Developing an Interface and Investigating Optimal Parameters for Real-Time Intracardiac Subharmonic-Aided Pressure Estimation

This study focuses on evaluating the real-time functionality of a customized interface and investigating the optimal parameters for intracardiac subharmonic-aided pressure estimation (SHAPE) utilizing Definity (Lantheus Medical Imaging Inc., North Billerica, MA, USA) and Sonazoid (GE Healthcare, Oslo, Norway) microbubbles. Pressure measurements within the chambers of the heart yield critical information for managing cardiovascular diseases. An alternative to current, invasive, clinical cardiac catheterization procedures is utilizing ultrasound contrast agents and SHAPE to noninvasively estimate intracardiac pressures. Therefore, this work developed a customized interface (on a SonixTablet, BK Ultrasound, Peabody, MA, USA) for real-time intracardiac SHAPE. In vitro, a Doppler flow phantom was utilized to mimic the dynamic pressure changes within the heart. Definity (15.0-22.5 μL microspheres corresponding to 0.1-0.15 mL) and Sonazoid (GE Healthcare; 0.4-1.2 μL microspheres corresponding to 0.05-0.15 mL) microbubbles were used. Data were acquired for varying transmit frequencies (2.5-4.0 MHz), and pulse shaping options (square wave and chirp down) to determine optimal transmit parameters. Simultaneously obtained radio frequency data and ambient pressure data were compared. For Definity, the chirp down pulse at 3.0 MHz yielded the highest correlation (r = -0.77 ± 0.2) between SHAPE and pressure catheter data. For Sonazoid, the square wave pulse at 2.5 MHz yielded the highest correlation (r = -0.72 ± 0.2). In conclusion, the real-time functionality of the customized interface has been verified, and the optimal parameters for utilizing Definity and Sonazoid for intracardiac SHAPE have been determined.