Multiphysics Medical Imaging

Note: Please view the desktop site in order to see images.

Our work in multi-physics imaging focuses on developing novel techniques that allow us to push the limits of conventional approaches in a variety of applications.

We work on detection and imaging using the thermoacoustic (TA) effect, in which the target being imaged generates acoustic waves due to thermal expansion upon the absorption of microwave energy. Microwave-induced TA combines the contrast of microwave imaging, which is based on the dielectric properties of different materials, with the high resolution of ultrasound detection. Unlike photoacoustic imaging, which is best suitable for superficial applications, TA has the potential to achieve penetration depths greater than 5 cm, even in dispersive tissue.

Illustration of the thermoacoustic effect.

Conventional microwave-induced TA uses a high-power RF source to generate a short pulse – necessitating large and expensive equipment and suggesting possible safety concerns. Our research instead focuses on continuous-wave (CW) approaches utilizing lower peak powers. We have demonstrated coherent frequency domain signaling in the form of SFCW and FMCW [1-3] approaches. Coherent processing is usually used to detect weak signals and improve SNR by exploiting the information in the frequency domain. Our FMCW approach implements a matched-filtering receiver to achieve significant SNR improvement while also reducing the peak power requirement by exploiting increased pulse durations. With recent improvements in III-V semiconductor RF power amplifiers, our CW approach could potentially allow for low-cost, portable (or even wearable) TA imaging systems.

(a) Imaging sample, (b) matched filtering image, (c) measured signal after matched filtering, (d) reconstructed image using FD-SAR algorithm.

In addition to frequency domain EM excitation techniques, we also explore the use of beamforming to further reduce the peak power of the individual microwave applicators [4-5]. By applying proper amplitudes and phases across the applicators, we have the ability to focus the microwave energy to a desired location within the imaged sample. This provides a more efficient link and reduces the power absorbed at the point of applicator contact. In the example of breast imaging, this technique reduces the skin heating while providing sufficient power at depth to the location of interest with steering capability. Combining the abovementioned frequency domain signaling with this beamforming technique could further reduce the peak power and allow for an integrated wearable imager.

Left: Wearable beamforming imager concept, Center: Simulation setup of beamforming, Right: Simulated microwave absorption profile focused at depth.

We have also extended our system to be able to image the first few millimeters of tissue (with applications in imaging superficial veins) by using electrical structures that concentrate pulsed microwave excitation near the dermis, combined with conventional antennas that radiate CW deeper into the tissue. With this approach, we have demonstrated proof-of-concept TA imaging of microcapillaries and plant vasculature using substantially reduced pulsed-excitation power compared to the state of the art [6-7].

Left: Application of TA imaging of microcapillaries, Right: TA imaging of an earthworm and a scallion plant with xylem.

Another avenue that we explore for applications of thermoacoustic imaging is in non-invasive remote temperature monitoring [8]. By exploiting the temperature dependent parameters of the generated pressure upon microwave absorption, we estimate the temperature on a millimeter scale of imaged samples. This technology is widely desirable specifically in the application of non-invasive thermotherapies or other ablative procedures. With a high-resolution temperature image, TA temperature monitoring could be integrated with the therapy system to allow for real-time feedback to adjust the incident power.

Left: Calibration curve derived from temperature dependent parameters of generated pressure, Right: (a) Red tube temperature variant, (b) Baseline image, (c) Temperature monitoring images.

Our other projects in this area include: using microwave-induced TA to non-invasively extract spectroscopic information from human tissue [9]; using a fast iterative reconstruction algorithm to speed up TA imaging [10]; using an interferogram-based machine learning algorithm to improve beast tumor classification using TA signals [11]; and using the magnetoacoustic effect, in which electric currents interact with magnetic fields to produce acoustic waves via the Lorentz force, to demonstrate detection and imaging [12].

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

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

[3] 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, pp. 2607-2616, July 2017.

[4] H. Nan, S. Liu, N. Dolatsha and A. Arbabian, "A 16-Element Wideband Microwave Applicator for Breast Cancer Detection Using Thermoacoustic Imaging," Progress in Electromagnetics Research Symposium (PIERS) Proceedings, 243-247, July 6-9, Prague, 2015.

[5] 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.

[6] M. Aliroteh and A. Arbabian, "Microwave-Induced Thermoacoustic Imaging of Subcutaneous Vasculature with Near-Field RF Excitation,” accepted to IEEE Trans. Microw. Theory Tech.

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

[8] H. Nan, A. Fitzpatrick, K. Wang and A. Arbabian, "Non-Invasive Remote Temperature Monitoring Using Microwave-Induced Thermoacoustic Imaging," 2019 International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Berlin, July 2019.

[9] S. Liu, H. Nan, N. Dolatsha, and A. Arbabian, "Extracting Dielectric Spectroscopic Properties from Microwave-Induced Thermoacoustic Signals," Proc. 2016 Int. Conf. IEEE Eng. Med. Biol. Soc., Orlando, FL, 2016, pp. 3618-3621.

[10] 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.

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

[12] 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.