Simultaneous water and fat MRI with chemical-shift correction

Abstract

We have developed a new MRI technique that simultaneously acquires both water and fat images in a single acquisition time, and combines the water and fat images to produce chemical-shift free water-fat images. The new technique was implemented on a 3D gradient echo (GRE), and 2D dual-echo spin echo (SE) and GRE imaging sequences at 1.5 Tesla. Binomial spatial-spectral selective Shinnar-Le Roux RF and gradient excitation pulses were used for excitation. In the GRE sequences, the phase-encoding lines in the slice selection direction were interlaced with alternate water and fat excitation separated by half repetition time (TR). For the 2D SE sequences, the water signal was first excited and acquired, followed by fat signal excitation. A non-spectral selective /spl pi/ pulse then refocused the spins and generated the first echo for fat and the second echo for water. The water-only and fat-only images were reconstructed on a workstation where they were realigned and combined to form chemical-shift free images. Results from phantoms and human subjects demonstrated that there were no cross-talk between the water and fat excitation, and the image contrast was the same as the regular sequences. With the chemical shift corrected, shadow artifacts often seen at water and fat boundaries were removed. Since this technique simultaneously provides water-only images showing soft tissue and bone pathology, and water-fat images depicting the anatomy, it could be useful in evaluation of musculoskeletal conditions. The superb selectivity for water signal resulting from this technique may also enhance tumor conspicuity in brain and other organs.