In vitro analysis of colour Doppler flow with the use of proximal isovelocity surface area: Improved flow estimates using a nonhemispherical model

OBJECTIVE: To examine the geometry of the proximal isovelocity surface area (PISA) envelope and its associated isotach, and to evaluate the accuracy o f two models of calculating volumetric flow by using the PISA technique. DESIGN: A new model for determining isotach geometry from the PISA envelope was developed and rested in an in vitro simulation. SETTING: Echocardiography Laboratory, Hotel Dieu Hospital, Kingston, Ontari o. MATERIALS AND METHODS: PISA envelopes were visualized using an in vitro flo w simulator with a series of sharp-edged orifices (2.5 to 16 mm diameter) a t a range of flow rates (10 to 110 mL/s). INTERVENTIONS: Flow calculations based on the traditional hemispherical geo metric assumption for the isotach and the new model were made and compared with measured flow rates. MAIN RESULTS: The hemispherical model systematically and significantly unde restimated flow. The nonhemispherical model, which requires measurement of both the height (a) and lateral width (2d) of the PISA envelope, provided i mproved estimates of flow. CONCLUSIONS: The nonhemispherical model provides a better estimate of flow through an orifice. Flow rate Q can be calculated directly from the size of the PISA envelope and the aliasing velocity (V-A) by using the relationshi p Q = (3.14d(2) + 5.97da + 1.37a(2))V-A or can be read from a nomogram.