High-intensity Focused Ultrasound Treatment Monitoring Research Articles

Weighted ultrasound entropy imaging for HIFU ablation monitoring with improved sensitivity and contrast.

Although B-mode imaging has been widely used in ultrasound-guided high-intensity focused ultrasound (HIFU) treatment, challenges remain in improving its quality and sensitivity for monitoring the thermal dose. Recently, quantitative ultrasound (QUS) imaging has been recognized with the potential to better sense the changes in the microstructure of ablated tissues. This study proposed to use a QUS method called weighted ultrasound entropy (WUE) imaging to monitor the HIFU ablation. Based on ex-vivo and in-vivo experiments, WUE images reflecting tissue changes during HIFU treatment under different acoustic power levels (174-308W) were reconstructed with a newly established imaging framework. The performance of the proposed WUE imaging in the monitoring of HIFU treatment was compared with the corresponding B-mode images in terms of their contrast-to-noise ratios (CNRs) between the focal region and the background. It was found that HIFU irradiation with higher power generated larger WUE values in the focal region, and the bright spots grew in size as the acoustic sonication proceeded. Compared with the in-situ B-mode images, the WUE images had higher image quality in indicating lesion formation, with a 39.2%-53.4% improvement in the CNR at different stages. Meanwhile, a correlation (R=0.84) between the damage area estimated in WUE images and that measured from the dissected ex-vivo tissue samples was found. WUE imaging is more sensitive and accurate than B-mode imaging in monitoring HIFU therapy. These findings suggest that WUE imaging could be a promising technique for assisting ultrasound-guided HIFU ablation.

Ultrasound Monitoring of Simultaneous high-intensity focused ultrasound (HIFU) therapy using minimum-peak-sidelobe coded excitation

Bipolar sequences can be readily transmitted by ultrasound (US) pulser hardware with the full driving voltage to boost the echo magnitude in B-mode monitoring of HIFU treatment. In this study, a novel single-transmit bipolar sequence with minimum-peak-sidelobe (MPS) level is developed not only to restore the image quality of US monitoring but also remove acoustic interference from simultaneous HIFU transmission. The proposed MPS code is designed with an equal number of positive and negative bits and the bit duration should be an integer multiple of the period of the HIFU waveform. In addition, different permutations of code sequence are searched in order to obtain the optimal encoding. The received imaging echo is firstly decoded by matched filtering to cancel HIFU interference and to enhance the echo magnitude of US monitoring. Then, Wiener filtering is applied as the second-stage pulse compression to improve the final image quality. Simulations and phantom experiments are performed to compare the single-transmit MPS decoding with conventional two-transmit methods such as pulse-inversion subtraction (PIS) and Golay decoding for their performance in simultaneous US monitoring of HIFU treatment. Results show that the MPS decoding effectively removes HIFU interference even in the presence of tissue motion. The image quality of PIS and Golay decoding, on the other hand, is compromised by the uncancelled HIFU components due to tissue motion. Simultaneous US monitoring of tissue ablation using the proposed MPS decoding has also demonstrated to be feasible in ex-vivo experiments. Compared to the notch filtering that also allows single-transmit HIFU elimination, the MPS decoding is preferrable because it does not suffer from the tradeoff between residual HIFU and speckle deterioration in US monitoring images.

Viscoelastic characterization of HIFU ablation with shear wave by using K-space analysis combined with model-fitting correction method

The viscoelastic properties of tissues can reflect human physiological and pathological conditions. During and after the high-intensity focused ultrasound (HIFU) treatment, measuring the viscoelasticity of HIFU ablated tissue is important for therapy evaluation. Two-dimensional Fourier transform (2DFT) method has been reported to quantify elasticity and viscosity. However, a deviation is induced by under-sampling in practical application. This work proposes an approach based on the convolution theorem and model fitting to solve the finite spatial data problem. A model using the convolution theorem was constructed, and mean-square error (MSE) was calculated to determine the optimal fitting between the model and experimental data. For validation, HIFU therapeutic experiments were conducted in polyacrylamide-bovine serum (BAS) transparent tissue-mimicking phantoms. This approach was used to quantify the viscoelasticity of HIFU ablation and untreated phantoms. Acoustic-radiation-force (ARF) shear wave was generated by the same HIFU therapeutic transducer, and laser Doppler vibrometer (LDV) was used for the high-resolution measurement of shear wave signals. Results suggest that the shear elasticity and viscosity of untreated phantoms are generally smaller than those of HIFU ablation. Thus, the proposed method may be helpful for HIFU treatment monitoring.

Real-Time Photoacoustic Thermometry Combined With Clinical Ultrasound Imaging and High-Intensity Focused Ultrasound.

High-intensity focused ultrasound (HIFU) treatment is a promising non-invasive method for killing or destroying the diseased tissues by locally delivering thermal and mechanical energy without damaging surrounding normal tissues. In HIFU, measuring the temperature at the site of delivery is important for improving therapeutic efficacy, controlling safety, and appropriately planning a treatment. Several researchers have proposed photoacoustic thermometry for monitoring HIFU treatment, but they had many limitations, including the inability to image while the HIFU is on, inability to provide two-dimensional monitoring, and the inability to be used clinically. In this paper, we propose a novel integrated real-time photoacoustic thermometry system for HIFU treatment monitoring. The system provides ultrasound B-mode imaging, photoacoustic structural imaging, and photoacoustic thermometry during HIFU treatment in real-time for both in vitro and in vivo environments, without any interference from the strong therapeutic HIFU waves. We have successfully tested the real-time photoacoustic thermometry by investigating the relationship between the photoacoustic amplitude and the measured temperature with in vitro phantoms and in vivo tumor-bearing mice. The results show the feasibility of a real-time photoacoustic thermometry system for safe and effective monitoring of HIFU treatment.

Real-Time HIFU Treatment Monitoring Using Pulse Inversion Ultrasonic Imaging

Real-time monitoring of high-intensity focused ultrasound (HIFU) surgery is essential for safe and accurate treatment. However, ultrasound imaging is difficult to use for treatment monitoring during HIFU surgery because of the high intensity of the HIFU echoes that are received by an imaging transducer. Here, we propose a real-time HIFU treatment monitoring method based on pulse inversion of imaging ultrasound; an imaging transducer fires ultrasound twice in 0° and 180° phases for one scanline while HIFUs of the same phase are transmitted in synchronization with the ultrasound transmission for imaging. By doing so, HIFU interferences can be eliminated after subtracting the two sets of the signals received by the imaging transducer. This function was implemented in a commercial research ultrasound scanner, and its performance was evaluated using the excised bovine liver. The experimental results demonstrated that the proposed method allowed ultrasound images to clearly show the echogenicity change induced by HIFU in the excised bovine liver. Additionally, it was confirmed that the moving velocity of the organs in the abdomen due to respiration does not affect the performance of the proposed method. Based on the experimental results, we believe that the proposed method can be used for real-time HIFU surgery monitoring that is a pivotal function for maximized treatment efficacy.

High-Intensity Focused Ultrasound Thermal Lesion Detection Using Entropy Imaging of Ultrasound Radio Frequency Signal Time Series.

Background:During the past few decades, high-intensity focused ultrasound (HIFU) modality has been gaining surging interest in various therapeutic applications such as non- or minimally-invasive cancer treatment. Among other attributes, robust and real-time HIFU treatment monitoring and lesion detection have become essential issues for successful clinical acceptance of the modality. More recently, ultrasound radio frequency (RF) time series imaging has been studied by a number of researchers.Materials and Methods:The objective of this study is to investigate the applicability of entropy parameter of RF time series of ultrasound backscattered signals, a. k. a. Entropy imaging, toward HIFU thermal lesion detection. To this end, five fresh ex vivo porcine muscle tissue samples were exposed to HIFU exposures with total acoustic powers ranging from 30 to 110 Watts. The contrast-to-speckle ratio (CSR) values of the entropy images and their corresponding B-mode images of pre-, during- and post-HIFU exposure for each acoustic power were calculated.Results:The novelty of this study is the use of Entropy parameter on ultrasound RF time series for the first time. Statistically significant differences were obtained between the CSR values for the B mode and entropy images at various acoustic powers. In case of 110 Watt, a CSR value 3.4 times higher than B-mode images was accomplished using the proposed method. Furthermore, the proposed method is compared with the scaling parameter of Nakagami imaging and same data which are used in this study.Conclusion:Entropy has the potential for using as an imaging parameter for differentiating lesions in HIFU surgery.

Fast lesion mapping during HIFU treatment using harmonic motion imaging guided focused ultrasound (HMIgFUS) in vitro and in vivo

The successful clinical application of high intensity focused ultrasound (HIFU) ablation depends on reliable monitoring of the lesion formation. Harmonic motion imaging guided focused ultrasound (HMIgFUS) is an ultrasound-based elasticity imaging technique, which monitors HIFU ablation based on the stiffness change of the tissue instead of the echo intensity change in conventional B-mode monitoring, rendering it potentially more sensitive to lesion development. Our group has shown that predicting the lesion location based on the radiation force-excited region is feasible during HMIgFUS. In this study, the feasibility of a fast lesion mapping method is explored to directly monitor the lesion map during HIFU. The harmonic motion imaging (HMI) lesion map was generated by subtracting the reference HMI image from the present HMI peak-to-peak displacement map, as streamed on the computer display. The dimensions of the HMIgFUS lesions were compared against gross pathology. Excellent agreement was found between the lesion depth (r2 = 0.81, slope = 0.90), width (r2 = 0.85, slope = 1.12) and area (r2 = 0.58, slope = 0.75). In vivo feasibility was assessed in a mouse with a pancreatic tumor. These findings demonstrate that HMIgFUS can successfully map thermal lesions and monitor lesion development in real time in vitro and in vivo. The HMIgFUS technique may therefore constitute a novel clinical tool for HIFU treatment monitoring.

Tumor characterization and treatment monitoring of postsurgical human breast specimens using harmonic motion imaging (HMI).

BackgroundHigh-intensity focused ultrasound (HIFU) is a noninvasive technique used in the treatment of early-stage breast cancer and benign tumors. To facilitate its translation to the clinic, there is a need for a simple, cost-effective device that can reliably monitor HIFU treatment. We have developed harmonic motion imaging (HMI), which can be used seamlessly in conjunction with HIFU for tumor ablation monitoring, namely harmonic motion imaging for focused ultrasound (HMIFU). The overall objective of this study was to develop an all ultrasound-based system for real-time imaging and ablation monitoring in the human breast in vivo.MethodsHMI was performed in 36 specimens (19 normal, 15 invasive ductal carcinomas, and 2 fibroadenomas) immediately after surgical removal. The specimens were securely embedded in a tissue-mimicking agar gel matrix and submerged in degassed phosphate-buffered saline to mimic in vivo environment. The HMI setup consisted of a HIFU transducer confocally aligned with an imaging transducer to induce an oscillatory radiation force and estimate the resulting displacement.Results3D HMI displacement maps were reconstructed to represent the relative tissue stiffness in 3D. The average peak-to-peak displacement was found to be significantly different (p = 0.003) between normal breast tissue and invasive ductal carcinoma. There were also significant differences before and after HMIFU ablation in both the normal (53.84 % decrease) and invasive ductal carcinoma (44.69 % decrease) specimens.ConclusionsHMI can be used to map and differentiate relative stiffness in postsurgical normal and pathological breast tissues. HMIFU can also successfully monitor thermal ablations in normal and pathological human breast specimens. This HMI technique may lead to a new clinical tool for breast tumor imaging and HIFU treatment monitoring.

Real-time monitoring of HIFU treatment using pulse inversion

Ultrasound (US) imaging is widely used for the real-time guidance of high-intensity focused ultrasound (HIFU) treatment at a relatively low cost. However, ultrasound image guided HIFU (USgHIFU) is limited in the real-time monitoring of HIFU treatment due to the large amplitude HIFU signals received by the US imaging transducer. The amplitude of the HIFU scattered signal is generally much higher than the amplitude of the pulse-echo signal received by the imaging transducer. This creates an interference pattern obscuring the image of the tissue. As such, it is difficult to monitor lesion location. This paper proposes a real-time monitoring method to be performed concurrently with the HIFU insonation, but without HIFU interference, which allows for the improvement of treatment accuracy and safety in USgHIFU. The proposed method utilizes the physical properties of pulse inversion which is capable of removing the fundamental and odd harmonic components of the HIFU interference. Therefore, it is possible to secure the desired spectral bandwidth used to construct US images for HIFU treatment monitoring. The performance of the proposed method was evaluated through experiments with both a bovine serum albumin phantom and a chicken breast. The results demonstrated that the proposed method is capable of providing interference-free US images, thus successfully allowing for US imaging during HIFU treatment.

Monitoring temperature elevations in tissues using quantitative ultrasound.

High intensity focused ultrasound (HIFU) is a noninvasive technique that has great potential for improving thermal therapies but requires accurate monitoring of lesion formation. Quantitative ultrasound (QUS) is a novel imaging technique that can improve monitoring of HIFU treatment by quantifying tissue changes. Ultrasonic backscatter experiments were performed on tissue‐mimicking phantoms, fresh rabbit liver, and beef liver samples versus increases in temperature from 37 to 50 °C in 1 °C increments. Two parameters were estimated from the backscatter coefficient [effective scatterer diameter (ESD) and effective acoustic concentration (EAC)] and two parameters were estimated from envelope statistics (k parameter and μ parameter) of the backscatter. No significant changes in ESD were observed for the phantoms but the ESD increased by more than 10% with increasing temperature in the liver samples. Significant decreases in EAC of 20%–40% were observed in all the samples. No specific trends were observed in e...

Passive Spatial Mapping of Inertial Cavitation During HIFU Exposure

A novel method for mapping inertial cavitation activity during high-intensity focused ultrasound (HIFU) exposure is presented. Inertial cavitation has been previously shown to result in increased heat deposition and to be associated with broadband noise emissions that can be readily monitored using a passive receiver without interference from the main HIFU signal. In the present study, the signals received passively by each of 64 elements on a standard diagnostic array placed coaxially with the HIFU transducer are combined using time exposure acoustics to generate maps of inertially cavitating regions during HIFU exposure of an agar-based tissue-mimicking material. The technique is shown to be effective in localizing single-bubble activity, as well as contiguous and disjoint cavitating regions instigated by creating regions of lower cavitation threshold within the tissue phantom. The cavitation maps obtained experimentally are also found to be in good agreement with computational simulations and theoretical predictions. Unlike B-mode imaging, which requires interleaving with the HIFU pulse, passive array-based mapping of cavitation activity is possible during HIFU exposure. If cavitating regions can be directly correlated to increased tissue damage, this novel cavitation mapping technique could enable real-time HIFU treatment monitoring.

Thermal ablation monitoring using radiation force-induced steady-state tissue motion

High-intensity focused ultrasound (HIFU) increases temperature in tissue and also induces local tissue movement during HIFU ablation. Such induced motion can be exploited to detect changes in tissue stiffness to monitor HIFU treatment. To implement real-time HIFU treatment monitoring, a HIFU duration is segmented into a sequence of on and off periods. The off periods are required for unaffected interrogation and are sufficiently short to minimize interruption to the intended thermal treatment. It is demonstrated that the displacements generated during the relatively long on period reach steady state and undergo recovery during the next off period. Our study focuses on the investigation of the steady-state displacement and its recovery to detect changes in tissue elasticity without additional push pulses during an HIFU treatment exposure. An integrated model and finite difference algorithm are developed to study how the dynamic displacements are related to HIFU characteristics and tissue properties. Our experiments utilized an ultrasound imaging system. The induced displacement and its recovery are estimated from the acquired backscattered signals using a cross-correlation algorithm. Optimal HIFU on and off periods are investigated. Our results indicate that the steady-state displacements characterize the changes in tissue elasticity accompanying lesion formation during HIFU ablation.