Numerical model for radio-frequency ablation of the endocardium andits experimental validation

A theoretical model for the study of the radiofrequency (RF) ablation technique is presented. The model relies on a finite-element time-domain calculation of the temperature distribution in a block of tissue, resulting from the flow of RF (<1 MHz) electrical current. A thermal damage function is used to calculate the extent of the lesion on the basis of the temperature elevation and the duration of exposure. This work extends the model proposed by D.E. Haines and D.D. Watson (PACE, vol.12, p.962-76, 1989) by including a more realistic and variable geometry, the cooling effect of the blood flow and a transient analysis. Furthermore, the nonlinearity caused by the temperature dependence of the tissue properties is also considered. The complexity of the model being appreciable, an experiment demonstrating its validity is also described. While remaining workable, the experiment is sophisticated enough to lead to convincing conclusions. It consists in measuring the temperature distribution and the time-dependent electrode resistance during “ablation” of a tissue-equivalent material. Various electrode configurations and electrical excitations are investigated. In all cases, the experimental results agree reasonably well with the numerical calculations. This confirms that the model is accurate for the investigation of RF ablation     

Finite-element analysis of hepatic multiple probe radio-frequency ablation

Radio-frequency (RF) ablation is an important means of treatment of nonresectable primary and metastatic liver tumors. RF ablation, unlike cryoablation (a method of tumor destruction that utilizes cold rather than heat), must be performed with a single probe placed serially. The ablation of any but the smallest tumor requires the use of multiple overlapping treatment zones. We evaluated the performance of a configuration incorporating two hooked probes (RITA model 30). The probes were lined up along the same axis in parallel 20 mm apart. Three different modes applied voltage to the probes. The first mode applied energy in monopolar mode (current flows from both probes to a dispersive electrode). The second mode applied the energy to the probes in bipolar mode (current flows from one probe to the other). The third method applied the energy sequentially in monopolar mode (in 2-s intervals switched between the probes). We used the finite-element method (FEM) and analyzed the electric potential profile and the temperature distribution at the end of simulation of a 12-min ablation. The alternating monopolar mode allowed precise independent control of the amount of energy deposited at each probe. The bipolar mode created the highest temperature in the area between the probes in the configuration we examined. The monopolar mode showed the worst performance since the two probes in close vicinity create a disadvantageous electric field configuration. We, thus, conclude that alternating monopolar RF ablation is superior to the other two methods.     

A computer simulation of radio-frequency ablation of theendocardium

A computer simulation of radio-frequency (RF) ablation of the endocardium is performed. The objective is to quantify some of the parameters affecting lesion growth, and to obtain theoretical data which can be used as a guide to maximize the lesions obtained with the procedure. The model under consideration consists of a block of heart tissue with the catheter electrode making contact at a right angle on one side (endocardium) and a large grounded electrode on the other side. An RF electrical current flows between the electrodes, heating the tissue. The simulations provide information on the time evolution of the tissue temperature, lesion dimension and tissue resistance. A first set of calculations is based on an applied RF voltage that maintains the maximum tissue temperature at 100°C. The results reveal that: 1) the lesions achievable by RF ablation are considerably larger than those obtained with a hot-tip catheter of the same size; 2) increasing the electrode radius enlarges the lesion because of an associated increase in contact surface area; 3) an increase in electrode length also enlarges the lesion because of the larger convective losses to the blood flow; 4) a large difference in temperature may exist between the electrode and the tissue because of the cooling effect of the blood flow; and 5) the lesions grow as long as power is applied. Other simulations in which the RF voltage is constant show that the lesions can be enlarged by lowering the applied voltage while increasing the duration. Agreement and discrepancies between the simulations and reported experimental results are identified. Finally, suggestions for improving the procedure are given     

Hepatic bipolar radio-frequency ablation between separated multiprong electrodes

Radio-frequency (RF) ablation has become an important means of treatment of nonresectable primary and metastatic liver tumors. Major limitations are small lesion size, which make multiple applications necessary, and incomplete killing of tumor cells, resulting in high recurrence rates. We examined a new bipolar RF ablation method incorporating two probes with hooked electrodes (RITA model 30). We performed monopolar and bipolar in vivo experiments on three pigs. The electrodes were 2.5 cm apart and rotated 45 degrees relative to each other. We used temperature-controlled mode at 95 degrees C. Lesion volumes were 3.9+/-1.8 cm3 (n=7) for the monopolar case and 12.2 +/- 3 cm3 (n=10) for the bipolar case. We generated finite-element models (FEMs) of monopolar and bipolar configurations. We analyzed the distribution of temperature and electric field of the finite element model. The lesion volumes for the FEM are 7.95 cm3 for the monopolar and 18.79 cm3 for the bipolar case. The new bipolar method creates larger lesions and is less dependent on local inhomogenities in liver tissue-such as blood perfusion-compared with monopolar RF ablation. A limitation of the new method is that the power dissipation of the two probes cannot be controlled independently in response to different conditions in the vicinity of each probe. This may result in nonuniform lesions and decreased lesion size.     

Guidelines for predicting lesion size at common endocardial locations during radio-frequency ablation

We used the finite element method to study the effect of radio-frequency (RF) catheter ablation on tissue heating and lesion formation at different intracardiac sites exposed to different regional blood velocities. We examined the effect of application of RF current in temperature- and power-controlled mode above and beneath the mitral valve annulus where the regional blood velocities are high and low respectively. We found that for temperature-controlled ablation, more power was delivered to maintain the preset tip temperature at sites of high local blood velocity than at sites of low local blood velocity. This induced more tissue heating and larger lesion volumes than ablations at low velocity regions. In contrast, for power-controlled ablation, tissue heating was less at sites of high compared with low local blood velocity for the same RF power setting. This resulted in smaller lesion volumes at sites of low local velocity. Our numerical analyzes showed that during temperature-controlled ablation at 60 degrees C, the lesion volumes at sites above and underneath the mitral valve were comparable when the duration of RF current application was 10 s. When the duration of RF application was extended to 60 s and 120 s, lesion volumes were 33.3% and 49.4% larger above the mitral valve than underneath the mitral valve. Also, with temperature-controlled ablation, tip temperature settings of 70 degrees C or greater were associated with a risk of tissue overheating during long ablations at high local blood velocity sites. In power-controlled ablation (20 W), the lesion volume formed underneath the mitral valve was 165.7% larger than the lesion volume above the mitral valve after 10 s of ablation. We summarized the guidelines for energy application at low and high flow regions.     

Finite element analyses of uniform current density electrodes for radio-frequency cardiac ablation

The high current density at the edge of a metal electrode causes hot spots, which can lead to charring or blood coagulation formation during radio-frequency (RF) cardiac ablation. We used finite element analysis to predict the current density distribution created by several electrode designs for RF ablation. The numerical results demonstrated that there were hot spots at the edge of the conventional tip electrode and the insulating catheter. By modifying the shape of the edge of the 5-mm tip electrode, we could significantly reduce the high current density at the electrode-insulator interface. We also studied the current density distribution produced by a cylindrically shaped electrode. We modified the shape of a cylindrical electrode by recessing the edge and filled in a coating material so that the overall structure was still cylindrical. We analyzed the effects of depth of recess and the electrical conductivity of the added material. The results show that more uniform current density can be accomplished by recessing the electrode, adding a curvature to the electrode, and by coating the electrode with a resistive material.     

Three-dimensional finite element analysis of current density andtemperature distributions during radio-frequency ablation

This study analyzed the influence of electrode geometry, tissue-electrode angle, and blood flow on current density and temperature distribution, lesion size, and power requirements during radio-frequency ablation. The authors used validated three-dimensional finite element models to perform these analyses. They found that the use of an electrically insulating layer over the junction between electrode and catheter body reduced the chances of charring and coagulation. The use of a thermistor at the tip of the ablation electrodes did not affect the current density distribution. For longer electrodes, the lateral current density decreased more slowly with distance from the electrode surface. The authors analyzed the effects of three tissue-electrode angles: 0, 45, and 90°. More power was needed to reach a maximal tissue temperature of 95°C after 120 s when the electrode-tissue angle was 45°. Consequently, the lesions were larger and deeper for a tissue-electrode angle of 45° than for 0 and 90°. The lesion depth, volume, and required power increased with blood flow rate regardless of the tissue-electrode angle. The significant changes in power with the tissue-electrode angle suggest that it is safer and more efficient to ablate using temperature-controlled RF generators. The maximal temperature was reached at locations within the tissue, a fraction of a millimeter away from the electrode surface. These locations did not always coincide with the local current density maxima. The locations of these hottest spots and the difference between their temperature and the temperature read by a sensor placed at the electrode tip changed with blood flow rate and tissue-electrode angle     

Noncontact method for sleep stage estimation

This paper describes a novel method to estimate sleep stage through noninvasive and unrestrained means. The Rechtschaffen and Kales (R-K) method is a standard to estimate sleep stage. However, it involves restraining the examinee and, thus, induces psychological stress. Furthermore, it requires specialists with a high degree of technical expertise and the use of an expensive polygraph. The sleep estimation method presented here is based on the noninvasive and unrestrained pneumatic biomeasurement method presented by the authors. Sleep stage transition in overnight sleep and the relationship between sleep stage and biosignals measured using the pneumatic method was analyzed and from the results, a mathematical model of sleep was created. Based on this model, a sleep stage estimator, including a sleep stage classifier and observer, was designed. The sleep state transition equation was the basis for the design of this observer, while the observed relationships were the basis for designing a classifier. Agreement of the estimated sleep stages with those obtained using the R-K method for the non-REM stage was 82.6%, for the REM stage was 38.3 % and for Wake was 70.5 %, including disagreement. However, the new method might ultimately result in better estimation of sleep stage due to the fact that it does not physically restrain the patient and does not induce psychological stress.     

Slice-to-volume registration and its potential application to interventional MRI-guided radio-frequency thermal ablation of prostate cancer

In this study, we registered live-time interventional magnetic resonance imaging (iMRI) slices with a previously obtained high-resolution MRI volume that in turn can be registered with a variety of functional images, e.g., PET, SPECT, for tumor targeting. We created and evaluated a slice-to-volume (SV) registration algorithm with special features for its potential use in iMRI-guided radio-frequency (RF) thermal ablation of prostate cancer. The algorithm features included a multiresolution approach, two similarity measures, and automatic restarting to avoid local minima. Imaging experiments were performed on volunteers using a conventional 1.5-T MR scanner and a clinical 0.2-T C-arm iMRI system under realistic conditions. Both high-resolution MR volumes and actual iMRI image slices were acquired from the same volunteers. Actual and simulated iMRI images were used to test the dependence of SV registration on image noise, receive coil inhomogeneity, and RF needle artifacts. To quantitatively assess registration, we calculated the mean voxel displacement over a volume of interest between SV registration and volume-to-volume registration, which was previously shown to be quite accurate. More than 800 registration experiments were performed. For transverse image slices covering the prostate, the SV registration algorithm was 100% successful with an error of <2 mm, and the average and standard deviation was only 0.4 mm +/- 0.2 mm. Visualizations such as combined sector display and contour overlay showed excellent registration of the prostate and other organs throughout the pelvis. Error was greater when an image slice was obtained at other orientations and positions, mostly because of inconsistent image content such as that from variable rectal and bladder filling. These preliminary experiments indicate that MR SV registration is sufficiently accurate to aid image-guided therapy.     

SOI technology for radio-frequency integrated-circuit applications

This paper presents a silicon-on-insulator (SOI) integration technology, including structures and processes of OFF-gate power nMOSFETs, conventional lightly doped drain (LDD) nMOSFETs, and spiral inductors for radio frequency integrated circuit (RFIC) applications. In order to improve the performance of these integrated devices, body contact under the source (to suppress floating-body effects) and salicide (to reduce series resistance) techniques were developed for transistors; additionally, locally thickened oxide (to suppress substrate coupling) and ultra-thick aluminum up to 6 /spl mu/m (to reduce spiral resistance) were also implemented for spiral inductors on high-resistivity SOI substrate. All these approaches are fully compatible with the conventional CMOS processes, demonstrating devices with excellent performance in this paper: 0.25-/spl mu/m gate-length offset-gate power nMOSFET with breakdown voltage (BV/sub DS/) /spl sim/ 22.0 V, cutoff frequency (f/sub T/)/spl sim/15.2 GHz, and maximal oscillation frequency (f/sub max/)/spl sim/8.7 GHz; 0.25-/spl mu/m gate-length LDD nMOSFET with saturation current (I/sub DS/)/spl sim/390 /spl mu/A//spl mu/m, saturation transconductance (g/sub m/)/spl sim/197 /spl mu/S//spl mu/m, cutoff frequency /spl sim/ 25.6 GHz, and maximal oscillation frequency /spl sim/ 31.4 GHz; 2/5/9/10-nH inductors with maximal quality factors (Q/sub max/) 16.3/13.1/8.95/8.59 and self-resonance frequencies (f/sub sr/) 17.2/17.7/6.5/5.8 GHz, respectively. These devices are potentially feasible for RFIC applications.     

Toroidal inductors for radio-frequency integrated circuits

Toroidal inductors achieve low loss by constraining magnetic flux to a well-defined path and away from ground planes and semiconducting substrates. This paper presents a micromachined implementation of the toroidal inductor, with focus primarily on microwave integrated circuits on a low-resistivity silicon wafer achieving a Q of 22 and a self-resonant frequency greater than 10 GHz. A verified analytic model is developed.     

Low-power radio-frequency ICs for portable communications

The contributions of integrated circuits to the RF front-end of wireless receivers and transmitters operating in broadcast and personal communications bands are surveyed. It is seen from this that when ICs enable a rethinking of the RF architecture, the wireless device can sometimes become significantly smaller, and consume much less power. Examples are taken from FM broadcast receivers, pagers, and cellular telephone handsets. Many semiconductor technologies are competing today to supply RF-ICs to cellular telephones. The various design styles and levels of integration are compared, with the conclusion that single-chip silicon transceivers, combined with architectures which substantially reduce off-chip passive components, will likely dominate digital cellular telephones in the near future. The survey also projects future trends for ICs for miniature spread-spectrum transceivers offering robust operation in the crowded spectrum. With sophistication in baseband digital signal processing, its increasing interaction with the RF sections, and with increasing experience in simplified radio architectures, all-CMOS radios appear promising in the 900 MHz to 2 GHz bands. A specific CMOS spread-spectrum transceiver project underway at the author's institution is discussed by way of example     

Multifunctional radio-frequency generator for cold atom experiments

We present a low cost radio-frequency (RF) generator suitable for experiments with cold atoms. The RF source achieves a sub-hertz frequency with tunable resolution from 0 MHz to 400 MHz and a maximum output power of 33 dBm. Based on a direct digital synthesizer (DDS) chip, we implement a ramping capability for frequency, amplitude and phase. The system can also operate as an arbitrary waveform generator. By measuring the stability in a duration of 600 s, we find the presented device performs comparably as Agilent33522A in terms of short-term stability. Due to its excellent performance, the RF generator has been already applied to cold atom trapping experiments.     

用于非接触超声洁牙的压电换能器设计

设计了一种非接触式的超声洁牙装置。通过12个超声变幅单元并联组合成牙套式阵列结构,突破了口腔有限空间内对换能器声发射能力的限制。采用声-结构耦合有限元模拟和回归分析,在300~400 kHz工作频段优选PZT-5H 为压电相,优化了透声层内空心圆锥形变幅杆设计。其辐射到牙列表面的平均声功率为2.32 W,正、负相最小声压幅值分别为794.668 kPa、-800.854 kPa。声场分布分析表明,在300~400 kHz频段内扫频激励产生的混响声场可以覆盖整个牙列,实现全方位的超空化非接触式洁牙。     

非接触式弱电实验供电平台的设计

非接触式弱电实验供电平台是一种新型非接触式电能供应系统,通过电磁感应耦合,实现非接触式能量传输,为负载提供电能。整个系统主要由电能转换、耦合变压器和能量调节三部分组成。电能转换主要完成能量逆变;耦合变压器将逆变后的能量耦合到用户端;能量调节主要为提高耦合到用户端能量的传输能力。该平台克服了传统导线多点接触式电能传输方式的不可靠和不可迁移等缺点,为移动电气设备、易燃易爆环境和水下设备的能量供给提供便捷、安全的解决方案。     

一种表面粗糙度非接触快速测量的新方法

照射在样品表面的激光束随着表面粗糙度的不同,反射光密度分布将不同;表面粗糙度增大时,反射光密度将被扩展。本文根据这一原理,提出一种使用激光束快速测量表面粗糙度的无触点光学法。通过测量反射光密度分布曲线的半宽度,由高斯曲线系数的标准差计算表面粗糙度。文中给出了测量结果。     

Broadband phase switches for radio-frequency and microwave interferometry

Two wideband phase switches have been built for radio and microwave interferometry. In one, the directions of current flow in a balanced transmission line are reversed periodically. The line is coupled into the interferometer via broadband baluns. The second device switches between the E plane outputs of a magic T.     

Noncontact Binocular Eye-Gaze Tracking for Point-of-Gaze Estimation in Three Dimensions

Binocular eye-gaze tracking can be used to estimate the point-of-gaze (POG) of a subject in real-world 3D space using the vergence of the eyes. In this paper, a novel noncontact model-based technique for 3D POG estimation is presented. The noncontact system allows people to select real-world objects in 3D physical space using their eyes, without the need for head-mounted equipment. Remote 3D POG estimation may be especially useful for persons with quadriplegia or Amyotrophic Lateral Sclerosis. It would also enable a user to select 3D points in space generated by 3D volumetric displays, with potential applications to medical imaging and telesurgery. Using a model-based POG estimation algorithm allows for free head motion and a single stage of calibration. It is shown that an average accuracy of 3.93 cm was achieved over a workspace volume of 30 times 23 times 25 cm (W times H times D) with a maximum latency of 1.5 s due to the digital filtering employed. The users were free to naturally move and reorient their heads while operating the system, within an allowable headspace of 3 cm times 9 cm times 14 cm.     

非接触式智能卡门锁红外系统的设计

本文介绍在感应式智能卡门锁电路的设计中应用到的一种红外技术。由于充分利用了红外电路和单片机10口特性,以最小的电路实现了较强的性能．     

Self‐Powered Noncontact Electronic Skin for Motion Sensing

The advancement of electronic skin envisions novel multifunctional human machine interfaces. Although motion sensing by detecting contact locations is popular and widely used in state‐of‐the‐art flexible electronics, noncontact localization exerts fascinations with unique interacting experiences. This paper presents a self‐powered noncontact electronic skin capable of detecting the motion of a surface electrified object across the plane parallel to that of the electronic skin based on electrostatic induction and triboelectric effects. The displacement of the object is calculated under the system of polar coordinates, with a resolution of 1.5 mm in the lengthwise direction and 0.76° in the angular direction. It can serve as a human machine interface due to its ability to sense noncontact motions. An additional self‐powered feature, enabled by its physical principles, solves the problem of power supply. This electronic skin consists of trilayers of polyethyleneterephthalate–indium tin oxide–polydimethylsiloxane (PDMS) films, and microstructured PDMS as the electrified layer, which can be achieved through simplified, low cost, and scalable fabrication. Transparency, flexibility, and less number of electrodes enable such electronic skin to be easily integrated into portable electronic devices, such as laptops, smart phones, healthcare devices, etc.