Optimization of Microbubble Concentration and Acoustic Pressure for Left Ventricular High-Frame-Rate EchoPIV in Patients

Abstract

High frame rate (HFR) echo-particle image velocimetry (echoPIV) is a promising tool for measuring intracardiac blood flow dynamics. In this study we investigate the optimal ultrasound contrast agent (UCA: SonoVue ®) infusion rate and acoustic output to use for HFR echoPIV (PRF = 4900 Hz) in the left ventricle (LV) of patients. Three infusion rates (0.3, 0.6 and 1.2 ml/min) and five acoustic output amplitudes (by varying transmit voltage: 5V, 10V, 15V, 20V and 30V-corresponding to Mechanical Indices of 0.01, 0.02, 0.03, 0.04 and 0.06 at 60 mm depth) were tested in 20 patients admitted for symptoms of heart failure. We assess the accuracy of HFR echoPIV against pulsed wave Doppler acquisitions obtained for mitral inflow and aortic outflow. In terms of image quality, the 1.2 ml/min infusion rate provided the highest contrast-to-background (CBR) ratio (3 dB improvement over 0.3 ml/min). The highest acoustic output tested resulted in the lowest CBR. Increased acoustic output also resulted in increased microbubble disruption. For the echoPIV results, the 1.2 ml/min infusion rate provided the best vector quality and accuracy; and mid-range acoustic outputs (corresponding to 15V-20V transmit voltages) provided the best agreement with the pulsed wave Doppler. Overall, the highest infusion rate (1.2 ml/min) and mid-range acoustic output amplitudes provided the best image quality and echoPIV results.

Left ventricular high frame rate echo-particle image velocimetry: clinical application and comparison with conventional imaging

“…We used four repeated diverging-waves, with two alternating polarity transmits (+ 7˚, -7˚), at a depth of 12 cm (Fig. 1 , Additional file 1 ), providing an effective frame rate of 1225 fps [ 6 – 8 ].

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“…UCA was infused using a Bracco VueJect pump (VueJect BR-INF 100, Bracco Imaging, Milan Italy), aiming for a steady-state relatively low-concentration of bubbles into the LV, allowing for the tracking of individual bubble motion between frames [ 8 ]. In the same session, complete echocardiographic studies were obtained using a clinical ultrasound system (Philips Epiq 7, with a X5-1 probe), including LV UCA.…”

“…The beamforming and detection of the vector field have already been described in previous works [ 6 – 8 ]. The HFR radiofrequency data was converted offline to B-mode images by successive filtering and beamforming onto a polar coordinate system, using the Verasonics beamformer.…”

“…Current clinical ultrasound systems use a line-by-line approach in order to construct an echocardiographic image, and lines are generated through focused beams. In order to increase the frame rate and maintain a low acoustic pressure we used a diverging-wave acquisition scheme [ 4 – 8 ]. While in non-enhanced high frame rate (HFR) echocardiography, the use of nonfocused beams generates little harmonic signal from the tissue, by adding UCA the harmonic signal comes from the interaction of the nonfocused beams with the UCA microbubbles [ 5 ].…”

Nanomaterials as Ultrasound Theragnostic Tools for Heart Disease Treatment/Diagnosis

“…UTMD can also result in cavitation, hence promoting the migration of stem cells in areas where cell replacement is needed such as ischemic myocardium [16]. In addition to their applications in therapy, MBs can be used in diagnosis, for example, by providing an accurate measurement of intracardiac blood flow dynamics in the left ventricle through the so-called high-frame-rate echo-particle imaging using an optimal combination of MB infusion rate (1.2 mL/min) and mechanical indices (MI = 0.03-0.04), [54]. An additional interesting feature of MBs comes from their functionalization to enable their targeting of a part of the heart that is of interest such as the thrombus.…”