and bg ROIs were compared with the global GFR based on (51)chromium-ethylene diaminic tetra-acetic acid ((51)Cr-EDTA) plasma clearance in nine healthy European domestic shorthair cats. Paired Student's t-tests and linear regression analysis were used to analyse the data. Different time intervals seemed to cause significant variation (P <0.01) in absolute GFR values, regardless of the choice of bg ROI. Significant differences (P <0.01) between bg ROIs were only observed in the 120-180s time interval between the C-shape and cranial + caudal bg ROI, and between the caudolateral and cranial + caudal bg ROI. The caudolateral bg ROI in the 60-180 s time interval showed the highest correlation coefficient (r = 0.882) between (99m)Tc-DTPA and (51)Cr-EDTA, although a significant difference (P <0.05) was present between both techniques.

Methods for Assessment of the Glomerular Filtration Rate in Laboratory Animals

“…However, this seems inaccurate. In one study, there was a significant difference when different time intervals and background regions of interest were chosen as determining factors when calculating the glomerular filtration ratio based on the uptake percentage of 99m Tc-DTPA [ 63 ]. It was also proven that following intravenous saline administration, changes in the time to peak activity and mean renal transit time may create inaccuracies in GFR estimates based on the conventional regression formula, thereby underestimating the true GFR value [ 64 ].…”

Repeatability and Reliability of Glomerular Filtration Rate Determination via Gamma Camera Uptake of Tc‐99m‐dtpa in Cats With Chronic Kidney Disease

“…Scintigraphic glomerular filtration rate (GFR) studies (as well as nonimaging techniques) can also provide serial measurements of renal function, which can help evaluate the effects of interventions such as response to drug therapy, progression of disease, or improvement of renal function . Because individual kidney GFR may be measured repeatedly in a clinical setting and these changes may affect the clinical classification of a cat, sources of variability must be quantified . In a research setting, it is essential that the inherent variability is estimated to evaluate whether posttherapeutic changes in GFR measurements are in response to treatment or simply inherent variation.…”

“…There are many potential sources of variability when measuring GFR, and the manual drawing of kidney and background regions of interest (ROI) has been shown to be a major component of variability . In a previous study comparing intra‐ and interobserver variation in GFR measurement via uptake of 99mTechnetium‐diethylenetriaminepentaacetic acid (99mTc‐DTPA) in dogs using manual vs. semiautomatic renal ROIs, the predominant source of variation affecting the 99mTc‐DTPA percentage uptake came from the ROI drawing technique .…”