Estimating the concentration of ultrasound contrast agents using ultrasonic backscatter in vitro

Ultrasound contrast agents (UCAs) are tiny microbubbles used clinically to enhance the contrast of B-mode images. Recently, UCAs have been combined with therapeutic ultrasound techniques to increase their effectiveness. These therapeutic techniques often require high concentrations of UCAs at varying pressure amplitudes, which increases the risk of adverse bioeffects. Therefore, the quantification of UCA concentration at a target location inside the body is necessary to reduce the risk of unwanted bioeffects and to determine the in vivo concentration of UCAs as a result of their injection. In this work, a method for extracting estimates of UCA concentration using backscatter coefficients (BSCs) was developed and verified in vitro. Experiments to verify the method were performed with both UCAs and glass bead microspheres in degassed water using a beaker setup and a flow system setup. Experimentally obtained estimates of the BSC were fit to ultrasound scattering models to extract concentration estimates of either the UCAs or the glass beads. The fitting was accomplished with a Levenberg-Marquardt regression algorithm, which resulted in UCA concentration and size estimates. In order to verify the estimates of UCA concentration, a sample of the UCA and degassed water mixture was extracted after the ultrasonic data were acquired, and the sample was inserted into a hemacytometer. Concentration estimates with the hemacytometer were acquired by counting the number of UCAs in a known volume of the mixture. Initial experiments with the flow system and UCAs in porcine whole blood were also conducted. The experimental BSCs of the blood by itself were compared to a calculated theoretical BSC for blood, and the experimental BSCs of the UCAs in blood were compared to experimental BSC estimates of UCAs in water. A summary of the results is as follows. First, the estimated concentration of glass beads was within 4% of the concentration of beads flowing through the experimental flow chamber. Next, an optimal peak rarefactional pressure (PRP) amplitude range of 140-390 kPa was determined for extracting UCA concentration estimates within one standard deviation of the hemacytometer based estimates and with the UCA scattering model that was used. Finally, future investigation must focus on improving the quantification technique with UCAs in blood to be able to extract accurate concentration estimates of UCAs in blood.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Leithem, Scott M.

Contributors dc:contributor

• Oelze, Michael L.

• ultrasound contrast agents
• ultrasonic backscatter
• quantitative ultrasound

Statement dc:rights

• Copyright 2011 Scott M. Leithem

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/26264

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/26264