Ultrasound thermal mapping based on a hybrid method combining cross-correlation and zero-crossing tracking

Abstract

A hybrid method for estimating temperature with spatial mapping using diagnostic ultrasound, based on detection of echo shifts from tissue undergoing thermal treatment, is proposed. Cross-correlation and zero-crossing tracking are two conventional algorithms used for detecting echo shifts, but their practical applications are limited. The proposed hybrid method combines the advantages of both algorithms with improved accuracy in temperature estimation. In vitro experiments were performed on porcine muscle for preliminary validation and temperature calibration. In addition, thermal mapping of rabbit thigh muscle in vivo during high-intensity focused ultrasound heating was conducted. Results from the in vitro experiments indicated that the difference between the estimated temperature change by the proposed hybrid method and the actual temperature change measured by the thermocouple was generally less than 1 °C when the increase in temperature due to heating was less than 10 °C. For the in vivo study, the area predicted to experience the highest temperature coincided well with the focal point of the high-intensity focused ultrasound transducer. The computational efficiency of the hybrid algorithm was similar to that of the fast cross-correlation algorithm, but with an improved accuracy. The proposed hybrid method could provide an alternative means for non-invasive monitoring of limited temperature changes during hyperthermia therapy.

Thermometry and ablation monitoring with ultrasound

“…Some continued work on temperature estimation using frequency shifts in the spectral domain due to thermal strain has been reported (92, 93). Frequency domain estimation of pulse-echo time shifts has also been reported using a zero-crossing detector (94–96). Recently, axial-shear strain elastograms have been proposed as an improvement to traditional axial-strain elastograms in thermal strain imaging, especially when cavitation bubbles are present (97).…”

A survey of ultrasound elastography approaches to percutaneous ablation monitoring

“…88 For the validation of ultrasound thermometry, the use of thermocouples to measure temperatures at different locations in tissue is the most frequently used method. 14,15,17,39 The main limitation is that a practical temperature map of tissue is not available for comparison with ultrasound temperature imaging. To clarify the correlation between ultrasound temperature imaging and the practical temperature distribution in tissue, Geng et al 40 designed an experimental setup to compare ultrasound temperature imaging with infrared imaging, which is used as a standard temperature map.…”

“…7–9 Therefore, many ultrasound-based thermal ablation monitoring techniques have been investigated. 6,10…”

“…88 Changes in sound speed and thermal expansion with temperature cause echo shifts in the backscattered signal. [10][11][12][13][14][15][16][17][18][19][20][21][22] Changes in ultrasound attenuation coefficient with temperature are explored for temperature estimation. [23][24][25] Changes in backscattered energy (CBE) with temperature are primarily caused by thermal effects on the backscatter coefficient.…”

Thermoacoustic Lensing in Ultrasound Imaging of Nonechogenic Tissue During High-intensity Focused Ultrasound Exposure

“…12 Researchers have combined speckle tracking with zero crossing detection to improve the computational efficiency. 13 The accuracy of temperature estimation can be improved by using an adaptive coefficient for the relation between temperature change and echo time shift. 14 An adaptive approach considers a nonlinear temperature coefficient for the speed of sound and thermal expansion of the tissue.…”