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Session: Vascular III
Session starts: Friday 27 January, 14:00
Presentation starts: 15:15
Room: Room 559

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Peiran Chen (Eindhoven University of Technology)
Andreas Pollet (Eindhoven University of Technology)
Simona Turco (Eindhoven University of Technology)
Miguel de Vargas (Solstice Pharmaceuticals)
Lisa te Winkel (Solstice Pharmaceuticals)
Wim van Hoeve (Solstice Pharmaceuticals)
Jaap den Toonder (Eindhoven University of Technology)
Hessel Wijkstra (Eindhoven University of Technology)
Massimo Mischi (Eindhoven University of Technology)

Abstract:
Introduction Contrast-enhanced ultrasound (CEUS) imaging provides real-time analysis of the vasculature with the help of injected ultrasound contrast agent (UCA) microbubbles. Recently, CEUS super-localization imaging has shown promise for the assessment of fine microvascular networks by localizing and tracking microbubbles, achieving resolutions beyond the diffraction limit. Compared to commercial UCAs, monodisperse microbubbles have a narrow size distribution. Therefore, proper frequency and pressure tuning have the potential to improve the signal to noise ratio and resolution of CEUS acquisitions, which can be expected to increase the performance of CEUS super-localization imaging. Moreover, both bubble size and insonating settings can be jointly optimized. In this work, the impact of monodisperse microbubble size on CEUS imaging quality and the efficacy of super-localization imaging was investigated by jointly tuning different frequencies and pressures for different monodisperse microbubble size. Methods A sugar-printed dual-bifurcation microvasculature phantom was perfused with UCA microbubbles. The channel diameter varies from 330 to 650 µm through the subsequent bifurcations. SP1 monodisperse microbubbles (Solstice) having dominant size of 3.7, 3.3, 2.9, 2.7 and 2.6 µm, corresponding respectively to resonance frequencies of 3.43, 4.09, 4.58, 5.08 and 5.42 MHz, were infused into the phantom at a flow rate of 0.08 mL/min. CEUS imaging was performed in contrast-specific mode using a Vantage 256 system (Verasonics Inc., USA) equipped with a L12-3 probe. For each microbubble size, seven transmit frequencies varying from 3.0 to 6.0 MHz with 0.5-MHz steps and four pressure values corresponding to mechanical index (MI) of 0.1, 0.13, 0.2 and 0.3 were used. The obtained CEUS acquisitions were then post-processed to generate a super-localization output using the Gaussian-centroid localization approach. Results/Discussion Metrics including generalized contrast-to-noise ratio of the CEUS acquisitions, full-width half-maximum of the pixel intensity profile extracted across a flow channel and number of localization events, were employed to quantify the CEUS imaging quality and super-localization performance. In general, jointly optimizing the transmit frequency and pressure for monodisperse microbubbles with smaller size lead to improved CEUS imaging and better super-localization performance. Yet, the weaker backscatter of smaller microbubbles must also be considered.