Clinical ultrashort echo time imaging of bone and other connective tissues

The background underpinning the clinical use of ultrashort echo time, SPRITE and other pulse sequences for imaging bone and other connective tissues with short T-2 is reviewed. Features of the basic physics relevant to UTE imaging are described, including the consequences when the radiofrequency pulse duration is of the order of T-2 so that rotation of tissue magnetization into the transverse plane is incomplete. Consequences of the broad linewidth of short T-2 components are also discussed, including partial saturation by off-resonance fat suppression pulses as well as those used in multislice and multiecho imaging. The need for rapid data acquisition of the order of T-2 is explained. The basic two-dimensional UTE pulse sequence with its half excitation pulse and radial imaging from the centre of k-space is described, together with options that suppress fat and/or reduce the signal from long T-2 components. The basic features of SPRITE and other sequences with very short TE are described. Image interpretation is discussed. Clinical features of the imaging of cortical bone, tendons, ligaments, menisci, periosteum and the spine are illustrated. The source of the short T-2 signal in these tissues is predominantly collagen and water tightly bound to collagen. Short T-2 components in all of these tissues are detectible and may show high signals. Possible future developments are outlined, as are technical limitations of clinical magnetic resonance systems. Copyright (C) 2006 John Wiley & Sons, Ltd.