A novel method for fat suppression in rare sequences

✍ Scribed by N. Higuchi; K. Hiramatsu; R. V. Mulkern

• Book ID: 102953595
• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 550 KB
• Volume: 27
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.1910270111

✦ Synopsis

Abstract

Rapid acquisition relaxation‐enhanced (RARE) sequences (Hennig et al., Magn. Reson. Med. 3, 823 (1986)) utilize one or several Cam‐Purcell–Meiboom–Gill (CPMG) echo trains to sample a number of k‐space lines each repetition time TR. The technique can rapidly generate multislice T~2~‐weighted images which, as a rule, are strikingly similar in contrast to conventional T~2~‐weighted spin‐echo (SE) images. An exception to this rule is the appearance of very bright signal from fat in T~2~‐weighted RARE images as compared to conventional T~2~‐weighted SE images. To reduce this fat signal, we introduce a time delay, τ~c~, between the 90^o^~x~ and first 180^o^~y~ pulse of each echo train such that a phase angle of π/2 develops between fat and the reference (water) line at echo maxima. The technique leads to single‐acquisition fat suppression without the use of frequency‐selective saturation pulses and concomitant loss of slices per TR. A Bloch equation analysis is used to identify two major mechanisms contributing to suppression of off‐resonance spins such that Wτ~c~ = π/2. Namely, the CPMG sequence becomes a CP sequence with no self‐correction properties for imperfect 180° pulses leading to enhanced signal decay, and the raw k‐space data matrix become segemented into blocks alternately multiplied by ±i, leading to signal dispersion following Fourier transformation.