用于经颅神经刺激的超声环型相控阵探头的设计和研制

发布时间：2018-06-12 00:49

本文选题：超声换能器 + 环型相控阵　；参考：《深圳大学》2017年硕士论文

【摘要】：调控神经元活动于神经和精神方面的疾病治疗,有着巨大的潜力,并且也能有助于科学的研究人类脑神经在感觉、运动及认知方面的潜在机制。脑刺激技术在脑的研究和治疗方面已经成为一种非常重要的方法,目前所有常用的脑刺激方法都有着自身的缺陷或者局限性。比如,经颅电流刺激(Transcranial Direct Current Stimulation,tDCS和经颅磁刺激(Transcranial Magnetic Stimulation,TMS)尽管是无创的,但二者空间分辨率较差(~1 cm),另外深部脑刺激(Deep Brain Stimulation,DBS)有着很高的空间分辨率,但需要外科手术植入电极。近几年出现一种经颅聚焦超声刺激(Transcranial Focused Ultrasound Stimulation,tFUS)技术,它作为一种新型的脑刺激方式在确保无创刺激的同时,仍具有较高的空间分辨率,可以对更深的脑组织进行刺激,且整个过程无需外科手术,吸引了越来越多的专家学者的关注。在进行经颅神经刺激时,颅骨的存在使得无法进行定量的超声刺激,为了更加安全有效的将超声能量传送至目标区域,测试评估颅骨的声透射率是非常有必要的,这是设计经颅类设备系统最基本,也是最重要的环节,对于医疗应用来说不希望存在不确定的声透射率。此外,传统的单阵元换能器空间分辨率不够高,无法更进一步的针对特定的、更深的区域进行超声刺激,有时需要借助声准直器来约束声束的大小。综合各方面的因素,本文采用耐热性较好的PZT-4压电陶瓷为压电材料,研制了一个中心频率为0.5 MHz,外径为30 mm,用于经颅神经刺激的5阵元环型相控超声换能器,并采用该换能器进行颅骨的声透射率测试。环型相控阵通过给每个阵元施加不同的电子延时以达到动态聚焦的目的,这种方式焦点可控,不固定,利于对不同深度的脑组织进行刺激,同时提高了换能器的空间分辨率。本文系统的测试了换能器的电学参数、声学参数以及聚焦声场,测试的结果表明超声换能器的5个阵元有较好的一致性,机电偶合系数kt在0.40以上,换能器中心频率为0.5 MHz,-6 dB带宽范围为0.38 MHz-0.60 MHz。通过声强测试系统(Acoustic Intensity Measurement System,AIMS)测试得到声束焦点直径可以达到2 mm。同样采用AIMS测试了人体颅骨在不同实验条件下的声透射率,改变超声波频率、颅骨的厚度,通过拟合比较得出声透射率的实际测试值与计算得到的理论值较为一致,但实际值比理论值略小。得到了声透射率随超声频率改变而变化的规律,并验证了本文设计的换能器符合经颅超声神经刺激的需求。
[Abstract]:The regulation of neuronal activity in the treatment of neurological and mental diseases has great potential and is also helpful to the scientific study of the potential mechanisms of the human brain nerve in sensory, motor and cognitive aspects. Brain stimulation technology has become a very important method in the research and treatment of brain. At present, all the commonly used brain stimulation methods have their own defects or limitations. For example, transcranial current DCS and transcranial magnetic stimulation are noninvasive, but their spatial resolution is less than 1 cm. In addition, deep brain stimulation Deep brain stimulation has high spatial resolution, but surgical electrode implantation is needed. In recent years, there has been a transcranial focused ultrasound (TFU) technique for transcranial focused ultrasound stimulation. As a new type of brain stimulation, it still has higher spatial resolution and can stimulate deeper brain tissues while ensuring non-invasive stimulation. And the whole process does not require surgery, attracting more and more attention of experts and scholars. During transcranial nerve stimulation, the presence of skull makes it impossible to carry out quantitative ultrasound stimulation. In order to transfer ultrasonic energy more safely and effectively to the target area, it is necessary to test and evaluate the acoustic transmittance of skull. This is the most basic and important step in the design of transcranial equipment systems, and it is not desirable for medical applications to have uncertain acoustic transmittance. In addition, the spatial resolution of the traditional single array transducer is not high enough to further the ultrasonic stimulation for specific and deeper regions. Sometimes, the size of the sound beam is constrained by the acoustic collimator. In this paper, the PZT-4 piezoelectric ceramic with good heat resistance was used as piezoelectric material to synthesize various factors. A 5-array ring phase controlled ultrasonic transducer with a central frequency of 0.5 MHz and an external diameter of 30 mm was developed for transcranial nerve stimulation. The transducers were used to measure the acoustic transmittance of the skull. The ring phased array achieves the purpose of dynamic focusing by applying different electronic delay to each element. This way the focus is controllable and not fixed, which is conducive to the stimulation of brain tissue at different depths and improves the spatial resolution of the transducer. In this paper, the electrical parameters, acoustic parameters and focused sound field of the transducer are systematically measured. The test results show that the five elements of the ultrasonic transducer are in good agreement, and the electromechanical coupling coefficient kt is above 0.40. The center frequency of the transducer is 0.5 MHz / 6 dB bandwidth range is 0.38 MHz ~ 0.60 MHz. The sound beam focus diameter can reach 2 mm by acoustic intensity measurement system measurement AIMS. At the same time, the acoustic transmittance of human skull under different experimental conditions was measured by aims, the ultrasonic frequency and the thickness of skull were changed, and the actual measured value of acoustic transmittance was in agreement with the calculated theoretical value by fitting and comparing. But the actual value is slightly smaller than the theoretical value. The change of acoustic transmittance with ultrasonic frequency is obtained, and it is verified that the transducer designed in this paper accords with the requirement of transcranial ultrasound nerve stimulation.
【学位授予单位】：深圳大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R318.6;TB552

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