Contrast‐Enhanced Renal MRA

The rapid growth of magnetic resonance imaging systems with enhanced gradient systems together with improved pulse sequences has improved the ability to image blood vessels with a spatial and temporal resolution similar to conventional X‐ray angiography. With patients who cannot undergo X‐ray angiography because they are contraindicated for iodinated contrast agents (having a creatinine level > 2.0), MRA (magnetic resonance angiography) has proven to be the modality of choice. Since the first demonstration of such contrast‐enhanced studies in the abdominal aorta, there have been continual improvements in methods due to improved hardware/software capabilities. This unit presents the MR protocols to image vascular morphology using contrast‐enhanced 3‐D‐MRA techniques. The pulse sequences described herein are based on the authors’ experience with a Siemens 1.5 T Vision and 1.5 T Sonata scanners, but are expected to be equally applicable to machines from other manufacturers.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145369/1/cpmia2801.pd

Dragon-kings: mechanisms, statistical methods and empirical evidence

This introductory article presents the special Discussion and Debate volume "From black swans to dragon-kings, is there life beyond power laws?" published in Eur. Phys. J. Special Topics in May 2012. We summarize and put in perspective the contributions into three main themes: (i) mechanisms for dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii) empirical evidence in a large variety of natural and social systems. Overall, we are pleased to witness significant advances both in the introduction and clarification of underlying mechanisms and in the development of novel efficient tests that demonstrate clear evidence for the presence of dragon-kings in many systems. However, this positive view should be balanced by the fact that this remains a very delicate and difficult field, if only due to the scarcity of data as well as the extraordinary important implications with respect to hazard assessment, risk control and predictability.Comment: 20 page