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1.
We show that electrical impedance tomography (EIT) image reconstruction algorithms with regularization based on the total variation (TV) functional are suitable for in vivo imaging of physiological data. This reconstruction approach helps to preserve discontinuities in reconstructed profiles, such as step changes in electrical properties at interorgan boundaries, which are typically smoothed by traditional reconstruction algorithms. The use of the TV functional for regularization leads to the minimization of a nondifferentiable objective function in the inverse formulation. This cannot be efficiently solved with traditional optimization techniques such as the Newton method. We explore two implementations methods for regularization with the TV functional: the lagged diffusivity method and the primal dual–interior point method (PD-IPM). First we clarify the implementation details of these algorithms for EIT reconstruction. Next, we analyze the performance of these algorithms on noisy simulated data. Finally, we show reconstructed EIT images of in vivo data for ventilation and gastric emptying studies. In comparison to traditional quadratic regularization, TV regulariza tion shows improved ability to reconstruct sharp contrasts.   相似文献   

2.
The goal of this experiment was to determine the electrical properties of the tissue reaction to implanted microelectrode arrays. We describe a new method of analyzing electrical impedance spectroscopy data to determine the complex impedance of the tissue reaction as a function of postimplantation time. A model is used to extract electrical model parameters of the electrode-tissue interface, and is used to isolate the impedance of the tissue immediately surrounding the microelectrode. The microelectrode arrays consist of microfabricated polyimide probes, incorporating four 50-mum-diameter platinum microelectrodes. The devices were implanted in the primary motor cortex of adult rats, and measurements were performed for 12 weeks. Histology was performed on implants at three time points in one month. Results demonstrate that the tissue reaction causes a rapid increase in bioimpedance over the first 20 days, and then stabilizes. This result is supported by histological data.  相似文献   

3.
The "magic angle" effect consists of the increase in signal intensity observed at a tendon or cartilage in a magnetic resonance image, when the tissue is oriented at an angle of approximately 55deg with respect to the main magnetic field B0. The exploitation of this phenomenon is often used to assist diagnosis of tendinous and other diseases, although practical difficulties derived from positioning target tissue at the desired orientation inside closed-bore scanners has made this exploitation hard to implement. A 3-DOF MR-compatible mechatronic system has been developed to position a variety of limbs at the magic angle inside a closed- bore scanner, actuated by a custom-developed pneumatic air motor. The system is capable of locating the desired anatomy with high accuracy, and is designed to position the target tissue at a minimal distance from the isocenter. The compatibility of the system is demonstrated, producing negligible artifacts and an insignificant reduction in signal to noise of the image. Preliminary clinical trials scanning the Achilles tendon of healthy volunteers prove the functionality of the device. An increase in signal intensity of up to 21-fold has been recorded in the tendon at the magic angle.  相似文献   

4.
While the mathematics, physics, and technology behind magnetic resonance (MR) and fluorescence image formation are distinctively different, the two modalities have significant complementary features to impart strong preclinical and clinical application synergies. Traditionally, hybrid MR and fluorescence imaging implied the use of a system where optical and MR signals can be concurrently acquired. In this case, the common geometry allows for the superposition of fluorescence images of cellular and subcellular processes onto anatomical and functional MR images. More recently, a different hybrid imaging paradigm is strongly evolving by utilizing hybrid MR-fluorescence nanoparticles. This approach offers a second paradigm of hybrid visualization where the common underlying contrast enables the coregistration of MR and fluorescence images acquired under different geometries. We review herein progress with the evolving field of multimodality MR and fluorescence imaging and discuss how these strategies offer a highly promising outlook in established and in novel preclinical and clinical applications.  相似文献   

5.
Epiretinal prostheses are being developed to bypass a degenerated photoreceptor layer and excite surviving ganglion and inner retinal cells. We used custom microfabricated multielectrode arrays with 200-mum-diameter stimulating electrodes and 10-mum-diameter recording electrodes to stimulate and record neural responses in isolated tiger salamander retina. Pharmacological agents were used to isolate direct excitation of ganglion cells from excitation of other inner retinal cells. Strength-duration data suggest that, if amplitude will be used for the coding of brightness or gray level in retinal prostheses, shorter pulses (200 mus) will allow for a smaller region in the area of the electrode to be excited over a larger dynamic range compared with longer pulses (1 ms). Both electrophysiological results and electrostatic finite-element modeling show that electrode-electrode interactions can lead to increased thresholds for sites half way between simultaneously stimulated electrodes (29.4 plusmn 6.6 nC) compared with monopolar stimulation (13.3 plusmn 1.7 nC, < 0.02). Presynaptic stimulation of the same ganglion cell with both 200- and 10- m-diameter electrodes yielded threshold charge densities of 12 plusmn 6 and 7.66 plusmn 1.30 nC/cm2, respectively, while the required charge was 12.5 plusmn 6.2 and 19 plusmn 3.3 nC.  相似文献   

6.
Noninvasive molecular and functional imaging in vivo is promising for detecting and monitoring various physiological conditions in animals and ultimately humans. To this end, we present a novel noninvasive technology, spectroscopic photoacoustic tomography (SPAT), which offers both strong optical absorption contrast and high ultrasonic spatial resolution. Optical contrast allows spectroscopic separation of signal contributions from multiple optical absorbers (e.g., oxyhemoglobin, deoxyhemoglobin, and a molecular contrast agent), thus enabling simultaneous molecular and functional imaging. SPAT successfully imaged with high resolution the distribution of a molecular contrast agent targeting integrin overexpressed in human U87 glioblastomas in nude mouse brains. Simultaneously, SPAT also imaged the hemoglobin oxygen saturation and the total hemoglobin concentration of the vasculature, which revealed hypoxia in tumor neovasculature. Therefore, SPAT can potentially lead to better understanding of the interrelationships between hemodynamics and specific biomarkers associated with tumor progression.  相似文献   

7.
In this letter, for the first time, we have successfully fabricated silicon-oxide-nitride-oxide-silicon (SONOS) devices with embedded silicon nanocrystals (Si-NCs) in silicon nitride using in situ method. This process is simple and compatible to modern IC processes. Different Si-NCs deposition times by in situ method were investigated at first. SONOS devices with embedded Si-NCs in silicon nitride exhibit excellent characteristics in terms of larger memory windows (> 5.5 V), lower operation voltage, high P/E speed, and longer retention time (> 108 s for 13% charge loss).  相似文献   

8.
Unresectable liver tumors are often treated with interstitial probes that modify tissue temperature, and efficacious treatment relies on image guidance for tissue targeting and assessment. Here, we report the in vivo evaluation of an interstitial applicator with a mechanically oscillating five-element dual-mode transducer. After thoroughly characterizing the transducer, tissue response to high-intensity ultrasound was numerically calculated to select parameters for experimentation in vivo. Using perfused porcine liver, B-mode sector images were formed before and after a 120-s therapy period, and M-mode imaging monitored the therapy axis during therapy. The time-averaged transducer surface intensity was 21 or 27 W/cm$^2$. Electroacoustic conversion efficiency was maximally 72 $pm$ 3% and impulse response length was 295 $pm$ 1.0 ns at $-$6 dB. The depth of thermal damage measured by gross histology ranged from 10 to 25 mm for 13 insertion sites. For six sites, M-mode data exhibited a reduction in gray-scale intensity that was interpreted as the temporal variation of coagulation necrosis. Contrast ratio analysis indicated that the gray-scale intensity dropped by 7.8 $pm ;$3.3 dB, and estimated the final lesion depth to an accuracy of 2.3 $pm ;$2.4 mm. This paper verified that the applicator could induce coagulation necrosis in perfused liver and demonstrated the feasibility of real-time monitoring.   相似文献   

9.
Fingerprint recognition is one of the dominant methods among all biometric techniques. However, current commercial fingerprint reader systems are based on analysis of surface topography of a finger and, thus, have tremendous security vulnerability for simply made artificial fingerprint dummies. In this letter, we demonstrate that a novel optical coherence tomography-based method for depth-resolved 2-D and 3-D imaging and assessment of artificial and real fingerprints could significantly enhance spoof-proofing of fingerprint reader systems as well as provide information of both artificial and real ridge and furrow patterns (that form the fingerprint patterns) simultaneously.  相似文献   

10.
Warped wafers can affect device performance, reliability, and linewidth control in various processing steps. We propose in this paper an in situ fault detection technique for wafer warpage in lithography. The use of advanced process control results in very small temperature disturbance making it suitable for industrial implementation  相似文献   

11.
We present the first in vivo cross-sectional conductivity image of the human leg with 1.7 mm pixel size using the magnetic resonance electrical impedance tomography (MREIT) technique. After a review of its experimental protocol by an Institutional Review Board (IRB), we performed MREIT imaging experiments of four human subjects using a 3 T MRI scanner. Adopting thin and flexible carbon–hydrogel electrodes with a large surface area and good contact, we could inject as much as 9 mA current in a form of 15 ms pulse into the leg without producing a painful sensation and motion artifact. Sequentially injecting two imaging currents in two different directions, we collected induced magnetic flux density data inside the leg. Scaled conductivity images reconstructed by using the single-step harmonic $B_{z}$ algorithm well distinguished different parts of the subcutaneous adipose tissue, muscle, crural fascia, intermuscular septum and bone inside the leg. We could observe spurious noise spikes in the outer layer of the bone primarily due to the MR signal void phenomenon there. Around the fat, the chemical shift of about two pixels occurred obscuring the boundary of the fat region. Future work should include a fat correction method incorporated in the MREIT pulse sequence and improvements in radio-frequency coils and image reconstruction algorithms. Further human imaging experiments are planned and being conducted to produce conductivity images from different parts of the human body.   相似文献   

12.
Glomerular capillary hemorrhage (GCH) in rat kidney provided a model for assessing in vivo gas body efficacy in diagnostic or therapeutic applications of ultrasound. Two diagnostic ultrasound machines were utilized: one monitored the harmonic B-mode contrast enhancement of the left kidney and the other exposed the right kidney for GCH production. Definity contrast agent was infused at 1, 2, 5, or 10 $mu$L/(kg·min) and infusion durations were 30, 60, 120, or 300 s. Exposure of the right kidney was at a peak rarefactional pressure amplitude of 2.3 MPa at 1.5 MHz. The circulating dose was estimated with a simple model of agent dilution and gas body loss. For 300 s infusion at 5 $mu$L/(kg·min), the left kidney image brightness increased to a plateau with an estimated 6.4 $pm$ 1.3 $mu$L/kg circulating dose with no GCH in histological sections. Exposure of the right kidney with a 1-s image interval reduced the estimated circulating dose to 1.3 $pm$ 0.3 $mu$ L/kg and induced 68.4% GCH. Dose and duration increases gave rapidly diminishing treatment effectiveness per gas body. The effective in vivo agent dose in rats can be reduced greatly due to high gas body destruction in the small animal, complicating predictions for similar conditions of human treatment.   相似文献   

13.
We developed a new exposure system to irradiate microwaves locally on a rabbit eye using a small coaxial-to-waveguide adapter filled with low-loss dielectric material as an antenna. A numerical rabbit model was also developed using X-ray computer tomography images, and the specific absorption rates (SARs) in the rabbit, especially in the eye, were analyzed with the finite-difference time-domain method. The temperature elevation in the exposed eye was also evaluated by solving a bioheat equation. Our exposure system can generate incident power density of 15 mW/cm2 at the surface of a rabbit eye with input power of 1 W. When the incident power density on the rabbit eye is 300 mW/cm2 , average SAR over the exposed eye and the whole body were approximately 108 and 1.8 W/kg, respectively. The exposure system can realize localized exposure to the eye with the ratio of exposed-eye averaged SAR to the whole-body averaged SAR was 60. The developed exposure system can achieve high-intensity exposure such as the threshold of cataracts, i.e., the eye-averaged SAR over 100 W/kg or the lens temperature over 41 degC with the incident power density of 300mW/cm2 without significant whole-body thermal stresses  相似文献   

14.
This paper discusses the design of a novel photoacoustic microscopy imaging system with promise for studying the structure of tissue microvasculature for applications in visualizing angiogenesis. A new 16 channel analog and digital high-frequency array based photoacoustic microscopy system (PAM) was developed using an Nd:YLF pumped tunable dye laser, a 30 MHz piezo composite linear array transducer, and a custom multichannel receiver electronics system. Using offline delay and sum beamforming and beamsteering, phantom images were obtained from a 6 $mu{hbox {m}}$ carbon fiber in water at a depth of 8 mm. The measured $-6~{rm dB}$ lateral and axial spatial resolution of the system was $100pm 5~mu{hbox {m}}$ and $45pm 5~mu{hbox {m}}$, respectively. The dynamic focusing capability of the system was demonstrated by imaging a composite carbon fiber matrix through a 12.5 mm imaging depth. Next, 2-D in vivo images were formed of vessels around 100 $mu{hbox {m}}$ in diameter in the human hand. Three-dimensional in vivo images were also formed of micro-vessels 3 mm below the surface of the skin in two Sprague Dawley rats.   相似文献   

15.
We present an interferometric setup for in situ monitoring of fiber tip positions when inserting optical fibers for fixation in fiber connector components. It ensures an accurate fiber tip position at the fiber connector's front facet and across the fiber array in cases where postinsertion polishing is not possible. We demonstrate our technique by populating a plastic fiber connector for optical interconnect applications, and compare the fiber tip position measured in situ using our setup with the position measured off-line using a commercial white light interferometer, showing a deviation smaller than 5%.   相似文献   

16.
We report the experimental in situ characterization of 30-40 MHz and 868 MHz wireless transmission schemes for ingestible capsules, in porcine carcasses. This includes a detailed study of the performance of a magnetically coupled near-field very high-frequency (VHF) transmission scheme that requires only one eighth of the volume and one quarter of the power consumption of existing 868-MHz solutions. Our in situ measurements tested the performance of four different capsules specially constructed for this study (two variants of each transmission scheme), in two scenarios. One mimicked the performance of a body-worn receiving coil, while the other allowed the characterization of the direction-dependent signal attenuation due to losses in the surrounding tissue. We found that the magnetically coupled near-field VHF telemetry scheme presents an attractive option for future, miniturized ingestible capsules for medical applications.  相似文献   

17.
A conventional differential pair LC oscillator is capable of generating only a single fundamental oscillation frequency. This brief presents the theoretical study of a novel oscillator that incorporates higher order LC filters to produce multiple oscillation frequencies that may be several octaves apart. These multiple oscillation frequencies are obtained from a single oscillator, thereby reducing the area of the circuit when being used for multistandard wireless applications. Moreover, a multi-order oscillator does not suffer from large parasitic capacitances from switches, which is a common drawback in switched-inductor tuned oscillators. A detailed analysis is carried out, and useful design insights are provided  相似文献   

18.
In order to advance biomechanical modeling, knee joint implant design and clinical treatment of knee joint pathology, accurate in vivo kinematic data of the combined patellofemoral and tibiofemoral joint during volitional activity are critical. For example, one cause of the increased prevalence of anterior knee pain in the female population is hypothesized to be altered tibiofemoral kinematics, resulting in pathological patellofemoral kinematics. Thus, the objectives of this paper were to test the hypothesis that knee joint kinematics vary based on gender and to explore the correlation between the 3-D kinematics of the patellofemoral and tibiofemoral joints. In order to accomplish these goals, a large (n = 34) normative database of combined six degree of freedom patellofemoral and tibiofemoral kinematics, acquired noninvasively during volitional knee extension-flexion using fast-PC (dynamic) magnetic resonance imaging, was established. In this normative database, few correlations between tibiofemoral and patellofemoral kinematics were found. Specifically, tibial external rotation did not predict lateral patellar tilt, as has been stated in previous studies. In general, significant differences could not be found based on gender. Further investigation into these relationships in the presence of pathology is warranted.  相似文献   

19.
An electromechanical microactuator comprised of shape memory polymer (SMP) and shape memory nickel-titanium alloy (nitinol) was developed and used in an endovascular thrombectomy device prototype. The microactuator maintains a straight rod shape until an applied current induces electro-resistive (Joule) heating, causing the microactuator to transform into a corkscrew shape. The straight-to-corkscrew transformation geometry was chosen to permit endovascular delivery through (straight form) and retrieval of (corkscrew form) a stroke-causing thrombus (blood clot) in the brain. Thermal imaging of the microactuator during actuation in air indicated that the steady-state temperature rise caused by Joule heating varied quadratically with applied current and that actuation occurred near the glass transition temperature of the SMP (86degC). To demonstrate clinical application, the device was used to retrieve a blood clot in a water-filled silicone neurovascular model. Numerical modeling of the heat transfer to the surrounding blood and associated thermal effects on the adjacent artery potentially encountered during clinical use suggested that any thermal damage would likely be confined to localized areas where the microactuator was touching the artery wall. This shape memory mechanical thrombectomy device is a promising tool for treating ischemic stroke without the need for infusion of clot-dissolving drugs.  相似文献   

20.
The link quality of mobile phones suffers from antenna mismatch due to fluctuating body effects. Techniques for adaptive control of impedance-matching L networks are presented, which provide automatic compensation of antenna mismatch. To secure reliable convergence, a cascade of two control loops is proposed for independent control of the real and imaginary parts of impedance. A secondary feedback path is used to enforce operation into a stable region when needed. These techniques exploit the basic properties of tunable series and parallel LC networks. A generic quadrature detector that offers a power-independent orthogonal reading of the complex impedance value is presented, which is used for direct control of variable capacitors. This approach renders calibration and elaborate software computation superfluous and allows for autonomous operation of adaptive antenna-matching modules.   相似文献   

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