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Though historically recall referendum mechanism has been the least used, and the most controversial, in the last decades it has expanded in Latin America. This expansion is caused by its inclusion in laws and frequent activations or attempts to activate this direct democracy mechanism (DDM). The aim of this paper is to identify the institutional, social and political conditions that have an impact in the success or failure of the attempts to use this mechanism, by analyzing the experiences in large cities in South America with this DDM. ; A pesar de que la revocatoria del mandato ha sido históricamente un mecanismo poco utilizado y bastante cuestionado, en las últimas décadas se ha expandido en América Latina. Dicha expansión se debe a su introducción en las leyes y a frecuentes activaciones o intentos de activación del mecanismo. En esta línea, el objetivo del presente artículo es identificar las condiciones institucionales, sociales y políticas que inciden en el éxito o fracaso de estos intentos de revocatoria de autoridades locales. Con dicha finalidad, se analizan las experiencias de revocatoria en las grandes ciudades de América del Sur.

Four-dimensional (4D) flow magnetic resonance imaging (4D Flow MRI) enables acquisition of time-resolved three-directional velocity data in the entire heart and all major thoracic vessels. The segmentation of these tissues is typically performed using semi-automatic methods. Some of which primarily rely on the velocity data and result in a segmentation of the vessels only during the systolic phases. Other methods, mostly applied on the heart, rely on separately acquired balanced Steady State Free Precession (b-SSFP) MR images, after which the segmentations are superimposed on the 4D Flow MRI. While b-SSFP images typically cover the whole cardiac cycle and have good contrast, they suffer from a number of problems, such as large slice thickness, limited coverage of the cardiac anatomy, and being prone to displacement errors caused by respiratory motion. To address these limitations we propose a multi-atlas segmentation method, which relies only on 4D Flow MRI data, to automatically generate four-dimensional segmentations that include the entire thoracic cardiovascular system present in these datasets. The approach was evaluated on 4D Flow MR datasets from a cohort of 27 healthy volunteers and 83 patients with mildly impaired systolic left-ventricular function. Comparison of manual and automatic segmentations of the cardiac chambers at end-systolic and end-diastolic timeframes showed agreements comparable to those previously reported for automatic segmentation methods of b-SSFP MR images. Furthermore, automatic segmentation of the entire thoracic cardiovascular system improves visualization of 4D Flow MRI and facilitates computation of hemodynamic parameters. ; Funding details: 310612; Funding details: FP7, Seventh Framework Programme; Funding details: 621-2014-6191, VR, Vetenskapsrådet; Funding details: 223615; Funding details: 20140398; Funding text: This work was partially funded by the FP7-funded project DOPPLER-CIP [grant number 223615]; the European Union's Seventh Framework Programme ( FP7/2007-2013 ) [grant number 310612 ]; the Swedish Research Council [grant number 621-2014-6191 ]; and the Swedish Heart and Lung Foundation [grant number 20140398 ].