Acoustic micro-vortexing of fluids,particles and cells in disposable microfluidic chips

We demonstrate an acoustic platform for micro-vortexing in disposable polymer microfluidic chips with small-volume (20 μl) reaction chambers. The described method is demonstrated for a variety of standard vortexing functions, including mixing of fluids, re-suspension of a pellet of magnetic beads collected by a magnet placed on the chip, and lysis of cells for DNA extraction. The device is based on a modified Langevin-type ultrasonic transducer with an exponential horn for efficient coupling into the microfluidic chip, which is actuated by a low-cost fixed-frequency electronic driver board. The transducer is optimized by numerical modelling, and different demonstrated vortexing functions are realized by actuating the transducer for varying times; from fractions of a second for fluid mixing, to half a minute for cell lysis and DNA extraction. The platform can be operated during 1 min below physiological temperatures with the help of a PC fan, a Peltier element and an aluminum heat sink acting as the chip holder. As a proof of principle for sample preparation applications, we demonstrate on-chip cell lysis and DNA extraction within 25 s. The method is of interest for automating and chip-integrating sample preparation procedures in various biological assays.     

MR‐monitored focused ultrasound using the acoustic‐coupling water bath as an intrinsic high‐mode dielectric resonator

The conventional set‐up for MR‐monitored focused ultrasound surgery includes a piezoelectric transducer and an acoustic‐coupling water bath integrated into the MR patient table; a large surface RF coil is placed close to the patient or, alternatively, the body coil is used as the MR receiver. Potential disadvantages of this approach are that the body coil has low sensitivity because of its low filling factor and the local RF coil can interfere with and cause reflections of the ultrasound irradiation. In this article, a completely new approach is presented, in which an MR transmit/receive coil is not needed at all. Instead, the dimensions of the water bath are adjusted so that a high‐order dielectric mode is excited, resulting in efficient MR excitation and reception at the transducer focal point. An example of monitoring ultrasound‐mediated heating in a phantom is shown on a 7‐T human system, although the new method can also be applied at lower fields. Copyright © 2014 John Wiley & Sons, Ltd.     

A differentiating pre-amplifier for the ultra-low frequency ballistocardiograph,and a method of calibrating the forces acting

The low frequency signals arising from the head-foot motion of the human body under the action of the heart, obtained from a coil and bar magnet velocity transducer, are differentiated by a series resonanceL, C andR circuit. This circuit, used in conjunction with small d.c. amplifiers of integrated circuit construction, is described. The method of calibrating the forces acting by means of the sinusoidal movement of a small mass is given with the relationships between the quantities used.

     

Asymmetric zonal shim coils for magnetic resonance applications

A method is presented for the systematic design of asymmetric zonal shim coils for magnetic resonance applications. Fourier-series methods are used to represent the magnetic field inside and outside a circular cylinder of length 2L and radius a. The current density on the cylinder is also represented using Fourier series. Any desired field can be specified in advance on the cylinder's radius, over some nonsymmetric portion pL相似文献   

Comparison of slotted tube versus coil stent implantation for ostial left anterior descending coronary artery stenosis: initial and late clinical outcomes.

Balloon angioplasty of ostial left anterior descending coronary artery (LAD) lesions has been associated with a high rate of acute complications and late restenosis. Recently, coronary stenting has been proposed as an effective treatment modality for ostial LAD lesions. To evaluate the effects of stent design on the development of late restenosis, we retrospectively analyzed the efficacy of slotted-tube stent implantation (40 patients, Palmaz-Schatz stent) and coil stent implantation (15 patients, tantalum Cordis stent) of ostial LAD stenosis. Six-month angiographic follow-up data were obtained in 31 patients (82%) with slotted-tube stent implantation and 12 patients (86%) with coil stent implantation. Angiographic restenosis was defined as > or =50% diameter stenosis. The angiographic restenosis rate was significantly lower in slotted-tube stent implantation (32%) than in coil stent implantation (67%) (p<0.05). Target lesion revascularization rate of slotted tube stent implantation was significantly lower (26%) than that of coil stent implantation (57%) (p<0.05). Coil stent implantation of ostial left anterior descending artery lesions was associated with higher late restenosis compared with slotted tube stent implantation. In conclusion, slotted-tube stent implantation might be considered to improve late clinical outcomes of ostial LAD lesions.     

Electromagnetic method forin situ stretch of individual muscles

A technique for stretching individual muscles in intact behaving animals via chronic intramuscular implantation of a permeable slug and use of an external electromagnet to apply force to the slug has been developed for use in the study of the role of sensory input due to muscle stretch in the control of skilled motor activity. This paper is an analysis of the force exerted on a permeable slug by a solenoid, and a discussion of practical aspects of design and control. The force exerted on a slug inside a coil is a function of slug length, cross-sectional area, and magnetisation properties and of coil size, geometry, and current. The force inside the coil may be increased by surrounding the coil with a permeable sleeve and thereby increasing the field strength inside the coil.     

Rat brain MRI at 16.4T using a capacitively tunable patch antenna in combination with a receive array

For MRI at 16.4T, with a proton Larmor frequency of 698 MHz, one of the principal RF engineering challenges is to generate a spatially homogeneous transmit field over a larger volume of interest for spin excitation. Constructing volume coils large enough to house a receive array along with the subject and to maintain the quadrature symmetry for different loading conditions is difficult at this frequency. This calls for new approaches to RF coil design for ultra‐high field MR systems. A remotely placed capacitively tunable patch antenna, which can easily be adjusted to different loading conditions, was used to generate a relatively homogeneous excitation field covering a large imaging volume with a transversal profile similar to that of a birdcage coil. Since it was placed in front of the animal, this created valuable free space in the narrow magnet bore around the subject for additional hardware. To enhance the reception sensitivity, the patch antenna was combined with an actively detunable 3‐channel receive coil array. In addition to increased SNR compared to a quadrature transceive surface coil, we were able to get high quality gradient echo and spin‐echo images covering the whole rat brain. Copyright © 2012 John Wiley & Sons, Ltd.     

Design study of a Miniaturized Displacement Transducer (MDT) for an active middle ear implant system

People suffering from moderate to severe hearing loss can be treated with active middle ear implants. A new approach in this field is to implant an electromechanical transducer onto the round window membrane in order to improve coupling and be able to treat patients with middle-ear problems. In this paper the design study for a miniaturized displacement transducer (MDT) for the round window is presented. Based on a requirement analysis, the basic principle and analytical modeling of the actuator is shown. A parameter variation study results in an optimized actuator configuration that is able to generate an amplification of 110 dB SPL theoretically. As a next step this actuator has to be manufactured and tested.     

Linearity of radio-frequency transducers

The paper outlines a method of monitoring changes in joint angle for a 2-dimensional movement of the limbs. The transducer described is acceptably linear over a range of 100°. It provides a useful alternative to goniometry in situations where the attachment of a goniometer across the joint would cause undue interference to the movement being studied. The transducer detects spatial movement by measuring the voltage induced in a sensing coil from a 1 MHz magnetic field produced by a small solenoid. 3-dimensional monitoring of body movements is discussed and shown to be feasible using a more complex system.     

极度非均匀磁场下的低场核磁共振成像技术研究进展

传统的磁共振成像设备系统庞大笨重、价格昂贵、检查噪声大、摆位困难等,因此限制其普及应用,而低场可移动式磁共振成像设备可以克服这些缺点。传统核磁共振成像采取大磁体包围小样品的模式,对高度均匀磁场环境(<5×10^-6/40 mm DSV)中的样品进行成像,相应的硬件设计和许可技术相对都比较成熟和完善。开放式核磁共振成像系统基于极度不均匀的磁场条件(>1 000×10^-6/mm DSV),相关的硬件设计、成像技术与传统的核磁共振成像系统差距很大,难度也急剧增加。全面论述低场开放式磁共振成像技术的起源、发展、关键技术,包括磁体、射频线圈、梯度线圈等硬件和射频脉冲设计、成像序列、图像后处理等方法,旨在为可移动式核磁共振成像设备的研发抛砖引玉。     

Design and construction of an esophageal phased array probe

The clinical urge for echocardiographic data from patients with inadequate image quality at the precordial examination has initiated the development of transesophageal scanning techniques. The orientation of heart structures with respect to the transducer position in the esophagus, the absence of interfering structures in the soundbeam and the constraints imposed by the anatomy of the esophagus result in a different set of parameters for the optimization of the transducer and its assembly. In this article, the design and construction of a miniaturized 5 MHz phased array transducer optimized for transesophageal scanning is described. Relevant parameters and their influence on the design will be discussed, such as: bandwidth, sensitivity, resolution (in three dimensions), focal depth and the production method.     

Diffusion tensor imaging using multiple coils for mouse brain connectomics

The correlation between brain connectivity and psychiatric or neurological diseases has intensified efforts to develop brain connectivity mapping techniques on mouse models of human disease. The neural architecture of mouse brain specimens can be shown non‐destructively and three‐dimensionally by diffusion tensor imaging, which enables tractography, the establishment of a connectivity matrix and connectomics. However, experiments on cohorts of animals can be prohibitively long. To improve throughput in a 7‐T preclinical scanner, we present a novel two‐coil system in which each coil is shielded, placed off‐isocenter along the axis of the magnet and connected to a receiver circuit of the scanner. Preservation of the quality factor of each coil is essential to signal‐to‐noise ratio (SNR) performance and throughput, because mouse brain specimen imaging at 7 T takes place in the coil‐dominated noise regime. In that regime, we show a shielding configuration causing no SNR degradation in the two‐coil system. To acquire data from several coils simultaneously, the coils are placed in the magnet bore, around the isocenter, in which gradient field distortions can bias diffusion tensor imaging metrics, affect tractography and contaminate measurements of the connectivity matrix. We quantified the experimental alterations in fractional anisotropy and eigenvector direction occurring in each coil. We showed that, when the coils were placed 12 mm away from the isocenter, measurements of the brain connectivity matrix appeared to be minimally altered by gradient field distortions. Simultaneous measurements on two mouse brain specimens demonstrated a full doubling of the diffusion tensor imaging throughput in practice. Each coil produced images devoid of shading or artifact. To further improve the throughput of mouse brain connectomics, we suggested a future expansion of the system to four coils. To better understand acceptable trade‐offs between imaging throughput and connectivity matrix integrity, studies may seek to clarify how measurement variability, post‐processing techniques and biological variability impact mouse brain connectomics.     

Ballistocardiogram of avian eggs determined by an electromagnetic induction coil

As an avian embryo grows within a eggshell, the whole egg is moved by embryonic activity and also by the embryonic heartbeat. A technical interest in detecting minute biological movements has prompted the development of techniques and systems to measure the cardiogenic ballistic movement of the egg or ballistocardiogram. (BCG). In this context, there is interest in using an electromagnetic induction coil (solenoid) as another simple sensor to measure the BCG and examining its possibility for BCG measurement. A small permanent magnet is attached tightly to the surface of an incubated egg, and then the egg with the magnet is placed in a solenoid. Preliminary model analysis is made to design a setup of the egg, magnet and solenoid coupling system. Then, simultaneous measurement with a laser displacement measuring system, developed previously, is made for chicken eggs, indicating that the solenoid detects the minute cardiogenic ballistic movements and that the BCG determined is a measure of the velocity of egg movements.     

New epidural intracranial-pressure transducer with reduced tissue stress interference

The literature pertaining to epidural-pressure measurement gives the impression that, with the use of coplanar transducers, errors due to dural bending are minimised and an epidural-pressure equivalent to the ventricular fluid pressure is obtained. By means of a simple theoretical analysis, it has been shown that, for chronic implantation measurements, coplanar systems do not have any special advantages over noncoplanar systems because both are subject to errors due to tissue compressive stresses of magnitudes considerably greater than the dural bending stresses. Therefore the considerably simpler noncoplanar transducers, together with a special approach toin vivo calibration, are adequate if they are of a form which selectively responds to c.s.f. pressure more than to tissue stresses. The conventional circular-diaphragm transducer does not satisfy the requirement. This limitation can be circumvented by reducing the deflection constraints. A new design proposed has the special feature that it responds directly to c.s.f. pressure, even though immediately over the transducer face the subarachnoid space is obliterated Model as well as animal experiments substantiate the claim. Simultaneous measurements with the new transducer and a direct c.s.f. pressure transducer show that the c.s.f. pressure changes are correctly indicated by the new transducer.     

Reduction of pulsed gradient settling time in the superconducting magnet of a magnetic resonance instrument

The implementation of electronic compensation for eddy currents to reduce the gradient settling times on a superconducting magnet is described. Field plots inside the magnet indicate the importance of assessing the field changes at several positions in the magnet. The effect of an asymmetry between the gradient coil system and the cryostat is demonstrated. A modified compensation circuit is described to overcome this mechanical asymmetry.     

Circular planar coil as electromagnetic movement detector of inside organs in biosystems: the fundamental design relationships

A simple analytical approach is suggested to study the fundamental properties of a circular planar coil used as an electromagnetic movement transducer for internal organs in biosystems. First, for this purpose a general expression for the reactance of the coil is derived when put near a semi-finite lossy dielectric medium Ω, secondly a new expression of the reactance variation is obtained in the case that a region Γ, with different electromagnetic characteristics, moves inside Ω. On this basis the existence is easily shown of a focal distance for this particular transducer as already foreseen by means of experimental measurements and numerical analysis. This characteristic is very interesting as it may be used to improve the very poor spatial resolution capability of this kind of transducers.     

Magnetic propulsion of a magnetic device using three square-Helmholtz coils and a square-Maxwell coil

We introduce a square coil system for remote magnetic navigation of a magnetic device without any physical movements of the coils. We used three square-Helmholtz coils and a square-Maxwell coil for magnetic propulsion of a small magnet along the desired path. All the square coils are mountable on a cubic frame that has an opening to accommodate a living subject. The square-Helmholtz coils control the magnetic propulsion direction by generating uniform magnetic field along the desired direction while the square-Maxwell coil controls the propulsion force by generating magnetic gradient field. We performed magnetic propulsion experiments with a downscaled coil set and a three-channel coil driver. Experimental results demonstrate that we can use the square coil set for magnetic navigation of a magnetic device without any physical movements of the coils.     

Flat crossed-coil detector for blood flow measurement using nuclear magnetic resonance

A new flat crossed-coil nuclear magnetic resonance (n.m.r.) detector can be used to measure flood flow at many regions of the body, is introduced. It is compared, bothin vitro andin vivo, with the already proven cylindrical crossed-coil n.m.r. detector. Both detectors use a single high-field homogenous magnet. A single-sideband receiver reduces the effect of transmitter leakage into the receiver coil to allow the use of a high-level transmitter field. Preliminary application of the flat crossed-coil detector to the detection of cerebral blood flow is presented.     

Experimental method to reveal the effect of rotor magnet size and air gap on artificial heart driving motor torque and efficiency

To investigate experimentally the effect of rotor magnet design on artificial heart driving motor performance, seven rotors with different magnet lengths or thicknesses, as well as different peripheral angles, were manufactured and tested in the same motor stator with different rotating speeds. The input power (voltage and current) and output torque were measured and the motor efficiency was computed. The results demonstrated that the reduction of rotor magnet size and the enlargement of the air gap between the rotor magnets and the stator coil core have no significant effect on motor efficiency, but will reduce the torque value on which the motor achieves the highest efficiency; it could be remedied however by increasing the rotating speed, because the torque at the high efficiency point will increase along with the rotating speed. These results may provide a basis for developing small rotor magnets, large air gap and high efficiency motors for driving an artificial heart pump.     

Measurement of the vibration of the middle ear ossicles with removed eardrum: A method for quantification of ossicular fixation

Chronic inflammation of the middle ear is a common disease in which the mobility of the middle ear ossicles may be reduced; resulting in hearing impairment. Knowledge of the degree of ossicular mobility is useful in helping a surgeon determine how to proceed with treatment. In advanced cases, mobility can be assessed by manually pressing on the ossicles, but in less advanced cases manual assessment can provide limited useful information. Ossicular vibration can be measured with a laser vibrometer, but only the manubrium of the malleus is optically visible without removing the eardrum. Since the eardrum is the means by which acoustic energy is translated into the mechanical motion of the ossicles, removing it renders any subsequent measurements of ossicular motion meaningless. We therefore devised a technique in which the ossicles are vibrated magnetically. After measuring the response of the umbo to acoustic stimulation, we removed the eardrum and attached a small magnet to the manubrium. An electromagnetic excitation coil was then used to vibrate the magnet, and the signal to the coil was adjusted until the vibration of the ossicles matches that achieved acoustically. In this paper we explain the method and describe some test measurements on a vinyl membrane, and some preliminary results obtained on a fresh-frozen human temporal bone before and after artificial fixation of the ossicles.