Kuen-Cheng Ju

Instantaneous frequency-based ultrasonic temperature estimation during focused ultrasound thermal therapy.

Focused ultrasound thermal therapy relies on temperature monitoring for treatment guidance and assurance of targeting and dose control. One potential approach is to monitor temperature change through ultrasonic-backscattered signal processing. The current approach involves the detection of echo time-shifts based on cross-correlation processing from segmented radiofrequency (RF) data. In this study, we propose a novel ultrasonic temperature-measurement approach that detects changes in instantaneous frequency along the imaging beam direction. Focused ultrasound was used as the heating source, and the 1-D beamformed RF signals provided from an ultrasound imager were used to verify the proposed algorithm for temperature change estimation. For comparison, a conventional cross-correlation technique was also evaluated. Heating experiments testing tissue-mimicking phantoms and ex vivo porcine muscles were conducted. The results showed that temperature can be well estimated by the proposed algorithm in the temperature range, where the relationship of sound speed versus temperature is linear. Compared with the cross-correlation-based algorithm, the proposed new algorithm yields a six-fold increase in computational efficiency, along with comparable contrast-detection ability and precision. This new algorithm may serve as an alternative method for implementing temperature estimation into a clinical ultrasound imager for thermal therapy guidance.

Thermal therapy for breast tumors by using a cylindrical ultrasound phased array with multifocus pattern scanning: a preliminary numerical study

The purpose of this study is to investigate the feasibility of using a 1 MHz cylindrical ultrasound phased array with multifocus pattern scanning to produce uniform heating for breast tumor thermal therapy. The breast was submerged in water and surrounded by the cylindrical ultrasound phased array. A multifocus pattern was generated and electrically scanned by the phased array to enlarge the treatment lesion in single heating. To prevent overheating normal tissues, a large planning target volume (PTV) would be divided into several planes with several subunits on each plane and sequentially treated with a cooling phase between two successive heatings of the subunit. Heating results for different target temperatures (T(tgt)), blood perfusion rates and sizes of the PTV have been studied. Furthermore, a superficial breast tumor with different water temperatures was also studied. Results indicated that a higher target temperature would produce a slightly larger thermal lesion, and a higher blood perfusion rate would not affect the heating lesion size but increase the heating time significantly. The acoustic power deposition and temperature elevations in ribs can be minimized by orienting the acoustic beam from the ultrasound phased array approximately parallel to the ribs. In addition, a large acoustic window on the convex-shaped breast surface for the proposed ultrasound phased array and the cooling effect of water would prevent the skin overheating for the production of a lesion at any desired location. This study demonstrated that the proposed cylindrical ultrasound phased array can provide effective heating for breast tumor thermal therapy without overheating the skin and ribs within a reasonable treatment time.

Split-focused ultrasound transducer with multidirectional heating for breast tumor thermal surgery

This study investigated the feasibility of using a split-focused ultrasound transducer to perform thermal surgery on breast tumors, based on a multidirectional heating scheme. The transducer is a square section of a sphere with a radius of 10 cm. The transducer was tilted such that its acoustic beam was 45 degrees relative to the rib surface, and its focal zone was arranged by a shift of 6 mm away from the center of the planning target volume. The multifocus switching technique was employed to enhance the heating efficiency. When a single transducer was used, the transducer sonicated from a certain position for a given duration, and then rotated sequentially to continue the heating. Computer simulations and in vitro phantom experiments have been studied for this heating system. Both simulation and experimental results demonstrated that the system based on a multidirectional heating scheme is capable of generating a proper thermal lesion within 8 min. Meanwhile, from the simulation results, the rib heating was effectively alleviated by tilting the transducer to induce the total reflection at the muscle/bone interface. While using multiple ultrasound transducers, an appropriate arrangement was designed to have the same configuration of acoustic beams as is used for a single-transducer strategy. The simulation results from the four-transducer strategy indicated that the heating results could be further improved. This study revealed that it is very promising to have an appropriate arrangement of a single split-focused ultrasound transducer with mechanical rotation, or to have multiple split-focused transducers that use multidirectional heating for breast tumor thermal therapy.

Investigation of a scanned cylindrical ultrasound system for breast hyperthermia

This paper investigates the feasibility of a scanned cylindrical ultrasound system for producing uniform heating from the central to the superficial portions of the breast or localized heating within the breast at a specific location. The proposed system consists of plane ultrasound transducer(s) mounted on a scanned cylindrical support. The breast was immersed in water and surrounded by this system during the treatment. The control parameters considered are the size of the transducer, the ultrasound frequency, the scan angle and the shifting distance between the axes of the breast and the system. Three-dimensional acoustical and thermal models were used to calculate the temperature distribution. Non-perfused phantom experiments were performed to verify the simulation results. Simulation results indicate that high frequency ultrasound could be used for the superficial heating, and the scan angle of the transducer could be varied to obtain an appropriate high temperature region to cover the desired treatment region. Low frequency ultrasound could be used for deep heating and the high temperature region could be moved by shifting the system. In addition, a combination of low and high frequency ultrasound could result in a portion treatment from the central to the superficial breast or an entire breast treatment. Good agreement was obtained between non-perfused experiments and simulation results. The findings of this study can be used to determine the effects of the control parameters of this system, as well as to select the optimal parameters for a specific treatment.

A novel strategy to increase heating efficiency in a split-focus ultrasound phased array.

Focus splitting using sector-based phased arrays increases the necrosed volume in a single sonication and reduces the total treatment time in the treatment of large tumors. However, split-focus sonication results in a lower energy density and worse focal-beam distortion, which limits its usefulness in practical treatments. Here, we propose a new heating strategy involving consecutive strongly focused and split-focus sonications to improve the heating efficiency. Theoretical predictions including linear and thermal-dose-dependent attenuation change were employed to investigate potential factors of this strategy, and ex vivo tissue experiments were conducted to confirm its effectiveness. Results showed that the thermal lesions produced by the proposed strategy could be increased when comparing with the previous reported strategies. The proposed heating strategy also induces a thermal lesion more rapidly, and exhibits higher robustness to various blood perfusion conditions, higher robustness to various power/heating time combinations, and superiority to generate deep-seated lesions through tissues with complex interfaces. Possible mechanisms include the optimization of the thermal conduction created by the strongly focused sonication and the temperature buildup gained from thermally induced tissue attenuation change based on the theoretical analysis. This may represent a useful technique for increasing the applicability of split-focus and multiple-focus sonication techniques, and solve the obstacles encountered when attempting to use these methods to shorten the total clinical treatment time.

One-dimensional phased array with mechanical motion for conformal ultrasound hyperthermia

This paper investigates the feasibility of conformal heating for external ultrasound hyperthermia by using a phased array transducer with mechanical motion. In this system, a one-dimensional phased array is arranged on a shaft and moves along the shaft, while dynamically focusing on the planning target volume (PTV) with numerous focal spots. To prevent overheating in the intervening tissue between the skin and the PTV, the shaft and the phased array are rotated together to enlarge the acoustical window. With the purpose of conformal heating, the power deposition of the PTV is constructed by combinations of the focal spots and an iterative gradient descent method is then used to determine an optimal set of power weightings for the focal spots. Different tumour shapes are evaluated and the simulation results demonstrate that the volume percentage of the PTV with temperatures higher than 43 degrees C is over 95%. The overheating volume outside the PTV is less than 25% of the PTV. This method provides good conformal heating for external ultrasound hyperthermia. The concept of combining electrical focusing and mechanical motion has the advantages of both enlarging the acoustic window and providing dynamic focusing ability, which is essential for successful conformal heating.

A novel ultrasonic-imaging based temperature estimation approach by instantaneous frequency detection

Focused ultrasound thermal therapy relies on temperature monitoring for treatment guidance and assurance of targeting and dose control; a potential approach to achieve these is ultrasonic temperature estimation. The approach used currently involves the detection of echo time shifts based on cross-correlation processing from the segmented radio-frequency (RF) data. In this study, we propose a novel 2D ultrasonic temperature measurement approach by detecting changes in instantaneous frequency. We proposed a novel echo time-shift based algorithm to perform fast temperature estimation from ultrasonic imaging. This new algorithm may serve as an alternative for implementing 2D temperature estimation into a clinical ultrasound imager. Focused ultrasound was used as the heating source, and the beamformed RF signals provided from a 2D ultrasound imager were used to verify the proposed algorithm for temperature change estimation. For comparison, a conventional cross-correlation technique was also evaluated. Heating experiments of tissue-mimicking phantoms and ex-vivo porcine muscles were conducted. Our results show that the proposed new algorithm yields up to six times better computational efficiency while its contrast detection ability and precision rival those of cross-correlation-based algorithm. In the ex-vivo tissue experiments, we also presented the irreversibility of the echo time-shift effect in the necrotic region, which is different from that in the tissue-mimicking phantoms. In this study, we propose a new approach for temperature estimation by employing instantaneous frequency detection; it was implemented by using a simple zero-crossing algorithm. Some of the features of this approach are its superior computational efficiency and the possibility of higher spatial resolution for temperature mapping. Further, the experimental results have demonstrated that the proposed algorithm can provide similar temperature detection ability and precision as compared to the cross-correlation algorithm. Tissue irreversibility when approaching the necrotic temperature encounters difficulty in accurate temperature estimation, which has been proposed and discussed as an alternative possibility to detect tissue necrosis rather than temperature. This provides useful information as well as an alternative for the clinical applications of such an ultrasound-based temperature estimation technology.

Heating Efficiency Improvement by Using A Spherically-Concaved Sectored Array in Focused Ultrasound Thermal Therapy

Focus splitting by using sector-sectioned phased arrays is one of effective methods to increase the necrosed volume in single sonication and to reduce the total treatment time in large tumor treatment. However, the split focus contains less concentrated energy and severer focal beam distortion, which limits its usefulness in practical treatments. In this study, we proposed a new heating strategy by combining sonications of strongly-focused and split-focused patterns to increase the heating efficiency. Theoretical predictions and ex-vivo tissue experiments showed that thermal lesions can be enlarged in dimensions after applying the proposed strategy. This may provide a useful way to solve current obstacles in low heating efficiency of split-focus sonications that attempted to shorten the total treatment time in current clinical application

Heating patterns of cylindrical ultrasound transducers for breast tumors

The purpose of this paper is to examine the optimal driving frequency and to configure the ultrasound energy deposition schema for a various size and location of breast tissues when a portion or the entire cylindrical ultrasound transducer is employed for breast hyperthermia treatments. This work employs a computer simulation program based on an ideal ultrasound power deposition from a cylindrical transducer. The distribution of specific absorption rate (SAR) ratio is employed to determine the heating pattern of a set of given parameters. The control parameters considered are the ultrasound frequency in the breast tissue, the active portion of cylindrical transducer, and the shifting distance between the central axes of the breast and the transducer. The effect of the breast size on the SAR ratio is also considered. Simulation results demonstrate that the breast size, the ultrasound frequency in breast tissue, the shifting distance and the active portion of cylindrical transducer are the potential parameters for influencing the distribution of SAR ratio. The distribution of SAR ratio indicates the domain of treatable tumor size and tumor depth for a given set of parameters (driving frequency, shifting distance and active portion of transducer, as well as breast diameter).

P3C-5 Split-Focused Ultrasound for Breast Tumor Thermal Surgery with Multidirectional Heating

This study investigated the feasibility of using split-focused ultrasound transducers with mechanical rotation to do multi-direction heating for breast tumor thermal therapy. The driving frequency, radius of curvature, and side length of the rectangle spherical transducer are 0.5 MHz, 10 cm, and 7 cm, respectively. In order to alleviate the rib heating, the transducer was tilted be 45 degree relative to the muscle/bone interface, and its focal zone was shifted with 6 mm away from the center of the planning target volume (PTV). Based on the multi-focus temporal switching technique, strategies employing single transducer and multiple transducers were both evaluated. As a single transducer was used, the transducer was rotated sequentially to achieve a uniform heating from four planned positions with 90 degree apart. While in multiple ultrasound transducers cases, an appropriate arrangement was designed to have the same configuration of acoustic beams in the single-transducer case. Computer simulations and in vitro phantom had been studied for this ultrasound heating system. The results demonstrated the capacity of this system design; it was able to effectively shorten the treatment time by generating a larger thermal lesion through multi-focus switching and sparing the cooling interval through multidirectional sonications. This study indicated that by appropriate arrangement of a single or multiple split-focused transducers with mechanical rotation, it is very promising to implement multi-direction heating for breast tumor thermal therapy.