Ultra-fast imaging.

The relatively long scan times with currently available technology restrict the range of MRI applications, increase the cost of scanning by limiting throughput, and lead to image artifacts from patient motion during scans. Ultrafast imaging, in several guises, is now poised for introduction into clinical practice. With the Instascan method, a descendant of the echo-planar technique, complete MR images may be obtained hundreds to thousands of times faster than in conventional approaches and now yield spatial resolution and contrast directly comparable to standard MRI. "Single-shot" imaging methods, such as Instascan, are utilized in the study of dynamic processes, in the direct evaluation of motion (as in diffusion sensitive imaging), and in dramatic new applications, including the interactive control of intraparenchymal laser surgery. Improvements to the small flip-angle method, FLASH, have also pushed scan times into the subsecond domain; this method may be implemented on presently available imaging equipment but yields contrast behavior different from the traditional spin-echo techniques and displays signal-to-noise ratios significantly lower than single-shot imaging. Ultimately, incorporating ultra-fast MR imaging techniques into the armamentarium of the radiologist will likely require changes to many aspects of the MRI practice, from expanded involvement with the scan process to management of the increased data load, and may lead to dramatic changes in the scope of the MRI practice.