Seminar: Backscatter Characterization of Nanobubbles Using Ultra High Frequency Ultrasound and Acoustic Flow Cytometry

Student: Matthew Santilli

Supervisor: Dr. Michael Kolios

Abstract

Contrast agents are a tool used in the field of medical imaging for the enhancement of contrast between internal structures. In Contrast Enhanced Ultrasound (CEUS) Imaging, microbubbles (MBs) are commonly used as contrast agents. Their gas core and shell properties give MBs the required nonlinear US scattering characteristics and acoustic impedance mismatch, to create CEUS images. In CEUS, techniques, such as Amplitude Modulation (AM), that depend on the nonlinear scattering of the contrast agents are used. MBs are intravascular contrast agents and therefore do not extravasate into tissue. In applications such as, molecular imaging this could be a limitation. As a result, nanobubbles (NBs) have gained research interest in the field of US imaging as their size allows for extravasation into surrounding tissue. Unlike MBs, the nonlinear scattering characteristics of NBs is not as well understood. Therefore, this study proposes the use of flow cytometry in combination with a single element high frequency ultrasound transducer to collect backscatter data of NBs and of NBs internalized in a Prostate Cancer cell line (PC3). In addition to this, an AM technique will be employed, whereby interleaved pulses with different pressures are sent from the transducer. A novel acoustic flow cytometer (AFC) will be used to detect scattering at different pressures. Backscatter data will first be collected for 4.5 μm polystyrene microspheres to validate the AFC, as they are linear scatterers, and their scattering characteristics are well documented. Using the same system, backscatter data at different incident pressures will then be collected for NBs and NBs internalized in PC3 cells. A better understanding of the nonlinear scattering of NBs could lead to the design of better CEUS pulse sequences.