Compartmental Analysis of the Complete Dynamic Scan Data for Scintigraphic Determination of Effective Renal Plasma Flow

We have developed an image-based compartmental analysis for estimating effective renal plasma flow (ERPF in units of milliliters per minute) from the full time-activity curves of regions of interest (ROI) placed over the heart, kidneys and bladder. Methods: Kidney or time-activity curves are corrected for physical attenuation using estimates of kidney depth derived from patient height and weight. Estimates of the calibration factors, K p and K b (mCi/counts/sec), for the plasma and bladder time-activity curves are determined by applying the following ROI analysis to each frame of the dynamic scan: (K p )P c (t) + (K b )B c (t) = D i - R q (t), where P c (t) and B c (t) represent the counting rates measured in ROI placed over the left ventricle blood pool and bladder at time t; D i is the known total injected dose, and R q (t) represents the millicurie of tracer in the kidneys at time t. Once K p and K b have been determined by regression, the calibrated time activity curves are used to solve for the physiological parameter fERPF (min 1 ), which represents the fraction of the total body plasma cleared of mertiatide per min. The ERPF calculated by the product of fERPF and plasma volume, determined from patient weight, was compared to the ERPF as calculated by blood samples and the Schlegel and renal uptake plasma volume product scintigraphic techniques. Results: Twenty-five adult patients with a wide range of ages and renal function were studied. The results of this image-based method for calculating ERPF correlated well with the values obtained from blood samples (linear regression slope = 1.06; y-int = -34.68 ml/min, r = 0.905) and offered a significant improvement over both the Schlegel and renal uptake plasma volume product estimates (p < 0.05). Conclusion: A scintigraphic estimation of ERPF without blood samples using time-activity data from the heart, kidneys and bladder acquired over the entire renogram is feasible and correlates well with more invasive techniques requiring blood samples.