Ho-taik Lee

Optimal patterns for sequentially multiple focusing in high intensity focused ultrasound and their application to thermal dose

The purpose of this study is to propose a new method for multiple-focus generation to shorten overall treatment time as well as to avoid the formation of high intensity regions outside the target volume. A numerical simulation of the acoustic fields produced by a 1017-element spherical-section ultrasound phased array transducer operating at a frequency of 1.0MHz with 16 cm radius of curvature is performed for the proposed multiple-focus generation. The total foci are partitioned into the several patterns because multiple focusing generally gives rise to the grating lobes outside of the three dimensional region of interest even if applying the optimization of intensity gain in determining the phases and amplitudes of the excitation source vector. The optimization problem is repeatedly formulated in term of the focal points until the multiple-focus patterns cover all the focal points. Genetic algorithm is used for selecting the patterns without the grating lobes. The obtained set of multiple-focus patterns ...

Extended Lifetime In Vivo Pulse Stimulated Ultrasound Imaging

An on-demand long-lived ultrasound contrast agent that can be activated with single pulse stimulated imaging (SPSI) has been developed using hard shell liquid perfluoropentane filled silica 500-nm nanoparticles for tumor ultrasound imaging. SPSI was tested on LnCAP prostate tumor models in mice; tumor localization was observed after intravenous (IV) injection of the contrast agent. Consistent with enhanced permeability and retention, the silica nanoparticles displayed an extended imaging lifetime of 3.3±1 days (mean±standard deviation). With added tumor specific folate functionalization, the useful lifetime was extended to 12 ± 2 days; in contrast to ligand-based tumor targeting, the effect of the ligands in this application is enhanced nanoparticle retention by the tumor. This paper demonstrates for the first time that IV injected functionalized silica contrast agents can be imaged with an in vivo lifetime ~500 times longer than current microbubble-based contrast agents. Such functionalized long-lived contrast agents may lead to new applications in tumor monitoring and therapy.

Design of a sparse sub-array for focused ultrasound surgery of large tumors

High Intensity Focused Ultrasound (HIFU) has gained considerable interest for clinical applications in recent decades due to its noninvasive characteristics. However current HIFU systems have limitations due to treatment times. Specifically it takes about two to three hours for the treatment of large tumors such as uterine fibroids. Optimal treatment with reduced time and costs as well as enhanced safety need fundamental innovation in HIFU technologies like transducer architecture and beam focusing to enable fast ablation of large tumors. The ultimate purpose of this research is the evaluation of the feasibility of rapid HIFU treatment of large-sized tumors. To enable this, new multi-element HIFU transducer architecture, which can generate multiple foci simultaneously with minimal grating lobes, has been designed and evaluated. Adopting the proposed transducer architecture provides a 70% reduction of RF driving channels but retains similar sonication effect with the full array. This might reduce the number of RF driving channels and cut down the cost.