Determining temperature distribution in tissue in the focal plane of the high (>100 W/cm(2)) intensity focused ultrasound beam using phase shift of ultrasound echoes

Piotr Karwat; Tamara Kujawska; Peter A Lewin; Wojciech Secomski; Barbara Gambin; Jerzy Litniewski

doi:10.1016/j.ultras.2015.10.002

Determining temperature distribution in tissue in the focal plane of the high (>100 W/cm(2)) intensity focused ultrasound beam using phase shift of ultrasound echoes

Ultrasonics. 2016 Feb:65:211-9. doi: 10.1016/j.ultras.2015.10.002. Epub 2015 Oct 13.

Authors

Piotr Karwat¹, Tamara Kujawska², Peter A Lewin³, Wojciech Secomski², Barbara Gambin², Jerzy Litniewski²

Affiliations

¹ Department of Ultrasound, Institute of Fundamental Technological Research, Polish Academy of Sciences, Pawińskiego 5b, 02-106 Warsaw, Poland. Electronic address: pkarwat@ippt.pan.pl.
² Department of Ultrasound, Institute of Fundamental Technological Research, Polish Academy of Sciences, Pawińskiego 5b, 02-106 Warsaw, Poland.
³ Biomedical Ultrasound Research and Education Center, Drexel University, Bossone 7 701, 3141 Chestnut Street, Philadelphia, PA 19104, USA.

PMID: 26498063
DOI: 10.1016/j.ultras.2015.10.002

Abstract

In therapeutic applications of High Intensity Focused Ultrasound (HIFU) the guidance of the HIFU beam and especially its focal plane is of crucial importance. This guidance is needed to appropriately target the focal plane and hence the whole focal volume inside the tumor tissue prior to thermo-ablative treatment and beginning of tissue necrosis. This is currently done using Magnetic Resonance Imaging that is relatively expensive. In this study an ultrasound method, which calculates the variations of speed of sound in the locally heated tissue volume by analyzing the phase shifts of echo-signals received by an ultrasound scanner from this very volume is presented. To improve spatial resolution of B-mode imaging and minimize the uncertainty of temperature estimation the acoustic signals were transmitted and received by 8 MHz linear phased array employing Synthetic Transmit Aperture (STA) technique. Initially, the validity of the algorithm developed was verified experimentally in a tissue-mimicking phantom heated from 20.6 to 48.6 °C. Subsequently, the method was tested using a pork loin sample heated locally by a 2 MHz pulsed HIFU beam with focal intensity ISATA of 129 W/cm(2). The temperature calibration of 2D maps of changes in the sound velocity induced by heating was performed by comparison of the algorithm-determined changes in the sound velocity with the temperatures measured by thermocouples located in the heated tissue volume. The method developed enabled ultrasound temperature imaging of the heated tissue volume from the very inception of heating with the contrast-to-noise ratio of 3.5-12 dB in the temperature range 21-56 °C. Concurrently performed, conventional B-mode imaging revealed CNR close to zero dB until the temperature reached 50 °C causing necrosis. The data presented suggest that the proposed method could offer an alternative to MRI-guided temperature imaging for prediction of the location and extent of the thermal lesion prior to applying the final HIFU treatment.

Keywords: Echo phase shift; HIFU; Ultrasonic temperature imaging; Velocity image contrast.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Body Temperature / physiology*
Body Temperature / radiation effects
Computer Simulation
High-Energy Shock Waves
High-Intensity Focused Ultrasound Ablation / methods*
Image Interpretation, Computer-Assisted / methods
In Vitro Techniques
Models, Biological
Muscle, Skeletal / diagnostic imaging*
Muscle, Skeletal / physiology*
Muscle, Skeletal / radiation effects
Phantoms, Imaging
Reproducibility of Results
Scattering, Radiation
Sensitivity and Specificity
Swine
Thermography / methods*
Ultrasonography / methods*