A preliminary phantom study on a proposed model for quantification of renal planar scintigraphy.

A method for estimation of the absolute renal activity within background activity in renal planar scintigraphy will be presented. This method corrects for oversubtraction of background activity with consideration of background activity of the kidney volume, and employs the depth-independent buildup factor (DIBF) method for the correction of attenuation and scatter of photons. This method requires the depth and thickness of the organ and the thickness of background for a background activity correction. The transmission factor (TF) for a volume source is derived from integrating TF for a thin source over the thickness of the organ for the DIBF method. To validate this method, phantom studies with various uniform background activity concentrations were performed and the data were compared with conventional background subtraction that do not consider the organ's volume. The results showed that with the conventional background subtraction method at all depth activity was underestimated with errors of 5%-30% for organ/background concentration ratios of 5-40, while this method estimated the true count rate with errors of less than 5%. More accurate quantifications of renal functions such as renal uptake, glomerular filtration rate (GFR) and renogram may be obtained by this proposed method on the planar images.