Abstract
CHESS pulse can suppress the signal originating from aliphatic fat protons but cannot suppress the signal from olefinic fat protons, which is near the resonance frequency of water protons. Adipose tissue contains various fat species; aliphatic fat comprises about 90 % and olefinic fat about 10 % of adipose tissue. Thus, CHESS pulse cannot be used to suppress the signal from adipose tissue completely. The purpose of this study was to find a method to suppress the signal from adipose tissue completely. The Fatsat train pulse, created with an arbitrary flip angle and insensitive to B1 inhomogeneity, was used. Because B1 inhomogeneity is larger on higher field magnetic resonance imaging, the fat suppression radiofrequency pulse needs to be B1-insensitive. To investigate a percentage of olefinic fat in adipose tissues, the excitation frequency of the Fatsat train pulse was varied from −240 to +400 Hz and the images and fat-suppressed images were obtained. The presence of olefinic fat comprising about 10 % of abdominal adipose tissue was identified. The result agreed with some previous papers. Complete fat suppression could be achieved by partial (10 %) inversion of longitudinal aliphatic fat magnetization and by canceling out the two fat magnetizations. The flip angle was identified to about 95°. In conclusion, the cause that the signal from adipose tissues cannot be suppressed completely has been found. Improved images that signals from adipose tissues were suppressed completely have been demonstrated. This technique can also be applied to several pulse sequences.
Highlights
Fat suppression is used in routine clinical magnetic resonance imaging (MRI)
A chemical shiftselective (CHESS) radiofrequency (RF) pulse is commonly used for fat saturation (Fatsat) [1, 2]
The CHESS RF pulse can suppress the signal from aliphatic fat, it cannot suppress the signal from olefinic fat
Summary
T. Abe artifact occurs in diffusion-weighted imaging (DWI). Abe artifact occurs in diffusion-weighted imaging (DWI) These signals can interfere with the diagnosis of certain diseases. To suppress the signal from lipid (aliphatic fat), which precesses at a lower frequency of 3.5 ppm than water, the CHESS pulse nutates the lipid magnetization to the transverse plane, while leaving the water magnetization unperturbed along the longitudinal axis. There are two components of fatty tissues, lipid (aliphatic fat) and olefinic fat, which precesses at the same frequency as water [3, 4]. The CHESS RF pulse can suppress the signal from aliphatic fat, it cannot suppress the signal from olefinic fat. The conventional CHESS RF pulse does not completely suppress the signal from adipose tissue, and a residual signal from olefinic fat remains
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