1,720,954 research outputs found
An Evolutionary-Optimized Surgical Path Planner for a Programmable Bevel-Tip Needle
Full text linkPath planning algorithms for steerable needles in medical applications must guarantee the anatomical obstacle avoidance, reduce the insertion length, and ensure the compliance with the needle kinematics. The majority of the solutions from the literature focus either on fast computation or on path optimality, the former at the expense of suboptimal paths, the latter by making unbearable the computation in case of a high-dimensional workspace. In this article, we implement a three-dimensional path planner for neurosurgical applications, which keeps the computational cost consistent with standard preoperative planning algorithms and fine-tunes the estimated pathways in accordance to multiple optimization objectives. From a user-defined entry point, our method confines a sample-based path search within a subsection of the original workspace considering the degree of curvature admitted by the needle. An evolutionary optimization procedure is used to maximize the obstacle avoidance and reduce the insertion length. The pool of optimized solutions is examined through a cost function to determine the best path. Simulations on one dataset showed the ability of the planner to save time and overcome the state of the art in terms of obstacle avoidance, insertion length, and probability of failure, proving this algorithm as a valid planning method for complex environments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Novel methods for steerable needle 3D path planning based on NURBS and genetic algorithm
No full textLAUREA MAGISTRALELa chirurgia mininvasiva, insieme di tecniche atte a ridurre al minimo il trauma arrecato alle strutture anatomiche, è diventata negli ultimi anni un'alternativa valida alla chirurgia tradizionale in molte aree. In particolare, nel campo della neurochirurgia robotica, tale approccio viene applicato ad esempio a procedure come la biopsia, la stimolazione profonda cerebrale, la stereoelettroencefalografia e la somministrazione locale di farmaci.
Questo approccio chirurgico ha portato alla creazione di particolari sonde che consentano di congiungere un entry point (EP) con un target point (TP). Le sonde impiegate nella chirurgia mininvasiva possono essere divise in sonde rettilinee e sonde orientabili lungo traiettorie curvilinee. Quest'ultime sono di crescente interesse poichè l'utilizzo delle prime potrebbe essere non sempre ottimale qualora la presenza di strutture tra EP ed TP impedisca la fattibilità di traiettorie rettilinee.
Il lavoro esposto in questa tesi è stato sviluppato presso il laboratorio di Neuroingegneria e Robotica Medica (Nearlab), dipartimento di "Elettronica, Informazione e Bioingegneria" (DEIB, Politecnico di Milano), e si inserisce nel progetto EDEN2020 (Enhanced Delivery Ecosystem for Neurosurgery). Tale progetto si pone, tra i suoi vari obiettivi, quello di realizzare sonde orientabili che possano rimanere in-situ per lunghi periodi per il trattamento di malattie neuro-oncologiche croniche. La tecnologia principale di tale progetto, attualmente in fase di sviluppo, è una sonda del tipo PBN (Programmable Bevel-tip Needle), composta da quattro segmenti assialmente collegati. Questi segmenti sono azionati automaticamente alla base della sonda in modo che, scorrendo uno sull'altro, possano generare un disallineamento, sulla prossimità distale, che determina il grado di curvatura nello spazio.
La soluzione presentata intende realizzare un nuovo pianificatore di traiettorie tridimensionali per applicazioni neurochirugiche eseguite tramite sonda PBN. Inoltre, le strutture anatomiche su cui viene eseguita la pianificazione sono ricostruite a partire dalle immagini diagnostiche del paziente.
Il pianificatore proposto in questa tesi si basa su una serie di algoritmi eseguiti in cascata. Dati ET e TP, selezionati dal chirurgo, viene generata un'area di ingresso (i.e. vengono evidenziati ulteriori EP nell'intorno del primo) e successivamente lo spazio di lavoro viene limitato tenendo conto dei limiti cinematici imposti dalla sonda. In seguito, vengono generati dei percorsi lineari a tratti tramite un algoritmo RRT*, che consiste in un'evoluzione del classico RRT (Rapidly-Exploring Random Trees). Tali percorsi vengono quindi sottoposti ad un'interpolazione NURBS (Non Uniform Rational Basis Splines), integrata in un algoritmo genetico. Quest'ultimo intende ottimizzare le traiettorie generate in termini di distanza dagli ostacoli, valore di curvatura e lunghezza del percorso.
Infine, la soluzione migliore in termini di funzione di costo viene proposta al chirurgo. La funzione di costo tiene conto contemporanemente della distanza media e minima dagli ostacoli, della curvatura massima e della sua deviazione standard e della lunghezza del catetere.
Per la validazione di questo progetto, sono stati eseguiti diversi test di confronto tra lo stato dell'arte ed il nuovo pianificatore. In particolare, le prestazioni della soluzione presentata sono state confrontate con quelle di due algoritmi proposti in letteratura nell'ambito della pianificazione di traiettorie. I risultati hanno evidenziato prestazioni incoraggianti riguardo tutti i parametri di interesse.Nowadays, minimally invasive surgery (MIS), which is a set of surgical techniques that aims at reducing trauma to anatomical structures, has become a viable alternative to open surgery in many areas. In the robotic neurosurgery field, this approach is used in procedures such as biopsy, deep brain stimulation, stereoelectroencephalography and local drug delivery.
This surgical approach has led to the creation of specific probes that allow to connect an entry point (EP) with a target point (TP). These probes can be divided into straight probes and steerable devices. The latter are of increasing interest because the use of the first ones may not always be optimal due to the presence of structures that prevent the feasibility of straight trajectories between EP and TP.
The work presented in this thesis has been developed at the Neuroengineering and Medical Robotics laboratory (Nearlab), department of "Elettronica, Informazione e Bioingegneria" (DEIB, Politecnico di Milano), and is part of EDEN2020 (Enhanced Delivery Ecosystem for Neurosurgery ) project. Among its various goals, EDEN2020 project aims at developing steerable probes that can remain in-situ for long periods for the treatment of chronic neuro-oncological diseases. The main technology of this project, currently under development, is a PBN (Programmable Bevel-tip Needle) composed of four axially interlocked segments. These robotic segments are activated at the base of the probe so that, sliding one on the other, they can generate an offset which determines the degree of curvature at the needle's tip.
The herein proposed solution aims at developing a new three dimensional path planner for neurosurgical PBN applications. Furthermore, the anatomical structures taken into account during the path planning are obtained from the patient's diagnostic images.
The path planner proposed in this thesis is based on a series of algorithms run one after the other. Given ET and TP, selected by the surgeon, an entry area is generated (i.e. more EPs are highlighted in the neighbor of the first one) and subsequently the work space is limited taking into account the kinematic constraints of the PBN. Then, piecewise linear paths are generated through an RRT* algorithm, which is an improved version of the classic RRT (Rapidly-Exploring Random Trees). These paths undergo a NURBS interpolation (Non-Uniform Rational Basis Splines), integrated into a genetic algorithm. The latter aims at optimizing the smooth trajectories generated taking into account the distance from obstacles, the curvature value and the path length.
Finally, the best solution in terms of a specific cost function is proposed to the surgeon. The cost function takes into account the mean and minimum distance from the obstacles, the maximum curvature and its standard deviation and the path's length.
Several tests has been carried out in order to evaluate the novel proposed path planner's performances. In particular, the performances of the herein presented solution has been compared with those of two algorithms proposed in literature in the path planning field. The results show encouraging performances regarding all the parameters of interest
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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