Search results for "Artifact"
showing 10 items of 193 documents
Directionlets: Anisotropic Multidirectional representation with separable filtering
2006
In spite of the success of the standard wavelet transform (WT) in image processing in recent years, the efficiency of its representation is limited by the spatial isotropy of its basis functions built in the horizontal and vertical directions. One-dimensional (1-D) discontinuities in images (edges and contours) that are very important elements in visual perception, intersect too many wavelet basis functions and lead to a nonsparse representation. To efficiently capture these anisotropic geometrical structures characterized by many more than the horizontal and vertical directions, a more complex multidirectional (M-DIR) and anisotropic transform is required. We present a new lattice-based pe…
Ero ja immersio. Tutkimus artefaktin ongelmasta ja aineellisen ja käsitteellisen välisistä suhteista
2021
Tutkimus on kulttuurifilosofinen ja kulttuurintutkimuksellinen väitöskirja aineellisen artefaktin ongelmasta ja filosofinen tutkimus aineellisen mieltämisen ehdoista. Ihmistekoisen statuksen uudelleen arvioinnin pohjalta kehitän siinä uuden tavan ajatella aineellista ja ruumiillista. Historiallisesti suhteellisen nuoreen artefaktin käsitteeseen on tullut materiaalisuuksien kasvun myötä sen painon sivuuttavaa itsestäänselvyyttä, kuten tapahtui ikivanhalle olemisen käsitteelle Martin Heideggerin käänteentekevän huomion mukaan. Käsitteen neutraloituminen onkin siitä välittymättömän aineellisuuden neutraloitumista, mitä kutsun konstituutioharhaksi. Konstituutioharha on modernissa vallitseva tap…
Evolution of Digital Innovations Based on Entrepreneurial Opportunities
2019
Digital innovations evolve unpredictable as the characteristics of digital technology provide diverse opportunities for entrepreneurs. The flexible, malleable, and unbounded nature of digital technologies makes the evolution process unpredictable as entrepreneurs can rarely estimate beforehand how new digital technologies might impact the evolution process. It is also hard to predict how customers will react to the changes enabled by digital technologies. In this longitudinal case study, we were interested in different competitive moves that entrepreneurs apply to effectuate changes in the evolutionary pathway of digital innovations. Further, we were fascinated by how the evolution of digit…
Value Co-Creation and Co-Destruction in an IS Artifact: Contradictions of Geocaching
2016
In this paper we study how value co-creation and value co-destruction are present in an IS artifact. We apply the concept of contradiction (structural tension) to study an IS artifact, geocaching. Based on the analysis of interview data and discussion forum postings, we identified the following contradictions: i) introducing secret society to outsiders, ii) geocaching by breaking its rules, iii) experiencing nature while consuming it, iv) building community occurs with competition. These contradictions show that value co-creation and co-destruction interacts in this IS artifact. Based on the results, we propose that IS research should adopt the concepts of value co-creation and co-destructi…
Spurious source generation in mapping from noisy phase-self-calibrated data
2008
Phase self-calibration (or selfcal) is an algorithm often used in the calibration of interferometric observations in astronomy. Although a powerful tool, this algorithm presents strong limitations when applied to data with a low signal-to-noise ratio. We analyze the artifacts that the phase selfcal algorithm produces when applied to extremely noisy data. We show how the phase selfcal may generate a spurious source in the sky from a distribution of completely random visibilities. This spurious source is indistinguishable from a real one. We numerically and analytically compute the relationship between the maximum spurious flux density generated by selfcal from noise and the particulars of th…
Experimental study on the effects of physical training on the defibrillation threshold
2011
Background: Chest compression artifacts during cardiopulmonary resuscitation (CPR) deteriorate the rhythm diagnosis of automated external defibrillators (AED). Cardiopulmonary resuscitation must therefore be interrupted for a reliable shock/no-shock decision. However, these hands-off intervals adversely affect the defibrillation success, and, in addition, pauses in chest compressions compromise circulation. An accurate diagnosis of the rhythmwhile performing CPR is therefore needed to minimize these hands-off intervals. Methods: The characteristics of the CPR artifact are very variable, and the artifact presents an important spectral overlap with human cardiac arrest rhythms. Consequently, …
Impact of the Tiloop Bra mesh in CT images and dose delivery in breast radiotherapy
2012
A new titanized breast mesh, TiLOOP Bra, is currently available for implantation in patients who require radiotherapy. The purpose of this work is to study the dosimetric effect of the presence of a TiLOOP Bra mesh on breast radiation treatment and radiographic imaging. The dosimetric effects have been measured for three X‐ray energies: 1.25 MeV, 6 MV and 18 MV, using radiochromic films placed at three different depths. These depths are representative of mesh location in breast during the radiotherapy treatment and hence, are of interest in this study. In order to assess the disturbance in a radiographic image, different computed tomographic (CT) studies of the mesh have been performed. The…
Artefacts in CBCT: a review
2011
Artefacts are common in today's cone beam CT (CBCT). They are induced by discrepancies between the mathematical modelling and the actual physical imaging process. Since artefacts may interfere with the diagnostic process performed on CBCT data sets, every user should be aware of their presence. This article aims to discuss the most prominent artefacts identified in the scientific literature and review the existing knowledge on these artefacts. We also briefly review the basic three-dimensional (3D) reconstruction concept applied by today's CBCT scanners, as all artefacts are more or less directly related to it.
A practical MRI-based reconstruction method for a new endocavitary and interstitial gynaecological template
2015
Purpose: There are perineal templates for interstitial implants such as MUPIT and Syed applicators. Their limitations are the intracavitary component deficit and the necessity to use computed tomography (CT) for treatment planning since both applicators are non-magnetic resonance imaging (MRI) compatibles. To overcome these problems, a new template named Template Benidorm (TB) has been recently developed. Titanium needles are usually reconstructed based on their own artifacts, mainly in T1-weighted sequence, using the void on the tip as the needle tip position. Nevertheless, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these …
Diffusion-weighted MRI of cholesteatomas of the petrous bone
2002
Purpose To investigate if primary cholesteatomas of the petrous bone show high signal in diffusion-weighted imaging (DWI). Materials and methods In this blinded study, we compared 15 patients with clinically certain cases and later surgically proven cholesteatomas vs. 12 patients with clinically acute otitis of the middle ear and 20 volunteers without petrous bone disease. Two blinded readers without knowledge of the clinical data decided in consensus agreement whether there was a pathologic signal increase in the petrous bone in an anisotropic single-shot echo-planar imaging (EPI) DWI sequence, an artifact, or no signal increase. Results Thirteen of 15 patients with cholesteatomas showed b…