and the resulting speed of the entire image acquisition. In fact, the FLASH sequence eliminated all waiting periods previously included to accommodate effects from T1 saturation. FLASH reduced the typical sequence interval to what is minimally required for imaging: a slice-selective radio-frequency pulse and gradient, a phase-encoding gradient, and a (reversed) frequency-encoding gradient generating the echo for data acquisition. For radial data sampling, the phase- and frequency-encoding gradients are replaced by two simultaneously applied frequency-encoding gradients that rotate the Fourier lines in data space. In either case, repetition times are as short as 2 to 10 milliseconds, so that the use of 64 to 256 repetitions results in image acquisition times of about 0.1 to 2.5 seconds for a two-dimensional image. Most recently, highly undersampled radial FLASH MRI acquisitions have been combined with an iterative image reconstruction by regularized nonlinear inversion to achieve real-time MRI at a temporal resolution of 20 to 30 milliseconds for images with a spatial resolution of 1.5 to 2.0 millimeters. This method allows for a visualization of the beating heart in real time – without synchronization to the electrocardiogram and during free breathing. History FLASH MRI was invented in 1985 by Jens Frahm, Axel Haase, W Hänicke, KD Merboldt, and D Matthaei (German Patent Application P 35 04 734.8, 12 February 1985) at the Max-Planck-Institut für biophysikalische Chemie in Göttingen, Germany. The technique is revolutionary in shortening MRI measuring times by up to two orders of magnitude. FLASH was very rapidly adopted commercially. RARE was slower, and echo-planar imaging (EPI) – for technical reasons – took even more time. Echo-planar imaging had been proposed by Mansfield's group in 1977, and the first crude images were shown by Mansfield and Ian Pykett in the same year. Roger Ordidge presented the first movie in 1981. Its breakthrough came with the invention of shielded gradients. The introduction of FLASH MRI sequences in diagnostic imaging for the first time allowed for a drastic shortening of the measuring times without a substantial loss in image quality. In addition, the measuring principle led to a broad range of completely new imaging modalities. In 2010, an extended FLASH method with highly undersampled radial data encoding and iterative image reconstruction achieved real-time MRI with a temporal resolution of 20 milliseconds (1/50th of a second). Taken together, this latest development corresponds to an acceleration by a factor of 10,000 compared to the MRI situation