OP09.01: Evaluation of the vascularization index; a flow phantom study

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Three-dimensional power Doppler (3D-PD) ultrasound provides flow indices to quantify blood flow characteristics within a chosen volume of interest (e.g. ovary, tumor, placenta). The aim of the study was to assess and evaluate Vascularization Index (VI) data, using a specially built flow phantom with a known vascular diameter and a known volume of fluid pumped through it. A Voluson 730 Expert 3D-PD ultrasound machine was used, with a vaginal probe (RIC5–9) clipped onto a holding apparatus. ‘Fractional moving blood volume’ (FMBV) was simulated by pumping blood-mimicking fluid flow (10–100 ml/hr) through a plastic tube (diameter 0.65 mm) within a virtual spherical volume (content 137.12 cm3) of the ultrasound machine. VI was determined at different pulse repetition frequency (PRF) settings, with minimal and maximal wall motion filter (WMF) settings. The flow phantom showed that detection of FMBV at different flow velocities, depends on PRF—and WMF settings. At a PRF of 0.3 KHz, flow velocities of about 2 cm/s are fully registered. Using VI, at fully detected flow, actual FMBV within the tube is about 37 times overestimated. We find there is a significant overestimation of FMBV in 3D PD mode when a single small vessel is investigated, which is inherent to the method, because of limited spatial resolution. If reference vessels or objects with known vascularity can be established, the overestimation effect may be reduced.