Towards Aberration Correction of Transcranial Ultrasound Using Acoustic Droplet Vaporization

Abstract

We report on the first experiments demonstrating the transcranial acoustic formation of stable gas bubbles that can be used for transcranial ultrasound aberration correction. It is demonstrated that the gas bubbles can be formed transcranially by phase-transitioning single, superheated, micron-size, liquid dodecafluoropentane droplets with ultrasound, a process known as acoustic droplet vaporization (ADV). ADV was performed at 550 kHz, where the skull is less attenuating and aberrating, allowing for higher-amplitudes to be reached at the focus. Additionally, it is demonstrated that time-reversal focusing at 1 MHz can be used to correct for transcranial aberrations with a single gas bubble acting as a point beacon. Aberration correction was performed using a synthetic aperture approach and verified by the realignment of the scattered waveforms. Under the conditions described below, time-reversal aberration correction using gas bubbles resulted in a gain of 1.9 ± 0.3 in an introduced focusing factor. This is a small fraction of the gain anticipated from complete transmitreceive of a fully-populated two-dimensional array with sub-wavelength elements.

Phase-transition Perfluorocarbon Nanoparticles for Ultrasound Molecular Imaging and Therapy

“…As a result, the gas phase can rapidly formed by the "driving force" if the time window is long enough (low ultrasonic frequency) or the internal pressure is small enough (high acoustic amplitude). These process has been observed by several reports [50][51][52].…”

Scavenging dissolved oxygen via acoustic droplet vaporization

“…Further, n O 2 in equation 4 is equal to n b as defined in equation 2. The total volume of the microbubbles (V b ) can therefore be rewritten by expressing the first term in equation 4 in terms of the total volume of droplets that were vaporized during ADV and the expansion factor of 125, as: (5) By solving equations 1, 2, and 5, simultaneously, the number of moles of oxygen in the liquid per unit volume n l /V l can be calculated. The percent dissolved oxygen in the surrounding fluid after ultrasound exposure is predicted to be: (6) where DO l0 is the initial dissolved oxygen in the liquid surrounding the PFP droplets and DO l is the predicted dissolved oxygen in the surrounding liquid in equilibrium with phasetransitioned PFP droplets after ultrasound exposure.…”

“…Submicron-sized perfluorocarbon droplets extravasate from leaky tumor vessels, undergo ADV, and provide contrast on ultrasound images of cancerous tissue [1,2]. ADV-induced microbubbles generated from micron-sized droplets have also been investigated as point targets for phase aberration correction [3][4][5]. Further, contrastenhanced photoacoustic images have been created using ADV to trigger the localized release of cardiogreen dye from a perfluoropentane (PFP) double emulsion [6].…”

A super‐resolution ultrasound method for brain vascular mapping

“…19,20 With our hemispherical array, and using passive beamforming, we can optimize the imaging resolution for a given frequency and achieve sufficient SNR to image single bubbles through a human skullcap. Here we transcranially excite single microbubbles flowing through a tube phantom and generate threedimensional maps of the bubbles, using a bubble-based phase correction technique, similar to those proposed by others for phase correction of the transmit beam, 21,22 but modified to apply to the receive case. The result is a high resolution, transcranial, diffraction limited image of the tube phantom.…”