High-Frequency Array-Based Nanobubble Nonlinear Imaging in a Phantom and In Vivo.

ABSTRACT

There has been growing interest in nanobubbles (NBs) for vascular and extravascular ultrasound contrast imaging and therapeutic applications. Studies to date have generally utilized low frequencies (<12 MHz), high concentrations (>109 mL-1), and uncalibrated B-mode or contrast-mode on commercial systems without reporting investigations on NB signatures upon which the imaging protocols should be based. We recently demonstrated that low concentrations (106 mL-1) of porphyrin-lipid-encapsulated NBs scatter nonlinearly at low (2.5, 8 MHz) and high (12.5, 25, 30 MHz) frequencies in a pressure threshold-dependent manner that is advantageous for amplitude modulation (AM) imaging. Here, we implement pressure-calibrated AM at high frequency on a commercial preclinical array system to enhance sensitivity to nonlinear scattering of three phospholipid-based NB formulations. With this approach, improvements in contrast to tissue ratio relative to B-mode between 12.4 and 22.8 dB are demonstrated in a tissue-mimicking phantom, and between 6.7 and 14.8 dB in vivo.