The snakes and ladders of user involvement:moving beyond Arnstein

For 35 years, Arnstein's ladder of citizen participation has been a touchstone for policy makers and practitioners promoting user involvement. This article critically assesses Arnstein's writing in relation to user involvement in health drawing on evidence from the United Kingdom, the Netherlands, Finland, Sweden and Canada. Arnstein's model, however, by solely emphasizing power, limits effective responses to the challenge of involving users in services and undermines the potential of the user involvement process. Such an emphasis on power assumes that it has a common basis for users, providers and policymakers and ignores the existence of different relevant forms of knowledge and expertise. It also fails to recognise that for some users, participation itself may be a goal. We propose a new model to replace the static image of a ladder and argue that for user involvement to improve health services it must acknowledge the value of the process and the diversity of knowledge and experience of both health professionals and lay people.

Universality in the merging dynamics of parametric active contours:a study in MRI based lung segmentation

Measurement of lung ventilation is one of the most reliable techniques in diagnosing pulmonary diseases. The time-consuming and bias-prone traditional methods using hyperpolarized H 3He and 1H magnetic resonance imageries have recently been improved by an automated technique based on 'multiple active contour evolution'. This method involves a simultaneous evolution of multiple initial conditions, called 'snakes', eventually leading to their 'merging' and is entirely independent of the shapes and sizes of snakes or other parametric details. The objective of this paper is to show, through a theoretical analysis, that the functional dynamics of merging as depicted in the active contour method has a direct analogue in statistical physics and this explains its 'universality'. We show that the multiple active contour method has an universal scaling behaviour akin to that of classical nucleation in two spatial dimensions. We prove our point by comparing the numerically evaluated exponents with an equivalent thermodynamic model. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.