Noninvasive calibrated tissue temperature estimation using backscattered energy of acoustic harmonics

Elyas Shaswary; Hisham Assi; Celina Yang; J Carl Kumaradas; Michael C Kolios; Gholam Peyman; Jahan Tavakkoli

doi:10.1016/j.ultras.2021.106406

Noninvasive calibrated tissue temperature estimation using backscattered energy of acoustic harmonics

Ultrasonics. 2021 Jul:114:106406. doi: 10.1016/j.ultras.2021.106406. Epub 2021 Mar 2.

Authors

Elyas Shaswary¹, Hisham Assi¹, Celina Yang¹, J Carl Kumaradas¹, Michael C Kolios², Gholam Peyman³, Jahan Tavakkoli⁴

Affiliations

¹ Department of Physics, Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada.
² Department of Physics, Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada; Institute for Biomedical Engineering, Science and Technology (iBEST), Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Ontario, Canada.
³ Basic Medical Science, University of Arizona, Phoenix Campus, AZ, USA; College of Optical Sciences, University of Arizona, Tucson Campus, AZ, USA; Cancer Rx Inc., Sun City, AZ, USA.
⁴ Department of Physics, Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada; Institute for Biomedical Engineering, Science and Technology (iBEST), Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Ontario, Canada. Electronic address: jtavakkoli@ryerson.ca.

PMID: 33691235
DOI: 10.1016/j.ultras.2021.106406

Abstract

Purpose: A real-time and non-invasive thermometry technique is essential in thermal therapies to monitor and control the treatment. Ultrasound is an attractive thermometry modality due to its relatively high sensitivity to change in temperature and fast data acquisition and processing capabilities. A temperature-sensitive acoustic parameter is required for ultrasound thermometry in order to track the changes in that parameter during the treatment. Currently, the main ultrasound thermometry methods are based on variation in the attenuation coefficient, the change in backscattered energy of the signal (CBE), the backscattered radio-frequency (RF) echo-shift due to change in the speed of sound and thermal expansion of the medium, and change in the amplitudes of the acoustic harmonics. In this work, an ultrasound thermometry method based on second harmonic CBE (CBE_h2) and combined fundamental and second harmonic CBE (CBE_comb) is used to produce 2D temperature maps, detect localized heated region generated by low intensity focused ultrasound (LIFU), and control temperature in the heated region.

Materials and methods: Ex vivo pork muscle tissue samples were exposed to localized LIFU heating source and 2D temperature maps were produced from the RF data acquired by a 4.2 MHz linear array probe using a Verasonics Vantage™ ultrasound scanner (Verasonics Inc., Redmond, WA) after the exposure. Calibrated needle thermocouples were also placed in the ex vivo tissue sample close to the LIFU focal zone for temperature calibration purposes. The estimated temperature maps were the established echo-shift technique. A tissue motion compensation algorithm was also used to reduce the susceptibility to motion artifacts.

Results: 2D temperature maps were generated using CBE of acoustic harmonic and echo-shift techniques. The results show a direct correlation between the CBE of acoustic harmonics and focal tissue temperature for a range of temperatures from 37 °C (baseline) to 47 °C.

Conclusions: The findings of this study show that the CBE of acoustic harmonics technique can be used to noninvasively estimate temperature change in tissue in the hyperthermia temperature range.

Keywords: Acoustic harmonics; Backscattered energy; Noninvasive ultrasound thermometry; Nonlinear ultrasound; Temperature estimation.