Single-Slab 3D Fast Spin Echo and Its Variants With Very Long Echo Trains for Clinical T2-Weighted Contrast

Single-slab three-dimensional (3D) fast spin echo (FSE) imaging with very long echo trains and its variants are used for producing clinical T2-weighted image contrast. Singleslab 3D FSE imaging with variable refocusing flip angle management strategies permit very long echo trains and, thus, can highly enhance 3D encoding efficiencies. For the flexible control of imaging slabs, both nonselective and selective types of T2-weighted single-slab 3D FSE imaging are described in this review. For clinical applications requiring high lesion sensitivity, the single-slab 3D FSE can be modified to accommodate phasesensitive dual acquisition to enable the attenuation of cerebrospinal fluid (CSF) signals without using conventional long inversion recovery. This approach can be further extended to suppress both CSF and white matter signals for high resolution gray matter-only imaging. Lastly, the single-slab 3D gradient and spin echo (GRASE), which incorporates multiple echoes with phase encoding blips between neighboring refocusing pulses in single-slab 3D FSE imaging, is presented as an effective means for minimizing energy deposition on human tissues and enhancing imaging efficiency. Chemical shift encoding can be applied with single-slab 3D GRASE imaging to efficiently differentiate between fat and water in the presence of magnetic field inhomogeneities.