Automatic correction of registration errors in surgical navigation systems

Surgical navigation systems are used widely among all fields of modern medicine, including, but not limited to ENT- and maxillofacial surgery. As a fundamental prerequisite for image-guided surgery, intraoperative registration, which maps image to patient coordinates, has been subject to many studies and developments. While registration methods have evolved from invasive procedures like fixed stereotactic frames and implanted fiducial markers toward surface-based registration and noninvasive markers fixed to the patient's skin, even the most sophisticated registration techniques produce an imperfect result. Due to errors introduced during the registration process, the projection of navigated instruments into image data deviates up to several millimeter from the actual position, depending on the applied registration method and the distance between the instrument and the fiducial markers. We propose a method that allows to automatically and continually improve registration accuracy during intraoperative navigation after the actual registration process has been completed. The projections of navigated instruments into image data are inspected and validated by the navigation software. Errors in image-to-patient registration are identified by calculating intersections between the virtual instruments' axes and surfaces of hard bone tissue extracted from the patient's image data. The information gained from the identification of such registration errors is then used to improve registration accuracy by adding an additional pair of registration points at every location where an error has been detected. The proposed method was integrated into a surgical navigation system based on paired points registration with anatomical landmarks. Experiments were conducted, where registrations with deliberately misplaced point pairs were corrected with automatic error correction. Results showed an improvement in registration quality in all cases.     

A report on HIPERLAN standardization

HIPERLAN is the new European standard for radio LANs currently being formulated by ETSI RES10 for operation at 5 GHz and 17 GHz. It will be suitable for radio replacement of wired LANs and for ad hoc networking providing a user data rate of 10–20 Mbit/s. This paper is a review of the work of ETSI RES10 on the formulation of the HIPERLAN standard. The origins of ETSI RES10 are documented. The targets set for HIPERLAN and the problems in achieving these targets are discussed. The paper reviews the technical arguments for and against the proposed solutions to these problems, concentrating on the design of the transmission scheme and the channel access mechanism. The discussions leading to significant decisions about the standard are summarized. If the FCC in the United States of America allocate the equivalent 5 GHz band to unlicensed wireless LAN systems, many of these discussions will be revisited for future standards in this band. The paper will be of interest to anyone in academia or industry wishing to be brought quickly up to date with the state of the standard in order to focus their research or development activities. The paper also gives a general insight into the technical side of the standards formulation process in ETSI.     

Fully differential operational amplifiers using CMOS compatible lateral bipolar transistors with improved common-mode regulation

A new bias circuit for a CMOS compatible lateral bipolar transistor differential pair is presented. The circuit compensates for all process and bias dependent variations of the lateral collector current to emitter current ratio alpha . Experimental results show that its application to a fully differential amplifier improves the precision of the common-mode output voltage regulation by at least an order of magnitude.<>     

Experimental Study of Capture Effect for Medium Access Control with ALOHA

In this paper, we investigate the capture effect through experiments conducted with Iris nodes equipped with AT86RF230 radio transceivers. It is shown that the first arriving packet in a collision can capture the radio channel for equal power transmissions and may be decoded depending on the amount of overlap. A new 3‐packet‐capture scenario is introduced and implemented. To be able to understand the impact of capture on the throughput performance of wireless sensor networks, we present an analysis of the capture coefficient using our practical results. For real‐world implementations, the throughput of pure ALOHA considering a finite number of users is presented in analytical form. The capture coefficient is then applied to pure ALOHA as a case study. Using analytical and practical implementations of the capture effect on ALOHA, a very good match in channel throughput performance enhancement is demonstrated over the non‐capture effect case. TinyOS‐2.x is used to program the nodes and to observe data exchange on a computer through a base station.     

A nonlinear operator-based speech feature analysis method withapplication to vocal fold pathology assessment

Traditional speech processing methods for laryngeal pathology assessment assume linear speech production with measures derived from an estimated glottal flow waveform. They normally require the speaker to achieve complete glottal closure, which for many vocal fold pathologies cannot be accomplished. To address this issue, a nonlinear signal processing approach is proposed which does not require direct glottal flow waveform estimation. This technique is motivated by earlier studies of airflow characterization for human speech production. The proposed nonlinear approach employs a differential Teager energy operator and the energy separation algorithm to obtain formant AM and FM modulations from filtered speech recordings. A new speech measure is proposed based on parameterization of the autocorrelation envelope of the AM response. This approach is shown to achieve impressive detection performance for a set of muscular tension dysphonias. Unlike flow characterization using numerical solutions of Navier-Stokes equations, this method is extremely computationally attractive, requiring only a small time window of speech samples. The new noninvasive method shows that a fast, effective digital speech processing technique can be developed for vocal fold pathology assessment without the need for direct glottal flow estimation or complete glottal closure by the speaker. The proposed method also confirms that alternative nonlinear methods can begin to address the limitations of previous linear approaches for speech pathology assessment     

High-resolution venography of the brain using magnetic resonance imaging

The purpose of this study was to evaluate a non-flow related magnetic resonance imaging method to visualize small veins independent of arteries in the human brain. A long TE, high-resolution 3D gradient echo MR acquisition was used to highlight venous information. The method is based on the paramagnetic property of deoxyhemoglobin and the resulting phase difference between veins and brain parenchyma at long echo times. The MR magnitude images were masked with a phase mask filter to enhance small structure visibility.. Venous information down to sub-pixel vessel diameters of several hundred microns is visible. Venous data are displayed in an angiographic manner using a minimum intensity projection algorithm. Both superficial veins and deep white matter veins are visible. The method has been successfully applied in volunteers. Preliminary results in patients with cerebral arteriovenous malformations indicate its potential in clinical applications. The proposed method is easy to implement and does not require administration of a contrast agent or application of specially designed rf pulses to highlight the veins. Rather it exploits the intrinsic magnetic properties (BOLD-effect) and the prolonged T ^_2* of venous blood. The method may be of diagnostic potential in the assessment of arteriovenous malformations or other vascular venous lesions. © 1998 Elsevier Science B.V. All rights reserved.     

The diversity of potential cheese ripening characteristics of lactic acid starter bacteria: 1. Resistance to cell lysis and levels and cellular distribution of proteinase activities

By reference to subcellular fraction markers, the resistance to lysis of 23 strains of Lactococcus lactis subsp. cremoris, 30 strains of L. lactis subsp. lactis and five strains of Streptococcus thermophilus and the levels and distribution of proteinase activity in the strains were determined. Strains of L. lactis subsp. cremoris were readily lysed by transfer to hypotonic buffer after treatment with lysozyme alone, whilst strains of L. lactis subsp. lactis and S. thermophilus could be efficiently lysed in this way only after treatment with a combination of lysozyme and mutanolysin. With a few notable exceptions, those strains which gave the fastest rates of acid production also generally presented higher levels of cell surface proteinase, as determined by activity on fluorescein isothiocyanate-labelled β-casein. The highest levels of cell surface proteinase detected were found for strains of L. lactis subsp. cremoris. However, the levels of total proteinase activity in the lactococcal strains did not correlate with the rate of acid production in milk, some slow acid-producers yielding similar or greater total proteinase levels than fast acid-producers. Homology to DNA probes for the lactococcal cell surface proteinase gene and to the conserved region encoding the serine proteinase active site was shown by the fast acid-producing lactococcal strains, but not by most of the slow acid-producing lactococcal strains or by the strains of S. thermophilus. A significant proportion of the total proteinase activity was recovered in the subcellular fractions in which high levels of cytoplasmic marker enzyme activity were found. The total proteinase levels detected in strains ofL. lactis subsp. lactis showed a greater range of variation than in the strains of L. lactis subsp. cremoris. High levels of total proteinase activity were found in the slow acid-producers despite the strains having been grown in the presence of yeast extract. For many of the strains, the levels of proteinase released from the cell surface during cell wall degradation with lytic enzyme treatment were higher than those found using whole cells, suggesting that a significant amount of proteolytic activity was either inaccessible to substrate or present in an inactive form.     

Thermal stabilities of nanoporous metallic electrodes at elevated temperatures

Currently Pt-based metals are the best catalytic electrodes for fuel cells at operating temperatures below 500 °C. Pure platinum electrodes suffer degradation of microstructure over time at elevated temperatures due to Ostwald ripening. In this paper, better thermal stability of Pt–Ni nanoporous thin films relative to pure Pt is reported. Based on ab initio calculations, it was found that both the surface energy of a Pt_0.7Ni_0.3 cluster and the energy change of the Pt–Ni alloy cluster upon ripening on yttria stabilized zirconia (YSZ) solid electrolyte were lower than pure Pt. This suggested a better thermal stability of Pt_0.7Ni_0.3 than Pt. In addition, annealing impacts on microstructures and properties of nanoporous Pt and Pt–Ni alloy thin films were examined experimentally. SEM images show dramatic porosity reduction for pure Pt after annealing at temperatures of 400–600 °C but insignificant microstructure change for Pt–Ni nanoporous thin films. As a result, in solid oxide fuel cells using nanoporous Pt–Ni cathodic catalysts instead of pure Pt, better stability, lower electrode impedances, and higher power densities were achieved at elevated operating temperatures (350–500 °C).     

The value of monophasic capacitance of few-electron systems

Due to the discreteness of electronic charges in a nanoscale system, capacitance is defined in terms of the total interaction energy of N-electrons confined in a dielectric sphere. Specifically, the distribution of N-electrons is obtained from minimization of the total Coulomb and polarization interaction energy and the formation energy, the work done on the system. Our discrete charge dielectric (DCD) model gives rise to an electrostatic capacitance agreeing with the N=1 and ∞ cases. For nanometer-size devices, the Schrödinger equation should be used; however, for size greater than 10 nm, the Poisson equation accounts for spatial symmetry properties resulting from the discrete nature of interacting electrons. Without metallic components, the equal potential landscape does not coincide with our spherical boundary except for the N=1 case. There is a special configuration associated with each N. Hence, the capacitance defined is monophasic, representing a single electrostatic phase. The most important application of this work may lie in optoelectronics and biological systems.     

Networking lessons in delivering ‘Software as a Service’—part I

This is a two‐part paper. In part I, we describe the origins of Software as a Service (SaaS) and its value proposition to Corporate IT, Service Providers, Independent Software Vendors, and End Users. In part II, we examine the networking lessons learned in researching, building, and running a SaaS service. Copyright © 2002 John Wiley & Sons, Ltd.