Publication Date

Summer 2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical, Chemical & Materials Engineering

Advisor

Sang-Joon J. Lee

Keywords

ablation, cancer treatment, high-intensity focused ultrasound, tissue-mimicking material

Subject Areas

Biomedical engineering

Abstract

Local blood flow near a high-intensity focused ultrasound (HIFU) target has been shown to decrease ablation effectiveness and predictability, creating a barrier to clinical use for breast cancer treatment. This study investigated the effects of compression on HIFU ablation of a perfused tissue-mimicking material. Gellan gum-based phantoms, with thermal and acoustic properties similar to those of soft tissue, were ablated with a 1.13 MHz HIFU transducer while being subjected to varying levels of external compression. Phantoms were designed with an embedded 6 mm diameter vessel meant to mimic a thermally significant blood vessel near a breast tumor. The internal temperature profile was measured using T-type thin-wire thermocouples embedded in the phantom along the transverse axis. The temperature distributions on opposing lateral sides of the HIFU focal point were measured to determine the effects of compression on heating symmetry. After heating with 30 W for 30 s, the maximum discrepancy between a pair of thermocouples located 2 mm left and right of centerline, respectively, was 40 °C. This maximum discrepancy was observed at a fluid flow rate of 38 mL/min. With applied compression reducing flow to between 28 mL/min and 25 mL/min, the discrepancy between left and right thermocouples was reduced to as low as 5.7 °C. Numerical predictions revealed an agreement with experimental results in the reduction of heating asymmetry as the flow rate decreased from 40 mL/min to 20 mL/min.

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