Thermalacoustic Imaging(TAI)

 Currently, X-ray mammography is the most extensively applied tomography for breast cancer screening and has been reported to be able to significantly reduce the mortality rate since its clinical applications. However, mammography has several drawbacks such as high false-positive and false-negative rates, ionizing radiation, poor accuracy in the presence of glandular tissue (common in younger women), and discomfort due to applied compression.Two other clinically available techniques are magnetic resonance imaging (MRI) and ultrasound imaging. But, they also have limitations. The huge static magnetic field demanded in MRI systems is expensive and requires long scan times. Contrast with conventional ultrasound is poor in soft tissues, making it difficult to reliably separate normal and malignant breast tissues.

The insufficiencies of the current breast cancer imaging technologies have motivated an escalation in interests in developing complementary breast screening methodologies. Microwave-induced thermoacoustic imaging (TAI) based on thermoacoustic (TA) effect is a promising candidate.

In this work, we develop a complete microwave-induced thermoacoustic imaging (TAI) model for potential breast cancer imaging application. Acoustic pressures generated by different breast tissue targets are investigated by finite-difference time-domain (FDTD) simulations of the entire TAI process including the feeding antenna, matching mechanism, fluidic environment, three-dimensional breast model, and acoustic transducer. Simulation results achieve quantitative relationships between the input microwave peak power and the resulting specific absorption rate (SAR) as well as the output acoustic pressure. Microwave frequency dependence of the acoustic signals due to different breast tissues is established across a broadband frequency range (2.3 to 12 GHz), suggesting key advantages of spectroscopic TAI compare to TAI at a single frequency. Reconstructed thermoacoustic images are consistent with the modeling results. This model will contribute to design, optimization and safety evaluation of microwave-induced thermoacoustic imaging and spectroscopy.

(a) Pressures at the sensors on the y axis. Beamformed images in the (b) x-z plane and (c) y-z plane. The actual boundary of the target is marked by white dashed lines.

X. Wang; D.R. Bauer; R. Witte; H. Xin, "Microwave-Induced Thermoacoustic Imaging Model for Potential Breast Cancer Detection," IEEE Transactions on Biomedical Engineering, vol.59, no.10, pp.2782-2791, Oct. 2012

The feasibility of contrast-enhanced thermoacoustic imaging (CETAI) for breast cancer detection is investigated by a systematic computational study using realistic numerical breast phantoms with tumors. Single-walled carbon nanotubes with a nontoxic concentration are applied as the contrast agents to increase the dielectric properties of the breast tumors and enhance their detectability. Complete CETAI models are developed and solved for generated thermoacoustic signals by numerical techniques. Back-projection imaging and differential imaging are performed to visualize the tumors. The presented results bolster the applications of CETAI as a potentially safe, rapid, sensitive, accurate, high-resolution and breast-density-insensitive technology for three-dimensional breast cancer detection.

3-D differential images of the reconstructed tumors for the (a) class 1 phantom, (b) class 2 phantom, (c) class 3 phantom, and (d) class 4 phantom in isometric views. The transparent cyan spheres represent the actual tumors.

X. Wang, T. Qin, R. S. Witte,and H. Xin, "Computational Feasibility Study of Contrast-Enhanced Thermoacoustic Imaging for Breast Cancer Detection Using Realistic Numerical Breast Phantoms," Unpublished..