医用高斯型聚焦超声换能器

本文说明了具有高斯型表面速度分布的医用聚焦超声换能器的理论分析、结构设计和声场测试方法。该换能器由N_8S_2压电陶瓷制成,等效半径3mm,谐振频率2.5MHz。焦长5.9cm的声透镜由环氧树脂制作。利用声场测试仪测量了该换能器的发射声压分布状况,其发射声束出声光衍射装置成象。所研制的换能器的近场特性比常用的具有均匀振速分布的平片换能器及具有4.8mm等效半径的高斯聚焦超声换能器好得多。在发射束中几乎见不到声压的极大和极小值起伏,而且副瓣减少。     

新型相控聚焦超声声场测量实验研究

目的:相控聚焦超声是热物理治疗领域的研究热点之一,而对其声场的研究是其中最重要的技术环节.本文分析了新型相控聚焦超声声场仿真和实验测量的声场结果.方法:运用LabVIEW虚拟仪器平台开发了超声声场测量系统.该系统用水听器声场扫描法测量了单焦点模式下新型相控聚焦超声声场分布,并用MATLAB等工具包对单焦点模式下的声场分布进行仿真.结果:仿真数据和实验结果基本一致.结论:本文验证了理论模型的正确性及本系统测量相控型聚焦超声声场可行性和有效性.     

任意三角形和六边形超声阵元及其高填充率阵列的声场仿真研究

为提高超声设备中二维相控阵列聚焦换能器的面积填充率,提升聚焦区域的超声能量和治疗效率,本研究利用空间脉冲响应理论对任意三角形阵元进行声场计算,通过对三角形阵元进行二维平面旋转完成了六边形阵元声场仿真,并通过对六边形阵元进行三维空间旋转实现了球面阵列聚焦换能器声场仿真。仿真结果显示,六边形7阵元球面填充率提高了6.1%,其-6 dB焦域横向宽度为2.0 mm、纵向长度为30.1 mm; 19阵元球面填充率提高了5.5%,其-6 dB焦域横向宽度为1.2 mm、纵向长度为9.8 mm,可实现高精度超声治疗。本研究可为任意三角形和六边形及不规则形状阵元声场仿真提供新方法,且为高填充率的球面聚焦超声换能器设计提供新思路。     

用于实时超声成象的12个同芯圆环式超声换能器的进展

同芯圆环式超声换能器近来取得较大进展,从而引起人们广泛地注意。本文介绍一种同芯圆环式超声换能器的研制、特性、声脉声场的理论模型和最佳同芯圆环式换能器参数的选择。并讨论影响成象分辨率和对比度的因素,如声束宽度、旁瓣、圆环数、声场深度和延时时间取值等。作者选用12个同芯圆环,4.5MHz的频率,外直径为30mm     

开口柱面换能器声场分析

目的:聚焦超声治疗妇科浅表组织疾病中存在聚焦换能器和定位探头同时放置的问题,在实际的治疗头设计中必须考虑放置B超探头对聚焦声场的影响,本文涉及一种开口柱面换能器聚焦超声声场的数值计算与仿真,通过计算得出声场的三维空间分布,同时研究柱面自聚焦换能器中不同开口形状、位置、面积大小对声场的影响,以指导开口换能器的实际设计。方法:本文通过建立三维直角坐标系,应用Rayleigh积分得出柱面换能器聚焦区域内每一点的声强表达式,运用C语言和matlab采用变步长辛卜生二重积分的方法对开口柱面聚焦超声换能器的声场进行了数值计算和仿真,得出声场的三维分布。结果:对开口的不同形状、大小、位置的声场分布仿真结果表明:不同开口形状都会使聚焦区域声压幅值下降,开口半径增大,声压表现为下降的趋势,Z轴向的声压在换能器的边缘较大,中间小。随着开口中心位置距原点的距离越大,Z轴向的声压分布越不均匀,而对聚焦位置影响不大。结论:通过不同开口参数对声场三维分布影响可以看出:柱面超声换能器的开口形状、位置、面积对聚焦区域的声压均有明显影响。与给定的条件相比,选择位置居中、面积较小、的换能器,能使聚焦性能得到提高,而换能器的开口形状对聚焦效果影响不大。     

线阵B超的声场分布

线阵B超的成象区域都是在近中场,用简单的Fraunhofer近似研究组织中的声场分布是不恰当的。然而,整个阵列的激励声场是各单个阵元的激励声场的迭加,而且单个阵元的声场在大部分成象区域内都满足远场条件,可以用Fraunhofer近似处理得到较简单的声场分布函数。用单阵元分布函数迭加所得的换能器声场分布的数值计算,比计算经典的Fresnel积分的运算量要小得多。计算结果表明:换能器阵列在成象区域内的非聚焦声场与矩形平板换能器声场的近中场分布规律相近,适当引入延时可以使阵列换能器的声束有效会聚而实現电子聚焦。当换能器口径一定时,电子聚焦的最小焦距受阵元宽度限制。超声仪器对组织后向散射信号的接收是发射的逆过程,可以用相同的函数描述。同样,也可以通过适当的延时实現电子聚焦,从而进一步提高成象的分辨力。     

用于治疗宫颈疾病的微型自聚焦超声换能器聚焦特性与图像特征

目的:设计用于治疗妇科宫颈疾病的环状凹球面自聚焦超声换能器,并对其聚焦性能进行检验.方法:采用正负声源的方法,对该环状凹球面自聚焦超声换能器的轴向声场强度分布进行模拟仿真,并利用自定义的声场分布系数(SIDC)的物理意义对该换能器进行优化设计.最后采用离体器官组织牛肝实验所得损伤区域的图像特征分析来检验该换能器的聚焦特性.结果:在保证一定的机械强度和设计约束条件的基础上(固有频率为6 MHz～12 MHz),所设计的内环直径为6 mm,外环直径为12mm的Ⅰ型和内环直径为3 mm,外环直径为7.5 mm的Ⅱ型换能器的SIDC都达到了各自约束条件下的最大值.离体器官组织牛肝实验的结果也显示了焦点附近的损毁区域的轴向长度与仿真结果一致:且Ⅱ型换能器的SIDC值大于Ⅰ型换能器,其损伤区域的轴向长度更长且分布也更加均匀.结论:相同能量条件下,SIDC值较大的自聚焦超声换能器的损伤区域轴向长度更大且分布更加均匀.     

高强度聚焦超声换能器声场的数值仿真与实验测量

目的 高强度聚焦超声(HIFU)肿瘤治疗过程中,HIFU换能器形成的声场分布是决定其治疗效果的关键因素之一,为了提高HIFU肿瘤治疗的安全性和可靠性,需要对HIFU换能器形成的声场进行预测.方法 采用时域有限差分(FDTD)法数值仿真水体内形成的声压分布与实验测量结果对比的研究方法,分析讨论了HIFU换能器在不同激励功...     

国外医学生物医学工程分册1992年第15卷主题索引

(按汉语拼音字母排列) B变形性,红细胞表面处理,生物材料表面修饰,生物材料 CCT图像测t,凝血酶比值成像,超声磁刺激磁共振成像磁共振血管造影术除颇器,植入式治流传感器,电化学~,光纤式~,集成式~,葡萄掩~,微系统~,智能化超声~,成像一,换能器~,脉冲多普勒~,声场~,生物效应~,图像~,显徽镜~,应用~,诊断~,治疗触变性,全血 D电磁波,医学应用电刺激等离子喷涂电化学疗法电极,薄膜阵列式~,心脏起搏~,束内~,皮层内电外科装置电子体温计243 77254 213 303 338 62,121 214 357 37,335 49 20 21,51 45 1 12 43 47 13,222 15,338 15 58 22 22 176 340 …     

一种用于神经刺激研究的触屏控制小型超声发生器

超声发生器是研究超声刺激的重要工具,但是目前并无可供选择的专用设备。目前实验室所用超声发生器通常都用多台通用仪器搭建而成,体积大,操作复杂。本文设计了一种用于神经刺激研究的小型超声发生器,用触屏作为控制界面,方便刺激参数的输入和修改;独立的E类末级功放非常小巧,可接近换能器放置,换能器的电抗参数纳入功放从而省去了匹配电路,整机体积进一步缩小。内置的现场可编程门阵列（FPGA）产生脉冲方波,经专门的驱动电路后控制E类功放中MOSFET的通断。测试表明,本文设计的超声发生器产生的波形准确,最高频率可达2 MHz。配接自制的500 kHz换能器,在30 V电源电压下输出功率6.23 W,最大声压达到168.3 kPa,并且还有可提升的空间。该发生器体积小,操作方便,电路设计简单,适用于超声神经刺激的研究。     

High power transcranial beam steering for ultrasonic brain therapy

A sparse phased array is specially designed for non-invasive ultrasound transskull brain therapy. The array is made of 200 single elements corresponding to a new generation of high power transducers developed in collaboration with Imasonic (Besan?on, France). Each element has a surface of 0.5 cm2 and works at 0.9 MHz central frequency with a maximum 20 W cm(-2) intensity on the transducer surface. In order to optimize the steering capabilities of the array, several transducer distributions on a spherical surface are simulated: hexagonal, annular and quasi-random distributions. Using a quasi-random distribution significantly reduces the grating lobes. Furthermore, the simulations show the capability of the quasi-random array to electronically move the focal spot in the vicinity of the geometrical focus (up to +/- 15 mm). Based on the simulation study, the array is constructed and tested. The skull aberrations are corrected by using a time reversal mirror with amplitude correction achieved thanks to an implantable hydrophone, and a sharp focus is obtained through a human skull. Several lesions are induced in fresh liver and brain samples through human skulls, demonstrating the accuracy and the steering capabilities of the system.     

A non-invasive method for focusing ultrasound through the human skull

A technique for focusing ultrasound through the human skull is described and verified. The approach is based on a layered wavevector-frequency domain model, which propagates ultrasound from a hemisphere-shaped transducer through the skull using input from CT scans of the head. The algorithm calculates the driving phase of each transducer element in order to maximize the signal at the intended focus. This approach is tested on ten ex vivo human skulls using a 0.74 MHz, 320-element array. A stereotaxic reference frame is affixed to the skulls in order to provide accurate registration between the CT images and the transducer. The focal quality is assessed with a hydrophone placed inside the skull. In each trial the phase correction algorithm successfully restored the focus inside the skull at a location within 1 mm from the intended focal point. The results demonstrate the feasibility of using the method for completely non-invasive ultrasound brain surgery and therapy.     

Investigation of a large-area phased array for focused ultrasound surgery through the skull

Non-invasive treatment of brain disorders using ultrasound would require a transducer array that can propagate ultrasound through the skull and still produce sufficient acoustic pressure at a specific location within the brain. Additionally, the array must not cause excessive heating near the skull or in other regions of the brain. A hemisphere-shaped transducer is proposed which disperses the ultrasound over a large region of the skull. The large surface area covered allows maximum ultrasound gain while minimizing undesired heating. To test the feasibility of the transducer two virtual arrays are simulated by superposition of multiple measurements from an 11-element and a 40-element spherically concave test array. Each array is focused through an ex vivo human skull at four separate locations around the skull surface. The resultant ultrasound field is calculated by combining measurements taken with a polyvinylidene difluoride needle hydrophone providing the fields from a 44-element and a 160-element virtual array covering 88% and 33% of a hemisphere respectively. Measurements are repeated after the phase of each array element is adjusted to maximize the constructive interference at the transducer's geometric focus. An investigation of mechanical and electronic beam steering through the skull is also performed with the 160-element virtual array, phasing it such that the focus of the transducer is located 14 mm from the geometric centre. Results indicate the feasibility of focusing and beam steering through the skull using an array spread over a large surface area. Further, it is demonstrated that beam steering through the skull is plausible.     

A numerical study of transcranial focused ultrasound beam propagation at low frequency

The feasibility of transcranial ultrasound focusing with a non-moving phased array and without skull-specific aberration correction was investigated using computer simulations. Three cadaver skull CT image data sets were incorporated into an acoustic wave transmission model to simulate transskull ultrasound wave propagation. Using a 0.25 MHz hemispherical array (125 mm radius of curvature, 250 mm diameter, 24 255 elements), the simulated beams could be focused and steered with transducer element driving phases and amplitude adjusted for focal beam steering in water (water-path). A total of 82 foci, spanning wide ranges of distance in the three orthogonal dimensions, were simulated to test the focal beam steering capability inside the three skulls. The acoustic pressure distribution in a volume of 20 x 20 x 20 mm(3) centred at each focus was calculated with a 0.5 mm spacing in each axis. Clearly defined foci were retained through the skulls (skull-path) in most cases. The skull-path foci were on average 1.6 +/- 0.8 mm shifted from their intended locations. The -3 dB skull-path beam width and length were on average 4.3 +/- 1.0 mm and 7.7 +/- 1.8 mm, respectively. The skull-path sidelobe levels ranged from 25% to 55% of the peak pressure values. The skull-path peak pressure levels were about 10%-40% of their water-path counterparts. Focusing low-frequency beam through skull without skull-specific aberration correction is possible. This method may be useful for applying ultrasound to disrupt the blood-brain barrier for targeted delivery of therapeutic or diagnostic agents, or to induce microbubbles, or for other uses of ultrasound in brain where the required power levels are low and the sharp focusing is not needed.     

A hemisphere array for non-invasive ultrasound brain therapy and surgery

Ultrasound phased arrays may offer a method for non-invasive deep brain surgery through the skull. In this study a hemispherical phased array system is developed to test the feasibility of trans-skull surgery. The hemispherical shape is incorporated to maximize the penetration area on the skull surface, thus minimizing unwanted heating. Simulations of a 15 cm radius hemisphere divided into 11, 64, 228 and 512 elements are presented. It is determined that 64 elements are sufficient for correcting scattering and reflection caused by trans-skull propagation. An optimal operating frequency near 0.7 MHz is chosen for the array from numerical and experimental thermal gain measurements comparing the power between the transducer focus and the skull surface. A 0.665 MHz air-backed PZT array is constructed and evaluated. The array is used to focus ultrasound through an ex vivo human skull and the resulting fields are measured before and after phase correction of the transducer elements. Finally, to demonstrate the feasibility of trans-skull therapy, thermally induced lesions are produced through a human skull in fresh tissue placed at the ultrasound focus inside the skull.     

An experimental high energy therapeutic ultrasound equipment: Design and characterisation

High energy ultrasound equipment for well controlled experimental work on extracorporeal shockwave lithotripsy (ESWL) and hyperthermia has been built. The design of two sets of equipment with operating frequencies of 0.5 and 1.6 MHz, respectively, is described and characterised in terms of measured generated pressure fields. The treatment heads consist of six or seven focused ultrasound transducers. The transducers have a diameter of 50 mm each and are mounted in a hemispherical Plexiglass fixture with a geometrical focus 100 mm from the transducer surfaces. Measurements were performed in a water bath in several planes perpendicular to the central axis of the ultrasound beam, using a miniature hydrophone which was positioned with a computer controlled stepping motor system. Resulting diagram plots show well defined pressure foci, located at the geometrical foci of the transducer units.     

Bio-acoustic thermal lensing and nonlinear propagation in focused ultrasound surgery using large focal spots: a parametric study

It is well known that the acoustic properties of soft tissue have a dependence on tissue temperature. This is of particular interest in focused ultrasound surgery since the mechanism of action of focused ultrasound surgery is to kill targeted tissue by inducing localized heating by ultrasound absorption, and hence cautery of that tissue. However, the act of localized heating induces a change in the acoustic properties of the targeted tissue and tissue surrounding it. This phenomenon distorts the incoming acoustic wavefront, and has been termed the thermal lens effect for this reason. Furthermore, nonlinear effects in acoustic propagation become non-negligible at the ultrasound intensities required for therapeutic action. This paper examines the importance of the thermal lens effect and nonlinear tissue properties by simulating a variety of clinically applicable phased array transducer configurations that have not yet been appropriately analysed using a full three-dimensional nonlinear treatment of acoustic propagation. The significance of the thermal lens effect is characterized by comparing the simulation of coupled acoustic and thermal propagation with an uncoupled treatment; neglecting thermal lensing typically produces a movement of 1 to 2 mm in the predicted position of the focus towards the transducer. The results also show that the classical methods of acoustic propagation can produce grossly erroneous results under certain clinically relevant transducer configurations and that an acoustic field scan with a hydrophone may not accurately predict therapeutic effect.     

HIFU在牛肝组织中的传播衰减研究

运用辐射压力法研究高强度聚焦超声在牛肝组织中的传播衰减。在室温 2 0℃下 ,利用 4种治疗超声换能器 ,在不同的换能器表面输出声功率下 ,分别测量 2 0、4 0、6 0、80 m m不同厚度新鲜离体牛肝在放入脱气水前后的声辐射力 F、F′,然后计算出声衰减。使用治疗超声换能器 4 ,对于不同辐照深度 ,以声强 ISATA=2 2 .0× 10 3W/cm2、辐照时间 5 s的超声剂量定点辐照新鲜离体牛肝 ,以断层方式剖开后测量凝固性坏死组织体积。研究结果表明 ,对于一个具体的治疗超声换能器 ,在牛肝厚度一定时 ,辐射力穿透率 F′/F法与换能器表面声强及样品近治疗超声换能器表面声窗面积无关。采用最小 F′/F法拟合得出辐射力穿透率随牛肝厚度增加呈指数规律递减 ,且与凝固性坏死组织体积随牛肝厚度 (辐照深度 )增加呈指数规律递减趋势一致。采用最小二乘法拟合得出高度聚集超声在牛肝组织中传播的声衰随频率近似线性增加且呈幂函数关系。这为进一步研究高强度聚焦超声治疗剂量学提供了实验依据     

Transcostal high-intensity-focused ultrasound: ex vivo adaptive focusing feasibility study

Ex vivo experiments have been conducted through excised pork rib with bone, cartilage, muscle and skin. The aberrating effect of the ribcage has been experimentally evaluated. Adaptive ultrasonic focusing through ribs has been studied at low power. Without any correction, the pressure fields in the focal plane were both affected by inhomogeneous attenuation and phase distortion and three main effects were observed: a mean 2 mm shift of the main lobe, a mean 1.25 mm spreading of the half width of the main lobe and up to 20 dB increase of the secondary lobe level. Thanks to time-reversal focusing, a 5 dB decrease in the secondary lobes was obtained and the ratio between the energy deposited at the target location and the total amount of energy emitted by the therapeutic array was six times higher than that without correction. Time-reversal minimizes the heating of the ribs by automatically sonicating between the ribs, as demonstrated by temperature measurements using thermocouples placed at different locations on the ribcage. It is also discussed how this aberration correction process could be achieved non-invasively for clinical application.     

Acoustic backscatter and effective scatterer size estimates using a 2D CMUT transducer

Compared to conventional piezoelectric transducers, new capacitive microfabricated ultrasonic transducer (CMUT) technology is expected to offer a broader bandwidth, higher resolution and advanced 3D/4D imaging inherent in a 2D array. For ultrasound scatterer size imaging, a broader frequency range provides more information on frequency-dependent backscatter, and therefore, generally more accurate size estimates. Elevational compounding, which can significantly reduce the large statistical fluctuations associated with parametric imaging, becomes readily available with a 2D array. In this work, we show phantom and in vivo breast tumor scatterer size image results using a prototype 2D CMUT transducer (9 MHz center frequency) attached to a clinical scanner. A uniform phantom with two 1 cm diameter spherical inclusions of slightly smaller scatterer size was submerged in oil and scanned by both the 2D CMUT and a conventional piezoelectric linear array transducer. The attenuation and scatterer sizes of the sample were estimated using a reference phantom method. RF correlation analysis was performed using the data acquired by both transducers. The 2D CMUT results indicate that at a 2 cm depth (near the transmit focus for both transducers) the correlation coefficient reduced to less than 1/e for 0.2 mm lateral or 0.25 mm elevational separation between acoustic scanlines. For the conventional array this level of decorrelation requires a 0.3 mm lateral or 0.75 mm elevational translation. Angular and/or elevational compounding is used to reduce the variance of scatterer size estimates. The 2D array transducer acquired RF signals from 140 planes over a 2.8 cm elevational direction. If no elevational compounding is used, the fractional standard deviation of the size estimates is about 12% of the mean size estimate for both the spherical inclusion and the background. Elevational compounding of 11 adjacent planes reduces it to 7% for both media. Using an experimentally estimated attenuation of 0.6 dB cm(-1) MHz(-1), scatterer size estimates for an in vivo breast tumor also demonstrate improvements using elevational compounding with data from the 2D CMUT transducer.