WO2016134581A1 - 双倍频共焦叠加聚焦超声球面分裂阵及分裂焦点控制方法 - Google Patents

双倍频共焦叠加聚焦超声球面分裂阵及分裂焦点控制方法 Download PDF

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WO2016134581A1
WO2016134581A1 PCT/CN2015/084678 CN2015084678W WO2016134581A1 WO 2016134581 A1 WO2016134581 A1 WO 2016134581A1 CN 2015084678 W CN2015084678 W CN 2015084678W WO 2016134581 A1 WO2016134581 A1 WO 2016134581A1
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frequency
array
spherical
confocal
splitting
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French (fr)
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陆明珠
万明习
关宇波
董腾驹
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Xian Jiaotong University
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N7/02—Localised ultrasound hyperthermia
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B17/00—Surgical instruments, devices or methods
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B18/02—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by cooling, e.g. cryogenic techniques
    • A61B18/0206—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by cooling, e.g. cryogenic techniques ultrasonic, e.g. for destroying tissue or enhancing freezing
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N7/02—Localised ultrasound hyperthermia
    • A61N7/022—Localised ultrasound hyperthermia intracavitary
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N2007/0056—Beam shaping elements
    • A61N2007/0065—Concave transducers
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N2007/0073—Ultrasound therapy using multiple frequencies
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N2007/0078—Ultrasound therapy with multiple treatment transducers
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N2007/0082—Scanning transducers

Definitions

  • the invention belongs to the technical field of medical focused ultrasound, and particularly relates to a double frequency confocal superimposed focused ultrasound spherical splitting array and a split focus control method.
  • Focused Ultrasound Surgery is a treatment method that focuses ultrasound energy on the deep target tissue of the human body to accurately select the target tissue of the injury without harming adjacent normal tissues.
  • HIFU High intensity focused ultrasound
  • tissue thermal injury treatment Thermal ablation
  • tissue damage Histotripsy
  • the existing HIFU thermal damage mechanism is mainly a thermal mechanism.
  • the effective use of cavitation heat production mechanism is still the subject of current research; general HIFU treatment uses single frequency (0.5MHz-10MHz). Due to the large size of the tumor, it usually reaches several cm 3 ; while the HIFU single focus is only a few mm 3 , the size of a single ultrasound irradiation is only large, so it takes hundreds of irradiation times to treat a tumor of several cm 3 . (a few hours), the treatment time is long. Therefore, how to improve the treatment efficiency and shorten the treatment time is a key problem to be solved.
  • the solution is to expand the focal zone size by using the phased array and multifocal form and time to adopt the cavitation synergy mechanism.
  • the previously useful dual frequency that is, a lower kHz frequency and a higher MHz frequency work together; the lower cavitation threshold of the lower kHz frequency is more prone to cavitation, while the higher MHz frequency has higher heat generation efficiency.
  • a geometric spherical crown (concave spherical surface) is generally used as the shape of the phased array therapeutic transducer, and the array elements are arranged on the spherical surface; the array elements are in the form of a ring, a circular shape, and a rectangular shape. , fan-shaped and fan-shaped, etc., in which the ring shape, the rectangle shape, the fan shape and the fan volute shape are closely arranged.
  • the size of the probe for the therapeutic transducer is generally large, and the diameter is about 3-20 cm, in order to obtain a large sound intensity gain; however, the phased array transducer is scanned in a certain area without generating a grating lobe.
  • phased array transducer element size is small, so the number of array elements is often greater than 128 array elements, such as 128, 256, 1024, 2048 array elements, etc., and the number of drive channels will be greater than 128 channels, so the structure of the driver and Control is very complicated.
  • the existing HIFU phased array technology is a single frequency drive.
  • Patent 4,865,042 inventor Umemura, invented under the name “Ultrasonic irradiation system", disclosed earlier in 1989, a spherical phased array transducer, namely a spherical annular phased array and a spherical fan snail phased array;
  • the control driving method can generate the multi-focus of the circular distribution of the focal plane, and the driving method single-phase only performs phase control, and the amplitude of each array element remains the same.
  • phased array focusing method there is a US patent document US 6,613,004 B1 filed by Israel InSightec-TxSonics, Ltd., entitled “System and The method for creating longer necrosed volumes using a phased array focused ultrasound", the corresponding Chinese invention patent 01813606.0, the patent name is "a system and method for increasing the necrotic volume by using a phased array focused ultrasound system", wherein a spherical fan snail phased array is used.
  • the full-frame equal-width and apodized focusing modes work alternately, increasing the treatment volume of tissue damage in phased array focused ultrasound surgery, overcoming the tissue damage volume generated by only apodization and easily causing overheating in the pre-focus area.
  • Another invention patent of the company US 6,503,171B1 uses a fan array to control only the phase to produce a circular multifocal focus on the focal plane.
  • the invention patent of the phased array is: Chinese invention patent application No. 2007100451792 applied by Shanghai Jiaotong University, the patent name is “phased array focused ultrasound multi-mode thermal field formation method” and invention patent ZL200610023637.8, and the patent name is “phase Control array Focusing on the formation of large focal lengths of ultrasound”; the two invention patents disclose a phased array mounted on a spherical cap surface using a circular array of 108 elements.
  • the working mode uses a rotating alternating focus mode to uniformly heat and increase the volume of the thermal field treatment.
  • the control is based on matrix pseudo-inverse and thermal field cost function optimization.
  • Chen Yazhu et al., 2006, published invention patent, application number: 2005101111028.3 "large focal length phase-controlled focusing system for heating deep tumor lesions” disclosed phase channel system phase and Amplitude control method and system structure.
  • the patent name is “focusing ultrasound therapy combined array elemental array and multifocal shear wave imaging system”, in which the combined array element structure of spherical rectangular array elements is used, and the driving channel is reduced when the total area of array elements is the same. The number also expands the focus area and multifocal scanning range of the multifocal, non-grating.
  • the transducer is a spherical 2 ring
  • the array element the method mainly involves small difference frequency, the difference frequency is less than 2% of the fundamental frequency, and the focusing radiation force is generated for detecting the excitation of the imaging.
  • This imaging method is called vibration acoustic imaging.
  • the object of the present invention is to provide a double frequency confocal superimposed focusing ultrasonic spherical splitting array and a split focus control method, It solves the problem that the existing single-frequency single-focus efficiency is low and the hundred-element phased array drive control is too complicated.
  • Double-frequency confocal superimposed focused ultrasound spherical splitting array including spherical confocal array elements, the number of array elements of spherical confocal array elements is even; half of the array elements work at low frequencies, and the other half of the array elements operate at high frequencies, The low frequency and the high frequency are both MHz high frequency; each array element is driven by one frequency, each array element beam does not overlap outside the focal area, and is only superimposed in the confocal area; each array element is connected with a channel amplifier through a corresponding impedance matching.
  • the multi-channel waveform controller is connected to the channel amplifier to control the amplitude and phase of each channel.
  • the frequency of the MHz high frequency ranges from 1 MHz to 10 MHz.
  • the ratio of the high frequency to the low frequency is a positive integer.
  • the number of elements is 2-12.
  • the spherical confocal array element is a spherical sector array, a spherical rectangular array, a spherical circular array or a spherical fan volute array.
  • the amplitude phase control method of the array element :
  • the array element width be ⁇ w
  • the element element height be ⁇ h
  • the area ⁇ A the xyz coordinate system be established as the origin at the apex of the spherical cap, and the beam direction is the z-axis; from the Reyleigh-Sommerfeld integral
  • the ball sound pressure p m of the mth array element is a simple calculation formula of N small rectangles superimposed:
  • Each array element m is divided into N squares with the same projected area and sufficiently small, generally having a side length smaller than one wavelength, and then calculating the sound pressure at each point of the focal plane by using the formula (1);
  • the negative peak of the sound pressure of the focal region of the double-frequency confocal superimposed focused ultrasound spherical splitting array is greater than a cavitation threshold.
  • the split focus control method for the double-frequency confocal superimposed focused ultrasound spherical splitting matrix specifically includes: the spherical confocal array element is a spherical sector element or a spherical rectangular element; under double frequency and phase control, the generation can be expanded
  • the focal plane of the radial focal zone size splits the multifocal point, and the focal zone is larger than the single focus; at double 2 times the frequency, the sound pressure of the control focal zone exceeds the cavitation threshold, and the low frequency and high frequency phase of the adjacent array element is 135°, the focus
  • the double-frequency negative peaks meet the focus superimposed negative sound pressure peak is the largest, more cavitation is generated, and the cavitation activity is strengthened; the adjacent phase elements are driven by the opposite phase to make the focus group cavitation strong interference.
  • the split focus control method for the double-frequency confocal superimposed focused ultrasound spherical splitting matrix comprises: the spherical confocal array element is a spherical annular array, specifically comprising: double frequency operation, controlling the ratio of the high frequency sound power to the low frequency sound power,
  • the splitting focus is generated in the direction of the sound axis of the focal zone, the peak of the intensity of the focus of the dual frequency superposition is greater than the sum of the dual frequency sound intensity; or the operation of the 3 times frequency, controlling the ratio of the high frequency sound power to the low frequency sound power and the phase is 60°,
  • the largest superimposed wave has positive and negative peaks.
  • the present invention has the following beneficial effects:
  • the invention provides a double-frequency spherical fan-shaped splitting array, which can generate splitting multi-points of the focal plane under dual frequency, thereby expanding the focal volume of a treatment, and also controlling the transient cavitation group at the adjacent focal point. Strong interference achieves good cavitation heat transfer efficiency.
  • the invention can also control the double frequency spherical ring array, and the cavitation enhancement effect is facilitated by controlling the amplitude of the sound power of the dual frequency to make the sound intensity of the focal region strongly interfere with the high sound intensity peak of the split focus of the focal region on the acoustic axis.
  • the double 3x frequency spherical ring array of 60° phase can obtain the best co-focus area cavitation heat increasing efficiency.
  • the invention is intended to design a double-frequency spherical sector element and a spherical rectangular array element, and generate a double-frequency simultaneous splitting focus, that is, increasing the focal zone volume while enhancing the focal region transient cavitation significantly improves the HIFU treatment efficiency; Phase control increases the thermal productivity by increasing the amount of cavitation in the focal region and interfering with cavitation groups that transient cavitation.
  • the invention intends to design a spherical ring array, and only needs to adjust the amplitude ratio of the dual-frequency driving sound power to obtain the axial splitting focus in the focal region and maximize the peak intensity of the focus (the intensity of the dual-frequency superimposed sound is greater than the dual-frequency sound intensity)
  • the sum of the double-frequency sound intensity is close to 2 times.
  • the phase control makes the interference between the cavitation groups of the transient cavitation increase the heat production efficiency; designing the spherical fan volute array can simultaneously generate the focal plane and the axial direction. Split focus.
  • Fig. 1(a) is a schematic diagram of a dual-frequency confocal spherical fan-shaped splitting array and system
  • Fig. 1(b) and Fig. 1(c) are the focal plane sounds of the splitting focus generated by the spherical fan-shaped splitting array in Fig. 1(a) in the focal plane. Strong map and focal plane sound intensity contour map.
  • 2(a) and 2(b) are schematic diagrams of a dual-frequency confocal spherical rectangular splitting array arranged by two array elements.
  • FIG. 3 is a schematic diagram of a dual frequency confocal spherical ring array.
  • 4(a) and 4(b) are schematic diagrams of a dual-frequency confocal spherical fan volute array arranged by two array elements.
  • FIG. 5 is a schematic diagram of a control and detection system for a cavitation cavitation mechanism of a dual-frequency confocal splitting array.
  • Fig. 6 is a waveform in which the phase of the double frequency is a double frequency relationship and the phase is inverted (180°) and a superimposed waveform.
  • Fig. 7(a) is a focal plane sound intensity diagram of a 4-split focus generated by a spherical 4-split array with a double frequency of 2 octave relationship, and a focal plane sound intensity contour of Fig. 7(b).
  • Fig. 8 is a waveform and a superimposed waveform in which the dual frequency is a doubling frequency phase with a phase of 135°.
  • Fig. 9(a) shows the focal plane sound intensity of a 2-split focus generated by a spherical four-segment splitting array with a double frequency of 2 octave, and a focal plane sound intensity map of Fig. 9(b). .
  • Fig. 10 is a sound intensity distribution diagram of the acoustic axis direction generated by the ratio of the driving power amplitudes of f 2 and f 1 having a double-frequency double-frequency relationship of a spherical 2 ring array; the two-frequency wave interference in the focal region is generated by about 9
  • the axial splitting focus, the superimposed sound intensity peak is about 2 times the sum of the two frequency sounds.
  • Figure 11 (a) is a focal plane sound intensity diagram produced by a spherical 2 ring array with a double frequency of 2 frequency relationship, a ratio of driving power amplitudes of f 2 and f 1 of 0.4, and Fig. 11 (b) is a sound intensity of xz, etc.
  • the two frequency waves in the focal region interfere with each other to produce about 9 axial splitting focal points.
  • Fig. 12(a) shows a waveform in which the phase of the double frequency is 3 times and the phase is 60°
  • Fig. 12(b) shows a waveform in which the phase of the dual frequency is 3 times and the phase is 0° and the superimposed waveform.
  • Figure 13 is a sound intensity distribution diagram of the acoustic axis direction generated by a spherical 2 ring array with a double frequency of 3 times frequency relationship, a ratio of driving amplitudes of f 2 and f 1 is 0.28; about 13 interferences of two frequency waves in the focal region are generated.
  • the axial splitting focus, the superimposed sound intensity peak is about 2 times the sum of the two frequency sounds.
  • Figure 14 (a) is a focal plane sound intensity diagram produced by a spherical 2 ring array with a double frequency of 3 times frequency relationship, a ratio of driving power amplitudes of f 2 and f 1 is 0.28;
  • Fig. 14 (b) is a sound intensity of xz, etc.
  • the two frequency waves in the focal zone interfere with each other to produce about 13 axial splitting focal points.
  • Figure 15 is a graphical representation of the experimental results of focal damage in a transparent phantom (including bovine serum albumin BSA) produced by a spherical 4-split array with a double frequency of 2 octave relationship at 180° and 135° phase control conditions, using video and High-speed photography and passive cavitation PCD detection (see Figure 16); where (a), (b), (c) are the result of 180° phase control, (a), (b) is the video, and (c) is High-speed camera image; (d), (e), (f) are the result of 135° phase control, (d), (e), is a video image, and (f) is a high-speed image.
  • a transparent phantom including bovine serum albumin BSA
  • Fig. 16 is a passive cavitation PCD detection map of a transparent phantom (including bovine serum albumin BSA) focus damage generated by a spherical 4-split array with a double frequency of 2 octave relationship at 180° and 135° phase control conditions.
  • the comb-like filtering, the mean square value of the broadband signal filtering out harmonics reflects the energy of the transient cavitation (inertial cavitation) in the focal region.
  • a double-frequency confocal superimposed focused ultrasound spherical splitting array comprises a spherical confocal array element, and the number of array elements is even (2-12);
  • the element works at low frequency, the other half operates at high frequency, and the double frequency is MHz high frequency (1MHz ⁇ 10MHz); each array element is driven by one frequency, and each array element beam does not overlap outside the focal area, only in total
  • the focal zone is superimposed; each element is connected to a channel amplifier 3 through a corresponding impedance matching 2, and the multi-channel waveform controller 4 is connected to the channel amplifier 3 for controlling the amplitude and phase of each channel.
  • the spherical confocal array element can be: spherical sector array 1 (Fig. 1(a)), spherical rectangular array 5, 6 (Fig. 2(a), Fig. 2(b)), spherical annular array 7 (Fig. 3) and spherical surface Fan volute arrays 8, 9 (Fig. 4(a), Fig. 4(b)).
  • the array element width be ⁇ w
  • the element element height be ⁇ h
  • the area ⁇ A the xyz coordinate system be established as the origin at the apex of the spherical cap, and the beam direction is the z-axis; from the Reyleigh-Sommerfeld integral
  • Each array element m is divided into N squares with the same projected area and sufficiently small, and then the sound pressure at each point of the focal plane is calculated by the formula (1);
  • the split focus control method for the double-frequency confocal superimposed focused ultrasound spherical splitting matrix is as follows:
  • the number of elements is even (2 ⁇ 12), the double frequency is MHz high frequency (1MHz ⁇ 10MHz); the frequency of each element is shown in Figure 1(a)
  • Figure 6 (a) shows six elements. Under double frequency and phase control conditions, six elements produce six split focal planes in the focal plane, which expands the size of the multifocal radial distribution, thus treating the focal region. Can be 8 times larger than a single focus.
  • the negative peak of the sound pressure in the focal zone is greater than the cavitation threshold, which can be known from the calculation simulation of the formula (1).
  • the cavitation threshold can be known from the calculation simulation of the formula (1).
  • the cavitation threshold In the case of 2 times frequency, if adjacent array elements are controlled in reverse, the focal point of the focal plane is in opposite phase vibration, and the adjacent focal points are separated by one wavelength. If the cavitation group is at the two focal positions, one is a positive peak. The cavitation is closed (collapsed), and the other negative peak cavitation is stretched to the maximum size. The broadband signal of the cavitation emission of the last vibrating cycle closed (collapsed) reaches this maximum size cavitation, so the absorption heat efficiency is the greatest, which is A kind of cavitation group strong interference.
  • Ultrasonic cavitation especially transient cavitation (inertial cavitation), causes thermal damage to be at least 6 times more efficient than without cavitation.
  • the present invention is intended to best utilize the mechanism of ultrasonic cavitation to achieve efficient and precise treatment.
  • the invention firstly proposes that the confocal double-frequency ultrasound is superimposed at the same time in the focal region, and the dual frequencies are both high frequency and integer multiple relationship of MHz, such as 1 MHz and 2 MHz or 1 MHz and 3 MHz; double frequency is suitable for continuous wave or string length exceeding 10 wavenumber pulse waves.
  • the superposition of double frequency waves in the focal region will reduce the cavitation threshold, which is lower than the cavitation threshold of the low frequency wave and enhance the transient cavitation and cavitation heat absorption, as shown in Fig. 6 for the double 2 frequency wave, each low frequency.
  • the superposition of the periodic wave peak increases, the negative wave peak also increases, and the speed increases, and the negative peak increases, and more cavitation occurs.
  • Spherical array elements can produce confocal control.
  • the array elements outside the focal region do not overlap, and only the focus element array beam is superimposed and strengthened; so our dual-frequency confocal will use a spherical array, a rectangle, a ring and a fan-shaped tight array.
  • the array element array device of the meta-displacement mode is the meta-displacement mode.
  • the spherical fan array produces a separate circular multifocal point.
  • Each array element is focused on a corresponding focus, so it is also called a split focus and a split matrix; and this multi-focus is the same as the multi-focus increase focal volume generated by the 128-element or 256-element phased array, but only needs to be controlled.
  • the phase of several spherical fan arrays can achieve the purpose of splitting the focus and expanding the volume of the focal zone.
  • the number of array elements is 2.
  • the splitting focus is generated in the direction of the sound axis of the focal zone, and the dual frequency is superimposed.
  • the peak of the focal intensity is greater than the sum of the dual-frequency sounds, which is close to the sum of the double-frequency sounds of 2 times, indicating the strong interference of the dual-frequency sound waves.
  • the sound pressure in the direction of the sound axis of the spherical ring array 7 can be obtained by the Reyleigh-Sommerfeld integral to obtain an accurate axial sound pressure analytical expression, and the exact analytical form of the sound pressure is derived, and the axial direction of each ring.
  • the sound pressure calculation formula is:
  • ⁇ is the attenuation coefficient
  • R SR is the radius of curvature of each ring
  • R 1 is the inner hole radius of each ring
  • R 2 is the outer ring radius of each ring
  • u is the array element proportional to the array element driving sound pressure Surface vibration speed.
  • Sound pressure calculation of two frequency rings firstly calculate the sound pressure of each frequency ring by using formula (2), and then add the axial sound pressure of the spherical ring array 7.
  • the number of array elements is even (4, 8, 12); all control methods and spherical fan array 1 Similar; it can produce a focal plane splitting multifocal enlarged focal zone treatment volume like a spherical sector element, and can also adjust the sound power ratio of the double frequency to obtain a high sound intensity value of the axial splitting focus.
  • the driving control of the spherical rectangular array, the spherical circular array, and the spherical fan volute array is the same as that of the spherical fan array of Fig. 1(a).
  • the experimental system for implementing the double-frequency splitting focus mode of several split arrays is shown in Figure 5.
  • the ultrasonic cavitation effect of the HIFU focus mode in the transparent tissue-like bovine serum albumin (BSA) can be used for cavitation high-speed cameras 15 and PCD.
  • the ultrasound imaging apparatus 14 evaluates; the master computer 13 is responsible for the split focus mode control and the cavitation high speed camera 15 and the PCD (passive cavitation detection) 14; the host computer 13 transmits the phase and amplitude information of the dual frequency split focus mode to the channel
  • the power amplification and control unit 12 transmits the waveforms required for each array element to the split matrix transducer 10 through the array element matching network 11 to transmit the split focus mode.
  • the element is f 1 and the other half is f 2 (arranged as shown in Figure 2 (5)).
  • the double 2x frequency superimposed waveform is shown in Fig. 6. After superposition, the positive peak value increases, the negative wave peak value also increases, and the speed increases, and the negative peak increases, there will be more space.
  • Figure 7 is the distribution of the 4 split focus sound intensity generated by the reverse operation of adjacent array elements, which proves that 4 split focus can also be generated under double 2 octave, and the sound pressure in the focal zone exceeds the cavitation threshold according to this control;
  • the adjacent focal point of the focal plane vibrates in opposite phase, and the adjacent focal points are separated by one wavelength.
  • the cavitation group at the adjacent focal point interferes strongly, and the result of efficient transient cavitation heat conversion efficiency can be obtained.
  • the adjacent co-frequency phase is in phase (0°)
  • the two adjacent 2 octave elements are phased at a low frequency of 135°
  • Figure 8 is the superimposed waveform of the adjacent 2 octave element phase 135°. After superposition, the positive wave broadening peak does not increase, the two negative peaks meet, and the superimposed negative peak is the largest. This situation is most beneficial to the occurrence of more cavitation;
  • Figure 9 is the adjacent in-phase phase in phase (0°) and adjacent The 2 split focus sound intensity distribution produced by the 2 octave phase phase 135° condition.
  • the radial splitting focus, the result of the confocal superposition, can only be the superposition of the focal zone; the axial sound pressure superposition result can be obtained by the analytical formula (2) of the accurate axial sound pressure, and the axial sound pressure of this condition is obtained in Fig.
  • Figure 14 is the focal intensity distribution of the spherical 2 circular array double 3 times frequency
  • Fig. 14(a) shows the focus intensity distribution of the focal plane. According to this sound power driving, the sound pressure in the focal region exceeds the cavitation threshold during the experiment, and Fig. 14(b) shows the 13 splitting focal points in the axial direction.
  • Fig. 15 The experimental results of the double-frequency, 180° and 135° phase control of the spherical 4-sector splitting array for one of the implemented splitting arrays are shown in Fig. 15; this is the two splitting focus modes with the best cavitation effect; In the 180° mode, the cavitation group interference at the four focal points in the focal zone can be seen from Figure 15(c), and the four focal cavitation groups are rapidly advanced in parallel to the transducer and produce effective thermal damage. 15(b); (c) and (b) The two figures are similar in shape, indicating that the cavitation is effective for thermal damage. In the 135° mode, there are large cavitation zones and cavitation group strong interference at the two focal points of the focal zone. The shape can be seen from Fig.

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Abstract

一种双倍频共焦叠加聚焦超声球面分裂阵及分裂焦点控制方法，包括球面共焦阵元，球面共焦阵元的阵元数为偶数；其中一半阵元工作在低频，另一半阵元工作在高频，所述低频和高频均为MHz高频；每一阵元对应一个频率驱动，每一阵元波束在焦区外不重叠；每一阵元通过一个对应的阻抗匹配（2）与一个通道放大器（3）连接，多通道波形控制器（4）连接通道放大器（3），用于控制每一通道的幅度和相位。双倍频球面扇形分裂阵，在双频下可产生焦平面的分裂多点，从而扩大一次治疗的焦区体积，同时也可控制相邻焦点处的瞬态空化群的强干涉获得好的空化转热效率。

Description

双倍频共焦叠加聚焦超声球面分裂阵及分裂焦点控制方法 【技术领域】
本发明属于医学聚焦超声技术领域，特别涉及一种双倍频共焦叠加聚焦超声球面分裂阵及分裂焦点控制方法。
【背景技术】
聚焦超声手术(Focused ultrasound surgery,FUS)是将超声能量聚焦在人体深部目标组织，以达到精确选定损伤的目标组织而丝毫不伤害临近正常组织的治疗方式，目前主要用于肿瘤和深部组织的非侵入性治疗。而高强度聚焦超声HIFU(High intensity focused ultrasound)分为主要利用超声热机制的组织热损伤治疗(Thermal ablation)和利用空化cavitation的局部机械力作用的组织损毁(Histotripsy)治疗两类。
现有的HIFU热损伤作用机制主要还是热机制，对于有效利用空化产热机制还是目前研究的课题；一般HIFU治疗采用单频(0.5MHz-10MHz)。由于肿瘤的尺寸较大，一般达数cm3；而HIFU单焦点仅几个mm3,单次超声辐照尺寸仅米粒大，因而治疗一个几cm3的肿瘤需数百次以上的辐照时间(几个小时)，治疗时间长。因而如何提高治疗效率、缩短治疗时间是要解决的关键问题。解决的方式有空间扩大焦区尺寸即采用相控阵同时多焦点的形式和时间上采用空化增效机制方式。关于空化增效,先前有用双频即一个较低kHz频率和一个较高MHz频率共同作用；较低kHz频率的空化阈值较低易产生空化，而较高MHz频率产热效率高。
为了获得大的声强增益，一般采用具有几何形状的球冠(凹球面)作为相控阵治疗换能器的外形，阵元排布在球面上；阵元的形式有环形、园形、矩形、扇形和扇蜗形等形式，其中环形、矩形、扇形和扇蜗形为紧密排布方式。目前，治疗换能器的探头尺寸一般较大，直径约在3-20cm之间，为的是获得大的声强增益；然而对相控阵换能器要在一定区域扫描不产生栅瓣，相控阵换能器阵元尺寸要小，这样阵元数往往会大于128阵元，如128、256、1024、2048阵元等，而驱动通道数也会大于128通道，因此驱动器的结构和控制是十分复杂的。现有的HIFU相控阵技术均为单频驱动方式。授权的美国专利4,865,042，发明人Umemura，发明名称为“Ultrasonic irradiation system”是较早于1989年披露了球冠相控阵换能器，也就是球面环形相控阵和球面扇蜗形相控阵；其控制驱动方式能够产生焦平面的环形分布的多焦点，而驱动方法单频只做相位控制，而各阵元的幅度保持一样。在相控阵聚焦方法方面有以色列InSightec-TxSonics，Ltd.公司申请的美国专利文献US 6,613,004B1，专利名称“System and  method for creating longer necrosed volumes using a phased array focused ultrasound”，相应的中国发明专利01813606.0，专利名称是“利用相控阵聚焦超声系统增加坏死体积的系统和方法”其中针对球面扇蜗形相控阵采用了全阵等幅和变迹的聚焦方式交替工作，,增大了的相控阵聚焦超声手术中组织损伤的治疗体积，克服了仅用变迹所生成的组织损伤体积易造成焦前区过热现象。该公司另一发明专利US 6,503,171B1，专利名称“System and method for controlling distribution of acoustic energy around a focal point using a focused ultrasound system”，采用扇形阵只控制相位产生焦平面上的环形多焦点。国内相控阵的发明专利情况为：上海交通大学申请的中国发明专利申请第2007100451792号、专利名称为“相控阵聚焦超声多模式热场形成方法”和发明专利ZL200610023637.8、专利名称为“相控阵聚焦超声的大焦域形成方法”；两发明专利中披露了采用圆形108阵元安装于球冠面的相控阵，工作方式采用旋转交替焦点方式来均匀加热和增加热场治疗体积，焦点的控制是采用矩阵伪逆和热场代价函数优化。陈亚珠等2006年公开的发明专利，申请号：2005101111028.3“加热深部肿瘤病灶的大焦域相控聚焦系统”中披露相控阵系统通道相位和幅度控制方法和系统构造。中国科学院申请的发明专利ZL200610114747.5，专利名称为“一种相控聚焦超声波源装置”中披露了采用圆形阵元安装于球冠中的相控阵阵元结构。西安交通大学的发明专利ZL200510096069.x、专利名称为“球面相控阵聚焦超声换能器的声场焦点模式驱动控制方法”，其中披露了球面矩形阵元相控阵的声场计算并结合多焦点的遗传算法优化的模式控制方法进行3维多焦点的控制；另一发明专利ZL200910024284.7、专利名称为“聚焦超声治疗组合阵元相控阵及多焦点剪切波成像系统”，其中采用球面矩形阵元的组合阵元结构，在阵元总面积相同的情况下减少了驱动通道数同时扩大了多焦点无栅瓣的聚焦区域和多焦点扫描范围。
最近中国发明专利申请号CN201410456237.0，专利名称“基于双频共焦超声分时激励的超声力学毁损和热凝固装置及方法”，其中用双频焦超声，但分时工作，主要针对相变液滴的增效作用。而中国发明专利公开第CN 102793980A号，专利名称“双频聚焦超声系统”，主要涉及小差频，差频小于基础频率的1％的系统。Fatemi M,et.al.,曾发表文章题为“Vibro-acoustic tissue mammography,”IEEE Trans.Medical Imaging,Vol.21,No.1,2002:1-8提及其换能器为球面2环形阵元，方法主要涉及小差频，差频小于基础频率的2％，而产生聚焦辐射力用于检测成像的激励，此成像方法称为振动声成像。
【发明内容】
本发明的目的在于提供一种双倍频共焦叠加聚焦超声球面分裂阵及分裂焦点控制方法，以 解决现有单频单焦点效率低和百阵元相控阵驱动控制过于复杂的问题。
为了实现上述目的，本发明采用如下技术方案：
双倍频共焦叠加聚焦超声球面分裂阵，包括球面共焦阵元，球面共焦阵元的阵元数为偶数；其中一半阵元工作在低频，另一半阵元工作在高频，所述低频和高频均为MHz高频；每一阵元对应一个频率驱动，每一阵元波束在焦区外不重叠，仅在共焦区叠加；每一阵元通过一个对应的阻抗匹配与一个通道放大器连接，多通道波形控制器连接通道放大器，用于控制每一通道的幅度和相位。
优选的，所述MHz高频的频率范围为1MHz～10MHz。
优选的，所述高频与低频的比值为正整数。
优选的，阵元数为2～12。
优选的，所述球面共焦阵元为球面扇形阵、球面矩形阵、球面环形阵或球面扇蜗形阵。
优选的，阵元的幅度相位控制方法：
设阵元宽度为Δw，阵元高度为Δh，面积ΔA，xyz坐标系的建立为原点在球冠的顶点，波束方向为z轴；从瑞利索莫费尔德积分(Reyleigh-Sommerfeld integral)推得第m个阵元的球声压pm由N个小矩形叠加的简洁计算公式：
Figure PCTCN2015084678-appb-000001
将每一阵元m划分成N个投影面积相同且充分小的方形，一般边长小于一个波长，然后用(1)式计算得到焦平面各点声压；
式(1)中复数声压Pm(x，y，z)，
Figure PCTCN2015084678-appb-000002
ρ和c分别是介质的密度和声速，k＝ω/c是波数，um是第m个阵元表面质点速度作为阵元驱动信号；其中各参数的计算为：
其中各参数的计算为：
Figure PCTCN2015084678-appb-000003
Figure PCTCN2015084678-appb-000004
Figure PCTCN2015084678-appb-000005
Figure PCTCN2015084678-appb-000006
Figure PCTCN2015084678-appb-000007
Figure PCTCN2015084678-appb-000008
优选的，所述双倍频共焦叠加聚焦超声球面分裂阵的焦区声压负峰值大于空化阈值。
双倍频共焦叠加聚焦超声球面分裂阵的分裂焦点控制方法，具体包括：所述球面共焦阵元为球面扇形阵元或球面矩形阵元；在双倍频和相位控制下，产生可以扩大径向焦区尺寸的焦平面分裂多焦点，焦区比单焦点大；在双2倍频率时，控制焦区声压超过空化阈值，相邻阵元低频和高频相位为135°，焦点处双频负峰相遇，焦点叠加负声压峰值最大，有更多的空化产生，空化活动加强；相邻阵元反相位驱动使焦点处空化群强干涉。
双倍频共焦叠加聚焦超声球面分裂阵的分裂焦点控制方法，具体包括：所述球面共焦阵元为球面环形阵，具体包括：双倍频工作，控制高频声功率与低频声功率之比，使焦区声轴方向产生若干分裂焦点，双频叠加的焦点声强峰值大于双频声强之和；或者3倍频工作，控制高频声功率与低频声功率之比和相位为60°时，得到最大的叠加波正峰值和负峰值。
相对于现有技术，本发明具有以下有益效果：
本发明给出了双倍频球面扇形分裂阵，在双频下可产生焦平面的分裂多点，从而扩大一次治疗的焦区体积，同时也可控制相邻焦点处的瞬态空化群的强干涉获得好的空化转热效率。本发明还可控制双倍频球面环阵，通过控制双频的声功率幅度比使焦区声波强干涉形成声轴上焦区的分裂焦点的高的声强峰值有利于空化增强效果。60°相位的双3倍频球面环阵能获得最佳共焦区空化增热效率。
本发明意在设计出双倍频球面扇形阵元和球面矩形阵元、产生双倍频同时作用的分裂焦点，即增加焦区体积同时增强焦区瞬态空化作用显著提高HIFU治疗效率；通过相位控制使增加焦区空化数量和使瞬态空化的空化群间产生干涉增加热产效率。本发明意在设计出球面环阵，仅需调节双频驱动声功率幅度比即可得到焦区内轴向分裂焦点和最大化焦点声强峰值(双频叠加的声强峰值大于双频声强之和，接近2倍的双频声强之和)，通过相位控制使瞬态空化的空化群间产生干涉增加热产效率；设计球面扇蜗形阵，可同时产生焦平面和轴向分裂焦点。
【附图说明】
图1(a)为双频共焦球面扇形分裂阵及系统示意图，图1(b)和图1(c)为图1(a)球面扇形分裂阵在焦平面产生的分裂焦点的焦平面声强图和焦平面声强等高图。
图2(a)和图2(b)为两种阵元频率排布的双频共焦球面矩形分裂阵示意图。
图3为双频共焦球面环形阵示意图。
图4(a)和图4(b)为两种阵元频率排布的双频共焦球面扇蜗形阵示意图。
图5为双频共焦分裂阵增强焦区空化机制的控制与检测系统示意图。
图6为双频为2倍频关系相位为反相(180°)的波形及叠加波形。
图7(a)为双频为2倍频关系用球面4扇形分裂阵，在180°相位控制时产生的4分裂焦点的焦平面声强图，图7(b)为焦平面声强等高图；
图8为双频为2倍频关系相位为135°的波形及叠加波形。
图9(a)为双频为2倍频关系用球面4扇形分裂阵，在135°相位控制时产生的2分裂焦点的焦平面声强，图9(b)为焦平面声强等高图。
图10为双频为2倍频关系用球面2环形阵，f2与f1的驱动功率幅度之比为0.4产生的声轴方向的声强分布图；焦区两频率波强干涉产生约9个轴向分裂焦点，叠加声强峰值是两频率声强和的约2倍。
图11(a)为双频为2倍频关系用球面2环形阵，f2与f1的驱动功率幅度之比为0.4产生的焦平面声强图，图11(b)为x-z声强等高图,焦区两频率波强干涉产生约9个轴向分裂焦点。
图12(a)为双频为3倍频关系相位为60°的波形及叠加波形，图12(b)为双频为3倍频关系相位为0°的波形及叠加波形。
图13为双频为3倍频关系用球面2环形阵，f2与f1的驱动幅度之比为0.28产生的声轴方向的声强分布图；焦区两频率波强干涉产生约13个轴向分裂焦点，叠加声强峰值是两频率声强和的约2倍。
图14(a)为双频为3倍频关系用球面2环形阵，f2与f1的驱动功率幅度之比为0.28产生的焦平面声强图；图14(b)为x-z声强等高图,焦区两频率波强干涉产生约13个轴向分裂焦点。
图15为双频为2倍频关系用球面4扇形分裂阵，在180°和135°相位控制条件产生的在透明仿体(含牛血清蛋白BSA)中焦点损伤的实验结果图，用视频和高速摄影及被动空化PCD检测(见图16)；其中，(a),(b),(c)为180°相位控制的结果，(a),(b)是视频图，(c)是高速摄像图；(d),(e),(f)为135°相位控制的结果，(d),(e),是视频图，(f)是高速摄像图。
图16为双频为2倍频关系用球面4扇形分裂阵，在180°和135°相位控制条件产生的在透明仿体(含牛血清蛋白BSA)焦点损伤的被动空化PCD检测图，经过类梳状滤波，滤除谐波的宽带信号的均方值反映了焦区瞬态空化(惯性空化)的能量。
图17为双频为2倍频和用球面2环形阵，在透明仿体(含牛血清蛋白BSA)中的焦点损伤的实验结果图；其中，(a)双频为2倍频在135°相位，f2与f1的驱动声功率幅度之比APf2/APf1＝0.371控制产生的视频结果图；双频为3倍频关系：相同的球面2环形阵结构参数，f2与f1的驱动功率幅度之比APf2/APf1＝0.28；(b)为0°相位控制的结果，(c)为60°相位控制的结果。
【具体实施方式】
请参阅图1(a)至图5所示，本发明一种双倍频共焦叠加聚焦超声球面分裂阵，包括球面共焦阵元，阵元数为偶数(2～12)；其中一半阵元工作在低频，另一半阵元工作在高频，双倍频均为MHz高频(1MHz～10MHz)；每一阵元对应一个频率驱动，每一阵元波束在焦区外不重叠，仅在共焦区叠加；每一阵元通过一个对应的阻抗匹配2与一个通道放大器3连接，多通道波形控制器4连接通道放大器3，用于控制每一通道的幅度和相位。
球面共焦阵元可以为：球面扇形阵1(图1(a))、球面矩形阵5、6(图2(a)、图2(b))、球面环形阵7(图3)和球面扇蜗形阵8、9(图4(a)、图4(b))。
阵元的幅度相位控制方法：
设阵元宽度为Δw，阵元高度为Δh，面积ΔA，xyz坐标系的建立为原点在球冠的顶点，波束方向为z轴；从瑞利索莫费尔德积分(Reyleigh-Sommerfeld integral)推得第m个阵元的球面矩形声压pm计算公式：
Figure PCTCN2015084678-appb-000009
将每一阵元m划分成N个投影面积相同且充分小的方形，然后用(1)式计算得到焦平面各点声压；
式(1)中复数声压Pm(x，y，z)，
Figure PCTCN2015084678-appb-000010
ρ和c分别是介质的密度和声速，k＝ω/c是波数，um是第m个阵元表面质点速度作为阵元驱动信号；其中各参数的计算为：
其中各参数的计算为：
Figure PCTCN2015084678-appb-000011
Figure PCTCN2015084678-appb-000012
Figure PCTCN2015084678-appb-000013
Figure PCTCN2015084678-appb-000014
Figure PCTCN2015084678-appb-000015
Figure PCTCN2015084678-appb-000016
双倍频共焦叠加聚焦超声球面分裂阵的分裂焦点控制方法具体为：
1、对于球面扇形阵元1：阵元数为偶数(2～12)，双倍频均为MHz高频(1MHz～10MHz)；每阵元频率见图1(a)频率不同的两种阵元间隔排布；也可一半(左半)阵元频率为f2，另一半为f1；f2/f1＝n，n＝2,3…整数。
图1(a)中所示为6阵元，在双倍频和相位控制条件下，6阵元产生焦平面6个分裂焦点，使多焦点在径向分布的尺寸扩大，这样治疗时焦区可比单焦点大8倍。
一般使得焦区声压负峰值大于空化阈值，从公式(1)的计算仿真图1(b)可得知。在2倍频情况下，如果相邻阵元反相控制，则焦平面相邻焦点峰点反相振动，相邻焦点相距一个波长，若空化群在此二焦点位置，一处为正峰值空化闭合(坍塌)，另一处负峰值空化拉伸达最大尺寸，上个振动周期闭合(坍塌)的空化发射的宽带信号到达此最大尺寸空化，所以吸收发热效率最大，这就是一种空化群强干涉。
超声空化特别是瞬态空化(Inertial cavitation惯性空化)的作用使产生热损伤的效率比没有空化作用的高出至少6倍。本发明就是要最好地利用超声空化的这种机制达到高效精细治疗的目的。本发明首先提出共焦双倍频超声在焦区同时作用叠加，双频都为MHz的高频且成整数倍关系，如1MHz和2MHz或1MHz和3MHz；双倍频适合连续波或串长超过10个波数的脉冲波。双倍频波在焦区的叠加会降低空化阈值，比低频波的空化阈值还要低同时强化瞬态空化和空化热吸收，如图6的双2倍频波，每个低频周期波峰值叠加增加，负波峰值也加大，同时速度加快，负波峰加大会有更多的空化产生。球面阵元能产生共焦控制，在焦区外阵元波束不重叠，仅在焦点区阵元波束叠加加强；所以我们双频共焦会选用球面扇形、矩形、环形和扇蜗形的紧密阵元换排布方式的阵元阵能器。在单频时，球面扇形阵会产生分开的环形多焦点， 每个阵元聚焦对应一个焦点，所以也称其为分裂焦点和分裂阵；而这种多焦点同128阵元或256阵元相控阵产生的多焦点增加焦区体积一样，但仅需控制几个球面扇形阵的相位就可达到分裂焦点扩大聚焦区体积的目的。
2、对于球面矩形阵(5、6)：见图2(a)和(b)所示，所有特征和控制与球面扇形阵一样。
3、对于球面环形阵7：见图3所示，阵元数为2；在一定的两个倍频频率的声功率幅度比情况下，焦区声轴方向产生若干分裂焦点，双频叠加的焦点声强峰值大于双频声强之和，接近于2倍的双频声强之和，预示双频声波的强干涉。
球面环形阵7的声轴方向的声压可用瑞利索莫费尔德积分(Reyleigh-Sommerfeld integral)得到精确的轴向声压解析式，推导出声压的精确解析式，每一环的轴向声压计算公式为：
Figure PCTCN2015084678-appb-000017
其中波数：
Figure PCTCN2015084678-appb-000018
α为衰减系数；RSR为每一环的曲率半径；R1为每一环的内孔半径，R2为每一环的外圈半径；u为与阵元驱动声压成正比的阵元表面振动速度。
两个频率环的声压计算：先采用公式(2)计算每个频率环的声压，然后相加就得到球面环形阵7的轴向声压。
在一定的频率幅度比条件下，在两频率相位条件下能够得到若干焦点的强空化干涉。
4、对于球面扇蜗形阵(8、9)，见图4(a)和图4(b)所示，阵元数为偶数(4，8，12)；所有控制方法与球面扇形阵1相似；可产生像球面扇形阵元的焦平面分裂多焦点扩大焦区治疗体积，也可调节两倍频频率的声功率比值得到轴向分裂焦点的高声强值。
球面矩形阵、球面环形阵和球面扇蜗形阵的驱动控制与图1(a)球面扇形阵的驱动控制结构相同。
具体实施几个分裂阵的双倍频分裂焦点模式的实验系统参见图5；在透明组织仿体含牛血清蛋白(BSA)中的HIFU焦点模式的超声空化效应可用空化高速摄像机15和PCD或超声成像设备14评价；主控计算机13负责分裂焦点模式控制和空化高速摄像机15以及PCD(被动空化检测)14；主控计算机13将双频分裂焦点模式的相位和幅度信息发送给通道功率放大及控制单元12将每一阵元所需的波形生成再通过阵元匹配网络11输送到分裂阵换能器10发送分裂焦点模式。
实施的分裂阵之一是球面4扇形阵(参见图1(1))，双2倍频率，f1＝1.2MHz和f2＝2.4MHz,每阵元频率排布为一半(左半)阵元为f1，另一半为f2(排布如图2(5))。在相邻阵元反相工作(相位180°)时双2倍频叠加波形见图6，叠加后正峰值增加，负波峰值也加大，同时速度加快，负波峰加大会有更多的空化产生；图7就是相邻阵元反相工作产生的4分裂焦点声强分布，证明双2倍频情况下也能产生4分裂焦点，同时依据此控制确保焦区声压超过空化阈值；焦平面相邻焦点处反相振动，相邻焦点相距一个波长，在瞬态空化发生条件下相邻焦点处空化群强干涉，可获得高效的瞬态空化热转换效率结果。还是相同的球面4扇形阵，相邻同频相位同相(0°)，两个相邻2倍频阵元相位为低频135°，图8就是相邻2倍频阵元相位135°的叠加波形，叠加后正波加宽峰值未增，两负波峰相遇，叠加负峰值最大，这种情况最有利于更多空化的发生；图9就是相邻同频相位同相(0°)和相邻2倍频阵元相位135°条件产生的2分裂焦点声强分布。
实施的分裂阵之二是球面2环形阵(参见图3(7))，双2倍频率，f1＝1.1MHz和f2＝2.2MHz；在这种环阵条件下，不会产生焦平面径向分裂焦点，共焦叠加结果，只能是焦区叠加；用精确的轴向声压的解析公式(2)可获得轴向声压叠加结果，图10是这一条件的轴向声压叠加结果，因为两频率焦区覆盖非常好，在焦区两波强干涉，在焦区叠加结果产生约7个分裂焦点，相邻焦点相距一个波长；产生分裂焦点不取决于两频率相位，只取决于高频声功率与低频声功率之比值，当这一比值为APf2/APf1＝0.4时两波强干涉，这时双频叠加的焦点声强峰值大于双频声强之和，接近2倍的双频声强之和。此2倍频波形的叠加和扇形阵的图6和图8相似，也是相位135°时，叠加负峰最大，空化产生最好；相位135°时，有2个相邻焦点处反相振动，在瞬态空化发生条件下此2焦点处空化群强干涉；图11是此球面2环形阵的焦点声强分布，图11(a)显示焦平面焦点声强分布，依此阵元声功率控制可确保实验时焦区声压超过空化阈值，图11(b)示出轴向的7个分裂焦点。
实施的分裂阵之三是球面2环形阵(参见图3(7))，双3倍频率，f1＝1.1MHz和f2＝3.3MHz； 在波形叠加方面，3倍频有一相位波叠加最有利于空化增效，就是低频波相位为60°时，两波正峰相遇，同时两波负峰也相遇，所以负峰和正峰都达最大，有利于空化的产生和坍塌，参见图12(a)；而低频波相位为0°时，两波正峰和负峰相遇，峰值最小，参见12(b)。图13显示在APf2/APf1＝0.28时两波强干涉，叠加产生约13个分裂焦点，相邻焦点相距半个波长；图14是此球面2环形阵双3倍频的焦点声强分布，图14(a)显示焦平面焦点声强分布，依此声功率驱动可确保实验时焦区声压超过空化阈值，图14(b)图显示出轴向的13个分裂焦点。
针对实施的分裂阵之一的球面4扇形分裂阵的双频为2倍频、180°和135°相位控制的实验结果，参见图15；这是空化效果最好的两个分裂焦点模式；180°模式中在焦区的4个焦点处空化群强干涉可从图15(c)看到形状，4个焦点空化群并行向换能器方向迅速推进，并产生有效热损伤见图15(b)；(c)和(b)两幅图形状相似，说明是空化有效的热产损伤。135°模式中在焦区的2个焦点处有较大的空化区和空化群强干涉可从图15(f)看到形状，2个焦点空化群并行向换能器方向迅速突进，并产生有效热损伤见图15(c)；(f)和(c)两幅图形状相似，说明空化有效热产的损伤；虽然135°模式总声功率较小于180°总声功率，为其0.8倍，但最终10s损伤尺寸几乎一样为10mm×10mm×11mm，说明可能是135°模式空化产生的更多和空化作用，这一组180°和135°相位控制的损伤实验还同时用被动空化PCD检测，其结果显示于图16中；经过类梳状滤波，滤除谐波的宽带信号的均方值反映了焦区瞬态空化(惯性空化)的能量；图16中显示135°相位控制惯性空化能量略高于180°的惯性空化能量，因而证实135°模式产生更多空化和空化作用更强些。
图17(a)是球面2环形阵双2倍频率的实验结果；治疗参数为2倍频率f1＝1.1MHz和f2＝2.2MHz，135°相位，低频声功率70w,高频声功率26w，治疗10s；图示损伤尺寸为3mm×3mm×8.7mm，由于焦区声轴上分裂焦点空化的作用产生损伤速度快，整体损伤像柱形，适合治疗规划时，焦点布置。
相同的球面2环形阵结构参数，图17(b)和(c)是双3倍频率的实验结果；治疗参数为3倍频率f1＝1.1MHz和f2＝3.3MHz，60°和0°相位，低频声功率70w,高频声功率20w，治疗10s；0°相位的损伤示于(b)，损伤尺寸为3.6mm×3.6mm×8mm；60°相位的损伤示于(c)，损伤尺寸为4.4mm×4.4mm×10.8mm；3倍频时虽然高频声功率小了6w,但损伤尺寸比2倍频率的大，0°时3倍频损伤尺寸是2倍频的1.3倍，60°时3倍频损伤尺寸是2倍频的2.6倍，损伤增加的原因可能是高频的频率增加和更近的分裂焦点距离。60°时3倍频损伤尺寸最大是因为两倍频峰值叠加使叠加正负峰值都达到最大，从而空化产生的更多和空化更强烈所至。

Claims (9)

  1. 双倍频共焦叠加聚焦超声球面分裂阵，其特征在于，包括球面共焦阵元，球面共焦阵元的阵元数为偶数；其中一半阵元工作在低频，另一半阵元工作在高频，所述低频和高频均为MHz高频；每一阵元对应一个频率驱动，每一阵元波束在焦区外不重叠，仅在共焦区叠加；每一阵元通过一个对应的阻抗匹配与一个通道放大器连接，多通道波形控制器连接通道放大器，用于控制每一通道的幅度和相位。
  2. 根据权利要求1所述的双倍频共焦叠加聚焦超声球面分裂阵，其特征在于，所述MHz高频的频率范围为1MHz～10MHz。
  3. 根据权利要求1所述的双倍频共焦叠加聚焦超声球面分裂阵，其特征在于，所述高频与低频的比值为正整数。
  4. 根据权利要求1所述的双倍频共焦叠加聚焦超声球面分裂阵，其特征在于，阵元数为2～12。
  5. 根据权利要求1所述的双倍频共焦叠加聚焦超声球面分裂阵，其特征在于，所述球面共焦阵元为球面扇形阵、球面矩形阵、球面环形阵或球面扇蜗形阵。
  6. 根据权利要求1所述的双倍频共焦叠加聚焦超声球面分裂阵，其特征在于，阵元的幅度相位控制方法：
    设阵元宽度为Δw，阵元高度为Δh，面积ΔA，xyz坐标系的建立为原点在球冠的顶点，波束方向为z轴；从瑞利索莫费尔德积分(Reyleigh-Sommerfeld integral)推得第m个阵元的声压pm由N个小矩形叠加的简洁计算公式：
    Figure PCTCN2015084678-appb-100001
    将每一阵元m划分成N个投影面积相同且充分小的方形，然后用(1)式计算得到焦平面各点声压；
    式(1)中复数声压Pm(x，y，z)，
    Figure PCTCN2015084678-appb-100002
    ρ和c分别是介质的密度和声速，k＝ω/c 是波数，um是第m个阵元表面质点速度作为阵元驱动信号；其中各参数的计算为：
    其中各参数的计算为：
    Figure PCTCN2015084678-appb-100003
    Figure PCTCN2015084678-appb-100004
    Figure PCTCN2015084678-appb-100005
    Figure PCTCN2015084678-appb-100006
    Figure PCTCN2015084678-appb-100007
    Figure PCTCN2015084678-appb-100008
  7. 根据权利要求1所述的双倍频共焦叠加聚焦超声球面分裂阵，其特征在于，所述双倍频共焦叠加聚焦超声球面分裂阵的焦区声压负峰值大于空化阈值。
  8. 双倍频共焦叠加聚焦超声球面分裂阵的分裂焦点控制方法，其特征在于，基于权利要求1至7中任一项所述的双倍频共焦叠加聚焦超声球面分裂阵，具体包括：所述球面共焦阵元为球面扇形阵元或球面矩形阵元；在双倍频和相位控制下，产生可以扩大径向焦区尺寸的焦平面分裂多焦点，焦区比单焦点大；在双2倍频率时，控制焦区声压超过空化阈值，相邻阵元低频和高频相位为135°，焦点叠加负声压峰值最大，空化活动加强；相邻阵元反相位驱动使相邻焦点处空化群强干涉。
  9. 双倍频共焦叠加聚焦超声球面分裂阵的分裂焦点控制方法，其特征在于，基于权利要求1至7中任一项所述的双倍频共焦叠加聚焦超声球面分裂阵，具体包括：所述球面共焦阵元为球面环形阵，具体包括：双倍频工作，控制高频声功率与低频声功率之比，使焦区声轴方向产生若干分裂焦点，双频叠加的焦点声强峰值大于双频声强之和；或者3倍频工作，控制高频声功率与低频声功率之比和相位为60°时，得到最大的叠加波正峰值和负峰值。
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