Quantitative in vivo measurements of inner ear tissueresistivities. I. In vitro characterization

An in vivo resistivity measurement system, based on the 4-electrode reflection-coefficient technique that nondestructively measures the complex resistivity of cochlear tissues, is described. Details of the theory and instrumentation used for noninvasive measurement of resistivity are presented. In vitro experiments both characterize the accuracy of the proposed resistivity measurement system and establish general criteria for ensuring that a particular theoretical model accurately represents the experimentally measured geometry. 2 Idealized geometries (2-layer planar and 2-layer spherical) are measured experimentally; error analyses using experimental results describe the maximum error with which the experimental system noninvasively estimates resistivity from experimental reflection coefficient measurements. The precise accuracy of a noninvasive resistivity estimate depends on both the variability for experimentally measuring the reflection coefficient of a particular geometry and the average value of the measured reflection coefficient. For example, 2-point measurements of an in vitro 2-layer planar interface allow noninvasive estimation of complex resistivity with total errors of less than 1%. In addition to characterizing accuracy of resistivity estimates for different in vitro geometries, 2 general criteria were established     

Planetary exploration using a small electromagnetic sensor

A prototype broadband electromagnetic (EM) sensor, GEM-5, has been built and tested as a possible new probe for the future Mars rover to seek an ice-bonded layer at a given depth below the Martian surface. The sensor, with a vertical coaxial coil configuration, will measure the terrain resistivity and susceptibility to determine lateral variations in resistivity and magnetic susceptibility. The lateral variations will indicate regions of resistivity/susceptibility anomalies that may contain ice or water at depth. The forward solution for the sensor geometry over a layered formation and inverse algorithms to convert the EM data into the apparent susceptibility and resistivity are developed to investigate the ability of the sensor in detecting and resolving a buried (wet) ice layer in Mars-like geologic formations. Based on the simulated study, we find that the prototype sensor design should be able to resolve the lateral variations in resistivity/susceptibility under conditions of the Martian subsurface.     

FEM analysis of predicting electrode-myocardium contact from RF cardiac catheter ablation system impedance

We used the finite-element method (FEM) to model and analyze the resistance between the catheter tip electrode and the dispersive electrode during radio-frequency cardiac catheter ablation for the prediction of myocardium-electrode contact. We included deformation of the myocardial surface to achieve accurate modeling. For perpendicular catheter contact, we measured the side view of myocardial deformation using X-ray projection imaging. We averaged the deformation contour from nine samples, and then incorporated the contour information into our FEM model. We measured the resistivity of the bovine myocardium using the four-electrode method, and then calculated the resistance change as the catheter penetrated into the myocardium. The FEM result of resistance versus catheter penetration depth matches well with our experimental data.     

A low driving voltage CCD with single layer electrode structure forarea image sensor

A new single layer electrode two-phase CCD was studied for the purpose of realizing low driving voltage operation in inter-line transfer CCD (IT-CCD) image sensor aiming for low power consumption. Conventional H-CCD with overlapping double layer electrode structure have not achieved signal charge transfer at very low driving voltage below 2 V due to appearance of potential pocket under the inter-electrode gap yet. The new CCD employs a new channel doping profile for potential pocket suppression at the inter-electrode gap. The new CCD also employs a stepped-oxide structure having a single layer transfer electrode covering both a thin gate oxide forming storage region and a thinner gate oxide forming barrier region. The inter-electrode gap of single layer electrode was decreased to as small as 0.3 μm. As a result of these measures, a fabricated 1/3 in format 270 K pixel IT-CCD image sensor reproduces a fine video image even when it is operated at a driving voltage as low as 1.8 V     

软磁非晶丝巨磁阻抗效应传感器研究进展与应用

基于软磁非晶丝巨磁阻抗效应(GMI)的传感器是近年来磁传感器领域的研究热点之一.非晶丝具有良好的软磁特性:如低电阻率、高磁导率、高饱和磁感应强度、低矫顽力、低损耗以及特殊的磁畴结构等,利用其GMI效应制成磁传感器,其突出优点是微型化、高灵敏度、快速响应、高温度稳定性和低功耗.本文讨论了软磁非晶丝巨磁阻抗效应的机理,叙述了非晶丝GMI传感器的研究进展,着重对敏感材料性能及制备、GMI器件结构形式、传感电路等作了介绍,并指出了GMI目前存在的问题及将来的发展趋势.最后对GMI的应用作了展望.     

左旋氨氯地平对急性心肌梗死犬心肌细胞的超微结构影响

目的：观察左旋氨氯地平(L-Amlodipine)对急性心肌梗死犬心肌酶和心肌细胞超微结构的影响。方法：采用麻醉开胸结扎犬的冠状动脉左前降支制备急性心肌梗死模型，取静脉血检测心肌天门冬氨酸转氨酶(AST)、磷酸肌酸激酶(CPK)和乳酸脱氢酶(LDH)活性；用透射电镜观察心肌细胞超微结构的改变。结果：左旋氨氯地平可以降低心肌酶的活性，减轻缺血造成的心肌细胞损伤程度。结论：左旋氨氯地平对缺血性心肌细胞损伤具有一定的保护作用。     

In-vivo measurement of swine myocardial resistivity

We used a four-terminal plunge probe to measure myocardial resistivity in two directions at three sites from the epicardial surface of eight open-chest pigs in-vivo at eight frequencies ranging from 1 Hz to 1 MHz. We calibrated the plunge probe to minimize the error due to stray capacitance between the measured subject and ground. We calibrated the probe in saline solutions contained in a metal cup situated near the heart that had an electrical connection to the pig's heart. The mean of the measured myocardial resistivity was 319 ohm x cm at 1 Hz down to 166 ohm x cm at 1 MHz. Statistical analysis showed the measured myocardial resistivity of two out of eight pigs was significantly different from that of other pigs. The myocardial resistivity measured with the resistivity probe oriented along and across the epicardial fiber direction was significantly different at only one out of the eight frequencies. There was no significant difference in the myocardial resistivity measured at different sites.     

Computational studies of transthoracic and transvenousdefibrillation in a detailed 3-D human thorax model

A method for constructing and solving detailed patient-specific 3D finite element models of the human thorax is presented for use in defibrillation studies. The method utilizes the patient's own X-ray CT scan and a simplified meshing scheme to quickly and efficiently generate a model typically composed of approximately 400,000 elements. A parameter sensitivity study on one human thorax model to examine the effects of variation in assigned tissue resistivity values, level of anatomical detail included in the model, and number of CT slices used to produce the model is presented. Of the seven tissue types examined, the average left ventricular (LV) myocardial voltage gradient was most sensitive to the values of myocardial and blood resistivity. Incorrectly simplifying the model, for example modeling the heart as a homogeneous structure by ignoring the blood in the chambers, caused the average LV myocardial voltage gradient to increase by 12%. The sensitivity of the model to variations in electrode size and position was also examined. Small changes (<2.0 cm) in electrode position caused average LV myocardial voltage gradient values to increase by up to 12%. It is concluded that patient-specific 3D finite element modeling of human thoracic electric fields is feasible and may reduce the empiric approach to insertion of implantable defibrillators and improve transthoracic defibrillation techniques     

刺五加冻干粉针剂(ASHFI)对实验性心肌梗死犬心肌的影响

目的：观察刺五加冻千粉针剂(Acanthopanax senticosus harms freeze-dry injection ASHFI)对心肌三酶、心肌梗死面积、心肌细胞超微结构的影响。方法：采用麻醉开胸结扎犬的冠状动脉左前降支制备急性心肌梗死模型，取血测心肌三酶(AST、CPK、LDH)；组织学切片染色法和落点求积法测量心肌梗死区面积和非梗死区面积；采用透射电镜观察心肌细胞超微结构。结果：刺五加冻千粉针剂可以减少心肌三酶的释放，降低缺血造成的心肌细胞损伤，减少缺血心肌的梗死范围，对缺血心肌具有保护作用。     

Normal and pathological NCAT image and phantom data based on physiologically realistic left ventricle finite-element models

The four-dimensional (4-D) NURBS-based cardiac-torso (NCAT) phantom, which provides a realistic model of the normal human anatomy and cardiac and respiratory motions, is used in medical imaging research to evaluate and improve imaging devices and techniques, especially dynamic cardiac applications. One limitation of the phantom is that it lacks the ability to accurately simulate altered functions of the heart that result from cardiac pathologies such as coronary artery disease (CAD). The goal of this work was to enhance the 4-D NCAT phantom by incorporating a physiologically based, finite-element (FE) mechanical model of the left ventricle (LV) to simulate both normal and abnormal cardiac motions. The geometry of the FE mechanical model was based on gated high-resolution X-ray multislice computed tomography (MSCT) data of a healthy male subject. The myocardial wall was represented as a transversely isotropic hyperelastic material, with the fiber angle varying from -90 degrees at the epicardial surface, through 0 degrees at the midwall, to 90 degrees at the endocardial surface. A time-varying elastance model was used to simulate fiber contraction, and physiological intraventricular systolic pressure-time curves were applied to simulate the cardiac motion over the entire cardiac cycle. To demonstrate the ability of the FE mechanical model to accurately simulate the normal cardiac motion as well as the abnormal motions indicative of CAD, a normal case and two pathologic cases were simulated and analyzed. In the first pathologic model, a subendocardial anterior ischemic region was defined. A second model was created with a transmural ischemic region defined in the same location. The FE-based deformations were incorporated into the 4-D NCAT cardiac model through the control points that define the cardiac structures in the phantom which were set to move according to the predictions of the mechanical model. A simulation study was performed using the FE-NCAT combination to investigate how the differences in contractile function between the subendocardial and transmural infarcts manifest themselves in myocardial Single photon emission computed tomography (SPECT) images. The normal FE model produced strain distributions that were consistent with those reported in the literature and a motion consistent with that defined in the normal 4-D NCAT beating heart model based on tagged magnetic resonance imaging (MRI) data. The addition of a subendocardial ischemic region changed the average transmural circumferential strain from a contractile value of -0.09 to a tensile value of 0.02. The addition of a transmural ischemic region changed average circumferential strain to a value of 0.13, which is consistent with data reported in the literature. Model results demonstrated differences in contractile function between subendocardial and transmural infarcts and how these differences in function are documented in simulated myocardial SPECT images produced using the 4-D NCAT phantom. Compared with the original NCAT beating heart model, the FE mechanical model produced a more accurate simulation for the cardiac motion abnormalities. Such a model, when incorporated into the 4-D NCAT phantom, has great potential for use in cardiac imaging research. With its enhanced physiologically based cardiac model, the 4-D NCAT phantom can be used to simulate realistic, predictive imaging data of a patient population with varying whole-body anatomy and with varying healthy and diseased states of the heart that will provide a known truth from which to evaluate and improve existing and emerging 4-D imaging techniques used in the diagnosis of cardiac disease.     

ACT3: a high-speed, high-precision electrical impedance tomograph

Presents the design, implementation, and performance of Rensselaer's third-generation adaptive current tomograph, ACT3. This system uses 32 current sources and 32 phase-sensitive voltmeters to make a 32-electrode system that is capable of applying arbitrary spatial patterns of current. The instrumentation provides 16 b precision on both the current values and the real and reactive voltage readings and can collect the data for a single image in 133 ms. Additionally, the instrument is able to automatically calibrate its voltmeters and current sources and adjust the current source output impedance under computer control. The major system components are discussed in detail and performance results are given. Images obtained using stationary agar targets and a moving pendulum in a phantom as well as in vivo resistivity profiles showing human respiration are shown     

Optimal Electrode Designs for Electrosurgery, Defibrillation, and External Cardiac Pacing

We have developed a simple and easily modifiable two-dimensional finite element computer model of the human torso, which allows us to predict current delivery from arbitrarily placed and designed electrodes. Using this model, the performance of many variations from the commonly used gelled-pad electrode, applied to a torso of uniform and isotropic resistivity, has been examined by independently varying the thickness, width, and resistivity of the gel layer, as well as the width of the conducting plate. We compared the electrode performances on the basis of their ability to maintain a uniform current density at the electrode-body interface, which is thought to be of critical concern in avoiding burn, pain, and other complications in electrosurgery, external cardiac pacing, and defibrillation. In addition to studying the effects of geometric and electrical design variations, we have isolated two electrode designs of particular importance: 1) a simple plate electrode with a uniformly high resistivity gel layer and intermediate conducting plate width, which could be used for low-energy applications such as external cardiac pacing, and 2) an annular electrode in which the resistivity of the gel varies as a function of distance to the electrode center, which could be used for high-energy applications such as electrosurgery and defibrillation, as well as for external cardiac pacing.     

A new catheter design using needle electrode for subendocardial RF ablation of ventricular muscles: finite element analysis and in vitro experiments

Radio-frequency (RF) cardiac ablation has been very successful for treating arrhythmias related with atrioventricular junction and accessory pathways with successful cure rates of more than 90%. Even though ventricular tachycardia (VT) is a more serious problem, it is known to be rather difficult to cure VT using RF ablation. In order to apply RF ablation to VT, we usually need to create a deeper and wider lesion. Conventional RF ablation electrodes often fail to produce such a lesion. We propose a catheter-electrode design including one or more needle electrodes with a diameter of 0.5-1.0 mm and length of 2.0-10 mm to create a lesion large enough to treat VT. One temperature sensor could be placed at the middle of the needle electrode for temperature-controlled RF ablation. From finite element analyses and in vitro experiments, we found that the depth of a lesion is 1-2 mm deeper than the insertion depth of the needle and the width increases as we increase the diameter of the needle and the time duration. We showed that a single needle electrode can produce a lesion with about 10-mm width and any required depth. If a wider lesion is required, more than one needle with suggested structures can be used. Or, repeated RF ablations around a certain area using one needle could produce a cluster of lesions. In some cases, a catheter with both conventional electrode and needle electrode at its tip may be beneficial to take advantage of both types of electrode.     

Myocardial kinematics from tagged MRI based on a 4-D B-spline model

Current research investigating the modeling of left ventricular dynamics for accurate clinical assessment of cardiac function is extensive. Magnetic resonance (MR) tagging is a functional imaging method which allows for encoding of a grid of signal voids on cardiac MR images, providing a mechanism for noninvasive measurement of intramural tissue deformations, in vivo. We present a novel technique of employing a four-dimensional (4-D) B-spline model which permits concurrent determination of myocardial beads and myocardial strains. The method entails fitting the knot planes of the 4-D B-spline model for fixed times to a sequence of triplets of orthogonal sets of tag surfaces for all imaged volumetric frames within the constraints of the model's spatio-temporal internal energy. From a three-dimensional (3-D) displacement field, the corresponding long and short-axis Lagrangian normal, shear, and principal strain maps are produced. As an important byproduct, the points defined by the 3-D intersections of the triplets of orthogonal tag planes, which we refer to as myocardial beads, can easily be determined by our model. Displaying the beads as a movie loop allows for the visualization of the nonrigid movement of the left ventricle in 3-D.     

An autocorrelation-based time domain analysis technique for monitoring perfusion and oxygenation in transplanted organs

In designing an implantable sensor for perfusion monitoring of transplant organs the ability of the sensor to gather perfusion information with limited power consumption and in near real time is paramount. The following work was performed to provide a processing method that is able to predict perfusion and oxygenation change within the blood flowing through a transplanted organ. For this application, an autocorrelation-based algorithm was used to reduce the acquisition time required for fast Fourier transform (FFT) analysis while retaining the accuracy inherent to FFT analysis. In order to provide data proving that the developed method is able to predict perfusion as accurately as FFT two experiments were developed isolating both periodic and quasi-periodic cardiac frequencies. It was shown that the autocorrelation-based method was able to perform comparably with FFT (limited to a sampling frequency of 300 Hz) and maintain accuracy down to acquisition times as low as 4 s in length.     

Methodology for Jointly Assessing Myocardial Infarct Extent and Regional Contraction in 3-D CMRI

Automated extraction of quantitative parameters from cardiac magnetic resonance images is crucial for the management of patients with myocardial infarct. This paper proposes a postprocessing procedure to jointly analyze Cine and delayed-enhanced (DE) acquisitions, in order to provide an automatic quantification of myocardial contraction and enhancement parameters and a study of their relationship. For that purpose, the following processes are performed: 1) DE/Cine temporal synchronization and 3-D scan alignment, 2) 3-D DE/Cine rigid registration in a region about the heart, 3) myocardium segmentation on Cine-MRI and superimposition of the epicardial and endocardial contours on the DE images, 4) quantification of the myocardial infarct extent (MIE), 5) study of the regional contractile function using a new index, the amplitude to time ratio (ATR). The whole procedure was applied to ten patients with clinically proven myocardial infarction. The comparison between the MIE and the visually assessed regional function scores demonstrated that the MIE is highly related to the severity of the wall motion abnormality. In addition, it was shown that the newly developed regional myocardial contraction parameter (ATR) decreases significantly in delayed enhanced regions. This largely automated approach enables the combined study of regional MIE and left ventricular function.     

掺杂改善SnO_2甲醛气敏元件灵敏度特性的研究

用纳米SnO2制作了旁热式气敏元件。用掺杂方法提高SnO2甲醛气敏元件的灵敏度,掺杂剂包括Pd,Sb,Ti,Zr,Cu,Ag,Mn等。在SnO2气敏元件中分别掺杂质量分数2%Pd和2%Zr对提高元件灵敏度有显著效果。未掺杂SnO2、掺杂质量分数2%Pd和2%Zr的气敏元件对体积分数为5×10-5甲醛的灵敏度分别为1.33,2.38,2.08,但是掺杂在改善元件对乙醇的选择性方面作用不大。分析了掺杂改善SnO2气敏元件灵敏度的原理,当SnO2表面吸附还原性气体时,吸附气体提供电子,使半导体表层的导电电子数增加,引起电导率增加、电阻下降。吸附气体浓度越高,电阻率变化越大,元件灵敏度越大。     

Design of an integrated sensor for in vivo simultaneous electrocontractile cardiac mapping

While there is extensive mapping of the spread of electrical activity in the heart, there have been no measurements of electrical and localized mechanical, or contractile, activity. Yet the development of effective treatments for diseases like chronic heart failure and cardiac hypertrophy depend on the ability to quantify improvements in electrocontractile function. In this paper, we present a sensor that is capable of making simultaneous, electrocontractile measurements. Its small size facilitates placement in multiple myocardial sites for multichannel studies. Semiconductor strain gages are used for force sensing, and Ag/AgCl-plated tungsten electrodes act as electrogram sensors. The sensor contains electronics on-board, including instrumentation amplifiers and a microprocessor for data sampling and analog-to-digital conversion. Each sensor can accurately detect 0-245+/-5 mV in two electrogram channels with a sensitivity of 0.96+/-0.2 mV/step and less than 2% error, and 0-144+/-29 g of contractile force with a sensitivity of 0.56+/-0.11 g/step in the analog-to-digital conversion and less than 6% error. The sensor has been tested in vivo in open-chest rabbit and pig mapping studies. These studies indicated that the average peak-to-peak contractile force at the apex is smaller in the rabbit than the pig (13.3 versus 40.3 g), that the average peak-to-peak contractile force in the pig is smaller near the base than near the apex (31.3 versus 40.3 g), and that contractile force is visibly decreased during ventricular fibrillation compared to normal sinus rhythm.     

Multiple sources of the impedance cardiogram based on 3-D finitedifference human thorax models

Two 3D electrical models of the human thorax, each consisting of 216,000 control volumes, were constructed based upon MR images taken at end diastole and end systole. Using the finite difference method, the contributions of various sources to the impedance cardiogram were studied for the traditional band electrode configuration. The contributions were categorized into three areas: 1) the structural changes between end diastole and end systole, 2) the flow-induced blood resistivity changes in major arteries and veins, and 3) the lung resistivity variation due to the lung blood volume change. Based on the models, Z₀ and ΔZ between end diastole and end systole were 24.4 Ω and -0.132 Ω, as compared with the measurements of 21.8 Ω and -0.123 Ω made on the same subject from whom the images were taken. Arterial and venous blood resistivity changes caused approximately 57% of the total impedance change. The lung resistivity change and the structural changes contributed 39% and 4%, respectively. The structural changes inside the thorax included the dimensional changes of blood vessels, the blood volume changes of the heart chambers, and heart movement. Although the net impedance change due to the structural changes was relatively small, the individual variation of various factors was large, with significant cancellation occurring. The results suggest that the thoracic impedance cardiographic signal is a mixed representation of many inseparable factors and may not be reliable for the stroke volume calculation. Also, the O-wave, which is clinically observed in various cardiac conditions, may be linked to the diastolic blood flow in the central veins