561 research outputs found
Positron Emission Tomography Compartmental Models
No full textThis paper presents theory for compartmental models used in positron emission tomography. Both plasma input models and reference tissue input models are considered. General theory is derived and the systems are characterised in terms of their impulse response functions. The theory shows that the macro parameters of the system may be determined simply from the coefficients of the impulse response functions. These results are discussed in the context of radioligand binding studies. It is shown that binding potential is simply related to the integral of the impulse response functions for all plasma and reference tissue input models currently used in positron emission tomography. The paper also introduces a general compartmental description for the behaviour of the tracer in blood, which then allows for the blood volume induced bias in reference tissue input models to be assessed
Positron emission tomography compartmental models: A basis pursuit strategy for kinetic modelling
No full textA kinetic modelling approach for the quantification of in vivo tracer studies with dynamic positron emission tomography (PET) is presented. The approach is based on a general compartmental description of the tracer’s fate in vivo and determines a parsimonious model consistent with the measured data. The technique involves the determination of a sparse selection of kinetic basis functions from an overcomplete dictionary using the method of basis pursuit denoising. This enables the characterization of the systems impulse response function from which values of the systems macro parameters can be estimated. These parameter estimates can be obtained from a region of interest analysis or as parametric images from a voxel based analysis. In addition, model order estimates are returned which correspond to the number of compartments in the estimated compartmental model. Validation studies evaluate the methods performance against two pre-existing data led techniques, namely graphical analysis and spectral analysis. Application of this technique to measured PET data is demonstrated using [ 11 C]diprenorphine (opiate receptor) and [ 11 C]WAY-100635 (5-HT1A receptor). Whilst, the method is presented in the context of PET neuroreceptor binding studies, it has general applicability to the quantification of PET/SPET radiotracer studies in neurology, oncology and cardiology
Rank-Shaping Regularization of Exponential Spectral Analysis for Application to Functional Parametric Mapping
No full textCompartmental models are widely used for the mathematical modelling of dynamic studies acquired with positron emission tomography (PET). The numerical problem involves the estimation of a sum of decaying real exponentials convolved with an input function. In exponential spectral analysis (SA), the nonlinear estimation of the exponential functions is replaced by the linear estimation of the coefficients of a predefined set of exponential basis functions. This set-up guarantees fast estimation and attainment of the global optimum. SA, however, is hampered by high sensitivity to noise and, because of the positivity constraints implemented in the algorithm, cannot be extended to reference region modelling. In this paper, SA limitations are addressed by a new rank-shaping (RS) estimator that defines an appropriate regularization over an unconstrained least-squares solution obtained through singular value decomposition of the exponential base. Shrinkage parameters are conditioned on the expected signal-to-noise ratio. Through application to simulated and real datasets, it is shown that RS ameliorates and extends SA properties in the case of the production of functional parametric maps from PET studies
Volunteer studies replacing animal experiments in brain research - Report and recommendations of a Volunteers in Research and Testing workshop
No full textWenken voor een veranderbare stad: Een studie naar veranderingspatronen van Amsterdamse buurten en bouwblokken
No full textDe stad is voortdurend onderhevig aan verandering, niet alleen door uitbreiding en groei buiten de bestaande stadsgrenzen, maar vooral doordat de bestaande stad voortdurend van binnenuit van gedaante verandert. Aard en hoedanigheid van de veranderingen verschillen van wijk tot wijk en van locatie tot locatie. In de lezing ‘The Open City’ (2006) breekt Richard Sennett een lans voor een stad en dus een vorm van stedenbouw die open staat voor verandering. Sennett mist in de huidige ontwerppraktijk ‘a sense of time [\u85], forward-looking time, the city understood as process’. In dit proefschrift is onderzocht op welke manier de stedenbouwkundige discipline kan bijdragen aan de veranderbaarheid van de bestaande stad en het ontwikkelen van de stad in het bestaande stedelijke weefsel door de analyse van Amsterdamse buurten en bouwblokken. Het eigendom van de bebouwing, de architectonische eenheid, de ontsluiting en de constructie van de bebouwing en de onderlinge relatie van deze eigenschappen zijn cruciaal gebleken voor de veranderbaarheid van het bouwblok. Werkend aan de ontwikkeling van de stad in het bestaande stedelijke weefsel is begrip van het schaalniveau waarop veranderingen plaatsvinden cruciaal in het onderzoek en de ontwerpopgave van de stedenbouwkundige discipline.UrbanismArchitecture and The Built Environmen
Cult: A Composite Novel
No full textCult (redacted)
The first component of the thesis is a composite novel called Cult which falls into two parts with seven narratives in each. Part 1 tracks the protagonist, Ellen, from her first involvement with the cult through to her eventually leaving it. Although fiction, the first half of the book answers the kinds of questions the author is asked when people discover that she was once a sannyasin (a follower of the guru Bhagwan Shree Rajneesh). While the experiences of meditation, group therapy and communal living are all faithfully rendered within the stories, the need for strong characters, narrative drive and a lightness of touch takes precedence.
Part 2 picks up Ellen’s story some twenty or so years later and explores what becomes of her in middle age. It also looks at other groups in society, such as academia, the law and the internet dating community which each have their own jargon, hierarchies, rituals and rules but are not considered to be cults.
The book examines the question raised in the Epigraph, ‘how do we be together when we feel so alone’ with a focus on relationships other than the familial and the romantic.
Collisions, Chasms and Connections: a Performative Exploration of the Composite Novel Form
The second part of the thesis is both a critical and creative response to three contemporary American books: Olive Kitteridge by Elizabeth Strout; A Visit from the Goon Squad by Jennifer Egan; and Legend of a Suicide by David Vann. The critical element comprises a close reading of the three books; a chronological reconstruction of their overarching storylines; and a consideration of what their authors have said about writing the books. It concludes that, in the composite novel, the simultaneous presentation of multiple views and storylines operate much like a 3D image to give the impression of depth to the characters and situations rendered. The creative element of the essay is a playful and personal response to the texts
Ontwerpen aan de stad: Stedenbouw in Nederlands-Indië en Indonesië (1905-1950)
No full textThis book describes the development and professionalization of Dutch Indian (Indische) town planning between 1905 and 1951. It simultaneously portrays the modernisation of the Dutch East Indies and the emergence of modern day Indonesia.UrbaniArchitectur
Blijvend aantrekkelijk: Tuinwijken van de jaren '30
No full textThe central question of this study is to determine the spatial characteristics that govern the lasting appeal of private garden-city neighbourhoods of the interwar period. What are the social characteristics and circumstances of the period, the urban development and architectonic conditions, the principles of composition and the development process that have made these neighbourhoods into a lasting success as a residential environment. And what lessons can be learned from this for the visual design and organisation of future ‘rural-urban’ living. De centrale vraagstelling van deze studie is welke ruimtelijke kenmerken de blijvende aantrekkelijkheid van particuliere tuinwijken uit het Interbellum bepalen. Welke toenmalige maatschappelijke kenmerken en omstandigheden, welke stedenbouwkundige en architectonische condities en compositieprincipes en welk ontwikkelingsproces deze wijken tot een bestendig succes als woonmilieu hebben gemaakt. En welke lering hieruit kan worden getrokken voor de vormgeving en organisatie van toekomstig ‘landstedelijk’ wonen. De publieksversie van het proefschrift is inmiddels verschenen bij uitgeverij Vantilt, Nijmegen onder de titel: "De magie van het jaren '30 huis".UrbanismArchitectur
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