Mark Bydder | PubMed Health

PubMed2002

Generalized SMASH imaging.

A generalized parallel imaging method has been developed that uses coil profiles to generate missing k-space lines. The proposed method is an extension of SMASH, which uses linear combinations of coil sensitivity profiles to synthesize spatial harmonics. In the generalized SMASH approach described here, coil sensitivity profiles are represented directly in the Fourier domain to provide a general description of the spatial properties of the coils. This removes restrictions imposed by conventional SMASH, so that the choice and position of the receiver coils can be made on the basis of sensitivity to the volume of interest rather than suitability for constructing spatial harmonics. Generalized SMASH also intrinsically allows the freedom to accommodate acquisitions with uniform or nonuniform k-space sampling. The proposed method places SMASH on an equal footing with other parallel imaging techniques (SENSE and SPACE-RIP), while combining strengths from each. The method was tested on phantom and human data and provides a robust method of data recovery.

Fourier Analysis↗

PubMedDate not supplied

Magnetic resonance: an introduction to ultrashort TE (UTE) imaging.

The background underpinning the clinical use of ultrashort echo-time (UTE) pulse sequences for imaging tissues or tissue components with short T2s is reviewed. Tissues properties are discussed, and tissues are divided into those with a majority of short T2 relaxation components and those with a minority. Features of the basic physics relevant to UTE imaging are described including the fact that when the radiofrequency pulse duration is of the order T2, rotation of tissue magnetization into the transverse plane is incomplete. Consequences of the broad line-width of short T2 components are also discussed including their partial saturation by off-resonance fat suppression pulses as well as multislice and multiecho imaging. The need for rapid data acquisition of the order T2 is explained. The basic UTE pulse sequence with its half excitation pulse and radial imaging from the center of k-space is described together with options that suppress fat and/or long T2 components. Image interpretation is discussed. Clinical features of the imaging of cortical bone, tendons, ligaments, menisci, and periosteum as well as brain, liver, and spine are illustrated. Short T2 components in all of these tissues may show high signals. Possible future developments are outlined as are technical limitations.

Humans↗