A 4-channel coil array interconnection by analog direct modulation optical link for 1.5-T MRI.

Optical glass fiber shows great advantages over coaxial cables in terms of electromagnetic interference, thus, it should be considered a potential alternative for magnetic resonance imaging (MRI) receive coil interconnection, especially for a large number coil array at high field. In this paper, we propose a 4-channel analog direct modulation optical link for a 1.5-T MRI coil array interconnection. First, a general direct modulated optical link is compared to an external modulated optical link. And then the link performances of the proposed direct modulated optical link, including power gain, frequency response, and dynamic range, are analyzed and measured. Phantom and in vivo head images obtained using this optical link are demonstrated for comparison with those obtained by cable connections. The signal-to-noise (SNR) analysis shows that the optical link achieves 6%-8% SNR a improvement over coaxial cables by elimination of electrical interference between cables during MR signal transmission.

Photorefractive solitons of arbitrary and controllable linear polarization determined by the local bias field.

We discuss and experimentally demonstrate a scheme to achieve photorefractive solitons of arbitrary linear polarization using the quadratic electro-optic effect and describe the observation of the self-trapping of a set of linear polarized beams in different positions of a paraelectric photorefractive crystal of potassium-lithium-tantalate-niobate (KLTN) biased by the inhomogeneous field produced by two miniaturized top electrodes. The polarization of the single solitons of the set is determined by the local electrostatic configuration and the underlying tunable anisotropy, which is detected through zero-field electro-activation.

The effect of transponder motion on the accuracy of the Calypso Electromagnetic localization system.

PURPOSE: To determine position and velocity-dependent effects in the overall accuracy of the Calypso Electromagnetic localization system, under conditions that emulate transponder motion during normal free breathing. METHODS AND MATERIALS: Three localization transponders were mounted on a remote-controlled turntable that could move the transponders along a circular trajectory at speeds up to 3 cm/s. A stationary calibration established the coordinates of multiple points on each transponder's circular path. Position measurements taken while the transponders were in motion at a constant speed were then compared with the stationary coordinates. RESULTS: No statistically significant changes in the transponder positions in (x,y,z) were detected when the transponders were in motion. CONCLUSIONS: The accuracy of the localization system is unaffected by transponder motion.

Non-invasive longitudinal assessment of facial growth in children and adolescents with hypohidrotic ectodermal dysplasia.

Facial growth patterns in 12 subjects (six boys and six girls) with hypohidrotic ectodermal dysplasia (HED) were analyzed and compared with facial growth patterns obtained in healthy reference peers. All subjects with HED were aged 7 yr (mean age +/- standard deviation: 7.08 +/- 0.41 yr) at the first examination and 14 yr (mean age +/- standard deviation: 14.56 +/- 0.34 yr) at the last examination. In each subject, the three-dimensional coordinates of facial landmarks were collected non-invasively at eight subsequent years. The volumes of forehead, nose, maxilla and mandible, upper lips, and lower lips were estimated. For each facial volume, differential values between different time points were calculated individually, separately for the 'childhood' (7-10 yr) and the 'adolescence' (11-14 yr) growth period in both HED and reference subjects. Children and adolescents with HED had a slightly reduced global facial growth in comparison with normal reference peers. The peak mandibular and maxillary development was delayed by approximately 2 yr towards later adolescence. The present non-invasive system seems to be useful for studying longitudinal changes of facial growth in healthy and syndromic subjects.

Local electric field enhancement and polarization effects in a surface-enhanced Raman scattering fiber sensor with chessboard nanostructure.

A surface-enhanced Raman scattering fiber sensor with chessboard nanostructure on a cleaved fiber facet is studied by finite-difference time-domain method. Surface plasmons at the metal coated nanostructured fiber facet can be effectively excited and strong local electric field enhancement is obtained. Studies on the influence of light polarization demonstrate a large polarization dependence of the field enhancement factor while the polarization effects on the plasmon resonance wavelength are relatively small.

Electromagnetic concentrators with reduced material parameters based on coordinate transformation.

Omni-directional electromagnetic field concentrators have been recently reported by Marco Rahm et al. [Photon. Nanostruct.: Fundam. Appl. 6, 87 (2008)] based on form-invariant coordinate transformations related to its Jacobi transformation matrix. Using transverse-electric wave illumination, we reduced the complex material parameters of the concentrator for future practical implementation. Concentrators with different set of permittivity and permeability tensors are proposed. The electromagnetic concentrating performance and the scattering properties at the inner and outer boundary of these concentrators are theoretically and numerically analyzed. Finally we obtain a set of material tensors for a concentrator that simultaneously has perfect matched interior and exterior interfaces.

Saturation recovery EPR and ELDOR at W-band for spin labels.

A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE(011) cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW(-1/2) with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T(1e) previously reported for these molecules in the range of 2-35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T(1) values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524-9529]. The values of T(1e) decrease at 94 GHz relative to values at 35 GHz.

The effect of brain hematoma location on volumetric inductive phase shift spectroscopy of the brain with circular and magnetron sensor coils: a numerical simulation study.

This numerical simulation study addressed the effects of the location of a discrete brain hematoma on the volumetric inductive phase shift of the brain measured with an induction circular sensor coil and an induction magnetron sensor coil. The theoretical study simulates the brain cavity as a circular sphere transversely centered with respect to the circular and magnetron sensor coils. As a case study for the effects of hematoma location, we employed similar size simulated spherical hematomas placed at three different positions from the center of the brain outward. A three-dimensional finite element analysis of the field equations in the frequency range from 100 kHz to 100 MHz revealed a substantial effect of hematoma location on the ability of both the circular and magnetron sensors to detect the hematomas. In particular it was found that there are frequencies, which may be related to resonance, at which the occurrence of the hematomas has no effect on the volumetric inductive phase shift of the brain. Furthermore it was found that the relative sensitivity of circular and magnetron sensor coils with respect to the occurrence of hematoma varies with the location of the hematoma.

Ultrabroadband polarization analysis of terahertz pulses.

We describe the characteristics of a sensitive photoconductive detector that simultaneously measures orthogonal electric field components of electromagnetic transients with bandwidths up to 30 THz. The device consists of an As(+) implanted GaAs photoconducting region at the centre of a pair of perpendicular bow-tie antennas. The performance is illustrated by studies of optical rectification in GaSe, retardation in a birefringent polymer film and THz emission from impulsively excited optical phonons in GaN.

Guided plasmonic modes in nanorod assemblies: strong electromagnetic coupling regime.

We demonstrate that the coupling between plasmonic modes of oriented metallic nanorods results in the formation of an extended (guided) plasmonic mode of the nanorod array. The electromagnetic field distribution associated to this mode is found to be concentrated between the nanorods within the assembly and propagates normally to the nanorod long axes, similar to a photonic mode waveguided by an anisotropic slab. This collective plasmonic mode determines the optical properties of nanorod assemblies and can be tuned in a wide spectral range by changing the nanorod array geometry. This geometry represents a unique opportunity for light guiding applications and manipulation at the nanoscale as well as sensing applications and development of molecular plasmonic devices.

A new simple asymmetric hysteresis operator and its application to inverse control of piezoelectric actuators.

Piezoelectric actuators (PEAs) are commonly used as micropositioning devices due to their high resolution, high stiffness, and fast frequency response. Because piezoceramic materials are ferroelectric, they fundamentally exhibit hysteresis behavior in their response to an applied electric field. The positioning precision can be significantly reduced due to nonlinear hysteresis effects when PEAs are used in relatively long range applications. This paper describes a new, precise, and simple asymmetric hysteresis operator dedicated to PEAs. The complex hysteretic transfer characteristic has been considered in a purely phenomenological way, without taking into account the underlying physics. This operator is based on two curves. The first curve corresponds to the main ascending branch and is modeled by the function f1. The second curve corresponds to the main reversal branch and is modeled by the function g2. The functions f(1) and g(2) are two very simple hyperbola functions with only three parameters. Particular ascending and reversal branches are deduced from appropriate translations of f(1) and g(2). The efficiency and precision of the proposed approach is demonstrated, in practice, by a real-time inverse feed-forward controller for piezoelectric actuators. Advantages and drawbacks of the proposed approach compared with classical hysteresis operators are discussed.

HYSCORE and DEER with an upgraded 95GHz pulse EPR spectrometer.

The set-up of a new microwave bridge for a 95 GHz pulse EPR spectrometer is described. The virtues of the bridge are its simple and flexible design and its relatively high output power (0.7 W) that generates pi pulses of 25 ns and a microwave field, B(1)=0.71 mT. Such a high B(1) enhances considerably the sensitivity of high field double electron-electron resonance (DEER) measurements for distance determination, as we demonstrate on a nitroxide biradical with an interspin distance of 3.6 nm. Moreover, it allowed us to carry out HYSCORE (hyperfine sublevel-correlation) experiments at 95 GHz, observing nuclear modulation frequencies of 14N and 17O as high as 40 MHz. This opens a new window for the observation of relatively large hyperfine couplings, yet not resolved in the EPR spectrum, that are difficult to observe with HYSCORE carried out at conventional X-band frequencies. The correlations provided by the HYSCORE spectra are most important for signal assignment, and the improved resolution due to the two dimensional character of the experiment provides 14N quadrupolar splittings.

[A magnetic therapy apparatus with an adaptable electromagnetic spectrum for the treatment of prostatitis and gynecopathies].

Problems of engineering and algorithm development of magnetic therapy apparatuses with pseudo-random radiation spectrum within the audio range for treatment of prostatitis and gynecopathies are considered. A typical design based on a PIC 16F microcontroller is suggested. It includes a keyboard, LCD indicator, audio amplifier, inducer, and software units. The problem of pseudo-random signal generation within the audio range is considered. A series of rectangular pulses is generated on a random-length interval on the basis of a three-component random vector. This series provides the required spectral characteristics of the therapeutic magnetic field and their adaptation to the therapeutic conditions and individual features of the patient.

Performance characterization of a rotary centrifugal left ventricular assist device with magnetic suspension.

The MiTiHeart (MiTiHeart Corporation, Gaithersburg, MD, USA) left ventricular assist device (LVAD), a third-generation blood pump, is being developed for destination therapy for adult heart failure patients of small to medium frame that are not being served by present pulsatile devices. The pump design is based on a novel, patented, hybrid passive/active magnetic bearing system with backup hydrodynamic thrust bearing and exhibits low power loss, low vibration, and low hemolysis. Performance of the titanium alloy prototype was evaluated in a series of in vitro tests with blood analogue to map out the performance envelop of the pump. The LVAD prototype was implanted in a calf animal model, and the in vivo pump performance was evaluated. The animal's native heart imparted a strong pulsatility to the flow rate. These tests confirmed the efficacy of the MiTiHeart LVAD design and confirmed that the pulsatility does not adversely affect the pump performance.

Towards THz medical imaging; reflective imaging of animal tissues.

A reflective THz imaging system has been developed, and features a photoconductive switch and zero-bias Schottky diode detector. The system was used to image deli meats and can distinguish between muscle and adipose tissue based on water content. This capability is a step towards the development of THz medical imaging systems.

Bronchoscopic implantation of a novel wireless electromagnetic transponder in the canine lung: a feasibility study.

PURPOSE: The success of targeted radiation therapy for lung cancer treatment is limited by tumor motion during breathing. A real-time, objective, nonionizing, electromagnetic localization system using implanted electromagnetic transponders has been developed (Beacon electromagnetic transponder, Calypso Medical Technologies, Inc., Seattle, WA). We evaluated the feasibility and fixation of electromagnetic transponders bronchoscopically implanted in small airways of canine lungs and compared to results using gold markers. METHODS AND MATERIALS: After approval of the Animal Studies Committee, five mongrel dogs were anesthetized, intubated, and ventilated. Three transponders were inserted into the tip of a plastic catheter, passed through the working channel of a flexible bronchoscope, and implanted into small airways of a single lobe using fluoroscopic guidance. This procedure was repeated for three spherical gold markers in the opposite lung. One, 7, 14, 28, and 60 days postimplantation imaging was used to assess implant fixation. RESULTS: Successful bronchoscopic implantation was possible for 15 of 15 transponders and 12 of 15 gold markers; 3 markers were deposited in the pleural space. Fixation at 1 day was 15 of 15 for transponders and 12 of 12 for gold markers. Fixation at 60 days was 6 of 15 for transponders and 7 of 12 for gold markers, p value = 0.45. CONCLUSIONS: Bronchoscopic implantation of both transponders and gold markers into the canine lung is feasible, but fixation rates are low. If fixation rates can be improved, implantable electromagnetic transponders may allow improved radiation therapy for lung cancer by providing real-time continuous target tracking. Developmental work is under way to improve the fixation rates and to reduce sensitivity to implantation technique.

A method for quantifying condylar motion in patients with osteoarthritis using an electromagnetic tracking device and computed tomography imaging.

PURPOSE: The purpose of this study was to develop a method to accurately study the kinematic changes of the temporomandibular joint (TMJ) in patients treated with hemijoint implant reconstruction for dysfunction of advanced degenerative osteoarthritis. MATERIALS AND METHODS: Mandibular kinematic motion data and patient-specific computed tomography (CT) data were acquired. Patients were fitted with custom dental stents that were embedded with metal markers to link the mandibular kinematics data with the 3-dimensional TMJ CT images. An electromagnetic tracking device was used to collect kinematic motion data during maximal mouth opening and closing. The coordinate systems of the kinematic data and CT data were registered to calculate the motion of the mandibular condyle. RESULTS: This technique was successfully used to study patients with motion aberration of the TMJ due to osteoarthritis. A typical case is illustrated in which the motion of both mandibular condyles was simulated preoperatively and postoperatively. CONCLUSIONS: The results of this study suggest that it is possible to use the proposed methodology to accurately quantify the motion of the mandibular condyle in 3 dimensions. The developed technique is user-friendly and noninvasive to the patient. The proposed methodology is a potential clinical tool that may be used in the management of patients with TMJ dysfunction.

Z-path SAW RFID tag.

Surface acoustic wave (SAW) radio-frequency identification (RFID) tags are soon expected to be produced in very high volumes. The size and cost of a SAW RFID tag will be key parameters for many applications. Therefore, it is of primary importance to reduce the chip size. In this work, we describe the design principles of a 2.4-GHz SAW RFID tag that is significantly smaller than earlier reported tags. We also present simulated and experimental results. The coded signal should arrive at the reader with a certain delay (typically about 1 micros), i.e., after the reception of environmental echoes. If the tag uses a bidirectional interdigital transducer (IDT), space for the initial delay is needed on both sides of the IDT. In this work, we replace the bidirectional IDT by a unidirectional one. This halves the space required by the initial delay because all the code reflectors must now be placed on the same side of the IDT. We reduce tag size even further by using a Z-path geometry in which the same space in x-direction is used for both the initial delay and the code reflectors. Chip length is thus determined only by the space required by the code reflectors.

Development of gas pulsing system for electron cyclotron resonance ion source.

A gas-pulsing system for an electron cyclotron resonance ion source with all permanent magnets (Kei2 source) at NIRS has been developed and tested. The system consists of a small vessel (30 ml) to reserve CH(4) gas and two fast solenoid valves that are installed at both sides of the vessel. They are connected to each other and to the Kei2 source by using a stainless-steel pipe (4 mm inner diameter), where the length of the pipe from the valve to the source is 60 cm and the conductance is 1.2 l/s. From the results of the test, almost 300 e microA for a pulsed (12)C(4+) beam was obtained at a Faraday cup in an extraction-beam channel with a pressure range of 4000 Pa in the vessel. At this time, the valve has an open time of 10 ms and the delay time between the valve open time and the application of microwave power is 100 ms. In experiments, the conversion efficiency for input CH(4) molecules to the quantity of extracted (12)C(4+) ions in one beam pulse was found to be around 3% and the ratio of the total amount of the gas requirement was only 10% compared with the case of continuous gas provided in 3.3 s of repetition in HIMAC.