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Positioning Error (positioning + error)

Distribution by Scientific Domains

Medical Sciences	37%
Life Sciences	37%

Selected Abstracts

An augmented reality system to guide radio-frequency tumour ablation

COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 1 2005
S. Nicolau
Abstract Radio-frequency ablation is a difficult operative task that requires a precise needle positioning in the centre of the pathology. This article presents an augmented reality system for hepatic therapy guidance that superimposes in real-time 3D reconstructions (from CT acquisition) and a virtual model of the needle on external views of a patient. The superimposition of reconstructed models is performed with a 3D/2D registration based on radio-opaque markers stuck on to the patient's skin. The characteristics of the problem (accuracy, robustness and time processing) led us to develop automatic procedures to extract and match the markers and to track the needle in real time. Experimental studies confirmed that our algorithms are robust and reliable. Preliminary experiments conducted on a human abdomen phantom showed that our system is highly accurate (needle positioning error within 3,mm) and enables the surgeon to reach a target in less than 1 minute on average. Our next step will be to perform an in vivo evaluation. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A semi-analytical estimation of the effect of second-order ionospheric correction on the GPS positioning

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2005
H. Munekane
SUMMARY We developed a semi-analytical method to evaluate the effect of the second-order ionospheric correction on GPS positioning. This method is based on the semi-analytical positioning error simulation method developed by Geiger and Santerre in which, assuming the continuous distribution of the satellites, a normal equation is formed to estimate the positioning error taking all the contributions of the ranging error by the visible satellites into account. Our method successfully reproduced the averaged time-series of three IGS sites which is comparable to the rigorous simulation. We then evaluated the effect of the ionospheric error on the determination of the reference frame. We evaluated the additional Helmert parameters that are required for the ionospheric effect. We found that the ionospheric effect can lead to annual scale changes of 0.1 ppb, with an offset of 1.8 mm and a semi-annual oscillation of 1 mm in the z -direction. However, these values are too small to explain the current deviations between the GPS-derived reference frame and the ITRF reference frame. Next, we estimated the apparent scale changes due to the ionospheric error in the GEONET coordinate time-series in Japan. We could qualitatively reproduce the observed semi-annual scale changes peaking at the equinoxes and having asymmetrical amplitudes between the vernal and autumnal equinoxes. [source]

Technical note: The effect of midshaft location on the error ranges of femoral and tibial cross-sectional parameters

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2010
Vladimír Sládek
Abstract In comparing long-bone cross-sectional geometric properties between individuals, percentages of bone length are often used to identify equivalent locations along the diaphysis. In fragmentary specimens where bone lengths cannot be measured, however, these locations must be estimated more indirectly. In this study, we examine the effect of inaccurately located femoral and tibial midshafts on estimation of geometric properties. The error ranges were compared on 30 femora and tibiae from the Eneolithic and Bronze Age. Cross-sections were obtained at each 1% interval from 60 to 40% of length using CT scans. Five percent of deviation from midshaft properties was used as the maximum acceptable error. Reliability was expressed by mean percentage differences, standard deviation of percentage differences, mean percentage absolute differences, limits of agreement, and mean accuracy range (MAR) (range within which mean deviation from true midshaft values was less than 5%). On average, tibial cortical area and femoral second moments of area are the least sensitive to positioning error, with mean accuracy ranges wide enough for practical application in fragmentary specimens (MAR = 40,130 mm). In contrast, tibial second moments of area are the most sensitive to error in midshaft location (MAR = 14,20 mm). Individuals present significant variation in morphology and thus in error ranges for different properties. For highly damaged fossil femora and tibiae we recommend carrying out additional tests to better establish specific errors associated with uncertain length estimates. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source]

Target registration and target positioning errors in computer-assisted neurosurgery: proposal for a standardized reporting of error assessment

THE INTERNATIONAL JOURNAL OF MEDICAL ROBOTICS AND COMPUTER ASSISTED SURGERY, Issue 4 2009
Gerlig Widmann
Abstract Background Assessment of errors is essential in development, testing and clinical application of computer-assisted neurosurgery. Our aim was to provide a comprehensive overview of the different methods to assess target registration error (TRE) and target positioning error (TPE) and to develop a proposal for a standardized reporting of error assessment. Methods A PubMed research on phantom, cadaver or clinical studies on TRE and TPE has been perfomed. Reporting standards have been defined according to (a) study design and evaluation methods and (b) specifications of the navigation technology. Results The proposed standardized reporting includes (a) study design (controlled, non-controlled), study type (non-anthropomorphic phantom, anthropomorphic phantom, cadaver, patient), target design, error type and subtypes, space of TPE measurement, statistics, and (b) image modality, scan parameters, tracking technology, registration procedure and targeting technique. Conclusions Adoption of the proposed standardized reporting may help in the understanding and comparability of different accuracy reports. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Contribution of the Reelin signaling pathways to nociceptive processing

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2008
Alin L. Akopians
Abstract The reeler gene encodes Reelin, a secreted glycoprotein that binds to the very-low-density lipoprotein receptor (Vldlr) and apolipoprotein E receptor 2 (Apoer,2), and induces Src- and Fyn-mediated tyrosine phosphorylation of the intracellular adaptor protein Disabled-1 (Dab1). This Reelin,Dab1 signaling pathway regulates neuronal positioning during development. A second Reelin pathway acts through Apoer,2,exon 19 to modulate synaptic plasticity in adult mice. We recently reported positioning errors in reeler dorsal horn laminae I,II and V, and the lateral spinal nucleus. Behavioral correlates of these positioning errors include a decreased mechanical and increased thermal sensitivity in reeler mice. Here we examined mice with deletions or modifications of both the Reelin,Dab1 signaling pathway and the Reelin,Apoer,2,exon 19 pathway on a Vldlr-deficient background. We detected reeler -like dorsal horn positioning errors only in Dab1 mutant and Apoer,2/Vldlr double mutant mice. Although Dab1 mutants, like reeler, showed decreased mechanical and increased thermal sensitivity, neither the single Vldlr or Apoer,2 knockouts, nor the Apoer,2,exon 19 mutants differed in their acute pain sensitivity from controls. However, despite the dramatic alterations in acute ,pain' processing in reeler and Dab1 mutants, the exacerbation of pain processing after tissue injury (hindpaw carrageenan injection) was preserved. Finally, we recapitulated the reeler dorsal horn positioning errors by inhibiting Dab1 phosphorylation in organotypic cultures. We conclude that the Reelin,Dab1 pathway differentially contributes to acute and persistent pain, and that the plasticity associated with the Reelin,Apoer,2,exon 19 pathway is distinct from that which contributes to injury-induced enhancement of ,pain' processing. [source]

An audit of intra-oral digital radiographs for endodontics

INTERNATIONAL ENDODONTIC JOURNAL, Issue 4 2010
R. Austin
Aim, The aim of this study was to improve the quality of digital radiographs taken during endodontic treatment at King's College Hospital Dental Institute, UK. There were three phases. The first phase compared the Schick CDR system with Digora Optime. The second and third phases involved ways of improving the quality of the digital radiographs produced by the Schick CDR system. Methodology, The Faculty of General Dental Practitioners Royal College of Surgeons of England (FGDP) guidelines on Selection Criteria for Dental Radiography and Guidance Notes for Dental Practitioners on the Safe Use of X-Ray Equipment-National Radiological Protection Board enabled the use of a three point quality scale (one excellent, two diagnostically acceptable, three unacceptable), which took into consideration sensor angulation, positioning, contrast and focusing. The recommended FGDP guidelines are not less than 70% images scoring excellent. For the first phase 50 exposures recorded with the Schick CDR system were compared with 50 recorded using Digora Optime. For the second and third phases 50 radiographs for each phase were evaluated with images generated by the Schick system with training provided between the phases. Results, Images produced by the Schick system showed an inferior quality compared with the images generated by the Digora method. Both systems failed to reach the desired quality FGDP standard of 70% excellent (Schick 55% Digora 69%). Comparison of the results in the second and third phases showed that training the operator improved the quality but recommended the purchase of a size 1 or 0 Schick sensors to improve positioning errors. Conclusions, This study was carried out in order to minimise the ionising radiation dose to patients and to maximise the clinical and administrative benefits of using a digital system. It demonstrated an improvement in the quality of radiographs across all criteria measured up to and beyond the desired standard, from 55% of radiographs scoring excellent in the first phase to 80% in the third phase. As a result of the study it was decided to install the Schick CDR system because of the speed it produced images even though the first phase of this study demonstrated inferior image quality. The audit had clear, measurable standards with explicit targets. The audits have been through the entire audit cycle, data collection, change and a further data collection to provide evidence of the benefit of the change. A third data collection, demonstrated an ongoing commitment to quality. [source]