Feasibility of the flash-replenishment concept in renal tissue: Which parameters affect the assessment of the contrast replenishment?

The purpose of the study was to evaluate whether power pulse inversion (PPI ) and pulse inversion (PI) techniques allow the measurement of indices of m icrocirculatory flow in real-time at low emission power using contrast micr obubbles. PPI and PI imaging were performed in a kidney perfusion model dur ing continuous infusion of Definity(TM) (0.12 mL/min). At steady state of t issue enhancement, contrast was destroyed by emission of echo bursts at hig h emission power (MI = 1.3). Consecutively, contrast replenishment was asse ssed at low emission power (MI = 0.09) in real-time imaging modes (PPI: 12 Hz; PI: 25 Hz). Regions-of-interest (ROI) of variable sizes were placed in the renal cortex and bigger arteries to compare replenishment of macro- and microcirculation. Nonlinear curve fitting was performed using the mathemat ical model y = s + A(l-e(-betat)), with A as the parameter describing blood volume and beta as a parameter describing the speed of microbubble contras t replenishment. Replenishment curves could be visually appreciated and qua ntitatively analyzed in all renal segments. A was significantly higher in b igger arteries compared to renal cortex (p<0.01). <beta> was found to be si gnificantly higher in the arteries as compared to the cortex (p<0.001). The SD of <beta> diminishes with increasing size of the ROI The acquisition of replenishment curves following ultrasound (US)-induced destruction of cont rast microbubbles is feasible at low power using PPI and PI. Assessment of replenishment kinetics allows the differentiation between macro- and microc irculation. Size and position of the ROI have an important impact on the ge neration of replenishment curves in both imaging modalities, which has to b e taken into account.