evaluating-targeting-accuracy-focal-plane-for-an-ultrasound-guided

Evaluating Targeting Accuracy in the Focal Plane for an Ultrasound-guided High-intensity Focused Ultrasound Phased-array System

Phased arrays are increasingly used as high-intensity focused ultrasound (HIFU) transducers in the existing extracorporeal ultrasound-guided HIFU ...

Shanghai Jiao Tong University

A conventional method of avoiding normal tissue overheating during focused ultrasound surgery (FUS) is to apply equal heating duration for each sonication in between cooling intervals. However, this method is time-consuming and expensive. A novel method with unequal heating duration in different scanning paths without cooling intervals was investigated in this paper. This method was compared with the conventional method through the ablation of a 10 × 10 cm(2) target. The simulation results indicated that the new method was able to reduce treatment time by more than 50%, with higher than 95% coverage index, and more uniform thermal dose distribution. The method was further verified through the ablation of a circular lesion. Ex vivo experiments were also performed to confirm the simulation results. Both simulation and experimental results have proven that the new method can increase heating efficiency, and are a promising new approach in FUS.

A study of heating duration and scanning path in focused ultrasound surgery.

This paper introduces the simulation and measurement results of the phased-array focused ultrasound field of two-foci pattern.

[Measurement and analysis of phased-array focused ultrasound field of two-foci pattern].

During the treatment of soft tissue tumors using focused ultrasound surgery (FUS), the focus can shift away from the desired point due to tissue inhomogeneity. In this paper, a numerical method to calculate the focus shift in multiple-layered tissues and a faster phase-correction method to restore the focus were developed. Data from the simulations showed that the focus shifted about 2 mm along the transducer axis in multiple-layered soft tissues. After phase correction, the focus was restored at the desired point. The ex vivo experiments were conducted to verify the simulations, and the results agreed well with those of the simulations. An empirical formula was obtained to estimate the focus shift in a two-layered water-tissue model and was verified by numerical calculations. Moreover, the focus shift in multiple-layered tissues can be summed by the shifts in the component of each layer of tissues. The factors affecting the focus shift were studied. The focus shift varied linearly with the tissue acoustic speed and tissue thickness, whereas it slightly changed with transducer F number (radius of curvature/diameter). Overall, the findings of this study can help in the development of a better treatment plan for FUS in soft tissues.

Focus shift and phase correction in soft tissues during focused ultrasound surgery.

A crystal is an object with translational symmetry. Basic research into and production of new materials necessitates the preparation of crystals of a particular morphology and with well-defined crystal defects. In this work, we found novel silica mesoporous crystal spheres with polyhedral hollows (icosahedral, such as those observed for proteins of virus capsids, decahedral, Wulff polyhedral, etc.) formed by the reverse multiply twinned bicontinuous double diamond mesostructure. Vesicles with a low-curvature lamellar structure were first formed by the self-assembly of amphiphilic carboxylic acid molecules in the presence of a nonionic surfactant and then underwent a structural transformation process that gave a reverse multiply twinned mesoporous shell while maintaining the hollow shape. These polyhedral hollow crystals showed an enhanced contrast of backscattering signatures relative to the incident acoustic signals and thus could be used as a potential contrast agent in medical ultrasonography with drug loadings in the mesopores.

Spontaneous formation and characterization of silica mesoporous crystal spheres with reverse multiply twinned polyhedral hollows.

This article introduces a new method using the servo motor which is controlled by ARM microcontroller to provide power for a pulsatile blood pump to beat. This method is featured with straightforward structure, accurate control, excellent timeliness, stable performance and small noise. And it can adjust the rate of beat, the rate of flow and the compression ratio according to actual demand.

[Calculation of parameters and accurate control with real-time compensator in drive system of pulsatile blood pump].

A novel system is proposed to control the liquid nitrogen cooling and radio frequency heating of tissue to achieve effective thermal ablation in the treatment using fuzzy logic controller and fuzzy logic PID type controller separately. Results of ex-vivo pig liver experiments demonstrate that this system is useful and could p control the desired treatment procedure.

[The control method design of thermal treatment system via fuzzy logic].

High-intensity focused ultrasound is a promising method for the noninvasive treatment of benign and malignant tumors. This study analyzes the effects of scanning path, applied power, and geometric characteristics of the transducer on ablation using fast scanning method, a new scanning method that uses high-intensity focused ultrasound at different blood perfusion levels.

Effects of different parameters in the fast scanning method for HIFU treatment.

In the high-intensity focused ultrasound treatment of liver tumors, ultrasound propagation is affected by the rib cage. Because of the diffraction and absorption of the bone, the sound distribution at the focal plane is altered, and more importantly, overheating on the rib surface might occur. To overcome these problems, a geometric correction method is applied to turn off the elements blocked by the ribs. The potential of steering the focus of the phased-array along the propagation direction to improve the transcostal treatment was investigated by simulations and experiments using different rib models and transducers. The ultrasound propagation through the ribs was computed by a hybrid method including the Rayleigh-Sommerfeld integral, k-space method, and angular spectrum method. A modified correction method was proposed to adjust the output of elements based on their relative area in the projected "shadow" of the ribs. The simulation results showed that an increase in the specific absorption rate gain up to 300% was obtained by varying the focal length although the optimal value varied in each situation. Therefore, acoustic simulation is required for each clinical case to determine a satisfactory treatment plan. 

Transcostal high-intensity focused ultrasound treatment using phased array with geometric correction.

With the popularity of ultrasound therapy in clinics, characterization of the acoustic field is important not only to the tolerability and efficiency of ablation, but also for treatment planning. A quantitative method was introduced to assess the intensity distribution of a focused ultrasound beam using a hydrophone and an infrared camera with no prior knowledge of the acoustic and thermal parameters of the absorber or the configuration of the array elements. This method was evaluated in both theoretical simulations and experimental measurements. A three-layer model was developed to calculate the acoustic field in the absorber, the absorbed acoustic energy during the sonication and the consequent temperature elevation. Experiments were carried out to measure the acoustic pressure with the hydrophone and the temperature elevation with the infrared camera. The percentage differences between the derived results and the simulation are <4.1% for on-axis intensity and <21.1% for -6-dB beam width at heating times up to 360 ms in the focal region of three phased-array ultrasound transducers using two different absorbers. The proposed method is an easy, quick and reliable approach to calibrating focused ultrasound transducers with satisfactory accuracy. 

Quantitative assessment of acoustic intensity in the focused ultrasound field using hydrophone and infrared imaging.

A small HIFU system was used to investigate the phase-shift droplet vaporization in vivo and its effect on thermal absorption in tissue-mimicking phantoms. The experiments demonstrated that droplets could be vaporized to bubbles in vivo by the small HIFU system and the volume of bubbles could increase by tens of times. With appropriate droplets concentration, lesion volume produced by HIFU could be increased significantly under the same HIFU parameter.

[Perfluoropentane droplets enhanced HIFU therapeutic effect].

Monte Carlo method was used for calculation of finite-diameter laser distribution in tissues through convolution operation. Photo-thermal ablation model was set up on the basis of Pennes bioheat equation, and tissue temperature distribution was simulated by using finite element method by ANSYS through the model. The simulation result is helpful for clinical application of laser.

[Temperature distribution based on Monte Carlo method of optical transmission in tissues of laser ablation].

Phase-Controlled high intensity focused ultrasound 3D temperature distribution is the key indicator for measuring the efficiency of HIFU transducer. Considerable progress has been achieved in the use of infrared (IR) imaging techniques for qualitative mapping of acoustic and thermal field of high intensity focused ultrasound (HIFU) transducers. This article proposes a method to measure phased-controlled characteristics of HIFU based on infrared thermal imaging and establishes a whole measurement system to make the method more quantitative and reliable. The result shows that the proposed measurement system is able to measure pHIFU characteristics rapidly and precisely, which will be of great significance in standardizing the measurement of pHIFU acoustic field.

Article	Year
A study of heating duration and scanning path in focused ultrasound surgery. Journal of medical systems\| PubMed ID: 20703731	2011
[Measurement and analysis of phased-array focused ultrasound field of two-foci pattern]. Zhongguo yi liao qi xie za zhi = Chinese journal of medical instrumentation\| PubMed ID: 20812638	2010
Focus shift and phase correction in soft tissues during focused ultrasound surgery. IEEE transactions on bio-medical engineering\| PubMed ID: 21245005	2011
Spontaneous formation and characterization of silica mesoporous crystal spheres with reverse multiply twinned polyhedral hollows. Journal of the American Chemical Society\| PubMed ID: 21469641	2011
[Calculation of parameters and accurate control with real-time compensator in drive system of pulsatile blood pump]. Zhongguo yi liao qi xie za zhi = Chinese journal of medical instrumentation\| PubMed ID: 21706790	2011
[The control method design of thermal treatment system via fuzzy logic]. Zhongguo yi liao qi xie za zhi = Chinese journal of medical instrumentation\| PubMed ID: 22916471	2012
Effects of different parameters in the fast scanning method for HIFU treatment. Medical physics\| PubMed ID: 23039619	2012
Transcostal high-intensity focused ultrasound treatment using phased array with geometric correction. The Journal of the Acoustical Society of America\| PubMed ID: 23927190	2013
Quantitative assessment of acoustic intensity in the focused ultrasound field using hydrophone and infrared imaging. Ultrasound in medicine & biology\| PubMed ID: 23972377	2013
[Perfluoropentane droplets enhanced HIFU therapeutic effect]. Zhongguo yi liao qi xie za zhi = Chinese journal of medical instrumentation\| PubMed ID: 24015607	2013
[Temperature distribution based on Monte Carlo method of optical transmission in tissues of laser ablation]. Zhongguo yi liao qi xie za zhi = Chinese journal of medical instrumentation\| PubMed ID: 24195389	2013
[Measurement of Phase-controlled Characteristics of HIFU Based on Infrared Thermal Imaging]. Zhongguo yi liao qi xie za zhi = Chinese journal of medical instrumentation\| PubMed ID: 29862679	2017

Jingfeng Bai

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