Development of an Active Intravascular MR Device With an Optical Transmission System

Magnetic resonance imaging (MRI) is a safe and reliable medical imaging method providing good soft tissue contrast while avoiding harmful ionizing radiation. It is highly desirable to use the MRI technology for interventional procedures. However, due to resonance effects that can result in tissue heating, long conducting cables must be avoided. Motivated by the need for more radio-frequency (RF) safety, we developed an optical transmission system for active intravascular MRI devices. An optical transmitter sends the MR signal via an optical fiber. A miniature optical modulator was designed to be integrated into a catheter tip. Furthermore, power is supplied optically to the transmitter. This system can target new medical applications, due to safe catheter tracking and safe intravascular imaging.      

SNOM光学探针高度控制技术研究

本文介绍采用非光学方法实现剪切力检测和轻敲模式微振动检测。通过检测压电片上的电压输出,用作探针与样品间距控制信号,实现扫描近场光学显微镜（ＳＮＯＭ）光学探针与样品间距控制。文中给出了探针－压电片检测系统的频率特性,并比较了剪切力探测和轻敲模式探测特性的区别。在剪切力作用下探针在正负半周振动时受到的作用力是对称加的,谐振状态受剪切影响,随作用力增大振幅宫续减小。而在轻敲模式荼时探针受到非对称力作用,     

In vivo measurement of swine endocardial convective heat transfer coefficient

We measured the endocardial convective heat transfer coefficient h at 22 locations in the cardiac chambers of 15 pigs in vivo. A thin-film Pt catheter tip sensor in a Wheatstone-bridge circuit, similar to a hot wire/film anemometer, measured h. Using fluoroscopy, we could precisely locate the steerable catheter sensor tip and sensor orientation in pigs' cardiac chambers. With flows, h varies from 2500 to 9500 W/m2 x K. With zero flow, h is approximately 2400 W/m2 x K. These values of h can be used for the finite element method modeling of radiofrequency cardiac catheter ablation.     

Development of a dual function sensor system for measuring pressureand temperature at the tip of a single optical fiber

A dual function sensor system has been developed for measuring pressure and temperature at the tip of a single optical fiber. The sensor contains three parts: a filter band-edge shift temperature sensor, a short-wavelength-reflecting dichroic filter, and a diaphragm-based spectral modulation pressure sensor. The sensor system uses a separate and distinct light-emitting diode (LED) for interrogating each sensor, three 100/140 mm step-index fused couplers for managing light, and separate paired photodiode assemblies for analyzing the return light signal from each sensor. In bench tests, each sensor performed to specification and there was no crosstalk between sensors. This sensor design has potential catheter applications where catheter size must be kept to an absolute minimum     

非本征F-P干涉仪式光纤触觉传感器的研究

基于法布里-珀罗(F-P)干涉原理,设计制作了具有核磁共振成像(MRI)兼容能力的光纤非本征F-P干涉仪(EFPI)结构的触觉传感器。在整个光纤触觉传感系统中,利用螺旋微控装置对传感器施加力,通过光谱分析(OSA)测量干涉光谱,利用交叉相关解调技术解调出传感器腔长,同时由FS20系列力传感器进行标定。对传感器的性能指标进行了分析,本文传感器的测量范围为0～3N,测量分辨率为0.02nm,多次测量结果显示和理论的吻合度较高。     

Fiber-optic sensors for continuous clinical monitoring

Optical sensors are prepared by attaching an indicating layer to the distal tip of an optical fiber. Light is sent down the optical fiber and is modulated by the indicating layer. The degree of modulation of the returned light is a direct measure of the amount of a particular chemical species in contact with the fiber tip. A variety of sensor designs can be employed along with a diverse array of supporting instrumentation. An overview of the various optical transduction mechanisms, instrumentation, and problems associated with optical sensors for continuous clinical monitoring is presented     

Extrinsic Fabry-Perot interferometer for measuring the stiffness of ciliary bundles on hair cells

We have developed an extrinsic Fabry-Perot interferometer (EFPI) to measure displacements of microscopic, living organelles in the inner ear. The EFPI is an optical phase-shifted instrument that can be used to measure nanometer displacements. The instrument transmits a coherent light signal to the end of a single glass optical fiber where the measurement is made. As the coherent light reaches the end of the fiber, part of this incident signal is reflected off the internal face of the fiber end (reference reflection) and part is transmitted through the end of the fiber. This transmitted light travels a short distance and is reflected off the surface whose displacement is to be measured (the target). This sensing reflection then reenters the fiber where it interferes with the reference reflection. The resulting interference signal then travels up the same optical fiber to a detector, where it is converted into a voltage that can be read from an oscilloscope. When the target moves, the phase relation between reference and sensing reflections changes, and the detector receives a modulated signal proportional to the target movement. Reflections of as little as 1% at both the sensor tip and target surfaces produce good results with this system. We use the EFPI in conjunction with fine glass whiskers to measure the stiffness (force per unit deflection) of stereociliary bundles on hair cells of the inner ear. The forces generated are in the tenths of picoNewton range and the displacements are tens of nanometers. Here we describe the EFPI and its development as a method for measuring displacements of microscopic organelles in a fluid medium. We also report experiments to validate the accuracy of the EFPI output and preliminary measurements of ciliary bundle stiffness in the posterior semicircular canal.     

差动式光纤微弯传感器

设计了一种新型的差动式光纤微弯传感器,并对传感器的位移特性和应变特性进行了实验研究。该传感器的特点是不仅可以测量位移、应力、应变等参量的大小,还可以判断参量的方向,且灵敏度比单一传感器增加一倍。实验证明,通过在传感器中加入变形齿限位装置和光纤定位槽,大大改善了差动式光纤微弯传感器的敏感性能和实用性。     

差动式光纤微弯传感器

设计了一种新型的差动式光纤微弯传感器，并对传感器的位移特性和应变特性进行了实验研究。该传感器的特点是不仅可以测量位移、应力、应变等参量的大小，还可以判断参量的方向，且灵敏度比单一传感器增加一倍。实验证明，通过在传感器中加入变形齿限位装置和光纤定位槽，大大改善了差动式光纤微弯传感器的敏感性能和实用性。     

A localized surface plasmon resonance DNA biosensor based on gold nanospheres coated on the tip of the fiber

A localized surface plasmon resonance (LSPR) biosensor was prepared with gold nanospheres (AuNSs) coated on the tip face of the optical silica fiber. AuNSs with the sizes of 20 nm and 80 nm were used. The sensitivities of AuNS20 nm and AuNS80 nm modified sensors to bulk refractive index (RI) variation are 82.86 nm/RIU and 218.98 nm/RIU, respectively. The AuNS80 nm modified sensor was used for the detection of 40 bases DNA hybridization and the limit of detection is 50 nmol/L, where the 40-bases DNA probe was covalently linked with AuNS80 nm. The complementary DNA sequence in tris-acetate-EDTA (TAE) buffer solution was detected as the target DNA. This fiber sensor has the advantages of small sample consumption, easy fabrication and high sensitivity.     

基于33耦合器Fox-Smith型光纤周界系统的定位技术

为了对长距离周界入侵进行定位,提出一种使用33耦合器作为基本元件的Fox-Smith干涉仪光纤入侵探测系统。对此结构及其定位方法进行了理论分析和实验验证。当有冲击作用在传感光纤上时,光纤中的光波受到相位调制,利用两束光波受到调制的时间不同从而产生相位差;通过对解调出的相位信号进行傅里叶变换,获取了一系列的陷波点。结果表明,在长度为34.793km传感光纤上,获得平均定位误差为83m,可见该种结构在长距离周界系统定位是可行的。这一结果在长距离周界入侵定位上具有一定的帮助。     

Characterization of Catheter Dynamics During Percutaneous Transluminal Catheter Procedures

Remote catheter navigation systems are being developed to reduce the occupational risk of the intervening physician. Despite the success of such systems, development has occurred with little fundamental knowledge of the catheter dynamics applied by the interventionalist. This paper characterizes the kinematics of a catheter during manipulation, the minimum applied force/torque during interventional procedures, and the maximum force/torque applied by an operator to overcome vasculature friction. Ten operators manipulated a 6F catheter inside a specialized catheter movement sensor to determine the velocities and accelerations of catheter motion. A mass-spring apparatus was constructed to measure the forces and torques required to overcome introducer sheath and vasculature friction. Results showed the catheter was manipulated at peak velocities and accelerations of (muplusmnsigma) : 360 plusmn 180 mmldrs^-1 and 22200 plusmn 14000 mmldrs^-2, and 19 plusmn 7 radldrs^-1 and 900 plusmn 510 radldrs^-2, for axial and radial directions of motion, respectively. A minimum force of 0.29 plusmn 0.06 N and a torque of 1.15 plusmn0.3 mNldrm was required to move the catheter through the introducer sheath; while the observed maximum applied torque was 15 mNldrm to overcome vasculature friction. The implications of these results for future design optimization of an intuitive remote catheter navigation system are considered.     

基于位置和压力的笔迹识别方法

针对当前生物测量学中签名鉴定方法发展的要求,基于光学微小角度检测和压电陶瓷(PZT)微力检测原理,研制了一种多参数签名鉴定电笔原型.该笔能检测X、y向的运笔特征和Z向的笔迹力,沿笔轴的Z向检测采用PZT力传感器,对X和y向的检测采用二维(2-D)角度传感器检测笔管对应X和Y坐标书写力的2-D倾斜角.为了使电笔的结构更加紧凑、移动更加灵活和仿真性强,采用无线传输的方式将所采集的信号传到PC机上处理验证.对汉字笔面和字母进行了三维(3-D)特征检测的可行性验证试验.结果表明,该方法具有可行性,并为笔迹识别判断提供了实验依据.     

光纤马赫曾德尔干涉曲率传感器的膝关节曲率检测系统研究

在人体运动监测的过程中,膝关节运动信息在中老年慢性疾病的诊断和康复评估方面具有重要意义。研制了一种基于光纤马赫曾德尔干涉曲率传感器（Mach-Zehnder interferometer-based directional bending,MZI-BDB）的膝关节弯曲检测系统。该系统由MZI-BDB传感器、扫频激光光源、光纤耦合器、光纤隔离器、光电探测器及信号处理系统构成。MZI-BDB传感器由偏心光纤和单模光纤错位熔接而成,封装于软硅树脂片内,通过绑带固定于膝关节处。当膝关节屈曲和伸展时,诱导MZI-BDB传感器发生弯曲,传感器内透射光信号干涉场的模场状态发生变化,谐振波长发生漂移,从而对膝关节的弯曲方向和曲率进行监测。MZI-BDB传感器在正向和负向弯曲的测量角度范围为0°~90°;在正向弯曲方向上灵敏度和分辨率分别为5.29 nm/m?1和0.11 m?1;在负向弯曲方向上的灵敏度和分辨率分别为?3.11 nm/m?1和0.12 m?1。实验测试MZI-BDB传感器温度敏感度为0.043 nm/℃,该结果显示传感器对温度的不敏感特性。光电编码器与MZI-BDB传感器同时进行数据的传感采集。实验结果表明:该检测系统和光电编码器验证平台在准确度和响应度上具有一致性。     

A novel all-fiber micro-displacement sensor based on long period grating and tip structure

A novel high sensitivity all-fiber micro-displacement sensor is proposed and experimentally demonstrated. This sensor consists of a long period fiber gating and a fiber tip, which is achieved only by a commercial arc discharge fusion splicer, and thus possesses a lower cost. The wavelength sensitivity of the proposed sensor could be up to 934 pm/μm,which is four times higher than that of the long period fiber grating （LPFG） with an air cavity structure. The intensitychange sensitivity is - 1.973 dB/μm.     

A system for real-time XMR guided cardiovascular intervention

The hybrid magnetic resonance (MR)/X-ray suite (XMR) is a recently introduced imaging solution that provides new possibilities for guidance of cardiovascular catheterization procedures. We have previously described and validated a technique based on optical tracking to register MR and X-ray images obtained from the sliding table XMR configuration. The aim of our recent work was to extend our technique by providing an improved calibration stage, real-time guidance during cardiovascular catheterization procedures, and further off-line analysis for mapping cardiac electrical data to patient anatomy. Specially designed optical trackers and a dedicated calibration object have resulted in a single calibration step that can be efficiently checked and updated before each procedure. An X-ray distortion model has been implemented that allows for distortion correction for arbitrary c-arm orientations. During procedures, the guidance system provides a real-time combined MR/X-ray image display consisting of live X-ray images with registered recently acquired MR derived anatomy. It is also possible to reconstruct the location of catheters seen during X-ray imaging in the MR derived patient anatomy. We have applied our registration technique to 13 cardiovascular catheterization procedures. Our system has been used for the real-time guidance of ten radiofrequency ablations and one aortic stent implantation. We demonstrate the real-time guidance using two exemplar cases. In a further two cases we show how off-line analysis of registered image data, acquired during electrophysiology study procedures, has been used to map cardiac electrical measurements to patient anatomy for two different types of mapping catheters. The cardiologists that have used the guidance system suggest that real-time XMR guidance could have substantial value in difficult interventional and electrophysiological procedures, potentially reducing procedure time and delivered radiation dose. Also, the ability to map measured electrical data to patient specific anatomy provides improved visualization and a path to investigation of cardiac electromechanical models.     

Sol-gel-based biosensor for use in stroke treatment

A fiber optic biosensor for the detection of fibrinolytic products produced during lysis of "soft" blood clots is described. The biosensor was constructed to be selective toward D dimer antigens, which form from the dissolution of cross-linked fibrin clots. The presence of D dimer antigens above a threshold level is a clinical diagnostic used to determine the presence of such occlusions following a stroke. Fluorescein-labeled D dimer antibodies are immobilized on the tip of an optical fiber by dip coating from a silica sol-gel solution. When D dimer antigens combine with the antibodies, fluorescence intensity decreases. The response of the sensor was examined in phosphate buffered saline, human plasma, and blood. Calibration plots for the sensor were obtained in the clinically significant D dimer concentration range from 0.54 microgram/ml to 6 micrograms/ml. Changes in spectroscopic properties as the sol-gel encapsulated tagged antibodies aged were examined; a decrease in fluorescence intensity with age was noted. The D dimer antibodies remain viable for at least 4 weeks while encapsulated in the sol-gel network when stored at 4 degrees C in PBS solution. This novel sensor is being developed for use with other catheter-based microtools to treat stroke resulting from occlusion in the vascular system.     

Statistical accuracy of a moving equivalent dipole method to identify sites of origin of cardiac electrical activation

While radio frequency (RF) catheter ablation (RCA) procedures for treating ventricular arrhythmias have evolved significantly over the past several years, the use of RCA has been limited to treating slow ventricular tachycardias (VTs). In this paper, we present preliminary results from computer and animal studies to evaluate the accuracy of an algorithm that uses the single equivalent moving dipole (SEMD) model in an infinite homogeneous volume conductor to guide the RF catheter to the site of origin of the arrhythmia. Our method involves measuring body surface electrocardiographic (ECG) signals generated by arrhythmic activity and by bipolar current pulses emanating from a catheter tip, and representing each of them by a SEMD model source at each instant of the cardiac cycle, thus enabling rapid repositioning of the catheter tip requiring only a few cycles of the arrhythmia. We found that the SEMD model accurately reproduced body surface ECG signals with a correlation coefficients > 0.95. We used a variety of methods to estimate the uncertainty of the SEMD parameters due to measurement noise and found that at the time when the arrhythmia is mostly localized during the cardiac cycle, the estimates of the uncertainty of the spatial SEMD parameters (from ECG signals) are between 1 and 3 mm. We used pacing data from spatially separated epicardial sites in a swine model as surrogates for focal ventricular arrhythmic sources and found that the spatial SEMD estimates of the two pacing sites agreed with both their physical separation and orientation with respect to each other. In conclusion, our algorithm to estimate the SEMD parameters from body surface ECG can potentially be a useful method for rapidly positioning the catheter tip to the arrhythmic focus during an RCA procedure.     

MRI/fMRI-compatible robotic system with force feedback for interaction with human motion

This paper presents a robotic system that is compatible with anatomical magnetic resonance imaging (MRI) as well as with the more sensitive functional MRI (fMRI), and can safely and smoothly interact with human motion during the imaging. The system takes advantage of the electromagnetic shield that encloses the MR room by placing the interfering or sensitive components outside the shield, in the control room. This eliminates the need for extensive compatibility testing before each use. The concept is based on a conventional actuator placed outside the scanner room and a hydrostatic connection to transmit force and motion to an MR-compatible slave placed next to or inside the MR scanner. A force sensor, based on reflected light intensity measurement over optical fibers, measures interaction forces with the human subject. A robotic interface for wrist motion demonstrates the MR compatibility of this concept and the possibility to interact with various dynamic environments during functional imaging. This technology provides a basis for applications such as assistive devices for interventional MRI and haptic interfaces for neuroscience investigations.     

An evaluation of the optical fiber beam as a force sensor

The present study reports the use of an intensity based plastic optical fiber (POF) as a force sensor. Different materials for beam, such as spring steel and mild steel, are used to evaluate the performance of the force sensor during macro-bending. The POF is surface bonded to a beam and subjected to force. The system relies on monitoring the light intensity, as the POF is subjected to transversal loading conditions. Experimentally obtained output of POF which could be measured with negligible hysteresis is compared with finite element analysis in the range between 0.0098 N to 19.613 N. The reproducibility of the sensor is observed in the limit of ±1%. The finding of this study highlights the potential use of POF sensors for various force sensing applications.