FLASH MRI

FLASH MRI (Fast Low Angle SHot Magnetic Resonance Imaging) is a basic measuring principle for rapid MRI invented in 1985 by Jens Frahm, Axel Haase, W Hänicke, KD Merboldt, and D Matthaei (German Patent Application P 35 04 734.8, February 12, 1985) at the Max-Planck-Institut für biophysikalische Chemie in Göttingen, Germany. The technique is as simple as revolutionary in shortening MRI measuring times by up to two orders of magnitude.

Different manufacturers of MRI equipment use different names for this experiment. Siemens uses the name FLASH, General Electric used the name SPGR (Spoiled Gradient Echo), and Philips uses the name CE-FFE-T1 (Contrast-Enhanced Fast Field Echo) or T1-FFE. Depending on the desired contrast, the generic FLASH technique provides spoiled versions that destroy transverse coherences and yield T1 contrast as well as refocused versions (constant phase per repetition) and fully balanced versions (zero phase per repetition) that incorporate transverse coherences into the steady-state signal and offer T1/T2 contrast.

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. For example,

• cross-sectional images with acquisition times of a few seconds enable MRI studies of the thorax and abdomen within a single breathhold,
• dynamic acquisitions synchronized to the electrocardiogram generate movies of the beating heart,
• sequential acquisitions monitor physiological processes such as the differential uptake of contrast media into body tissues,
• three-dimensional acquisitions visualize complex anatomic structures (brain, joints) at unprecedented high spatial resolution in all three dimensions and along arbitrary view directions, and
• magnetic resonance angiography (MRA) yields three-dimensional representations of the vasculature.

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 before 1985. In general, FLASH denoted a breakthrough in clinical MRI that stimulated further technical as well as scientific developments up to date.