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Optical and acoustical interrogation of submicron contrast agents.

Authors
Type
Published Article
Journal
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control
0885-3010
Publisher
Institute of Electrical and Electronics Engineers
Publication Date
Volume
49
Issue
12
Pages
1641–1651
Identifiers
PMID: 12546146
Source
Medline

Abstract

Unlike conventional ultrasound contrast agents with a diameter of several microns, in this paper we explore the use of submicron contrast agents for the detection and localization of lymph nodes. The submicron agents are gas-filled, double-walled microspheres that rupture when exposed to ultrasound energy at megahertz frequencies. In this study, three experimental systems are combined with model predictions to assist in understanding the response of these unique agents to a range of signal transmission parameters. Optical experimental results for each agent delineate the relative expansion as a function of acoustical peak negative pressure, pulse length, and center frequency. The optical images demonstrate an order of magnitude expansion in radius during the pulse rarefaction, in which the expansion magnitude is dependent on the transmitted pressure and frequency. Simulations using a modified Rayleigh-Plesset model predict an increasing relative expansion for the microbubbles (initial bubble radius ranging from 0.3-1.3 microm) with increasing pressure and decreasing initial radius. Acoustically recorded frequency spectra reveal the presence of harmonics for a range of transmitted pulses. In addition, in-vivo results from a normal canine model demonstrate marked contrast enhancement of first order lymph nodes. We hope to offer an alternative to present intra-operative procedures for sentinel node detection.

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