Validation of 1- and 2-mm transit-time ultrasound flow probes on mesenteric artery and aorta of rats.

The aim of this investigation was to validate and calibrate the 1- and 2-mm transit-time ultrasound, perivascular flow probes on the superior mesenteric artery and aorta of the rat by using an in vivo and in situ calibration system. The baseline blood flows measured by the flowmeter zero-flow function and the true-zero flow measurement, after complete occlusion of the vessels, were not different. The probes were then calibrated, in situ, by timed-volume measurements with a blood/saline pump-perfused circuit. The relationship between measured flow and true flow was linear for both probes. The slope of the 1-mm probe data was not significantly different from the line of identity, whereas the 2-mm probe data slightly overestimated the true flow (slope = 1.2, y-intercept = -3.2 ml/min). The slope of the middle region of the 2-mm probe data, however, was not significantly different from the line of identity, suggesting that the 2-mm probe has a window of accuracy over this range of flows. Progressive elimination of the low and high data points varying the most from the line of identity and reanalysis of the data revealed that the window of accuracy for the 2-mm probe, under our experimental conditions, was between 10.4 and 45.1 ml/min.