Clinical Value of the Equilibrium Phase in Renal Blood Flow Perfusion Curves Based on Renal Dynamic Imaging

Background In clinical practice, methods for comprehensive, stable, and quantitative assessment of renal microcirculatory blood flow perfusion remain limited. During renal dynamic imaging (RDI), SPECT acquires the renal blood flow time-activity curve (TAC), representing the temporal variation of radioactive count rates injected into the bloodstream within the kidneys. This count rate is directly proportional to the measured organ's blood flow perfusion. The equilibrium segment of the TAC reflects the dynamic equilibrium of renal microcirculation, representing the process of equilibrium between arterial and venous blood flow in and out of the kidneys. Due to variations in injected drug activity, the equilibrium segment of the TAC exhibits significant fluctuations, complicating quantitative assessment. This study proposes a Renal Blood Perfusion Rate (RBPR) calculation model that eliminates the influence of varying injected radiopharmaceutical activity through a ratio-based approach. Data was collected on patients undergoing renal radionuclide imaging (RDI) examinations between August 2020 and June 2025. Among these, 292 cases (involving 441 kidneys) met the criteria and were divided into five groups. The RBPR model was applied to quantitatively calculate renal microcirculatory blood perfusion. Results The RBPR distribution across 441 kidneys in the five groups was relatively concentrated, with small standard deviations within each group. RBPR showed a high correlation with GFR (r = 0.916, P < 0.01). Pairwise comparisons of RBPR between the five groups revealed significant differences (P < 0.001). Conclusion The RBPR model enables stable, quantitative assessment of renal microcirculatory perfusion and holds promise as a novel indicator for evaluating renal haemodynamics.