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This corrects the article DOI: 10.1103/PhysRevLett.116.118301.

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Solid, crystalline matter is now remarkably well understood, thanks mainly to the efforts of physicists during the last century. Building on this success, there has been an increasing trend among physicists in the past few decades to turn their attention to soft condensed matter -or"squidgy" stuff. Soft matter displays either viscous (liquid-like) or elastic (solid-like) behaviour, depending on the time scale of the measurement. Examples range from gelatine and pastes to liquid crystals and melted polymers. Physicists' interest in soft matter arises in part because it displays an intriguing universality in behaviour and can be described by "coarse-grained" models that ignore atomistic and chemical detail. A characteristic of soft matter is its tendency to arrange itself at hierarchical levels, such as the layering in liquid crystals and the ordering of colloidal particles into a cubic array. As such, the relevant length scales range between the molecular (nanometer) up to tens of micrometers.Many types of soft matter, such as concentrated emulsions, are not stable under high vacuum and are perturbed by even light mechanical forces. Phases that are confined to small volumes can only be studied by techniques that do not disturb the confining phase. Soft matter is continuously undergoing thermal fluctuations, and so its structure is dynamic. Because of all of these characteristics, it is not feasible to probe soft matter by many analytical techniques. Non-invasive and fast techniques are required.Natural substances, such as cells and tissues, can also be considered to be soft condensed matter. As aptly stated by William Burroughes, we humans are "soft machines:' In 1973 two groups independently developed a technique to '100k inside" these soft machines. Sir Peter Mansfield and colleagues at the University of Nottingham and Paul Lauterbur at the State University of New York in Stonybrook both announced that the resonance of magnetic nuclei could be exploited to non-invasively provide cross-sectional images in the technique known as magnetic resonance imaging (MRI).MRI soon became the imaging modality of choice in medical research and diagnosis. It is now coming of age in the study of soft condensed matter, too. The stage through which all new microscopies go -that of taking "pretty pictures" as the primary objective -has truly passed. Now, enabled largely by physicists across Europe, scientists are starting to answer some questions of real import to the study of soft matter. Principles of MRIMagnetic resonance relies upon the fact that magnetic nuclei of atoms, such as the hydrogen proton, precess in a magnetic field at a frequency directly proportional to the field strength. The frequency, which is in the radio-frequency (r-f) range, is detected via the current arising from the transient response of the nuclei to a resonant r-f stimulus. This current is induced in a detector coil around the sample. Magnetic resonance imaging, as depicted in figure 1, is achieved by superimposing on the sample a magnetic field gradi...