ThermoAcoustic Imaging for Biomedical Applications

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​​Our research focuses on hybrid electromagnetic–acoustic imaging techniques that convert electromagnetic energy into acoustic signals for high-resolution, deep-tissue biomedical imaging. Two complementary modalities are central to this work: thermoacoustic (TA) and magnetoacoustic (MA) imaging. In TA imaging, absorbed microwave energy causes rapid thermoelastic expansion, generating acoustic waves whose amplitude and timing reveal dielectric contrasts within biological tissue [3–11]. In MA imaging, Lorentz forces arise when induced electrical currents interact with an external magnetic field, producing acoustic waves that encode tissue conductivity [14]. Together, these methods bridge the strong contrast mechanisms of electromagnetic sensing with the spatial precision of ultrasound, enabling non-invasive, deep-penetration imaging well beyond the reach of optical photoacoustics.

Traditional TA imaging systems rely on high-power pulsed RF excitation, which requires bulky and expensive equipment and raises safety concerns. Our group has pioneered continuous-wave (CW) excitation schemes [3–5] that dramatically lower peak power while preserving high sensitivity. By employing stepped-frequency continuous-wave (SFCW) and frequency-modulated continuous-wave (FMCW) signaling, we exploit coherent frequency-domain processing and matched filtering to improve signal-to-noise ratio (SNR) without sacrificing resolution or depth. Building on recent advances in III–V semiconductor RF power amplifiers, we demonstrated multi-watt-level silicon PA architectures for portable and wearable TA imaging [1–2], marking a major step toward compact, low-cost diagnostic and biometric imaging systems.

To further reduce power requirements while enhancing spatial precision, we integrate beamforming-based microwave excitation that dynamically shapes the electromagnetic field across applicators [6–7]. By precisely controlling amplitude and phase, microwave energy can be focused deep within tissue to increase imaging efficiency and reduce surface heating. In breast cancer screening, for example, this approach enables targeted energy delivery to internal lesions while minimizing exposure at the skin. The combination of coherent CW signaling and dynamic beamforming allows for steerable, high-SNR TA imaging systems with both deep and superficial visualization capability—an essential step toward handheld and wearable microwave imaging platforms.

Beyond deep-tissue imaging, our work has demonstrated near-field TA imaging of microvasculature and plant structures using concentrated microwave excitation near the dermis [8–9], achieving high resolution with significantly reduced pulsed power compared to traditional methods. Building upon this foundation, we have extended TA principles to non-invasive temperature mapping for real-time feedback in thermal therapies [10], dielectric spectroscopy extraction from TA signals [11], and fast iterative image reconstruction algorithms that accelerate TA processing [12]. In parallel, our studies in magnetoacoustic imaging [14] utilize Lorentz-force coupling to sense electrical conductivity, offering a complementary diagnostic modality. Collectively, these efforts establish a unified framework for multi-physics electromagnetic–acoustic imaging, advancing the frontier of non-invasive biomedical diagnostics and functional tissue characterization.

Publications

[1] C. Sutardja, A. Singhvi, A. Fitzpatrick, A. Cathelin, and A. Arbabian, “Multi-Watt-Level 4.9-GHz Silicon Power Amplifier for Portable Thermoacoustic Imaging,” IEEE J. Solid-State Circuits, vol. 57, no. 5, pp. 1421–1431, May 2022.

[2] C. Sutardja, A. Cathelin, and A. Arbabian, “Portable Thermoacoustic Imaging for Biometric Authentication Using a 37.3 dBm Peak Psat 4.9 GHz Power Amplifier in 55nm BiCMOS,” IEEE RFIC Symposium, pp. 7–10, June 2021.

[3] H. Nan and A. Arbabian, “Stepped-Frequency Continuous-Wave Microwave-Induced Thermoacoustic Imaging,” Appl. Phys. Lett., vol. 104, no. 22, 224104, 2014.

[4] H. Nan and A. Arbabian, “Coherent Frequency-Domain Microwave-Induced Thermoacoustic Imaging,” Proc. IEEE Int. Microwave Symp., Tampa, FL, 2014.

[5] H. Nan and A. Arbabian, “Peak-Power-Limited Frequency-Domain Microwave-Induced Thermoacoustic Imaging for Handheld Diagnostic and Screening Tools,” IEEE Trans. Microw. Theory Tech., vol. 65, no. 7, pp. 2607–2616, July 2017.

[6] H. Nan, S. Liu, N. Dolatsha, and A. Arbabian, “A 16-Element Wideband Microwave Applicator for Breast Cancer Detection Using Thermoacoustic Imaging,” PIERS Proceedings, pp. 243–247, Prague, July 2015.

[7] H. Nan, S. Liu, J. G. Buckmaster, and A. Arbabian, “Beamforming Microwave-Induced Thermoacoustic Imaging for Screening Applications,” IEEE Trans. Microw. Theory Tech., vol. 67, no. 1, pp. 464–474, Jan. 2019.

[8] M. S. Aliroteh and A. Arbabian, “Microwave-Induced Thermoacoustic Imaging of Subcutaneous Vasculature with Near-Field RF Excitation,” IEEE Trans. Microw. Theory Tech., vol. 66, no. 1, pp. 577–588, Jan. 2018.

[9] M. S. Aliroteh, H. Nan, and A. Arbabian, “Microwave-Induced Thermoacoustic Tomography for Subcutaneous Vascular Imaging,” Proc. IEEE Ultrason. Symp., Tours, 2016.

[10] H. Nan, A. Fitzpatrick, K. Wang, and A. Arbabian, “Non-Invasive Remote Temperature Monitoring Using Microwave-Induced Thermoacoustic Imaging,” Proc. IEEE Eng. Med. Biol. Soc. (EMBC), Berlin, July 2019.

[11] S. Liu, H. Nan, N. Dolatsha, and A. Arbabian, “Extracting Dielectric Spectroscopic Properties from Microwave-Induced Thermoacoustic Signals,” Proc. IEEE Eng. Med. Biol. Soc. (EMBC), Orlando, FL, 2016, pp. 3618–3621.

[12] H. Nan, B. A. Haghi, M. S. Aliroteh, M. Fallahpour, and A. Arbabian, “Fast Iterative Reconstruction Algorithm for Microwave-Induced Thermoacoustic Imaging,” Proc. Biomed. Circuits Syst. Conf., Shanghai, 2016.

[13] H. Nan, S. Liu, N. Dolatsha, and A. Arbabian, “A 16-Element Wideband Microwave Applicator for Breast Cancer Detection Using Thermoacoustic Imaging,” Progress Electromag. Res. Symp., Prague, 2015, pp. 243–247. Best Student Paper Award.

[14] M. S. Aliroteh, G. C. Scott, and A. Arbabian, “Frequency-Modulated Magneto-Acoustic Detection and Imaging: Challenges, Experimental Procedures, and B-Scan Images,” arXiv preprint arXiv:1602.06931, 2016.

[15] A. Sawaby, M. L. Wang, E. So, J.-C. Chien, H. Nan, B. T. Khuri-Yakub, and A. Arbabian, “A Wireless Implantable Ultrasound Array Receiver for Thermoacoustic Imaging,” 2018 Symp. on VLSI Circuits, Honolulu, HI, June 18-22, 2018.