Multi-parametric monitoring and assessment of high-intensity focused ultrasound (HIFU) boiling by harmonic motion imaging for focused ultrasound (HMIFU): anex vivofeasibility study

Abstract

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a recently developed high-intensity focused ultrasound (HIFU) treatment monitoring method with feasibilities demonstrated in vitro and in vivo. Here, a multi-parametric study is performed to investigate both elastic and acoustics-independent viscoelastic tissue changes using the Harmonic Motion Imaging (HMI) displacement, axial compressive strain and change in relative phase-shift during high energy HIFU treatment with tissue boiling. Forty three (n=43) thermal lesions were formed in ex vivo canine liver specimens (n=28). Two dimensional (2D) transverse HMI displacement maps were also obtained before and after lesion formation. The same method was repeated in 10-s, 20-s and 30-s HIFU durations at three different acoustic powers of 8, 10, and 11W, which were selected and verified as treatment parameters capable of inducing boiling using both thermocouple and Passive Cavitation Detection (PCD) measurements. Although a steady decrease in the displacement, compressive strain, and relative change in the focal phase shift (Δφ) were obtained in numerous cases, indicating an overall increase in relative stiffness, the study outcomes also showed that during boiling, a reverse lesion-to-background displacement contrast was detected, indicating potential change in tissue absorption, geometrical change and/or, mechanical gelatification or pulverization. Following treatment, corresponding 2D HMI displacement images of the thermal lesions also mapped consistent discrepancy in the lesion-to-background displacement contrast. Despite unpredictable changes in acoustic properties with boiling, the relative change in phase shift showed a consistent decrease, indicating its robustness to monitor biomechanical properties independent of the acoustic property change throughout the HIFU treatment. In addition, the 2D HMI displacement images confirmed and indicated the increase in the thermal lesion size with treatment duration, which was validated against pathology. In conclusion, multi-parametric HMIFU was shown capable of monitoring and mapping tissue viscoelastic response changes during and after HIFU boiling, some of which were independent of the acoustic parameter changes.

Sparse Matrix Beamforming and Image Reconstruction for 2-D HIFU Monitoring Using Harmonic Motion Imaging for Focused Ultrasound (HMIFU) With In Vitro Validation

“…The displacement profile maps measured across different locations showed a strong consistency, thus validating the reproducibility of our beamforming and motion estimation algorithm and ensuring the performance reliability of the new 2D HMIFU system. Despite the fact that the HMIFU excitation was continuous for 1.2 seconds, tissue heating and the associated changes such as in speed of sound were expected to be negligible within such a short time window and the associated low temperature changes [43]. For monitoring of HIFU treatment studies, the focal excitation region was also clearly imaged across all the cases, where focal displacement decreased by 40%, 30%, and 33% for each initial feasibility study cases as well as decreased by 45.2±20.8% amongst the reproducibility study cases upon lesion formation with statistical significance (P=0.0003).…”

“…The localized tissue response is monitored continuously from the onset of HIFU treatment and aims to provide the onset of treatment termination to the surgeon based on the change in local tissue stiffness in order to prevent any overtreatment. Several studies have been published in order to investigate the principle in silico [40, 41], as well as feasibilities in vitro [42], ex vivo [43], and in vivo [44] using a 1D [42] and 2D [44] system. However, until now the systems used have required separate acquisition and processing units, where displacement estimation were performed offline in a different hardware unit.…”

High-intensity focused ultrasound monitoring using harmonic motion imaging for focused ultrasound (HMIFU) under boiling or slow denaturation conditions

“…The HMIFU system was comprised of a 4.75 MHz focused Lead Zirconate Titanate (PZT) (outer diameter 80 mm, inner diameter 16.5 mm, focal depth 9 cm) transducer (Riverside Research Institute, New York, NY) for providing HIFU treatment and radiation force based tissue probing with an AM frequency of 25 Hz, and a confocal 7.5 MHz single element pulse-echo transducer (Olympus-NDT, Waltham, MA, U.S.A.) with a diameter of 15 mm and a focal length of 6 cm for simultaneous RF signal acquisition for both imaging tissue displacement and cavitation detection at a pulse repetition frequency (PRF) of 1 kHz. Note that the Compared to our previous HMIFU studies with a limited RF acquisition window [43, 61], we have expanded our 1-D HMIFU system such that RF signals can now be acquired and stored continuously throughout the entire treatment window, which allows us to further investigate the tissue property change in detail. The HMIFU system was mounted onto, and controlled by, a 3D translational system (Velmex Inc., Bloomfield, NY, U.S.A.) for targeting purpose (Figure 1).…”

“…In addition to acoustic emission monitoring, focal temperature measurements were also applied in tandem in order to provide quantitative information regarding the thermal property change and the delivered thermal dosage. Therefore, the present study is a continuing effort from our previous work on multi-parametric assessment of HMIFU [61], where we demonstrated only the feasibility of HMIFU in monitoring HIFU treatment with presence of boiling. In this study, our objective is to further investigate the performance of HMIFU monitoring under slow denaturation (low treatment power and long treatment duration) as well as boiling (high treatment power and short treatment duration) regime based on the changes in focal displacement, focal displacement contrast, phase shift (Δϕ), and correlation coefficients during HIFU.…”

High intensity focused ultrasound (HIFU) focal spot localization using harmonic motion imaging (HMI)

“…Based on this relationship, the −3 dB and −6 dB focal zones were computed based on the maximum peak-topeak displacement amplitude in the same trial. In in vitro liver experiments, a 2-min tissue ablation was performed to generate a lesion in the targeted area as in our previous studies (Hou et al ., 2014a). Lesion locations were compared with the corresponding focal spot localization results.…”