DESIGN, FABRICATION, AND IN-VITRO EVALUATION OF AN IN-VIVO ULTRASONICDOPPLER WALL SHEAR RATE MEASURING DEVICE

In vivo wall shear rates have been obtained based on estimates from ei ther volume flow rate or single point velocity measurements along with the wall no slip assumption and a simple linear regression, Recent re sults [19] have shown that, under pulsatile Bow conditions, wall shear rates are more accurately predicted by using up to four velocity poin ts and a second- or third-order polynomial curve fit, It is the purpos e of this paper to evaluate the accuracy of a new, in vivo transducer capable of determining wall shear rates nonintrusively from velocities at three points along a line perpendicular to the vessel wall. Three 20-MHz ultrasound crystals were imbedded in an elastomer at distances of 1.5 and 2.1 mm with beam angles of 30 degrees, 45 degrees, and 60 d egrees to the horizontal plane. Microscopic examination showed that in tercrystal spacings were within 1.5% of the design and the crystal ang les were placed within 2.0%, In vitro calibration was performed under steady and pulsatile flow conditions with average shear rates being wi thin 4.3 +/- 17.3% and 0.2 +/- 0.6%, respectively, of the theoreticall y predicted values, Furthermore, peak and oscillatory shear rates were within -5.6 +/- 2.2% and -2,4 +/- 5.7% accuracy, respectively, Result s from this study show this device to be capable of providing accurate wall shear rates in vivo.