Factors affecting the Gates' measurement of glomerular filtration rate
Awdeh, M.; Kouris, K.; Hassan, I.M.; Abdel-Dayem, H.M.
American Journal of Physiologic Imaging 5(1): 36-41
1990
ISSN/ISBN: 0885-8276 PMID: 2196915 Document Number: 352132
The following technical factors affect the Gates' measurement of glomerular filtration rate (GFR): 1) net injected activity, 2) kidney depth, 3) corrected kidney counts. In the syringe measurement prior to injection, self-attenuation causes 16% data loss for a volume of 0.5 ml if the syringe is positioned perpendicular to the collimator face. A .+-. 1 cm error in true kidney depth may cause a 16% difference in GFR in an adult. The choice of the background region of interest (ROI) for background subtraction significantly affects the calculation. To minimize errors of the Gates' estimate of GFR we recommend 1) that syringe counting be done with the syringe parallel to the collimator face; 2) that the i.v. set be included in the postsyringe measurement; in cases of extravasation, the injection site should also be counted; 3) that kidney depth, especially for ectopic and transplanted kidneys be estimated by ultrasound or using lateral views; and 4) that a background ROI for each kidney be used.