Development of an ultrasonic nonlinear frequency compounding method with applications in tissue thermometry

Abstract

Frequency compounding is an ultrasound imaging technique used to improve signal-to-noise ratio (SNR). In this work, a nonlinear frequency compounding (NLFC) method was introduced, and its application in noninvasive tissue thermometry investigated. The NLFC method was used to produce two-dimensional maps of the temperature sensitive change in backscattered energy of acoustic harmonics (hCBE), during heating of ex vivo porcine tissue with a low intensity focused ultrasound transducer. A hCBE-to-temperature calibration was performed, and temperature maps produced and compared with a theoretical COMSOL based model. Last, a comparative study of the NLFC and previously used nonlinear single frequency (NLSF) methods was completed to quantify the improvement in SNR of the produced hCBE maps. When using the NLFC method, a SNR of 6.06 ± 1.28 was found. SNR values of 3.70 ± 0.53 and 4.38 ± 0.84 were found while using central frequencies of 4.31 and 5.43 MHz, respectively, with the NLSF method. This translates to an improvement of (64.13 ± 4.16)% over the 4.31 MHz NLSF, and (38.72 ± 2.97)% over the 5.43 MHz NLSF methods overall. It was concluded that the NLFC method can produce hCBE and temperature maps with superior image SNR over the NLSF method.

Ultrasound‐mediated nano‐sized drug delivery systems for cancer treatment: Multi‐scale and multi‐physics computational modeling

“…The sharpness of such necrosis in tissue is comparable to the surgeon's sharp incision; hence, it is also called FUS surgery. However, precise image‐based therapeutic planning and accurate treatment guidance and monitoring are necessary for the safe and effective use of FUS (T. Hornsby, Shaswary, et al, 2021; Lynn et al, 1942).…”

Monitoring Focused Ultrasound Thermal Therapy Using Synthetic Aperture Ultrasound Imaging With Decorrelated Compounding

“…For clinical guidance, a robust thermometry method is required to predict the tissue temperature, ideally with a temperature precision better than ±1°C [34]. The thermometry method must provide accurate and precise temperature estimations for hyperthermia treatments, as a 1 °C can change the treatment time by a factor of 2 to maintain the same biological effect [34], and an increase in a few degrees can result in thermal ablation instead of tissue heating [57].…”

“…The backscattered RF echo shift technique is based on the displacement of both tissue and speckle in response to heating [34]. Temperature dependent changes in the speed of sound causes apparent shifts in scatterer location, while thermal expansion of tissue induces actual changes in scatterer position [57]. These echo shifts are assumed to have a linear relationship with temperature changes up to 10 °C to allow for thermometry [52].…”

“…In a recent work, Shaswary et al [55] found that the CBE using the second harmonic signal, as well as a combination of the fundamental and the second harmonic signal, had direct correlations with tissue temperature and can be used to control tissue temperatures during hyperthermia treatments. Additionally, Hornsby et al [57] developed a non-linear frequency compounding (NLFC) technique to improve the SNR of B-mode images and CBE maps. Using this method, the fundamental and second harmonic frequencies corresponding to two distinct transmit frequencies were compounded, yielding a temperature precision of ±0.8 °C in temperature estimations [57].…”

“…Additionally, Hornsby et al [57] developed a non-linear frequency compounding (NLFC) technique to improve the SNR of B-mode images and CBE maps. Using this method, the fundamental and second harmonic frequencies corresponding to two distinct transmit frequencies were compounded, yielding a temperature precision of ±0.8 °C in temperature estimations [57].…”