Fiducial-based translational localization accuracy of electromagnetic tracking system and on-board kilovoltage imaging system.

PURPOSE: The Calypso medical four-dimensional localization system uses AC electromagnetics, which do not require ionizing radiation, for accurate, real-time tumor tracking. This investigation compared the static and dynamic tracking accuracy of this system to that of an on-board imaging kilovoltage X-ray system for concurrent use of the two systems. METHODS AND MATERIALS: The localization accuracies of a kilovoltage imaging system and a continuous electromagnetic tracking system were compared. Using an in-house developed four-dimensional stage, quality-assurance fixture containing three radiofrequency transponders was positioned at a series of static locations and then moved through the ellipsoidal and nonuniform continuous paths. The transponder positions were tracked concurrently by the Calypso system. For static localization, the transponders were localized using portal images and digitally reconstructed radiographs by commercial matching software. For dynamic localization, the transponders were fluoroscopically imaged, and their positions were determined retrospectively using custom-written image processing programs. The localization data sets were synchronized with and compared to the known quality assurance fixture positions. The experiment was repeated to retrospectively track three transponders implanted in a canine lung. RESULTS: The root mean square error of the on-board imaging and Calypso systems was 0.1 cm and 0.0 cm, respectively, for static localization, 0.22 mm and 0.33 mm for dynamic phantom positioning, and 0.42 mm for the canine study. CONCLUSION: The results showed that both localization systems provide submillimeter accuracy. The Calypso and on-board imaging tracking systems offer distinct sets of advantages and, given their compatibility, patients could benefit from the complementary nature of the two systems when used concurrently.

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.

Time domain simulation of electromagnetic cloaking structures with TLM method.

The increasing interest in invisible cloaks has been prompted in part by the availability of powerful computational resources which permit numerical studies of such a phenomenon. These are usually carried out with commercial software. We report here a full time domain simulation of cloaking structures with the Transmission Line Modeling (TLM) method. We first develop a new condensed TLM node to model metamaterials in two dimensional situations; various results are then presented, with special emphasis on what is not easily achievable using commercial software.

Setup and dosimetry for exposure of human skin in vivo to RF-EMF at 900 MHz.

The aim of this study was a dosimetrical analysis of an experimental setup used in the exposure of 10 female volunteers to GSM 900 radiation. The exposure was carried out by irradiating a small region of the right forearms of the volunteers for 1 h, after which biopsies were taken from the exposed skin for protein analysis. The source of irradiation was a half-wave dipole fed with a computer controlled GSM phone. The specific absorption rate (SAR) induced in the skin biopsy was assessed by computer simulations. The numerical model of the arm consisted of a muscle tissue simulating cylinder covered with thin skin (1 mm) and fat (3 mm) layers. The simulation models were validated by measurements with a homogeneous cylindrical liquid phantom. The average SAR value in the biopsy was 1.3 W/kg and the estimated uncertainty +/-20% (K = 2). The main source of error was found to be variations in the distance of the forearm from the dipole (10 +/- 1 mm). Other significant sources of uncertainty are individual variations of the fat layer and arm thicknesses, and the uncertainty of radio frequency (RF) power measurement.

Researching on resonance characteristics influenced by the structure parameters of 1-3-2 piezocomposites plate.

The 1-3-2 composite is made of 1-3 composite and ceramic base. Its effective properties are calculated based on the linear piezoelectric theory and uniform field theory. The influence of piezoelectric phase volume fraction and composite aspect (thickness/width) on resonance characteristic of square 1-3-2 piezoelectric composite plate has been researched. In addition, some 1-3-2 composite samples were fabricated by dice-fill technology. The resonance frequency of samples was investigated. The results show that the experiment agrees well with the calculation. The pure thickness resonance mode of 1-3-2 composite will be gained when the volume fraction of ceramic bottom is less than 30%; that of ceramic rods is in the range of 30 approximately 80% and the ratio of thickness to width is less than 0.35.

X-ray topography of piezoelectric La(3)Ta(14)Ga(5.5)O(14) crystal grown by Czochralski Method.

We performed synchrotron X-ray topography on a La(3)Ta0(0.5)Ga (5.5)O(14) (LTG) crystal grown by the Czochralski method. Since a synchrotron X-ray source can provide high-energy X-rays, one can detect bulk structures by X-ray topography. LTG is one of the most attractive piezoelectric crystals along with La(3)Ga(5)SiO(14) (LGS) because of its excellent acoustic properties (temperature compensation of acoustic losses). Since LTG single crystals can be grown from a stoichiometric melt, it was expected that single crystals with better quality than the LGS crystal, which cannot be grown from a stoichiometric system but only from a congruent melt, can be obtained. However, 60 keV X-ray topography revealed that the LTG crystal quality was not as high as the LGS crystal quality. The crystal quality of the central region was lower than that of the surrounding region.

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.

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.

[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.

Multi-institutional clinical experience with the Calypso System in localization and continuous, real-time monitoring of the prostate gland during external radiotherapy.

PURPOSE: To report the clinical experience with an electromagnetic treatment target positioning and continuous monitoring system in patients with localized prostate cancer receiving external beam radiotherapy. METHODS AND MATERIALS: The Calypso System is a target positioning device that continuously monitors the location of three implanted electromagnetic transponders at a rate of 10 Hz. The system was used at five centers to position 41 patients over a full course of therapy. Electromagnetic positioning was compared to setup using skin marks and to stereoscopic X-ray localization of the transponders. Continuous monitoring was performed in 35 patients. RESULTS: The difference between skin mark vs. the Calypso System alignment was found to be >5 mm in vector length in more than 75% of fractions. Comparisons between the Calypso System and X-ray localization showed good agreement. Qualitatively, the continuous motion was unpredictable and varied from persistent drift to transient rapid movements. Displacements > or =3 and > or =5 mm for cumulative durations of at least 30 s were observed during 41% and 15% of sessions. In individual patients, the number of fractions with displacements > or =3 mm ranged from 3% to 87%; whereas the number of fractions with displacements > or =5 mm ranged from 0% to 56%. CONCLUSION: The Calypso System is a clinically efficient and objective localization method for positioning prostate patients undergoing radiotherapy. Initial treatment setup can be performed rapidly, accurately, and objectively before radiation delivery. The extent and frequency of prostate motion during radiotherapy delivery can be easily monitored and used for motion management.

The cortical generators of P3a and P3b: a LORETA study.

The P3 is probably the most well known component of the brain event-related potentials (ERPs). Using a three-tone oddball paradigm two different components can be identified: the P3b elicited by rare target stimuli and the P3a elicited by the presentation of rare non-target stimuli. Although the two components may partially overlap in time and space, they have a different scalp topography suggesting different neural generators. The present study is aimed at defining the scalp topography of the two P3 components by means of reference-independent methods and identifying their electrical cortical generators by using the low-resolution electromagnetic tomography (LORETA). ERPs were recorded during a three-tone oddball task in 32 healthy, right-handed university students. The scalp topography of the P3 components was assessed by means of the brain electrical microstates technique and their cortical sources were evaluated by LORETA. P3a and P3b showed different scalp topography and cortical sources. The P3a electrical field had a more anterior distribution as compared to the P3b and its generators were localized in cingulate, frontal and right parietal areas. P3b sources included bilateral frontal, parietal, limbic, cingulate and temporo-occipital regions. Differences in scalp topography and cortical sources suggest that the two components reflect different neural processes. Our findings on cortical generators are in line with the hypothesis that P3a reflects the automatic allocation of attention, while P3b is related to the effortful processing of task-relevant events.

Effect of low-frequency rTMS on electromagnetic tomography (LORETA) and regional brain metabolism (PET) in schizophrenia patients with auditory hallucinations.

BACKGROUND: Auditory hallucinations are characteristic symptoms of schizophrenia with high clinical importance. It was repeatedly reported that low frequency (

Electromagnetic modelling of current flow in the heart from TASER devices and the risk of cardiac dysrhythmias.

Increasing use by law enforcement agencies of the M26 and X26 TASER electrical incapacitation devices has raised concerns about the arrhythmogenic potential of these weapons. Using a numerical phantom constructed from medical images of the human body in which the material properties of the tissues are represented, computational electromagnetic modelling has been used to predict the currents arising at the heart following injection of M26 and X26 waveforms at the anterior surface of the chest (with one TASER 'barb' directly overlying the ventricles). The modelling indicated that the peak absolute current densities at the ventricles were 0.66 and 0.11 mA mm(-2) for the M26 and X26 waveforms, respectively. When applied during the vulnerable period to the ventricular epicardial surface of guinea-pig isolated hearts, the M26 and X26 waveforms induced ectopic beats, but only at current densities greater than 60-fold those predicted by the modelling. When applied to the ventricles in trains designed to mimic the discharge patterns of the TASER devices, neither waveform induced ventricular fibrillation at peak currents >70-fold (for the M26 waveform) and >240-fold (for the X26) higher than the modelled current densities. This study provides evidence for a lack of arrhythmogenic action of the M26 and X26 TASER devices.

The anatomy of the medial part of the knee.

BACKGROUND: While the anatomy of the medial part of the knee has been described qualitatively, quantitative descriptions of the attachment sites of the main medial knee structures have not been reported. The purpose of the present study was to verify the qualitative anatomy of medial knee structures and to perform a quantitative evaluation of their anatomic attachment sites as well as their relationships to pertinent osseous landmarks. METHODS: Dissections were performed and measurements were made for eight nonpaired fresh-frozen cadaveric knees with use of an electromagnetic three-dimensional tracking sensor system. RESULTS: In addition to the medial epicondyle and the adductor tubercle, a third osseous prominence, the gastrocnemius tubercle, which corresponded to the attachment site of the medial gastrocnemius tendon, was identified. The average length of the superficial medial (tibial) collateral ligament was 94.8 mm. The superficial medial collateral ligament femoral attachment was 3.2 mm proximal and 4.8 mm posterior to the medial epicondyle. The superficial medial collateral ligament had two separate attachments on the tibia. The distal attachment of the superficial medial collateral ligament on the tibia was 61.2 mm distal to the knee joint. The deep medial collateral ligament consisted of meniscofemoral and meniscotibial portions. The posterior oblique ligament femoral attachment was 7.7 mm distal and 6.4 mm posterior to the adductor tubercle and 1.4 mm distal and 2.9 mm anterior to the gastrocnemius tubercle. The medial patellofemoral ligament attachment on the femur was 1.9 mm anterior and 3.8 mm distal to the adductor tubercle. CONCLUSIONS: The medial knee ligament structures have a consistent attachment pattern.

In vivo inductive phase shift measurements to detect intraperitoneal fluid.

Four different volumes of physiological saline were infused into the abdominal cavity of rats and the resulting inductive phase shift in the bulk of the abdomen was measured with a noncontact electrical induction system, built to measure phase shift in the bulk of the body in the frequency range from 1 MHz to 8.5 MHz. This experimental study shows that inductive bulk measurements of phase shift have the potential to detect changes in intraperitoneal fluid in vivo with measurements made at frequencies higher than approximately 1 MHz. The experiments also show that the bulk phase shift increases as a function of frequency and fluid volume in a way that is qualitatively consistent with earlier theoretical predictions.

A simple and accurate method for quantification of magnetosomes in magnetotactic bacteria by common spectrophotometer.

A simple apparatus for measuring the magnetism of magnetotactic bacteria was developed with a common laboratory spectrophotometer, which was based on measuring the change in light scattering resulting from cell alignment in a magnetic field. A multiple coils were built around the cuvette holder of the spectrophotometer to compensate geomagnetic field and to generate two mutually perpendicular magnetic fields. In addition, we defined a novel magnetism parameter, R(mag), by modifying the definition of C(mag) to a normalized parameter with the culture absorbance obtained without application of magnetic field. The number of magnetosomes in each cell was determined by transmission electron microscopy to assess the relationship between the two magnetism parameters and the distribution of magnetosomes in the cells. We found that both R(mag) and C(mag) were linearly correlated rather with the percentage of magnetosome-containing bacteria than with the average magnetosome numbers, and R(mag) exhibited a better linearity than C(mag) with respect to the percentage of magnetosome-containing bacteria.

Endoscopic pituitary surgery with and without image guidance: an experimental comparison.

BACKGROUND: The combination of image guidance and endoscopy is the newest trend in pituitary surgery. To assess the impact of image guidance on EPS, we measured and calculated the accuracy of the system and compared some critical surgical steps with and without image guidance under experimental conditions in terms of surgical time and precision. METHODS: Twenty cadaver heads were explored by standard endoscopic transsphenoidal surgical technique. Optic-radiologic correlations of topographic landmarks were photographed, and the system accuracy and actual visual accuracy were recorded. Some important anatomical parameters were measured in surgical field and on navigation system, and the differences were calculated and analyzed. Some critical surgical steps were recorded and compared between with and without image guidance. RESULTS: The system accuracy (root mean square), calculated by the computer automatically, showed a mean value of 0.28 +/- 0.06 mm. In some cases, there was a small discrepancy between the visible position of the pointer and its counterpart on the navigation system; we coined this actual visual accuracy. The average value was 1.53 +/- 0.49 mm. The maximum difference between the measurements from the navigation system and from their actual visual counterparts was less than 7%. With and without image guidance, in normal anatomical conditioning, there was no statistically significant difference between the duration of ostium sphenoidale exposure and sellar window creation; however, in anatomical variations, the surgical time was shown to be significantly shorter when navigation was used. CONCLUSION: We have demonstrated in this experimental setting that the electromagnetic tracking image guidance possesses a high accuracy at millimetric level and therefore provides precise localization and orientation in EPS. With the assistance of neuronavigation system, it is advantageous not only in saving operating time, but also, more importantly, in enhancing the orientation, thus, rendering surgeries safer and more efficient. During the in vivo pituitary surgery, EPS with image guidance can provide accurate and reliable stereoinformation to achieve better results with lesser risks, particularly in complex cases or in reoperations, even in the hands of experienced surgeons.

Time-domain reconstruction using sensitivity coefficients for limited view ultrawide band tomography.

This article addresses time-domain ultrawide band (UWB) electromagnetic tomography for reconstructing the unknown spatial characteristic of an object from observations of the arrivals of short electromagnetic (EM) pulses. Here, the determination of the first peak arrival of the EM traces constitutes the forward problem, and the inverse problem aims to reconstruct the EM property distribution of the media. In this article, the finite-difference time-domain method implementing a perfectly matched layer is used to solve the forward problem from which the system sensitivity maps are determined. Image reconstruction is based on the combination of a linearized update and regularized Landweber minimization algorithm. Experimental data from a laboratory UWB system using targets of different contrasts, sizes, and shapes in an aqueous media are presented. The results show that this technique can accurately detect and locate unknown targets in spite of the presence of significant levels of noise in the data.

Development of a stable source of atomic oxygen with a pulsed high-voltage discharge and its application to crossed-beam reactions.

To investigate the reactions of oxygen atoms with ethene and silane in a crossed-beam condition, we developed a stable, highly intense, and short-pulsed source of atomic oxygen with a transient high-voltage discharge. Mixtures of O(2) and He served as discharge media. Utilizing a crossed molecular-beam apparatus and direct vacuum-ultraviolet ionization, we measured the temporal profiles of oxygen atoms and the time-of-flight spectra of reaction products. With O(2) 3% seeded in He as a discharge medium, oxygen atoms might have a full width as small as 13.5 micros at half maximum at a location 193 mm downstream from the discharge region. Most population of oxygen atoms is in the ground state (3)P but some in the first excited state (1)D, depending on the concentration of precursor O(2). This discharge device analogously generates carbon, nitrogen, and fluorine atoms from precursors CO, N(2), and F(2), respectively.

Radio-frequency plasma transducer for use in harsh environments.

We describe a compact transducer used to generate and modulate low-intensity radio-frequency atmospheric pressure plasma (RF-APP) for high temperature gap measurement and generation of air-coupled ultrasound. The new transducer consists of a quarter-wave transmission line where the ground return path is a coaxial solenoid winding. The RF-APP is initiated at the open end of the transmission line and stabilized by passive negative feedback between the electrical impedance of the plasma and the energy stored in the solenoid. The electrical impedance of the plasma was measured at the lower-voltage source end of the transducer, eliminating the need to measure kilovolt-level voltages near the discharge. We describe the use of a 7 MHz RF-APP prototype as a harsh-environment clearance sensor to demonstrate the suitability of plasma discharges for a common nondestructive inspection application. Clearance measurements of 0-5 mm were performed on a rotating calibration target with a measurement precision of 0.1 mm and a 20 kHz sampling rate.