In several applications, MRI is used to monitor the time behavior of the signal in an organ of interest; e.g., signal evolution because of physiological motion, activation, or contrast-agent accumulation. Dynamic applications involve acquiring data in a k-t space, which contains both temporal and spatial information. It is shown here that in some dynamic applications, the t axis of k-t space is not densely filled with information. A method is introduced that can transfer information from the k axes to the t axis, allowing a denser, smaller k-t space to be acquired, and leading to significant reductions in the acquisition time of the temporal frames. Results are presented for cardiac-triggered imaging and functional MRI (fMRI), and are compared with data obtained in a conventional way. The temporal resolution was increased by nearly a factor of two in the cardiac-triggered study, and by as much as a factor of eight in the fMRI study. This increase allowed the acquisition of fMRI activation maps, even when the acquisition time for a single full time frame was actually longer than the paradigm cycle period itself. The new method can be used to significantly reduce the acquisition time of the individual temporal frames in certain dynamic studies. This can be used, for example, to increase the temporal or spatial resolution, increase the spatial coverage, decrease the total imaging time, or alter sequence parameters e.g., repetition time (TR) and echo time (TE) and thereby alter contrast. Magn Reson Med 42:813-828,

The main risks associated with magnetic resonance imaging (MRI) have been extensively reported and studied; for example, everyday objects may turn into projectiles, energy deposition can cause burns, varying fields can induce nerve stimulation, and loud noises can lead to auditory loss. The present review article is geared toward providing intuition about the physical mechanisms that give rise to these risks. On the one hand, excellent literature already exists on the practical aspect of risk management, with clinical workflow and recommendations. On the other hand, excellent technical articles also exist that explain these risks from basic principles of electromagnetism. We felt that an underserved niche might be found between the two, ie, somewhere between basic science and practical advice, to help develop intuition about electromagnetism that might prove of practical value when working around MR scanners. Following a wide‐ranging introduction, risks originating from the main magnetic field, the excitation RF electromagnetic field, and switching of the imaging gradients will be presented in turn. Level of Evidence: 5 Technical Efficacy: 1 J. Magn. Reson. Imaging 2018;47:28–43.

P ulmonary MRI has had limited clinical use for patients with lung disease, especially when compared with radiography, CT, and PET/CT. However, MRI has become practical in many countries due to advances in MRI pulse sequences, multicoil parallel imaging, and acceleration methods, along with the increased (but not universal) availability of postprocessing software. Recently, ultrashort echo time (UTE) and zero echo time proton MRI have extended the use of conventional or anatomic proton MRI for clinical examinations, and inhaled-gas methods have opened up avenues for functional lung imaging. The transition to MRI from radiography-based methods has been driven by the fact that MRI does not impart ionizing radiation, which is particularly important in younger patients with chronic illness (eg, cystic fibrosis [CF]), for young and pregnant women, or for those patients requiring extensive longitudinal follow-up (eg, severe asthma).The purpose of this Fleischner Society position paper is to familiarize our community with recent advances in pulmonary MRI and to provide a consensus expert opinion regarding appropriate clinical indications for this modality. These opinions were initially endorsed in consensus among the writing committee members, following which the manuscript was endorsed by the Society members at large and was approved by the Fleischner Society Publication Development and Oversight Committee and the Fleischner Executive Committee before submission to Radiology.Common clinical indications for pulmonary MRI were reviewed by members of the writing committee and have been divided into three groups: (a) group 1 indications are suggested for current clinical use of pulmonary MRI (four or more publications from multiple institutions with clinical studies of more than 100 patients); (b) group 2 indications are promising but require further validation or regulatory approval (two to three publications with fewer than 100 patients, those that use methods requiring further confirmation or regulatory approval, such as hyperpolarized gases); and (c) group 3 indications are appropriate for research investigations (clinical studies not meeting the above criteria or limited to preclinical research) (Table 1).

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